hybridfree/eevblog-posts huggingface dataset:
Interesting RF enclosures on ebay for scrap - Page 1
Forum section: electronics / rf-microwave

author: daqq
author_rank: Super Contributor
timestamp: January 20, 2017, 06:54:25 pm
content: I found this on ebay. See:http://www.ebay.com/itm/1LB-Gold-Scrap-Recovery-All-Gold-Plated-45-Connector-Pin-Mix-Heavy-Duty-454g-Old/201785377411?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40832%26meid%3D9cca4b59a48e486e92c236032c1b5902%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D201785406844Note: I have no relation with the seller.
#95 National NCX 3 Repair Part 1 Blooper to follow  - Page 1
Forum section: electronics / rf-microwave

author: Radio Tech
author_rank: Frequent Contributor
timestamp: January 23, 2017, 12:58:58 pm
content: This is part one of the National NCX-3 repair. We replace some capacitors and check out the receiver.At the end of the video I share a major blooper with the group.

author: voltz
author_rank: Frequent Contributor
timestamp: January 23, 2017, 10:07:43 pm
content: That was interesting. Thanks for posting! re:queston, thinking its because the two contact metals are different (bi-metal) so causes corrosion. Must admit, i dont know exactly why its only on the negative. Electrons flowing from negative to positive right? So i assume its some kind of electrolysis taking place.Great blooper fail, you get a gold star for that one

author: GreyWoolfe
author_rank: Unknown
timestamp: January 24, 2017, 01:22:55 am
content: for the repair job and, of course, afor the blooper! A few years back, I was given 2 old Tek tube scopes, 1 without the cover on it. Not having either a variac or a dim bulb tester, I still decided to plug them in. The one without the cover powered up fine with traces, the other didn't power up at all. I decided to check the plug-ins from that scope in the original one since the plug-ins were the same. The first went fine but when I powered up the scope with the 2nd plug-in,. I actually had a small flame coming out of the top of the scope until I pulled the plug out of the wall. Needless to say, I didn't have the door to my office closed so the smell made its' way into the house and lingered for a couple of days. SWMBO wasn't happy with me and made me put the scopes out for trash. Unfortunately, the trash pickup is early so she waited until she saw the scopes go into the garbage truck before she went to work because she didn't trust me. I now have both a dim bulb tester and a variac.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: January 24, 2017, 01:23:53 am
content: Quote from: voltz on January 23, 2017, 10:07:43 pmCorrect. There is a difference in the two metals. And also correct in the flow of electrons.QuoteThanks again. I will wear the gold star proudlyMost of the time I edit out the fails but let this one stay.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: January 24, 2017, 01:32:23 am
content: Quote from: GreyWoolfe on January 24, 2017, 01:22:55 amThanks, guess it happens to us all.Thanks for sharing that story. A exploding capacitor can stink up a place for a long time. Wife will not let me have a lab in the house for the last 30 years. We had a sun room where my lab was and was working on a tube amp. Like you no protection devices. I powered it up and next thing I know, the 6 220 uF and 500 volt capacitors went into melt down. Then a huge BANG. Took a week to get the smell out of the house. Month later I was still finding bits of paper and foil around the room.
Oscilloscope reference lead earth issue in audio circuits  - Page 1
Forum section: electronics / rf-microwave

author: Ötti
author_rank: Newbie
timestamp: January 30, 2017, 02:33:47 pm
content: Hi folks!Do u know Dave's blog #279? Please take a look at minute 6:35 (https://youtu.be/xaELqAo4kkQ). He sais that doing measurements on a floating audio circuit could cause problems when connecting the scopes reference lead to a particular point in the circuit.Can someone please explain me why. I have no idea. And I dont really unterstand the last word he sais at the end of the sentence at 6:35. What can happen worst case?Thanks a lot!

author: Andy Watson
author_rank: Super Contributor
timestamp: January 30, 2017, 04:40:38 pm
content: 6:28" It may not do anything, in most cases it is not going to cause a problem at all. Unless there is some, you know, your working at audio circuits and there is hum and all sorts of things ...".What he is saying is that if you connect the scope earth to a sensitive, high impedance part of the circuit under test it will behave like an antennae and inject some signal - probably main's hum - into your circuit. (It is actually your floating circuit that is the antennae, but the effect is that same.)

author: Ötti
author_rank: Newbie
timestamp: January 31, 2017, 08:12:30 am
content: Thanks a lot Andy!Greetings from overseas
How to design very high order filter while IFBW is small (10Hz) for VNA(E5071C) - Page 1
Forum section: electronics / rf-microwave

author: kongkevin
author_rank: Newbie
timestamp: January 17, 2017, 07:22:25 am
content: For VNA (for example E5071C), kinds of IFBWs can be set to balance the measure time and dynamical range. while IFBW is small, the IF filter should be very high order for IF receiver, how it is designed in VNA?i checked the E5071C spec, while the IFBW is bigger than 100KHz, the measure time keeps constant, since 100KHz IFBW can obtain more dynamical range compared with 500KHz or 1.5MHz, why E5071C need support 500KHz and 1.5MHz?My another question is why the measure time doesn't become shorter as IFBW bigger (>= 100KHz)?Can anyone help explain on these topic? Thanks very much in advance.
[SOLVED] Active LF Filter Design Topology - Page 1
Forum section: electronics / rf-microwave

author: jpanhalt
author_rank: Super Contributor
timestamp: January 15, 2017, 03:56:10 pm
content: I am working on a 500 kHz active filter and turned to the filter wizard of Analog Devices. Given a center frequency of 500 kHz, 20 kHz passband, gain of 10 dB, it came up with the attached design using three AD8055 op-amp sections. Only the first section is shown.Analog Devices calls it an MFB, but TI and others with similar design programs do not include feedback resistors R3A and R4A. Perhaps obviously, the design is pretty sensitive to the value of those resistors. I have seen similar topology called VCVS (voltage-controlled variable state), but all of the examples of that I have seen use the non-inverting input of the op-amp for signal input.1) What is the topology called? That is, is there a more specific name for it that includes the feedback resistors?2) Does anyone have a link to share that explains how to calculate the values for those two resistors?Regards, John

author: jpanhalt
author_rank: Super Contributor
timestamp: January 18, 2017, 11:31:46 pm
content: SOLVED:It is a variation on the Single Amplifier Biquad (SAB) originally designed by Delyiannia and Friend. Schaumann and Van Valkenburg's text (Oxford University Press, 2001) has a nice description and worked example beginning around p. 170.Regards, John
Use of copper tape and capacitance for loop antennas. - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: January 15, 2017, 10:20:30 pm
content: A way back I had built a pretty nifty loop for shortwave as sort of a proof of concept and now I can't find it. It may have accidentally been tossed out. But let me describe it. It was made from one leaf of a cut to size adjustable window shade. (Soft plastic, the kind that probably isnt so healthy because of all the plasticizers, etc) The plastic was fairly long and I just coated one side of it with aluminum foil and taped the edges. it was soft plastic. When the loop was folded back on itself (and the aluminum not touching the other side, it made a quite good loop antenna which could be adjusted in frequency by adjusting the amount of overlap. You could use it with a shortwave radio in the middle as a weight holding the thing down in the right position. It is very simple to make. Anyway, I recently bought some copper tape for repairing PCBs and taping shielding and the copper tape would also make a good loop. Smaller tape sizes would likely make good loops for VHF/UHF (with the limitation that the "q" or the capacitor becomes more critical if you intend to transmit. All you do is find a piece of thin, durable, bendable plastic and put the tape on it, then fold the loop back on itself, find the resonant frequency while your pickup loop whatever it is is in its intended position, and then hold it there with some non metal fastening. Tape, especially if its wider than the usual conductors used in loops works quite well. The beauty of this design is that you can also use aluminum foil and it makes not the slightest bit of difference that its aluminum as opposed to copper because there are no solder joints made to it. So you could literally make a really large, extremely efficient loop out of aluminum foil.You can tell this is a really hot loop by its extremely sharp tuning peak. When listening with an SDR, when you are off frequency there is literally nothing there but when its on frequency the signals, even weak signals become quite strong. So strong you might even be able to measure them on a voltmeter. This kind of antenna really allows the very best performance you are ever going to get with the extremely cheap USB dongle rtl2832 SDRs in direct sampling mode. I am not so excited about their performance on HF with upconverters but with a loop they do quite well for direct sampling. The received signal is cleaner.Some of my best experiences listening to shortwave have been with a mag loop setup.
Toshiro Kodera: Electromagnetic Gyrotropes - Page 1
Forum section: electronics / rf-microwave

author: chicken
author_rank: Frequent Contributor
timestamp: January 11, 2017, 03:38:45 am
content: I didn't understand half of it, but I think this is a pretty interesting talk for the RF aficionados on this board.http://hackaday.com/2017/01/04/toshiro-kodera-electromagnetic-gyrotropes/If I got the gist, and that's a big if, this uses carefully designed copper traces and a few basic components to construct circulators, tunable filters and steerable antennas for microwave applications.The word metamaterial is used a lot in this presentation, and I first thought he was referring to some specially engineered material that is created with complex processes. But in this talk it actually refers to the macro structure of stripline and components - I think

author: LaserSteve
author_rank: Super Contributor
timestamp: January 12, 2017, 09:48:57 pm
content: I enjoyed this, thanks for posting...Steve
ANRITSU MG3641A signal generator - Page 1
Forum section: electronics / rf-microwave

author: alexo
author_rank: Contributor
timestamp: December 18, 2016, 10:51:23 am
content: I'm looking for a spectrallycleansignal generator with low phase noise. For a physics experiment. Anritsu pops up often on eBay. I wonder how good they are, if they are repairable ( parts ? ) and maybe some comments on possible alternatives.I don't need more than 1Ghz but I would like to start low - around 200Khz or so.

author: ratmandu
author_rank: Newbie
timestamp: January 04, 2017, 04:50:59 am
content: I actually have one of these units on my bench right now, they work really well, and are pretty accurate (accurate enough for my work). If there are any tests you would like me to do, let me know. I have the MG3641A, with the DDS option, and a 200MHz agilent MSO-X 2014A scope.

author: Johncanfield
author_rank: Regular Contributor
timestamp: January 04, 2017, 07:25:13 pm
content: The HP-8640 has a reputation for a very clean output. They have a bunch of nylon gears that are known to break but there's a guy on eBay selling refurbished 8640s ( I bought one from him.)

author: metrol12
author_rank: Newbie
timestamp: January 05, 2017, 05:26:34 pm
content: Alexo,Low Phase noise performance is subjective. If you could provide what typical phase noise characteristics your experiment would need in noise performance at various frequencies you will be testing. That way we can comment on various generator available.

author: alexo
author_rank: Contributor
timestamp: January 08, 2017, 09:41:22 pm
content: Quote from: Johncanfield on January 04, 2017, 07:25:13 pmThat one was on my list but they're OLD. And I'm real bad at RF - little chance I'll be able to fix it. I could make the gears though, pretty easily.And there is something else - it starts pretty high at around 450Khz. It's not that I need lower but I'd like to have there just in case...

author: alexo
author_rank: Contributor
timestamp: January 08, 2017, 09:44:26 pm
content: Quote from: metrol12 on January 05, 2017, 05:26:34 pmGood point. I'd like to be SURE of 140dBc/Hz at 500Mhz. And I mean dead sure.

author: alexo
author_rank: Contributor
timestamp: January 08, 2017, 09:50:08 pm
content: Quote from: ratmandu on January 04, 2017, 04:50:59 amUnfortunatelyI think I'll have to stay away from those ones. The Anritsu MG3633 looked like the winning horse but if it breaks, I'm stuck with a 30Kg brick. I found that the only one I can hope to have fixed would be a Rhode & Schwartz SMB/V . Bad news as they cost money.I LOVE the look of the 3641 but my budget won't cover half of one anyway.

author: B1nary
author_rank: Contributor
timestamp: January 12, 2017, 02:20:53 am
content: Quote from: alexo on January 08, 2017, 09:41:22 pmI've been looking for a generator to do an alignment on my Revox B261FM Tuner so can you say who the guy is? There's a few on there and most look in bad shape. What I'd really like is something a whole lot newer than the 8640 or the Sencore SG165. If anyone had suggestions .....
RFID IC (MFRC522) with 50-Ohm antenna (taoglas fxr.01.A) - Page 1
Forum section: electronics / rf-microwave

author: filipe08
author_rank: Newbie
timestamp: January 10, 2017, 09:28:01 pm
content: I am trying to make the MFRC522 (https://www.nxp.com/documents/data_sheet/MFRC522.pdf) to work with a taoglas 50-Ohm antenna (http://taoglas.com/images/product_images/original_images/FXR.01.07.0100C.A.pdf)To start I based my schematic and layout in the arduino RFID board but the problem here is that this board uses a PCB antenna and the circuit is composed with EM filter and impedance matching.I think that as I am using a 50-Ohm antenna, I don´t need to build the impedance matching part, but the problem is that I can´t find a place I can get a circuit for MFRC522 with a 50-Ohm antenna.I appreciate all the help!Thanks!
mcHF Kit, issue with RF where it shouldn't be. - Page 1
Forum section: electronics / rf-microwave

author: TheBay
author_rank: Unknown
timestamp: January 16, 2017, 01:27:47 pm
content: I recently built a mcHF kit, but having an issue with a distorted output,basically what is happening is RF is getting through the Tx/Rx section and on to the Bias circuit for the Rx pin diodeso RF is getting all the way up to U7 which is a 74 series logic IC, it's either causing issues with neighbouring IC's through closetracks or directly from U7. I can see this RF with a RF probe or a spectrum analyser.RF is supposed to be blocked by a 47uh inductor labeled RFC2, if I remove either C78 or RFC2 from the circuit the issue has gone, but obviously I have no Rx!checking that path with the RF probe or SA there is no evidence of RF getting back so it's definitely getting in through RFC2.I've tried resistors inline or on top of the inductor and can remove the RF at some frequencies but it still appears on other bands.I have spoken to other owners some have it some claim they don't but having changed every component in that section and it remains I just think some don't notice it personally.It's unusable for me on JT65 as it's outputting awful distortion and causing a lot of spurious signals when using phone modes.Attached is a screenshot of the schematic and some screenshots of my SDR with and without the noise/distortion/oscillation.The link to the schematics are here:http://www.m0nka.co.uk/wp-content/uploads/2016/03/mcHF_rf.pdf

author: DimitriP
author_rank: Super Contributor
timestamp: January 16, 2017, 09:37:30 pm
content: Have you tried bodging 100nF on U7 p3 to p7 and p1 to P7?

author: TheBay
author_rank: Unknown
timestamp: January 18, 2017, 03:12:45 pm
content: Quote from: DimitriP on January 16, 2017, 09:37:30 pmI've tried another 100nF on R54 and also on Pin 2 of U7, I'm getting around -8v on R54 when I Tx but only -0.85 on the other side of R54If I remove R54, RFC2 or C78 the problem has gone.Really puzzled with this.

author: CJay
author_rank: Super Contributor
timestamp: January 18, 2017, 05:59:27 pm
content: Remove the drive through the PA/LPF and check the DC conditions on the PIN diodes to make sure you have the correct TX/RX switching happening.
Detect antenna transmission SX1276 - Page 1
Forum section: electronics / rf-microwave

author: littleboot
author_rank: Regular Contributor
timestamp: January 04, 2017, 03:34:07 pm
content: Hello,I'm currently working on a LoRa module that uses the sx1276 LoRa transceiver from Semtech based on the sx1276MB1MASreference design. (https://developer.mbed.org/components/SX1276MB1xAS/In this design there are RF-switches that are used to switch the transmission circuit or receiver circuit to the antanna. The are 2 options to control the RF-switches 1: software control from the MCU (default) 2: controlled by the transceiver RXTX/RF_MOD pin.The datasheet pin description states: "pin 20 = RXTX/RF_MOD = Rx/Tx switch control: high in Tx" but there isn't any information about the time it takes for this pin to go High and the actual start of the transmission. Because I use different RF switches and 2 inverters in serie (buffer and inverting the signal) to control these switches it takes some time to switch from RX to TX. If the transmission starts before the switch is complete a small part of this transmission may be lost so I would like to measure this delay with my logic analyser.Can I connect my logic analyser directly to the antenna and RF_MOD pin?(I think not) (Also I can't find anything about the voltages on transmission line when transmitting.)How do I measure this delay correctly? (maybe connect a 50ohm resistor and measure the voltage across it?)I already measured the delay between the software and the hardware RF_MOD pin, and the the software pin is activated 100uS earlier then the hardware pin (in de demo project).

author: mjs
author_rank: Regular Contributor
timestamp: January 09, 2017, 08:16:41 pm
content: You can probably see the transmission by putting a small diode (even 1n4148 should be ok) to the output and rectifying it to a small (22-100pF) cap paralleled with 1k resistor. Use oscilloscope to measure output and RXTX pin relative timing. Try with high transmit power and the PA_BOOST output to get enough signal for simple detector.
Please help identify this chip - Page 1
Forum section: electronics / rf-microwave

author: t0bias
author_rank: Newbie
timestamp: January 16, 2017, 09:20:45 pm
content: I *think* its a kind of wireless-transceiver, maybe a Bluetooth Module or something close...Can anyone help identify this chip, please?

author: t0bias
author_rank: Newbie
timestamp: January 27, 2017, 05:03:40 pm
content: Maybe as a first step: does anyone know this IC-Package?

author: NottheDan
author_rank: Frequent Contributor
timestamp: January 27, 2017, 05:36:36 pm
content: QFN38 package? Manufacturer MAL? At least that's what a search for 14939-1 gives me.

author: t0bias
author_rank: Newbie
timestamp: January 27, 2017, 07:47:57 pm
content: Thanks for your reply! Where did you find that information?Please forgive my ignorance - I've never heared of a manufacturer called MAL?What does it stand for? Googling "MAL" didn't return anything useful to me?(https://www.google.com/search?q=MAL+integrated+circuits&oq=MAL+integrated+circuits)

author: troyosaurus2014
author_rank: Newbie
timestamp: January 28, 2017, 02:34:51 am
content: This is the best I could do with my Google Search. The datasheets seem to be missing when pressing the link's link.http://www.kynix.com/Detail/1228745/14939-1.html

author: NottheDan
author_rank: Frequent Contributor
timestamp: January 28, 2017, 05:15:54 pm
content: Quote from: t0bias on January 27, 2017, 07:47:57 pmThe place troyosaurus linked. I only googled the various lines written on the chip until one made sense.
FM Receiver bandwidth. - Page 1
Forum section: electronics / rf-microwave

author: CJay
author_rank: Super Contributor
timestamp: January 05, 2017, 01:40:05 pm
content: Feeding single tone frequency modulated output from my sig gen into a 2M converted VHF PMR radio I get acceptable audio quality but off air speech is distorted, almost as if the IF filters are too narrow (seems unlikely as it was designed for 12.5KHz channel spacing)How do I measure the IF bandwidth?Do I sweep the sig gen to span the centre RX frequency and measure level at 1st IF or, as it's FM, do I sweep the modulating tone on a static carrier?What's the accepted definition of bandwidth, is it -3dB perhaps?

author: Yansi
author_rank: Super Contributor
timestamp: January 05, 2017, 01:48:29 pm
content: I think the modulation index is very low for these, like 1. I.e about 3kHz maximum.So the IF bandwidth of the 2m / 145MHz FM radio is like few kHz. (Compared to the commercial broadcast that uses something like 200kHz)

author: zl2wrw
author_rank: Regular Contributor
timestamp: January 06, 2017, 01:37:28 pm
content: Generally, amateur 2m NBFM uses ~ 3 kHz audio bandwidth, +/- 5 kHz deviation, 15 kHz BW IF filtering and 25 kHz channel spacing.Because PMR spectrum is crowded in some areas, the "new" NBFM standard used by a lot of PMR gear is +/- 2.5 kHz deviation, 7.5 kHz BW IF filtering and 12.5 kHz channel spacing.So, off-air receive probably sounds distorted because the 7.5 kHz BW IF filter(s) in your PMR radio will be clipping the deviation peaks of a signal which is 15 kHz wide. You probably won't hear this distortion between two radios "across a room" because at 7.5 kHz away from centre frequency, your 7.5 kHz BW IF filter is probably only something like -40 dB down, so enough IF energy will get through on the skirts of filter to make the FM limter clip and the demodulator produce undistorted audio. You should be able to fix this by replacing the IF filter(s) with 15 kHz ones and re-aligning the IF strip/demodulator.Your transmit audio will probably also sound a bit quiet (-6 dB down) to anyone receiving you on 2m until you increase the TX deviation to +/- 5 kHz.
Commercial Rabbit Ears, am I missing something here? - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: December 31, 2016, 10:42:07 pm
content: So I was at a dollar store yesterday and they had rabbit ears with a UHF loop for a buck! I bought 4 for a Doppler project. I opened up the bottom and the loop is just wired in parallel. OK a loop and a dipole are obviously different designs so isn't there a big chance of the signals cancelling each other and that kind of mess? I would think there should be at least a diplexer between the dipole and loop, in general do most passive rabbit ears with loop just wire the elements in parallel and call it a day or are these just extremely cheap?

author: retrolefty
author_rank: Super Contributor
timestamp: December 31, 2016, 10:57:36 pm
content: Just the cheapest minimalist approach that may or may not work depending on the signal strength of the frequency/channel of interest. Next step up would use a variable C or switched C to 'tune' the antenna to the frequency/channel of interest.

author: SeanB
author_rank: Super Contributor
timestamp: January 01, 2017, 09:52:11 am
content: They are designed for use in a high signal strength area, and in many cases you will get better reception in the TV set by simply cutting the cable off right at the base of the unit, and taping the cheap and nasty coax cable they use to the wall, where it will pick up enough signal. the loop is basically an inductor across the dipole ( well, sort of) and does provide some lower loss at some band, and at some it is a magnetic loop, but the biggest pick up is the flylead.There are quite a few cases where i had to replace all the RF interconnects between the antenna and the TV set with better quality ccable and decent connectors, as there was visible ghosting, caused by the signal from the external antenna being delayed by the downlead, and the cheap connector wires picking up enough signal in the house to be the stronger signal in some cases, though with bad multipath reflections.TLDR, rabbit ears work if you can look out the window and see the transmitter unaided.
Microwave doppler motion detector teardown/reverse engineer - Page 1
Forum section: electronics / rf-microwave

author: JimRemington
author_rank: Regular Contributor
timestamp: December 26, 2016, 05:39:40 am
content: There are a number of really cheap ($2) microwave motion detector modules appearing on the market, and they seem to work pretty well, detecting humans moving up to 10 m away through walls.For examplehttps://www.aliexpress.com/item/Microwave-Radar-Sensor-DC-5V-10M-180-degree-Angle-Human-Smart-Sensor-Switch-18-16MM/32760385272.htmlRecently, a nice video appeared, analyzing the ingenious RF oscillator/receiver/mixer/detector circuitry. It evidently consists of a single transistor with appropriate PCB delay lines/antennas/etc. Thanks, Bert!!

author: ataradov
author_rank: Super Contributor
timestamp: December 26, 2016, 06:11:27 am
content: BigClive did reverse engineering of this thing quite some time ago:EDIT: I watched again, and he did not actually draw the schematic.EDIT2: Apparently this video was inspired by BigClive's video

author: JimRemington
author_rank: Regular Contributor
timestamp: December 26, 2016, 04:24:17 pm
content: The video link I posted explains the "microwave" portion of the module (2.5 GHz, actually), which BigClive did not attempt to understand. It is by far the most interesting portion, and quite ingenious!

author: djnz
author_rank: Regular Contributor
timestamp: December 31, 2016, 02:26:57 pm
content: Some years ago we had used a similar design to detect motion of our heart and capture contractions of individual chambers. One of the early designs had helical antennas and I had noticed that we could easily use it as a motion detector - randomly placed on a table in the room, we could detect motion (of a person, not of the heart!) from a distance of many feet - I think over 10-15 feet. It was quite sensitive too.Later we shrunk it down to a single small PCB with no out of plane antennas - credit card sized. The topology was very similar to this design - patch antenna, microstrip line, BJT oscillator, diode mixer, filters, amplifiers and then sampling + DSP.
Angle of radiation/reception with various cheap HF wire/loop antennae? - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: December 27, 2016, 12:07:55 am
content: Does anybody know if a loop is the best non-tall non expensive HF receiving antenna as far as angle of radiation? It seems as if most of what I have read seems to say so. What are people's DX experiences with tuning a wire(s) shot way up into a tree(s) vs loop fairly close to the ground?

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: December 31, 2016, 08:11:27 pm
content: There is no one 'best' antenna for all purposes. And the best antenna for transmitting and receiving may not necessarily be the same. And even if there was there is likely to be a lot of compromise in relation to size, height, space etc.Assuming you want something optimised for DX you are likely to need something with good response at low angles. If your ground conditions are good (eg salt water) then a delta loop fed so it's vertically polarised can be a good performer on transmit. An example is shown below.Requirements for receive are slightly different. Whereas on transmit you want maximum gain at the desired angles in the desired direction, this is not so necessary on receive. This is because most receivers are adequately sensitive on HF. Instead the aim should be maximum signal to noise ratio. If you are in a populated area and you are trying to receive weak DX signals while there's stronger stations closer by then an antenna pattern with a null at undesirable directions and angles can be helpful. There may also be local electrical noise you wish to null.A small magnetic loop allows easier turning and nulling of local noise. It also comprises a sharp tuned circuit which may be helpful if your receiver front end has poor image rejection. One is described atBut unless you wish to receive weak DX signals over difficult paths where more attention must be paid, 'any old bit of wire' over a tree will hear a wide range of signals near and far.

author: cdev
author_rank: Super Contributor
timestamp: December 31, 2016, 10:22:46 pm
content: Basically I am talking about exactly what you described. I have a quite variable local noise situation. Sometimes there is broadband HF noise that seems impossible to get rid of, the only hope I have is to try to null it out.For that a small loop around the same size as yours works well.
HP  8711C as a VNA / SA - Page 1
Forum section: electronics / rf-microwave

author: lincoln
author_rank: Regular Contributor
timestamp: December 24, 2016, 07:40:00 pm
content: hello,I am starting to mess with more RF but am very much still a noob. Right now i have a cheep SDR dongle and have been looking at getting a spectrum analyzer but also really wanted a tracking generator so I could look at filter responses.At a local auction house, they have a HP 8711C VNA for a low starting bid. Looking at the manual, it seams that with some care, I could use it as an SA (looking at transmitter outputs). And of course it would be awesome for looking at filters ect, assuming it dose not have the front end blown out of it.What do you think?

author: cncjerry
author_rank: Unknown
timestamp: December 27, 2016, 07:24:00 pm
content: Friend of mine has one and he lurks on the HP yahoo group. I don't know why it wouldn't work, you would have to check the input power limit as it might be 0DBm or some low value which implies "easy to blow mixer".

author: eliocor
author_rank: Unknown
timestamp: December 27, 2016, 08:45:28 pm
content: take a look at:https://www.eevblog.com/forum/testgear/enable-those-extra-features-on-your-hp-8714c-network-analyzer/I think you can be interested in.....

author: mc172
author_rank: Frequent Contributor
timestamp: December 27, 2016, 08:58:55 pm
content: I've got an 8712C. The input power limit is +20 dBm.The 8711 is not avectornetwork analyser from the factory. The 8711 and 8713 are only capable of scalar measurements. The 8712 and 8714 are the vector variants.

author: TheSteve
author_rank: Unknown
timestamp: December 27, 2016, 09:31:27 pm
content: The 8711 is vector from the factory if accessed via GPIB, but it can also have the menu options enabled by following the thread linked above.

author: lincoln
author_rank: Regular Contributor
timestamp: December 28, 2016, 12:10:47 am
content: hey Guys,Thanks for the replies> Talking a look at it today, is seams that it is 75 ohm I/Os. I'm not sure what a set of matching networks would do since most of the things i'm interested in would be 50 ohms....

author: DimitriP
author_rank: Super Contributor
timestamp: December 28, 2016, 12:54:03 am
content: Quote from: lincoln on December 28, 2016, 12:10:47 amIt depends on how low this low bid is. The amount of mismatch between 50 to 75 is inversely proportional to the price of the equipment

author: mc172
author_rank: Frequent Contributor
timestamp: December 28, 2016, 12:56:39 pm
content: Quote from: TheSteve on December 27, 2016, 09:31:27 pmI didn't know that, thanks.
USB RFID reader to GPIO Pins - Page 1
Forum section: electronics / rf-microwave

author: ElecManiac
author_rank: Newbie
timestamp: December 23, 2016, 06:42:18 pm
content: Hello,I have a USB RFID reader and I would like to use it on one of my projects. The issue is that I dont want to use the USB port, but hard wire it on perfboard which I will attach it on my Raspberry Pi.How can I do that? I have used an RC522 before, but thats made for that purpose I guess. any advices?
Receive DVB-T transmission with scantenna? - Page 1
Forum section: electronics / rf-microwave

author: synoptica
author_rank: Contributor
timestamp: November 29, 2016, 11:43:03 pm
content: Hey all,Sorry if this isn't the right place for this question!I'm looking at picking a cheap(ish) discone scantenna that covers 25 - 1300 MHz.I live on the bottom floor of an apartment building; I have roof access, but I don't want to have to run an additional cable. As far as I can tell, each unit has its own antenna (it's a pretty old place.)Being in St. Kilda and in a 3-storey building, I have LOS to both Mt. Dandenong and the repeater in South Yarra.To avoid running an additional cable, I'd like to utilise the existing TV cable, and disconnect the current VHF/UHF Yagi.So, am I likely to be able to receive DVB-T transmissions without a directional antenna?Any advice appreciated!

author: PA0PBZ
author_rank: Super Contributor
timestamp: November 30, 2016, 01:17:07 pm
content: Nobody can anwer that for you, try it is the only way to be sure.It depends on:- transmit power- transmit antenna gain- path loss- cable loss- receiver sensivity- ...

author: synoptica
author_rank: Contributor
timestamp: December 05, 2016, 12:18:08 am
content: That's fair. I was more after a "nope not suitable" or "yes, potentially" sort of an answer, but of course there's dozens of factors at play.My understanding is that Yagi antennas are the common TV antenna design to reduce ghosting, which makes sense; but I'm not sure if this will less/more of a factor with DVB-T.Anyway - thanks for your input!

author: Lord of nothing
author_rank: Super Contributor
timestamp: December 12, 2016, 11:33:49 pm
content: How about an IP based System? I have the same Problem. TV Dish on the Attic and I live in the Basement. So i desisted to use an "TV Server" who is an old IBM with 3 TV Cards in who record the TV Channels I want.

author: cdev
author_rank: Super Contributor
timestamp: December 17, 2016, 08:09:13 pm
content: You can make a broadband "Planar Disk Antenna" out of two pizza plates - cost = almost nothing.http://wa5vjb.com/references/PlanarDiskAntennas.pdf
Solder type and heat range on power transistors - Page 1
Forum section: electronics / rf-microwave

author: Hawke
author_rank: Contributor
timestamp: December 11, 2016, 04:04:39 am
content: I have two RF transistors needing replaced that I've put off for years because of the heat required to desolder the old ones it just tortures the pcb. I have wafer matched mrf455 and 2sc2960 to put into an old project but as said I've been putting it off. The factory solder requires way to much heat. Is there a flux I can buy to soften this up or anything ? Thanks

author: tautech
author_rank: Super Contributor
timestamp: December 11, 2016, 04:21:31 am
content: Quote from: Hawke on December 11, 2016, 04:04:39 amWelcome to the forum.They're probably production soldered with that lead free muck.Try mixing some normal solder with the joints, suck it off and maybe do it again a time or two until you can sucker the holes clean. Do you have a temp controlled iron? Not using too smaller tip ?

author: SeanB
author_rank: Super Contributor
timestamp: December 11, 2016, 04:58:01 am
content: Chipquick will amalgamate with the existing solder to make it a very low melting point alloy that then is easy to remove with low temperature. A small roll will cost, but for this it probably is worth it. You just need to use solderwick and extra liquid flux afterwards to get it all off, then retin the pads, clean again with solderwick, retin then place the new device and just reflow the solder using more flux. Then clean the area with IPA and it will be done.

author: Hawke
author_rank: Contributor
timestamp: December 11, 2016, 05:15:03 am
content: Thanks guys and yes I have temp controlled irons and vacum desoldering equipment but the solder on those transistors is evil stuff. I will buy some of the mentioned product to soften the old ones up as it is worth the cost to not torture the pcb. Loving this forum. Cheers

author: David Hess
author_rank: Super Contributor
timestamp: December 11, 2016, 11:13:54 pm
content: I have faced the lead free solder situation recently with PC power supplies and have replaced RF power transistors before.To handle the lead free solder, I mix in some standard SnPb solder and then remove it all with braid. Then I use a lower temperature of 600F to remove the part. In both cases I used the largest possible tip for maximum heat capacity and transfer.

author: IdahoMan
author_rank: Regular Contributor
timestamp: December 13, 2016, 05:08:20 pm
content: Makes one want use some kind of component socket instead of soldering the component directly to the board.
Measuring 2.4g ISM in time domain - Page 1
Forum section: electronics / rf-microwave

author: Harvs
author_rank: Super Contributor
timestamp: December 13, 2016, 01:58:57 am
content: I'm working on a personal project in order to learn more about RF, in particular up in the 2.4GHz ISM band.So I'm having a go at building an RF front end (LNA/PA) for a Wifi chipset to hopefully increase its performance. Only it doesn't have switching control outputs for the LNA/PA.It seems simple enough to build a coupler and feed a detector circuit to trigger when the chipset is transmitting, but my question is how would one go about measuring the switching performance in terms of time to switch on and off?My lab is kind of setup for digital and analog sensor work apart from a USB VNA, so is there any way to observe this on a 200MHz DSO? Is some sort of down-converter the answer?Any points in the right direction would be great.

author: w2aew
author_rank: Super Contributor
timestamp: December 13, 2016, 02:05:07 am
content: One thing that you'll have to be very careful with is the timing of the turn on of the PA. Carrier sense might not be fast enough to enable the PA and still maintain the integrity of the preamble of the OFDM transmission. If the beginning of the preamble is truncated, the signal won't be able to be decoded in the receiver.

author: Harvs
author_rank: Super Contributor
timestamp: December 13, 2016, 02:48:51 am
content: Quote from: w2aew on December 13, 2016, 02:05:07 amThanks, this is really why I want to be able to measure it. The makers of these wifi boosters seem to be able to get it to work, with a spec of 1us switch time:http://www.ebay.com/itm/4W-2-4Ghz-WiFi-Wireless-Broadband-Amplifier-Power-Range-Signal-Booster-Extender-/232168129340?hash=item360e4c833c:g:cHMAAOSwA3dYSVWdThe integrated SMD PA's I've been looking at from Skyworks have typical rise and fall times of about 0.5us to 0.75us. So if I can get a detector + comparator timing to be < 0.25us.This video shows pretty much what I'd like to try and build, they show switching times around 0.8us.https://youtu.be/rTloqbtIMeI
Favorite caps, inductors for broadband DC block, bias-tees - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: December 09, 2016, 03:24:18 pm
content: I am wondering what the best approach to getting a better collection of capacitors and inductors for this critical area would be, that didn't have a lot of parts I would never use. As far as inductors Ive had good luck with coilcraft but they have been parts from random SMD parts collections. So I rarely have exactly what I have wanted.Is it okay to pick, say ceramic chip capacitors out of my random parts by value? The problem with this is that I never know their GHz range RF characteristics and am not experienced enough to tell by eye what they are. I guess what I am saying is I would like to get a few often used parts in moderate quantity and am looking for tips as to what those favorite often used parts might be? I am basically an SWL/satellite listener/future ham/non-professional
Ultra low power receiver system - Page 1
Forum section: electronics / rf-microwave

author: hayatepilot
author_rank: Frequent Contributor
timestamp: December 06, 2016, 10:34:33 am
content: Hello EEVblog Forum!I have a problem with a receiver for a remote controlled crane hook wich we have given to commission to an external engineering firm.Since I'm a mechanical engineer with electronics as a side hobby I need some expert advice.Use case of the receiver: the electronics need to control a small servo motor which triggers the release mechanism for the crane hook.Most of the time it would be in standby and only need to wake up if a release command is received.The main problem at the moment is that the first prototype needs way too much current. Over 5mA on average because the module needs to stay in receive mode pretty long (several 100 ms) to be able to receive the data.At least that is what the guy who developed the prototype says.The target average current consumpion was 100uA. Is this even possible?I know with wake-on-radio functionality (WOR) the RX would only need wo be active for a coulple of ms to check for a signal.What components (rf module, microcontroller, etc) are ideal for such a system?Has somebody done something similar already?How is the WOR best set up?I appreciate any advice you can give me.Greetings

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 07, 2016, 12:27:12 am
content: How much latency is acceptable?You can reduce the average current almost without limit by making the receiver sleep for a longer period of time between waking and checking for a signal. The downside of long sleep periods is that the transmitter must transmit for a longer period of time to be certain the receiver will wake up, and there can be a long lag between transmitting a command and having the receiver wake up and receive it.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: December 07, 2016, 07:57:33 am
content: The lower latency the better.But 2sec is the maximum.At the moment there is aAMB2520wireless module used in the prototype. The microprocessor is aEFM8 Sleepy Bee.But at the moment the WOR function of the module is not used because the module can't wake up the micro. At least that is what the guy who developed it tells me. Apparently because the RF module only has SPI connection.I need to know if he is right or if its BS.Greetings

author: Marco
author_rank: Super Contributor
timestamp: December 07, 2016, 12:59:39 pm
content: Google for AMB2520, read handbook, look up WoR, don't immediately find anything relevant, look at pins (you are looking for a way to wake up the micro, so a pin going high or low is the logical way to do it) see there is a !DATA_INDICATE pin which goes low a settable amount of time before it starts outputting data ... so yes it's BS.
What is Range Gating in RADAR? - Page 1
Forum section: electronics / rf-microwave

author: MrOmnos
author_rank: Frequent Contributor
timestamp: December 07, 2016, 07:23:51 am
content: What is Range Gating in RADAR?

author: coppice
author_rank: Super Contributor
timestamp: December 07, 2016, 09:17:06 am
content: Its just the steps into which range is quantised by the signal processing system.

author: salbayeng
author_rank: Frequent Contributor
timestamp: December 07, 2016, 09:28:55 am
content: Here's an interesting read:http://www.acfr.usyd.edu.au/pdfs/training/sensorSystems/13%20Range%20and%20Angle%20Tracking.pdf"Range gating" is a bit of a sloppy term, and means different things to different people. Most often range gating is used in sonar, lidar, and radar to blank out the receiver in the near field where back-scatter and clutter would overload the receiver front end. We once designed a lidar system to work in a blast furnace, and the near field dust reflects about 1000000 x the desired signal at 20m. If you are measuring range as the time to the largest reflection, you have to blank out the first 5m or so.

author: coppice
author_rank: Super Contributor
timestamp: December 07, 2016, 09:46:31 am
content: Blanking range spans which will overload the receiver is more often called range blanking than range gating.
Converting RF to power, changes the (original) RF signal somehow? - Page 1
Forum section: electronics / rf-microwave

author: onesixright
author_rank: Frequent Contributor
timestamp: December 01, 2016, 10:39:15 pm
content: Hey Guys,I have seen a few projects that claim to convert RF signals into usable power.Examples:http://www.nowi-energy.comhttp://www.ibtimes.co.uk/iphone-6-case-downloads-power-air-by-converting-radio-signals-into-electricity-1499696I always understood, there is no such thing as a free lunch. So, if you convert RF energy back to "some" current, would that effect (as in absorb?) the RF signal itself (i.e. less distance?) ? If it would not be the case, you could put a ton of these box and endless generate energy from the same source. I would think you can never, ever, generate more then you would output. Now im pretty sure, it doesn't work like that.Anybody that could "shine some light" on this?Thanks!

author: ataradov
author_rank: Super Contributor
timestamp: December 01, 2016, 11:01:11 pm
content: Yes, you are absorbing part of the signal energy, and whatever is located behind you (if you are looking at the source) will not receive that power.Every TV antenna "shadows" the signal for further consumers, but typically it is not noticeable, since its area is very small.Imagine complete absorbent sphere around the source, there is no way signal can get outside, and it will be entirely absorbed by the sphere. Individual antenna (or mentioned harvesting devices) is a very tiny part of this sphere.

author: CJay
author_rank: Super Contributor
timestamp: December 02, 2016, 08:12:39 am
content: There are, probably urban legend, stories of farmers near to radio masts causing 'odd' radiation patterns from the discovery that their cow sheds lighting would stay lit with no power due to the wiring being of some sub wavelength.