EEVblog #767 - Super Regenerative Receiver Problems - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: July 15, 2015, 10:46:45 am
content: Dave shows a potential problem with Super Regenerative Receiver circuits, and looks at the issue of interference with his LED light remote control mains switches.Some fun with two spectrum analysers, a scope, a H-Field probe, and yes, of course a teardown.The Tekbox EMC near field probes:http://amzn.to/1Ma20zh

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 15, 2015, 10:54:01 am
content: Saw this episode coming from a mile away.

author: EEVblog
author_rank: Unknown
timestamp: July 15, 2015, 11:36:45 am
content: Quote from: ElectroIrradiator on July 15, 2015, 10:54:01 amYeah, didn't take Nostradamus!

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 15, 2015, 11:47:06 am
content: Some additional comments:One needs to differentiate between a regular regenerative detector/receiver, and a superregenerative ditto. Their schematic may at first blush look eerily similar, yet their method of operation is completely different.A classic regenerative RX generates a continuous sinewave oscillation at or very near the intended receiving frequency. The RF input signal from the antenna is mixed with the LO signal and an audio or supersonic low frequency signal is the result. This is where the frequently seen audio transformer comes into play in your MW broadcast regenerative RX. So with a regenerative detector you'd expect to see a single frequency being radiated by the detector.Asuperregenerative detector is a completely different beast. In this the oscillator is continuously driven into and out of oscillation, usually at a supersonic rate, called the quench rate. Thus the name. The trick is that when the oscillator is turned on, the gain of the RF transistor is 'slowly' increased up until the onset of oscillation. This is done by using some form of positive ramp on the base current.When an oscillator starts up, it is the noise in the circuit, which provides the initial 'seed' for the amplifier in the circuit. This is the effect, which is (ab)used in a superregenerative detector. How this works is, that at the point of onset of oscillation, the time it takes for the oscillations to exponentially ramp up from the local noise level hugely depends on whether - by coincidence or design - a (very) low level signal is injected into the oscillator from the outside. This effect is ridiculously sensitive, so a supersonic detector is quite a bit more sensitive than your regular regenerative detector with continuous oscillations.The oscillator thus converts RF input level from the antenna/ambient into time it spends at full oscillation amplitude. Higher signal level means it ramps up much quicker. IE. the DC power input to the oscillator, averaged over many quench cycles, indicates the ambient RF level around the RX frequency. If, like in this case, the quench rate is several hundred kHz, then you can easily detect data bit rates from the transmitter of several thousands. Just measure the voltage drop across a fixed resistor, or, like what is maybe used here, use a simple diode detector of the RF oscillator signal.So the oscillator ramp up waveform depends heavily on the ambient RF noise/signal level. Which means the ambient RF noise around the RX frequency modulates the oscillator, which in turn is the main reason for the ridiculously wide noise piedestal you see on the SA.

author: EEVblog
author_rank: Unknown
timestamp: July 15, 2015, 11:53:12 am
content: Quote from: ElectroIrradiator on July 15, 2015, 11:47:06 amYes. Excellent additional detail, thanks.David2 and I discussed the possibility of a Fundamentals Friday video on this.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 15, 2015, 12:04:41 pm
content: Quote from: EEVblog on July 15, 2015, 11:53:12 amGreat idea! Superregen receivers can be bad tempered (with all sort of squeals and hash) yet still grudgingly likable for what it can do.A single MPF102 & 5 turns of wire wrapped around a pencil is good for the FM broadcast band. There may be some interesting effects when tuned to a station - definitely recommended as part of a FF demo. Sensitivity is incredibly high - even with no external antenna connected. Another thing that's magic is the tiny current required - eg about 1mA for a working receiver, eg

author: rs20
author_rank: Super Contributor
timestamp: July 15, 2015, 01:24:29 pm
content: How does the build quality of the units feel? I've been meaning to build a bluetooth-based mains timer, but got stuck on the mechanicals/case for it. For $13.30, this looks like a great compact empty box with Aussie mains plug and socket ready to use!

author: rollatorwieltje
author_rank: Unknown
timestamp: July 15, 2015, 01:58:13 pm
content: How would you shield this thing if the noise is actually emitted by the "antenna"? You obviously can't shield the antenna itself?

author: bktemp
author_rank: Super Contributor
timestamp: July 15, 2015, 02:03:06 pm
content: You can add a preamplfier for decoupling the antenne from the oscillator and shield the LC tank circuit.

author: N2IXK
author_rank: Frequent Contributor
timestamp: July 15, 2015, 03:40:25 pm
content: How about a Fundamentals Friday discussing the basics of RF receivers and detection schemes? You know, Regen/Superregen/TRF/Superhet and the strengths/weaknesses of each topology. Same for diode detector/synchronous detector/BFO/ratio detector/FM discriminator/etc.The basics of RF don't need to be such a "black art" as they are often made out to be, particularly at lower frequencies, where components like inductors and caps are still recognizable as such.

author: G7PSK
author_rank: Super Contributor
timestamp: July 15, 2015, 04:09:23 pm
content: You could try giving the receiver that wont work while close to the other tweak on the coil core, that sometimes helps by reducing the gain in the circuit.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 15, 2015, 07:27:21 pm
content: I wonder how much of the spikes you got on the SA just came from the mains and not from the receiver, you just placed the antenna on top of an AC fed box.Also, increase the RBW of the SA and decrease the span to get a faster update, there's no need to look at 5 MHz or 500Hz bandwidth when looking for noise produced by the receiver.

author: AF6LJ
author_rank: Unknown
timestamp: July 15, 2015, 07:29:35 pm
content: Well Dave welcome to the world of pure garbage engineering. Only the lowest of the low would use a regenerative receiver. I suppose you got what you paid for.And of course the transmitter looks much worse.Pure garbage as its lowest.

author: AF6LJ
author_rank: Unknown
timestamp: July 15, 2015, 07:36:54 pm
content: Just as post script on this...I paused the video and did a little quick reverse engineering and it looks like the extra lead length on coil L2 may be the actual antenna....I could be wrong but I don't think so.Give me an HP-8569 any day over that Rigol SA.or for that matter my old HP-8551 / 851. (it is almost older than I).

author: TheSteve
author_rank: Unknown
timestamp: July 15, 2015, 07:56:47 pm
content: Dave, this was a great video to see. Many years back in the numeric and alphanumeric pager days I came across a problem with a VHF pager made by NEC. It used a 17.9 MHz IF that leaked something fierce. You could pickup the LO 20 feet away, any other pager with a 17.9 MHz IF would lose reception if within 10 feet of the NEC pager. It was just a dream come true to track down, lol.

author: G0HZU
author_rank: Super Contributor
timestamp: July 15, 2015, 08:07:06 pm
content: I guess you could try putting a small sheet of RF absorber in between the two units but the absorber would probably cost much more than both unitsQuoteI think that regen and super regen receivers are actually quite elegant in terms of their performance vs simplicity .

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 15, 2015, 08:27:59 pm
content: Quote from: G0HZU on July 15, 2015, 08:07:06 pmEspecially if you can add an electret microphone to the superregen and exploit its radiation to make it a 1 transistor transceiver!Eghttp://www.vk2zay.net/article/156Two for the price of one.

author: f4eru
author_rank: Super Contributor
timestamp: July 15, 2015, 08:51:58 pm
content: what a heap of crap, these receivers.Seriously, a superhet IC with XTAL and PLL costs 85cent these days, and it works, even when there is another ISM receiver around.People building receivers that don't work should be shot at.

author: apis
author_rank: Super Contributor
timestamp: July 15, 2015, 08:53:37 pm
content: Nice screwdriver hack. I wonder why they bother with those screws, it won't stop anyone who has decided to open one and I imagine it cost extra. But maybe that's where the budget for an extra transistor went.Quote from: EEVblog on July 15, 2015, 11:53:12 amThat would be great!Quote from: N2IXK on July 15, 2015, 03:40:25 pmI suspect it has a lot to do with most hobyists not having access to GHz bandwith equipment (and then there is all the regulations surrounding transmitters).Quote from: bktemp on July 15, 2015, 02:03:06 pmBut why add another transistor when italmostworks without it!?

author: AF6LJ
author_rank: Unknown
timestamp: July 15, 2015, 10:07:54 pm
content: Quote from: f4eru on July 15, 2015, 08:51:58 pmYou don't even need a crystal with a superhet...The garage door receivers here in the states are superhets and the ones I have worked on are not crystal controlled. Just an LC oscillator at half the frequency of that remote lighting junk.

author: AF6LJ
author_rank: Unknown
timestamp: July 15, 2015, 10:09:08 pm
content: There is no black art to RF and it gets easier as you approach 1GHZ.

author: RupertGo
author_rank: Regular Contributor
timestamp: July 15, 2015, 10:09:26 pm
content: I've got a couple of commercial super-regen receivers here in actual radios. One is a super-crappy 1970s single channel CB walkie-talkie, which has (if I remember correctly) a whole three transistors - a 27.125 MHz crystal oscillator, one doing AF things, and one being a super-wide super-regen receiver. You can tell when it's on because anything else in the place that's tuned between 26-30 MHz makes a rude hissing noise; it doesn't have that much more range when you actually transmit. But a fine example of what you can do with very little. When conditions were good, I remember hearing Radio South Africa on the 26 MHz band come thundering in...The other is more interesting, it's the B set in my Wireless Sets 19, the classic British/Allied tank radio from WWII. The A set is a proper superhet transceiver on 2-8 MHz (actually, I think it's the first ever transceiver, in that the RX and TX are tuned by the same circuit) that puts out about 10 watts. The B set, though, is for 230-250 MHz (ish), also tuned by one knob, and I think that produces around 10mW. That was used for tank-to-tank comms. Most people who used the 19 set after the war pulled out the B set gubbins, because it produced enough interference to mess up VHF TV over quite a wide area and thus made a chap unpopular. I think that's around three valves (the A set has ten or so), which was really important in the days when valves were in critically short supply. It was also a very high frequency for the time, which made for a very short range and thus fewer security worries.I would love to see Dave do a teardown on a 19 Set - but it won't be mine, first because it's a prized piece of my collection, but also it weighs about 40 kilos all-in and I think I could afford a holiday in Oz for the cost of shipping the thing from Blighty.(odd radio fact: the German tank radios used 27 MHz, much like my little walkie-talkie, which was also short range enough to avoid interception nearby, but which during the excellent propagation of the time of the African desert war meant that receivers in the UK could pick up Radio Rommel just fine for large parts of the day.)

author: AF6LJ
author_rank: Unknown
timestamp: July 15, 2015, 10:11:38 pm
content: I have a good teardown for Dave but it costs too much to ship all the way across the pond.MY HP-5245L Universal Counter, there ain't no chips in that puppy and it works great all the way to 3GHZ.

author: apis
author_rank: Super Contributor
timestamp: July 16, 2015, 12:34:50 am
content: Found this 1998 article from arrl if anyone wants to build one:http://www.arrl.org/files/file/Technology/tis/info/pdf/9811qex026.pdf

author: AF6LJ
author_rank: Unknown
timestamp: July 16, 2015, 04:03:50 am
content: Quote from: apis on July 16, 2015, 12:34:50 amThat is a good article, the old school regen receivers had one or two stages of tuned RF amplification ahead of the detector. For a time I owned a LF/VLF regenerative receiver from the 1930s. (14KHZ to 600KHZ coverage.) It worked like a bomb and was well shielded.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 16, 2015, 04:15:13 am
content: Quote from: RupertGo on July 15, 2015, 10:09:26 pm"(actually, I think it's the first ever transceiver, in that the RX and TX are tuned by the same circuit)"Not so sure of that----the Aussie Number 11 does the same.I'm pretty sure the 11 set predates the 19,but they may be contemporaries.They were only a HF radio though!The 19s were always more expensive in the surplus shops,so I ended up with a Number 11.Unfortunately they used directly heated valves & were not directly usable from mains supplies.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 16, 2015, 04:45:34 am
content: Quote from: AF6LJ on July 15, 2015, 07:36:54 pmSue,I bit my tongue!Just kidding!73,VK6ZGO

author: 99tito99
author_rank: Regular Contributor
timestamp: July 16, 2015, 06:19:01 am
content: The scariest thing is you have stuffed your “crawl space” with OneHungLow random/spontaneous deflagration units.CheersMark********************

author: Muttley Snickers
author_rank: Unknown
timestamp: July 16, 2015, 07:17:16 am
content: As 433 MHz is very popular with alot of RF remotes such as car and home alarms, I was a bit concerned that these things could switch on if the neighbour sneezed which could be a hazard, particularly if someone was to use them on an electric heater or a kettle, anyway I read the online user manual and at least they do warn against using them on such devices as well as cooking equipment and power tools. I dont trust the Arlec stuff much and never have.Bloody cheap, $14 for one socket and one remote or $26 for three sockets and one remote, the book says 30 meter range, I'm guessing down hill with a favourable wind perhaps.Muttley

author: rs20
author_rank: Super Contributor
timestamp: July 16, 2015, 07:52:24 am
content: Quote from: 99tito99 on July 16, 2015, 06:19:01 amAre crawl spaces flammable? I mean, obviously spontaneous deflagration units are to be avoided, but perhaps a crawlspace is an ideal location for them?

author: AF6LJ
author_rank: Unknown
timestamp: July 16, 2015, 01:41:56 pm
content: Quote from: vk6zgo on July 16, 2015, 04:45:34 amI admit I am not much of a fan of the latest low cost test gear from China.I would rather have something I can repair like the gray and beige iron from around the SF bay aria.

author: AF6LJ
author_rank: Unknown
timestamp: July 16, 2015, 02:07:12 pm
content: As one who is known for looking down my nose at people who garnish their presentations with profanity, I would agree Dave isn't the worst offender out there, and his content is of great enough value that the occasional use of profanity is tolerable.More to the subject;The first issue I really have with the lighting setup is the use of an RF remote in an electronics lab. Just another source of noise, an IR remote would have been better.Those panels are nice they put out a healthy amount of light, I am even considering something like that here. My only concern is being an AM BCB DX'er I can't help but wonder how much noise those will generate.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 16, 2015, 03:19:28 pm
content: I can't think of a single instance of racist comments (and I'm very sure Dave wouldn't knowing do so), that is one hell of a serious accusation you just made.

author: mikerj
author_rank: Super Contributor
timestamp: July 16, 2015, 03:35:53 pm
content: How many people constantly complain about Dave's language on the forum? By my count, it's one person.

author: mikerj
author_rank: Super Contributor
timestamp: July 16, 2015, 03:38:39 pm
content: Quote from: 99tito99 on July 16, 2015, 06:19:01 amThat is the one thing that worries me about this kind of crap, and is why I never use e.g. shoddy Chinese mains chargers/adapters.

author: mmagin
author_rank: Frequent Contributor
timestamp: July 16, 2015, 03:43:11 pm
content: Well, it's a faulty design unless they put a big note in the instructions that you have to have the receivers spaced pretty distant from each other (I assume that's what they were thinking,) but it's kind of elegant in a way, if you're strictly optimizing for simplicity.Wonder if it meets the relevant government standards (e.g. Australian equivalent of the FCC).

author: G0HZU
author_rank: Super Contributor
timestamp: July 16, 2015, 04:15:41 pm
content: FWIW I've got experience of using several of the UK equivalent to these things. They are made by Status and have model number RCS K09.The most significant failure/reliability issue with them is that after a while they can stick in the ON position. I think the relay contacts weld or stick.So when it fails like this you can turn it off via the remote and the unit responds accordingly (LED goes out) and you can hear it try to click the relay but the relay contacts stay closed. So the mains power is still connected to the output!So you can't rely on these things to turn off something unless you can actually see the connected equipment lose its standby lights or the neons go out in a power strip.I've seen three of these devices fail like this. You can free up the relay by tapping the unit fairly hard but it isn't exactly what you want from something like this...Note that I didn't use them on high current devices. I'm guessing that the relay sticks on surge currents. But I only ever used them for devices that take maybe a total of 2A or 3A continuous. I managed to make one stick ON with just a desktop PC as the load.

author: bktemp
author_rank: Super Contributor
timestamp: July 16, 2015, 04:22:23 pm
content: Quote from: G0HZU on July 16, 2015, 04:15:41 pmYes, the cheap Chinese relais don't like high inrush currents. I have a similiar problem with one used to switch a TV. If I switch the TV off and back on, the relais sticks. Then I need to hit it hard so switch off. This only happens when the time between off and on is short. The TV probably has a NTC for inrush current limiting that needs some time to cool down. If you switch it back on too quickly, the inrush current ist much higher and the relais sticks in on position.Another failure mode are the capacitive power supplies: I have seen a lot of X2 capacitors with almost no capacity left (<10nF instead of 100-470nF).

author: G0HZU
author_rank: Super Contributor
timestamp: July 16, 2015, 04:29:56 pm
content: Quote from: bktemp on July 16, 2015, 04:22:23 pmI was editing my post as you replied and I agree it must be an inrush current issue. I've got three units here that have been faultless since new but the other three all suffered the stuck relay syndrome.So I guess you have to be careful what loads you connect to them in case they can generate a sharp surge.

author: SNGLinks
author_rank: Regular Contributor
timestamp: July 16, 2015, 07:13:00 pm
content: Quote from: RupertGo on July 15, 2015, 10:09:26 pmMy father was a radio operator in a tank in WW2. They could never get the B set to work - even to a tank along side. In the 50s he got his amateur license (G3NXU) and his first set was a 19 set. You could buy the complete kit - radio, headset, whip, ATU and rotary converter (so you could run it off 12v) for, I think. £19 19s.

author: andersjm
author_rank: Contributor
timestamp: July 16, 2015, 11:01:26 pm
content: I've been trying to figure out how the thing is connected at the mains-side.Is the relay connected in series with the X-class capacitor? If not, how is it connected? Is the purpose of the capacitor to act as a snubber, or some other purpose?

author: rs20
author_rank: Super Contributor
timestamp: July 16, 2015, 11:05:08 pm
content: Capacitative dropper perhaps?

author: apis
author_rank: Super Contributor
timestamp: July 17, 2015, 12:24:41 am
content: Yes, I would also guess on a capacitive power supply, it requires a X2-class safety cap. For details see:http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf

author: Goober_in_CA
author_rank: Newbie
timestamp: July 17, 2015, 12:32:27 am
content: Hi DaveYou might try to extend the range of your receivers by adjusting the frequency of each receiver.Since they are just a simple LC oscillator, the drift of each receiver is really poor.Most of these cheap receivers are still simple conversion type using an intermediate frequency (IF) and not regeneration types. So what happens when you have 2 receivers together like this is that the local oscillator (LO) from RX1 will get into the front end of RX2 or the reverse. This explains why 1 receiver has interference problems and not the second.Follow me here: Lets say both are designed to receive 400MHz and use low side injection of 389.3MHz.RX1 is tuned properly at 400MHs or the LO is at 389.3MHz giving us a IF freq of 10.7MHzBut RX2 has drifted.RX2 is at 390MHz and not where it should be at 400MHz. Or the LO is at 380Mhzish. This would let the RX1 LO leak into the front end of RX2 and swamp out the receiver.This is why 1 receiver works better than the other receiver.I have seen this same sort of problem with other poorly built receiver similar to your light switch receivers.So how do you fix it? Just tune the receivers. You don’t need any special RF test equipment.1. Plug in RX1 and not RX2, have Dave#2 operate the transmitter at a range that is on the edge of working.2. Tune the slug in the receiver until the sensitivity improves. Trial and error.3. Have Dave#2 continue to increase his distance from the receiver and repeat step 2. Do this until optimum distance is achieved.4. Repeat with RX2.Things to watch out for! The slugs break easily. DO NOT USES a metal screwdriver. You will break the slug and the metal diver will interfere with the tuning. Ceramic tools are the best but plastic will do the job. Something like Digikey 243-1013-NDAnother got-ya is the plastic case itself. Everything might tune up great without the case. Then install the case and nothing works. Just drill a hole in the case above the tuning slug and tune the receivers with the case enclosed.Thanks for the great podcast!Hope this helps.Daryl

author: vk6zgo
author_rank: Super Contributor
timestamp: July 17, 2015, 03:57:45 am
content: Quote from: AF6LJ on July 16, 2015, 01:41:56 pmSue,my comment was aimed at our mutual maturity--we just get better,like wine!On the other point,though.We had a small Atten SA at my last work--not much,but we found a PLL fault with it that the expensive IFR SA couldn't find.Digital-v-analog again--the IFR saw a rapidly changing frequency as a bunch of discrete carriers,whereas on the Atten you could see the damn thing move!From the look of it,the Rigol SA is digital,so would probably have the same problem as the IFR.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 17, 2015, 04:46:26 am
content: Quote from: ElectroIrradiator on July 15, 2015, 11:47:06 amYour description of a Regenerative Receiver sounds more like a Direct Conversion Rx.The description I first read back in the 1950s & have seen everywhere else since,goes something like this:-Positive feedback in a Regenerative Detector compensates for resistive & other losses in the Rx tuned circuit, effectively increasing its Q,& hence,both the sensitivity & selectivity of the receiver.When receiving full carrier AM,the feedback is set tojust belowthe point of oscillation,to obtain the positive effects efficiency enhancement without hearing a beat note against the carrier.For CW (Morse Code) & Single Sideband signals,the feedback is advanced until oscillation begins,so as to provide an audible beat note for CW,or to re-insert a carrier for the resolution of SSB.

author: abebarker
author_rank: Contributor
timestamp: July 17, 2015, 04:49:28 am
content: [Never mind, I talked myself out of this idea working]Do they interfere with each other less if the coils are turned 90 degrees from each other? I imagine that you are probably going to be able to get them closer together if one of them is turned on its side.They are coils and they are going to couple when they are right next to each other especially when the coils are pointed in the same direction. That mean one of them is going to push the other off frequency. I remember discussing that phenomena in this thread;https://www.eevblog.com/forum/chat/coupling-tuned-circuits/When the axis of one coil is 90 degrees from the axis of the other the magnetic field it generates can not induce any current in the other coil (for the most part).Although, now that I think about it, the cores may be susceptible to the field in any orientation and induce a current in its coil anyway. Oh well, defeated by a susceptible chunk of ferrite.

author: rs20
author_rank: Super Contributor
timestamp: July 17, 2015, 06:36:11 am
content: Quote from: abebarker on July 17, 2015, 04:49:28 amIf you flip the device upside down, the phase of the signal received by the other coil will be inverted. Therefore, at some point as you rotate the device around, there must exist a point where the signal received by the other coil is zero.Hmm, although that assumes that the gain can't be complex.

author: TSL
author_rank: Regular Contributor
timestamp: July 17, 2015, 06:57:48 am
content: Quote from: mmagin on July 16, 2015, 03:43:11 pmThe relevant standard says 25mW EIRP, so it probably does.Australian LIPD standard can be found here.http://www.acma.gov.au/Industry/Spectrum/Radiocomms-licensing/Class-licences/spectrum-opportunities-for-short-range-devicesregardsTim

author: andersjm
author_rank: Contributor
timestamp: July 17, 2015, 09:15:17 am
content: Quote from: apis on July 17, 2015, 12:24:41 amAh, so the capacitor isn't involved in the actual mains switching. It really is just the relay, with no MOV or capacitor or anything to protect the relay from arcing while switching off inductive loads?Shouldn't there be some sort of snubber? Am I correct in thinking this thing really isn't suitable to power inductive loads? Maybe it is only meant to power resistive loads, but I wonder if that is stated clearly on the box it came in?

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 17, 2015, 02:32:07 pm
content: Quote from: vk6zgo on July 17, 2015, 04:46:26 amThat is because a regenerative detector*is*a Direct Conversion Receiver when it is oscillating. It has been roughly 35 years since I built my first regen receiver, so I know how they work.Somewhere I should also have my little experimental superregen for the 88-108 MHz FM band if anyone would like to see it. (The superregen detector uses slope AM/FM detection like the receiver in the video shown previously). Caution! Contains vacuum tubes. May upset sensitive semiconducting souls.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 17, 2015, 02:53:40 pm
content: Quote from: ElectroIrradiator on July 17, 2015, 02:32:07 pmButonlywhen it is oscillating---it is not used in the oscillating mode when receiving AM.A true Direct Conversion receiver has a Local Oscillator which is always oscillating.I built my first Regen set 56 years ago!Quote

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 17, 2015, 03:06:39 pm
content: Quote from: vk6zgo on July 17, 2015, 02:53:40 pmAh, I see. You are splitting words in order to sound clever. OK, carry on.

author: apis
author_rank: Super Contributor
timestamp: July 17, 2015, 06:01:56 pm
content: Quote from: andersjm on July 17, 2015, 09:15:17 amI don't think there is any, there could be a MOV but couldn't see any. Ideally there would be a snubber inside the inductive load itself.They need to power the receiver somehow and in cheap low power devices that's typically done with a X2 cap so I'm guessing the cap is for dropping voltage in this case.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 17, 2015, 08:33:42 pm
content: Quote from: ElectroIrradiator on July 17, 2015, 03:06:39 pmI agree with vk6zgo.There are significant behaviour differences between a regenerative and direct conversion receiver, even when the former is oscillating.A regenerative receiver, when brought towards oscillation, narrows its selectivity as the Q of its tuned circuit is effectively heightened with increasing amounts of positive feedback.The maximum Q is just before oscillation, but it's still fairly high when it's gently oscillating.This effect is helpful when trying to tune a crowded HF band and pick signals apart.In contrast you don't have that effect with a direct conversion receiver - if you want high selectivity you need to apply audio filtering.The second difference is that a regenerative detector has a non-linear oscillating detector.In contrast a 4 diode balanced mixer, which is common on direct conversion receivers, is basically linear. This is beneficial when designing a receiver with good strong signal handling characteristics, making a good DC receiver superior, especially if there is reasonable band pass filtering between antenna and detector.You can blur the lines between the two by having both a regenerative detector (set just before the point of oscillation) and an external beat frequency oscillator on the reception frequency that is near but not physically connected to the detector. Personally I find this gives the best results when receiving weak signals. It also overcomes many of the problems of regenerative receivers, eg the local oscillator changing frequency when a different antenna is connected, tuning in the antenna circuit is adjusted or frequency pulling on strong signals. While off-topic, an external BFO is also beneficial with a crystal set style detector as it provides RF bias, better weak signal reception and even CW/SSB capability.Superregen detectors are different again - they are way less selective and are only good for AM and wideband FM signals (they'll cope with narrowband FM but you need to crank the volume up and the hiss can be hostile).

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 17, 2015, 09:41:17 pm
content: Quote from: vk3yedotcom on July 17, 2015, 08:33:42 pmThe I am afraid we will have to agree to disagree.I didn't bring up the DC RX. What I wrote was:Quote from: ElectroIrradiator on July 15, 2015, 11:47:06 amWhy are we having this debate, based on what I wrote?

author: SeanB
author_rank: Super Contributor
timestamp: July 18, 2015, 09:36:47 am
content: Those relays are very prone to sticking, or to arcing themselves to pieces. They are the standard relay used in those sealers you see al laround for sealing plastic bags, where they drive the 56VAC transformer used to heat the sealing element strip.Failure mode is either the contacts arc away ( lovely fireworks show and a burnt relay case with lots of smoke) or they simply weld closed. I buy a local version that is slightly better rated, with a 5A rating, and with slightly thicker current carrying pins, which means I have to drill the 2 holes in the SRBP board oversize to fit them.Standard addition is a VDR across the contacts, to reduce the arcing on the coils. They lead a hard life in those sealers, and I keep a few spares along with all the electronics for the control, which is a 5W resistor, some C106D SCR's, some 6V8 zener diodes and the single NPN transistor used there, along with the 10uF 400V capacitor and the 100uF 25V timing cap, and always add a 220k resistor across the control pot to reduce on time, as you never need more than a 2s pulse to seal, and they go all the way to 8s which cooks the element and the PVC bags.

author: VK3DRB
author_rank: Super Contributor
timestamp: July 19, 2015, 09:02:32 am
content: 433.920 MHz is the "CB band" or "Kiddies band" in the remote control world. I had a non-technical friend whose garage door opener became very insensitive to the remote, making it next to useless. He told me he paid a ripoff merchant about $1,000 to get the main board replaced, but the problem was still there. I investigated it and found one of his neighbours had installed some crappy Chinese weather station atop his house that transmitted on 433.920 MHz, wiping out the frequency for a radius for several houses around. 433.920 MHz is a risky frequency to use in Australia because you have no idea what RF crap is around to interfere on that frequency. Most modern car remote door openers have moved off that frequency.Was this Arlec piece of crap really designed in Australia?http://www.arlec.com.au/innovation-design/I doubt it!

author: vk6zgo
author_rank: Super Contributor
timestamp: July 19, 2015, 10:18:54 am
content: Quote from: ElectroIrradiator on July 17, 2015, 09:41:17 pmWe are having this debate precisely because of what you wrote.A Regenerative Receiver only generates a continuous sinewave oscillation at or near the received frequency in the special cases where it is receiving CW or SSB signals.When receiving AM signals,the level of feedback is kept below that which will cause oscillation.Positive feedback at just below the threshold of oscillation has the following beneficial effect--cancellation of losses in the Receiver input tuned circuit,leading to higher circuit Q,which in turn increases both selectivity & sensitivity of the receiver.It is this effect which is the primary benefit of Regeneration,rather than oscillation.Youcanreceive AM in the oscillating mode,but the "L.O." thus formed is unstable,so the demodulated audio drifts off into distortion due to audible beat notes mixed with the desired audioI know this happens--I've tried it!.It is hard enough to receive AM in this manner using a Superhet with a stable BFO!

author: G0HZU
author_rank: Super Contributor
timestamp: July 28, 2015, 07:54:06 pm
content: For a bit of fun I tried capturing an on and an off burst from the STATUS (UK model) transmitter using an Agilent E4406A and the 89601 VSA SW from Agilent. This allows the burst to be captured and saved as I and Q data to various file formats. It looks like simple OOK.For a bit more fun I then transferred the captured IQ burst directly into an Agilent vector sig gen as I and Q bin data (contained in I.bin and Q.bin files) and played the file data back at several mW via an antenna.This basic 'grabber' and replay system worked perfectly (no surprise) as I guessed there would be no security in the form of rolling codes etc.So the vector sig gen could turn the unit on and off the same as the real remote.

author: 99tito99
author_rank: Regular Contributor
timestamp: August 05, 2015, 04:23:40 am
content: Quote from: rs20 on July 16, 2015, 07:52:24 amAlthough your thought that this is the best spot if not to hot maybe right, this void devoid of sight causes some fright. (wow, that's a stinker!)Cheers,Mark*****************