Very basic antenna question - Page 1
Forum section: electronics / rf-microwave

author: casterle
author_rank: Regular Contributor
timestamp: January 02, 2021, 08:11:53 pm
content: I picked up an NESDR Smart, which came w/3 antennas. After getting it running, with the telescoping antenna attached, I tuned a local FM station. Watching the signal strength, I adjusted the length of the antenna expecting to see a change. I didn't see much difference regardless of the antenna length.Can someone kindly explain why I didn't see what I had expected?

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: January 02, 2021, 09:17:01 pm
content: So many things can affect reception of strong FM broadcast stations. Even placement of antenna in a room or where you stand near it.Signal transfer is affected by impedance matching - and who knows what the impedance of the SDR is (whereas transceivers are almost all 50 ohm).And a vertical whip with no ground is an incomplete antenna - but that hardly matters with strong stations.Antennas are best compared outside where there's no obstructions and on weak signals (eg an amateur radio beacon such as often found around 144 MHz).Even in this case a small movement can cause big changes in received signal level so multiple tests need to be done to clearly demonstrate the merit of one antenna over another.Very narrow bandwith antennas, like small tuned loops, have much more decisive adjustments where a peak is clearly audible.

author: cdev
author_rank: Super Contributor
timestamp: January 02, 2021, 09:39:47 pm
content: Receivers based on the RTL2832 TV dongles and TV tuners have irregularities which are built into them optimizing the gain in order to get the most use out of the 8 bits ADC they have available to them. They are optimized for video reception and a video channel thats typically around 6 MHz.The SDR mode was originally intended for FM reception. FM signals are ~200 Khz wide..Still they perform well as peope have used them to do amazing things, considering all this.But that flexibility - at the end of the day, comes at the cost of linearity.So, even when AGC is off (which it should be) they can't be used to reliably measure gain or power numerically, in the way one would wish.They do do much better than one would expect from anything so inexpensive, though.Where else are you going to find anything that can receive such a wide range of frequencies as well as RTLSDRs do at such a low cost? (as little as $7 plus shipping or $10 with for some of them)Also, assuming the antenna your dongle came with was attached to a magnet base did you affix the antenna to the top of a large metal object, like a car? That's the way its supposed to be used.the antennas thatsomeof them come with use cable which is not really coaxial cable. It may even be marked RG-174 but if sliced open, Ive found semi-shielded audio cable- a totally different kind of wire which is unlikely to be able to properly act as coaxial cable. So that combined with the lack of ground plane unless the antenna is stuck using its magnet to a large metallic object, means its likely that that wire is likely also acting as part of the antenna.If you bought your dongle from a company that's intending their dongle to be used as an SDR rather than for in-car TV viewing maybe you'll get a better antenna!

author: radiolistener
author_rank: Super Contributor
timestamp: January 02, 2021, 10:00:09 pm
content: most of these "antennas" that come with SDR dongles, actually just a piece of wireDon't expect good reception from such "antenna".If you want to tune antenna size and balun, you're needs vector network analyzer, such as NanoVNA.It's very hard to see the difference with receiver.You're needs to experiment with a very weak signal and check it's power in dB on the spectrum display.This is hard, because you never know if signal level is reduced due to propagation change or due to antenna tune.

author: casterle
author_rank: Regular Contributor
timestamp: January 02, 2021, 10:48:37 pm
content: Quote from: vk3yedotcom on January 02, 2021, 09:17:01 pmI've noticed a significant change in signal strength moving the antenna only a few feet.

author: casterle
author_rank: Regular Contributor
timestamp: January 02, 2021, 11:10:38 pm
content: Quote from: cdev on January 02, 2021, 09:39:47 pmExactly! I paid $24 for a well-reviewed NESDR Smart V4 including 3 antennas and the mount. At that price the cable may well be sans shielding, but I'm paying for the magic in the black aluminum dongle.Quote from: cdev on January 02, 2021, 09:39:47 pmNo. I attached it to a 3" steel disk which I affixed to the lens on an old magnifying lamp, which acts as a horizontal platform so I can raise it as high as possible (my office is in the lower level of a tri-level house, so my antenna is about 3' above ground level). So no ground plane at all, and an LED shop-style fixture not far away.Quote from: cdev on January 02, 2021, 09:39:47 pmIt is intended as an SDR, but at the price I paid that probably doesn't mean much.

author: casterle
author_rank: Regular Contributor
timestamp: January 02, 2021, 11:11:50 pm
content: Quote from: radiolistener on January 02, 2021, 10:00:09 pmI've got one on the way!

author: A.Z.
author_rank: Super Contributor
timestamp: January 03, 2021, 08:45:05 am
content: Quote from: casterle on January 02, 2021, 08:11:53 pmtry repeating the test with a "faint" station and you should see the difference; as for the SDR, is it this one ?https://www.nooelec.com/store/nesdr-smart.html

author: casterle
author_rank: Regular Contributor
timestamp: January 03, 2021, 10:25:36 pm
content: Quote from: A.Z. on January 03, 2021, 08:45:05 amThanks, I'll try that. With my current configuration they're all faint. One that my wife likes as a strong signal on her radio but shows peaks about 50% below another nearby (in frequency).Yes, that's the one I've got.

author: casterle
author_rank: Regular Contributor
timestamp: January 03, 2021, 10:34:52 pm
content: My SDR came with 3 antennas, 2 fixed and one telescoping. As I understand it, antennas are tuned to a frequency by the length of its elements, thus the various antennas. But why can I attach only one at a time to the SDR?Another question is why supply the longer fixed-length antenna? The telescoping unit can be made shorter, so it must be more than length...

author: cdev
author_rank: Super Contributor
timestamp: January 04, 2021, 12:37:48 am
content: Upselling?

author: antenna
author_rank: Frequent Contributor
timestamp: February 27, 2021, 06:10:58 pm
content: I have the same SDR with the up converter. Those 3 included antennas arejunk. I no longer have them, but I recall putting them on the VNA and none of them gave me a 50ohm match on anything I listen to. I couldn't even get good FM broadcast bands with the mag mount w/ telescopic antenna on the house roof. Best to build your own antennas.I am using mine exclusively for 88-108MHz FM music. I have a vertical dipole made of copper pipe with a larger pvc pipe as an insulator/dipole support. That is connected to 75ohm coax (i forgot what I did at the feed point for matching, pick a method) and on the other end I made a 75ohm to 50ohm L network in a metal box with F-type and SMA connectors to match the repurposed RG-6 tv coax to the SDR (not necessary if you don't mind 2:1 SWR.Keep the coax as short as possible at VHF!That SDR can also sound cruddy on FM broadcast if the gain, sample rate, buffer size, and bandwidth are not properly set. To get started listening to 88-108MHz, set the bandwidth to 192,000, the tuner gain about 17dB, 2.4M sample rate, 64kb buffer size, and I use a LO-Tuner offset of 550,000The antenna could be a piece of foil tape on the wall. Even that aluminum tape can be soldered to with a little practice, stuff makes for great window antennas!

author: cdev
author_rank: Super Contributor
timestamp: February 27, 2021, 11:12:58 pm
content: The wire some of those "antennas" come with is just microphone wire. Replacing that wire on them with RG-316 or similar would be a good investment in time and money.They are worthless without some aftermarket modifications. Also, it seems to me that the work done of the "RTLSDR blog version 3 is worth buying if you are early in the process and get a good price on them. Considering the low price on RTL dongles (as low as $6) its ridiculous buying them for $24. If you pay less then that ($11 is average) they make great gifts. People can use them with a Raspberry Pi to learn basic programming and linux skills.

author: cdev
author_rank: Super Contributor
timestamp: February 27, 2021, 11:32:33 pm
content: I would be extremely surprised if they were worth the 200% premium people are asked to pay. If youre going to pay $20 or more why not get an RTLSDR blog v. 3 that at least has a better chance of being more stable. But sans antennas as the antennas do not add to the value. That money would be better spent on two far ferrite beads to make a 9:1 unun, and the wire to make one. Or a binocular core. Since you can use the RTLSDR v3 dongle in direct sampling mode on HF.Exactly! I paid $24 for a well-reviewed NESDR Smart V4 including 3 antennas and the mount.Where is this review?At that price the cable may well be sans shielding, but I'm paying for the magic in the black aluminum dongle.Magic? You must mean marketing fluff-up. as in "tarting it up", as you UKers would say.Quote from: cdev on January 02, 2021, 09:39:47 pmNo. I attached it to a 3" steel disk which I affixed to the lens on an old magnifying lamp, which acts as a horizontal platform so I can raise it as high as possible (my office is in the lower level of a tri-level house, so my antenna is about 3' above ground level). So no ground plane at all, and an LED shop-style fixture not far away.Or maybe the ground plane is up.Quote from: cdev on January 02, 2021, 09:39:47 pmIt is intended as an SDR, but at the price I paid that probably doesn't mean much.Youre lucky you are a DVB-T country otherwise your ridiclously anal OFCOM would probably ban their sales. Which have probably done more to get young people interested in radio and communications engineering than almost every other successful electronics product.

author: frogg
author_rank: Regular Contributor
timestamp: March 01, 2021, 04:05:08 pm
content: Quote from: casterle on January 02, 2021, 08:11:53 pmWhy do you think that your received signal strength would change based on the length of the antenna?Not sure why everyone is responding with so much emphasis on the SDR or "junk antennas" (they are not "junk" even if they are cheaply made). What the OP is observing has nothing to do with the SDR or the antenna construction.Here's something the OP can try: Disconnect your antenna and tell us what happens to your radio station signal.

author: A.Z.
author_rank: Super Contributor
timestamp: March 01, 2021, 05:11:15 pm
content: to the signal, yes, but to the noise level too

author: edy
author_rank: Super Contributor
timestamp: March 01, 2021, 08:06:08 pm
content: I was about to post this exact topic and noticed this thread... I have questions as well on an antenna setup for some basic AM SW listening though. I have the RTL-SDR blog dongle with dipole antenna kit shown as the first item here for $35:https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/. I am using it on Linux with Gqrx and CubicSDR.With the included dipole I have no problem picking up FM and some local AM stations. However, I am having a difficult time picking out anything but a very few number of very strong SW stations (like 5950 kHz WRMI). I'm in Toronto. I have a Tecsun PL-310ET and it finds more SW stations.I have limited options right now with respect to external antennas. I have an MLA-30 loop antenna that I tried before but had to pack up. I used it both with external power and the Bias-tee power turned on from the dongle. I'm not sure if it made much difference, I have to systematically test things. Same with a long-wire strung out the window to the back fence. I may try to set them up in the office, I can't do so in the house at this point.Is this typical of the reception given the antenna limitation? I'd like to pick up stuff in the 2400 - 24,000 kHz range, find some far away stations, HAM chatter, CW or data signals to decode with fldigi, but it's frustrating. The Tecsun did a great job when I first got it, but of course I was pretty much limited to AM reception... my model does not have SSB capability. Hence why I wanted to give the RTL-SDR a try as I am on a budget (also the reason I opted for the MLA-30 loop). I may have to experiment with long-wires again. The problem is no matter where I set it up I have buildings and houses in the way everywhere, I'm in a city. I can't really get far off the ground either.NOTE:I have noticed that with my kit, if I don't use an antenna I get very poor reception. If I screw my SMA connector part way, it will work. If I screw it in ALL THE WAY (until tight) I lose signal. Somewhere along the way something is losing contact. I tried bending the middle "pin" on the male part from the antenna a bit sideways thinking it may make better contact with the female on the dongle, as I thought maybe the female is too loose and when tight it is too perfectly centered and actually doesn't touch the walls of the female.By the way, that drove me nuts for a while... I had everything connected yet poor reception only to realize the darn antenna connector was to blame. Is this defective, or is something else going on?

author: A.Z.
author_rank: Super Contributor
timestamp: March 02, 2021, 08:28:24 am
content: Quote from: edy on March 01, 2021, 08:06:08 pmWhich may mean that the internal PL310 ferrite is working better than the antenna you use with the RTLSDR... or either the RTLSDR settings weren't correctly configured, notice that to go down to HF and below, the RTLSDR must be configured in direct sampling mode and then you'll also want to fiddle a bit with gain/AGC and so on, that being saidQuoteThe unmodified MLA-30 works decently well at MW so may be a good pick, as for the longwire, it will work but if you are in an RFI "dense" area it will pick up much more noise, also, to connect the longwire to the receiver it would be a good idea using an UnUn, a cheap one is the NooElechttps://www.amazon.com/NooElec-Balun-One-Nine-Applications/dp/B00R09WHT6it can be used as either a BalUn or an UnUn by just cutting (or connecting) the "R1" (a track on the back of the board - seeherefor the schematic)Getting back to the MLA, I wonder why you had to pack it up, also notice that the MLA preamp could be used with other antennas, for example, if you have wooden window frame at home you may just wrap three turns of insulated wire around the window frame and connect the ends to the MLA preamp unit, that would make an invisible antennaAs for powering, while the MLA can be powered using the 5VDC from the RTLSDR bias-tee, the performance will be poorer since the original MLA BIAS-T box feeds the preamp with about 12VQuoteWell, the SDR has no internal antenna, so w/o a connected antenna you won't pick up much (aside from very strong local stations, maybe), what's strange is the fact that screwing the SMA connector all in (do not "force" it or you will break it) seems to "shunt" the antenna, I suspect that the connector may be damaged... but does it do the same with both the MLA and other antennas or just with one particular antenna ? Because, in the latter case that antenna connector/coax may be damaged, otherwise ... the SDR connector may be damaged

author: frogg
author_rank: Regular Contributor
timestamp: March 02, 2021, 03:11:14 pm
content: Quote from: edy on March 01, 2021, 08:06:08 pmNo, what you are experiencing has little to nothing to do with the antenna. It has everything to do with receiver gain, instantaneous bandwidth, and SNR.Do you have any front end filters installed?

author: edy
author_rank: Super Contributor
timestamp: March 02, 2021, 05:37:03 pm
content: Thanks for the responses. To answer your questions...I had my DIY PVC piping/tripod-mounted MLA in my upstairs bedroom and my wife is not a fan of my radio hobby.I like the idea of wrapping some wire around my window-frame (it's probably about 3x5 feet total as it contains 3 vertical panes next to each other, the middle one being the only one to open).The other option, at least for now, is to string a 25 ft length of speaker wire out my upstairs window and tie it to the fence at either corners of the back yard. I'll attach a photo so you can see what I mean. Then I connect up each end to a balun outside my window (the one mentioned by A.Z.) and then bring that in on a coax to the bedroom window to the radio or SDR. The problem is, this "dipole" will not be 180-degrees, it will be more like a "vee" dipole and the angle is probably even less than 90-degrees (see photo).As you can see the by "OLD HOUSE" if I connect from the house to each of the opposite corners of the backyard (about 28 ft away) the angle will be 43 degrees between the long-wires.The "NEW" shows also where the bedroom window is positioned on the house. To opposite corners of the backyard I have almost 30 ft on left side, and 40 ft on the right side. The angle between the two would be about 65 degrees.If I connect the wires to the middle of where the roof/wall corner in the exact middle, I only increase the angle to about 68 degrees and the wires even out to be about 35 ft each. So I'm not sure if I should even consider a "dipole" setup or just use the one longest 40 ft wire only, or try to run something along the back of the house (bending each 90-degrees at the fence) and then running a coax up to the bedroom window or into the living room. All this with the approval of the wife, of course, who is not going to like me putting wires up.If I am able to get up into the roof space that would be ideal, but I am not sure I can navigate and move around in there at this point. The "attics" in these houses are not designed for people to walk around in, you basically just fall through the drywall ceiling with one misstep.

author: A.Z.
author_rank: Super Contributor
timestamp: March 02, 2021, 06:33:52 pm
content: Edy, here's an idea for you; instead of running two arms, use some length of wire to form a loop, it may be a triangle or some irregular shape, then either connect the ends to the balun or, alternatively, to the MLA30 preamp, I believe it may be worth tryingjust an additional note; pick a short piece of pvc pipe and drill some holes around it at both ends, run the ends of the loop through the holes and lock them using nylon tiers, then connect the wires to the balun (placed inside an electrical junction box to protect it from weather) or to the MLA30 preamp box; that way the pipe will support the antenna wires strain and your balun/preamp won't be damaged

author: cdev
author_rank: Super Contributor
timestamp: March 02, 2021, 06:48:30 pm
content: Ifyoure using a balanced antenna like a yard-sized loop, you might try something like a balanced loop tuner or s-match.https://pa0fri.home.xs4all.nl/ATU/Smatch/smatcheng.htm. I like this concept because it has the potential to act a lot more like a preselector with more selectivity in rejecting signals you don't want. than many other ATUs. PA0FRI's web page has dozens of paths you can use to get to one. He uses iron powder cores, he suggests two T-240-2 cores stacked. I have not built this but I would like to. If you can wind nice coils from copper tubing that would be helpful. Some people use clear plexiglas to build a structure for them. Youll see lots of nice ATUS on his web site. This is also loosely coupled so as to not load the tuned circuit down much. As Iunderstand it thats what makes them sing. A.W. Now that would probably be a good use for the dual amp you mentioned. Making a very loosely coupled very sharp bandpass filter/preselector easier. people will build them with very low value caps bridging the parts of the circuit, maybe an inch with two wires twisted around one another as the cap. there are a number or varations possible. You can use the UKR ferrite rods too. (as opposed to iron powder toroid cores) for receive only the parts you use can be tiny and cheap.

author: edy
author_rank: Super Contributor
timestamp: March 02, 2021, 07:16:53 pm
content: I will give it a try. I'll pick up some speaker wire as it is cheap and can get long lengths. This is what I was thinking, $5.95 for 25ft (which I can split up into 2 pieces for 50 ft total length):https://secure.sayal.com/STORE2/View_SHOP.php?SKU=144048I don't have much room for more than 25 ft anyways, and I figure I can connect 2 wires together to get 50 ft. Hopefully the connection won't affect it much. I can either hang a big loop from my window or make a diamond (see attached photo), or just run as long a length as I can from the window to the fence as I did in the past.If I have a loop, then I can connect to the two sides of the MLA-30 junction box, or to the suggested 1:9 balun (see below) , but if I have a single wire, how do I interface it with my Tecsun or SDR? I assume it would just go to central conductor of the coax, or the "tip" of the 1/8" mono male antenna plug? And what, if anything, do I connect the outer part of the SMA (e.g. external shield) to or the outer ring of the 1/8" mono male antenna plug?I also found this on eBay, seems to be the same as noelec version but cheaper:https://www.ebay.com/itm/One-Nine-Tiny-Low-Cost-1-9-HF-Antenna-Input-Protection-SMA-Port-A5C2/265047479510Any reason why 1:9 should be used and not 1:4 or 1:1 or other ratios? I am planning this purely as a Rx antenna and I've seen lots of articles talking about Tx antenna baluns which talk about making sure you don't lose power or heat up your transmission/feed lines. I'm not sure how and whether the same thing applies with receiving but perhaps the signal also gets eaten up in the feed lines if things aren't balanced.I'm still very much not understanding any of this. I just got past a couple of chapters taking about complex impedance/admittance for the first time and learning about current/voltage not being in phase, standing waves, loss, etc. But actually putting that into practice is a different story. For now I am at a level of just duplicating what others have done and seem to work.

author: A.Z.
author_rank: Super Contributor
timestamp: March 02, 2021, 07:38:07 pm
content: first walk, then run; start from window, go to a corner, along the fence to the other corner, up to window, the result will be a triangular loop, feed it with the balun or the mla preamp and test it for some days, then we may discuss modifications, don't jump tye gun; also, try keeping the loop (all or most part of it as high as you can)

author: cdev
author_rank: Super Contributor
timestamp: March 02, 2021, 08:08:13 pm
content: Used as a balanced HF transmission line clear speaker wire has low loss up to around 14 MHz and a predictable impedance of around 100 ohms.

author: cdev
author_rank: Super Contributor
timestamp: March 02, 2021, 08:11:46 pm
content: Quote from: A.Z. on March 02, 2021, 07:38:07 pmThis is why I haven't done this. Some telescoping fiberglass poles for the corners would be super helpful in preventing it from becoming anNVIS antenna.

author: cdev
author_rank: Super Contributor
timestamp: March 02, 2021, 08:35:23 pm
content: Quote from: edy on March 02, 2021, 07:16:53 pm

author: A.Z.
author_rank: Super Contributor
timestamp: March 02, 2021, 08:36:07 pm
content: Quote from: cdev on March 02, 2021, 08:11:46 pmwhich part of "first walk, then run" was unclear to you?

author: cdev
author_rank: Super Contributor
timestamp: March 02, 2021, 08:46:31 pm
content: I think he means "just do it" which is always good advice for people like me who ruminate endlessly.

author: edy
author_rank: Super Contributor
timestamp: March 02, 2021, 09:00:57 pm
content: So part of the problem is that my home is in suburbia with houses packed next to each other like sardines as in the attached picture!If I could erect some poles on fences without upsetting the neighbors, wife, or both, it would be nice. If I even had some trees around that I could run wires to, that would be nice. We don't even have any mature trees around at this point.I feel like my only way around this is to eventually crawl up through the attic opening and try to run some various lengths of wires along the inside of my roof (access permitting). Alternatively, I may have to carry something portable to a park nearby and string it up between two trees, but that will be very inconvenient.If I do use anything like a vertical antenna it will have to be temporary, taken down each time I use it. There is no way I can mount anything permanently for now.I may try what is suggested here:https://www.hamradiosecrets.com/shortwave-antenna.htmlThey show a "sloper antenna" that is basically what I was doing before from my window to the fence. The only difference being, I didn't have a connection box outside the window, I was running the wire directly into the house through my window. I also didn't have a balun, I just alligator-clipped it to the end of my Tecsun antenna. Also, the lengths required I am unable to get anywhere close to. I max out around 25-30 ft tops... the backyard is just too small. They suggest not making any bends sharper than 90-degrees so even if I used a longer wire I would need to keep the angles less.By the way, is a 9:1 the same as a 1:9? Also I saw YouTube review of the noelec 1:9 balun and they didn't mention anything about turning it into a unun. So am I using it as a balun or unun? They seem to just connect it out of the box, no modifying of the resistor, straight into the SDR and it worked.

author: cdev
author_rank: Super Contributor
timestamp: March 03, 2021, 01:24:11 am
content: Here is how to make a 9:1 unun that will work better than a commercial one, I suspect, for almost nothing.Find two identical noise suppression split cores and enough thin insulated wire to make approximately ten to twelve turns trough the core three times. fold it into three equal portions, cut the ends so you have three parallel wires. Twist them around one another gently so they are held together tightly. These will be your coils. Notethat the way the coils will be wound around half of the wire will be enclosed completely by the split cores. Look at the image below. Obviously because yoiou are using two identical split beads (the heaviest you can find, it will be different but dont worry, you'll find that this way of winding this makes a better unun. Make sure the wires are close together and twisted, like the twisted pairs in Ethernet cables, in fact that kind of wire would be a great choice to use.Resistor? Ive never used resistors in ununs . All my 9:1 ununs are grounded so provide a DC path to ground. Dont use them with a bias tee, that could burn something out.

author: A.Z.
author_rank: Super Contributor
timestamp: March 03, 2021, 10:19:39 am
content: Quote from: edy on March 02, 2021, 05:37:03 pmLook at the attached pic, the idea is to use some ropes at the three corners to suspend the triangular loop at some distance (e.g. 19") from the building and from the fence, the two ends of the wire will then be connected to the MLA-30 preamp or to the BalUn with the coax coming in and feeding the SDR, if possible, before entering the building with the coax, wrap the coax in some turns to form a coil and apply somesnap-on ferrite chokesover the coil (as much as you can) and cover them with tape to both protect them and keep them in place, the whole setup will take quite little timeAn alternative may be putting the MLA-30 in the yard, but in such a case you'll need to add a connector to it (seehere) so that you'll be able to feed it using a longer run of coax, the latter may just be some cheap TV/sat coax running all the way to your listening post, that way your loop will be outside and possibly won't cause problems with "SWMBO"another alternative may be the antenna describedhereit's totally INVISIBLE and works pretty well up to around 14MHz, chechthisfor an idea about its performance, to feed this latter antenna you may use the 9:1 balun you already have and I do really doubt that it will cause any reaction from SWMBO[edit #2]Forgot, the PL-330 has a 3.5mm socket to connect an external antenna, so to connect it to the coax feeding your antenna you'll just need an adapter with a 3.5mm jack at one end and a connector matching the one used for the coax at the other end

author: A.Z.
author_rank: Super Contributor
timestamp: March 03, 2021, 10:26:45 am
content: Quote from: cdev on March 03, 2021, 01:24:11 amThat's the same UnUn described herehttps://vk6ysf.com/unun_9-1_v2.htmit will work, but the frequency response will depend from the kind of material used for the core and then you will also want to place a choke at the output, since, as is, it has no common mode current blocking, so it would be a good idea placing something like thishttps://vk6ysf.com/balun_guanella_current_1-1.htmat the output of the UnUn and then connect the output of the choke to the coax plug, that UnUn will work ok with unbalanced antennas like a random wire or the like, but while such antennas do work, I doubt it will fit well given the location of the OP, which being surrounded by other building is probably quite RFI "dense", so I believe a loop may serve him better and in that case we'll need a balun, the OP already owns a NooElec (or similar) balun, so he may just use it, as for the "resistor" it isn't a resistor but it's marked as "R1" in the balun schematic (see my other post with link to the schematic) and it goes between the transformer center tap and ground

author: cdev
author_rank: Super Contributor
timestamp: March 03, 2021, 10:47:06 pm
content: Thats the picture I was looking for, its much clearer to understand.One thing about the 9:1 unun and its important. A huge part of the improvement it offers is from the decoupling of the vertically polarized noise due to the grounding. The grounding is very important. Otherwise you wont get the full benefit of a good unun and it may even make things worse. Because the signal will be working againat the coax shield and the AC power system connected to your radio, which could mean the elusive DX signal is crapified. . Suppose you intend to use it with a vertical antenna. The ground will give you a very marked quieting and it has the effect of decoupling your feedline from the noise in the environment (in both of our cases a back yard) I live in a similar neighborhood with houses fairly close to one another. My back yard arrangement is quite similar to the picture. I have more space and I would guess, taller trees .. so its not so bad.. Problem is, I live close to light industrial that I suspects injects a lot of noise into my picture. I have some very modest grounding. Not much of a ground rod at all, and it was pushed into the ground by hand, with a hose's assistance. but it helps a lot. And it definitely does help decouple common mode junk. Thats one of the biggest benefits of a 9:1 unun. If its a decent ground, it will help a lot.The ground lead should be as short as possible.

author: A.Z.
author_rank: Super Contributor
timestamp: March 04, 2021, 11:35:50 am
content: Quote from: cdev on March 03, 2021, 10:47:06 pmYou seem pretty confused to me; when it comes to an unbalanced antenna, it needs the "missing half", otherwise it will use the coax feeder as part of the antenna, and we don't want that, so in those cases, we use counterpoise and/or ground systems; the UnUn described at that link does nothing to stop common mode current flowing toward the antenna and then back to the receiving system, so you may want to add some decent choke(s), a good one can be built by winding about 18 turns of RG174 around an FT140-43 toroidal core and connecting it between the UnUn and the coax feedline (and then you may add more chokes along the feedline, if needed); that said, if you live in a quite (RF) noisy location, a "random wire" antenna like the one you described won't exactly be the best choice, you may achieve lower noise levels by using a dipole or a loop, for the latter you may consider eitherthis designor, if you have the room for it,this one, both antennas offer pretty good performance on the HF bands (and below) and help a lot with noise, the transformer used for both is simple to put together or, not willing to build it, a NooElec 9:1 will work as wellAs for the NooElec, please refer tothis schematicfor the V1 and notice that the trace marked as "R1" in the schematic is just a "zero Ohm" resistor running from the transformer (a coilcraft one) center tap to the circuit ground, now, to use the V1 with the two suggested loops you'll need to cut the "R1" trace (it's easy to see, on the back of the PCB); if instead you'll go for the V2 (from NooElec too), that one has no tap, so it can be used "as is"; in either case, you will probably also want to add a decent choke between the BalUn and the coax feedline, also, regarding the latter, since you're in a noisy spot, it would be a good idea using some run of TV/sat cable (the so-called "RG6"), since not only it's cheap, but it also offers better shielding and lower loss when compared to the "garden variety" thin RG-174; the latter may still be useful to wind very effective common mode chokes, which, in your case, I highly recommend

author: A.Z.
author_rank: Super Contributor
timestamp: March 04, 2021, 03:32:15 pm
content: @EdyJust to expand the idea a bit, let's start from the triangular loop design I proposednow, willing to artificially increase the antenna length, we may consider the idea of turning that single wire loop into a linear loaded one, to do so, instead of using a single wire to form the loop we may use some length of 3-conductors cable which may be flat or round, something like thisnow, just run the cable around to form the loop, then connect the ends of the conductors in series as shown in the image and then connect the two endpoints marked "A" and "B" to the balun (or the MLA-30 preamp box), the result will be a loop with the same total physical length but with a longer "electrical" length which may help obtaining better reception at lower frequencies; again, it's just an idea, but may be worth a try

author: edy
author_rank: Super Contributor
timestamp: March 04, 2021, 05:43:01 pm
content: Thanks for all the help. I found this video which I will try to copy and make a 9:1 unun. Seems like it is a staple for longwire antennas, there are quite a few similar videos around all showing the same thing:And here:https://m0ukd.com/homebrew/baluns-and-ununs/91-magnetic-longwire-balun-unun/Seems like one lead goes to the longwire, one goes to the coax that leads to the radio, and one connects to a ground. For grounding, can I connect it to the ground wire of a 3-prong outlet? That's my best bet if I'm inside, as the plumbing in the house these days is all plastic.I understand for a longwire, I will have 1 terminal in the house and the other end outside tied to the fence. But if I loop it around back I'll have both ends available, I can't use an unun like the one described above. I would instead have to join the ends of the wire-loop to the 2 terminals on my MLA-30. On the other hand, the 1:1 Guanella balun you linked here (https://vk6ysf.com/balun_guanella_current_1-1.htm) has 2 terminals on the left, which I presume connect to each side of a loop wire, and 1 terminal on the right, which I guess connects to the coax feedline that leads off to my radio input (I don't see any "ground" connection unless I'm supposed to ground the outer sleeve of the coax):Perhaps I need to build both and try them out?Another confusing part is I'm not sure how much of the videos and builds I see are talking about Rx vs Tx antennas. My understanding is that with Tx you will need to use larger toroids, thicker wires, etc... to be able to handle the power of the transmitter. However, for simply a receiving antenna application, do I need such big toroid sizes and wire gauges? I have smaller ferrite toroids scavenged from devices and stranded insulated wire that will be easier to thread through and wrap around the toroid. It will not be able to handle Tx power levels but for Rx should it not be ok?

author: A.Z.
author_rank: Super Contributor
timestamp: March 04, 2021, 06:05:36 pm
content: no need to wind that, the balun you already have will work, but if you're going for a "random wire" then layout one wire to the fence and connect a second shorter piece of wire to the balun, just leave it dangling down, that will be your counterpoise, but, sincerely, given your QTH location, I don't think a random will be a good choice

author: edy
author_rank: Super Contributor
timestamp: March 04, 2021, 09:24:21 pm
content: I'm wondering for now if I should try and make myself another loop antenna, based on the YouLoop linked below. It seems simple enough. At the top, you cross over the conductors so essentially the loop becomes 2 loops of wire (by using the outer shielding as another conductor on the second pass around the loop).Based on the diagram is appears the loop itself continuous (one big loop just folded into 2 "windings") that at the bottom (the blue and yellow wires) runs through one side of a 1:1 transformer. However, on the other side (right) of the transformer (that heads to the radio receiver) it appears there is a "tap" (vertical black line) that connects part of the loop shielding to the radio shield, which I don't understand. However, it is easy enough to build with the materials I have at hand.YouLoop:https://airspy.com/wp-content/uploads/2020/03/YouLoop-2T.pngOr something like this:The 1:1 balun/choke in the above photo appears to have continuity for the red wire coming out of the loop and going to the BCN connector, same goes for the black wire. Whereas the schematic seems to show the two sides being "isolated" electrically from each other... that is, more like a 1:1 transformer using a toroid to wind around like this:So I'm confused.One seems to allow direct continuity between the loop and the connector, and the other seems to allow each side to wrap around the toroid so they are magnetically coupled so that the loop current causes it's toroidal windings to induce current in the windings that go to the connector.I'm not exactly sure what the application of this one is:http://www.arcticpeak.com/images/antenne/Balun/Balun5.gifAnd here is a transformer for a ground-loop antenna mentioned athttps://www.kk5jy.net/LoG/:As far as the 9:1 balun or unun goes (again I'm confused as I see various comments on what to call it), I could try to build one of these:So I assume the 9:1 seems to be used more for long-wire antennas because there is a bigger difference in the ohm value for the wire (especially if it is very long) as compared to a smaller loop? Intuitively the way the 9:1 is drawn feels like it should be a 3:1... the "tap" taken out of the toroid to the receiver seems to be at about the 1/3rd of the way along the full winding, yet it's called a 9:1? Here's another view:One answer I have found seems to be the 1:3 turns ratio leads to a 1:9 impedance ratio... that is, the square.At this point it all seems like voodoo to me.

author: A.Z.
author_rank: Super Contributor
timestamp: March 05, 2021, 09:42:04 am
content: Quote from: edy on March 04, 2021, 09:24:21 pmEdy, before digging down into UnUns, BalUns and other antenna ideas, I believe you may use what you already have and try putting together an antenna; in your case, the NooElec 9:1 (or clone) will fit, start by looking at its schematic (which hopefully will be the same even if you have a clone and not the original thing)now, if you cut that "0 Ohm" resistor marked R1 in the schematic (it's on the back of the board) you'll obtain a 9:1 transformer justlike the one used by KK5JY for his loops, at this point it would be easy putting up a simple wire loop (seemy other post, please) and testing it.As for the impedance transformation ratio, the "square rule" is correct; if you look at the KK5JY transformer you'll see that we have two turns on a side and 6 turns on the other, now if we divide 6 by 2 we obtain 3 and 3^2 will give us 9, which is the impedance transformation ratio; in the case of the UnUn, let's say we have a trifilar winding made with 4 turns and connected (in series) as an "autotransformer", now, in this case we consider the number of turns for the primary (4) and the total number of turns for all windings (12) and if we divide 12 by 4 we obtain 3 and, again, 3^2 gives us 9, that is the transformation ratioLet me make another example, let's say we want a 16:1 UnUn, we wind it quadrifilar (4 wires) and make 9 turns, the total number of turns will now be 36, and the primary will have 9 turns, now, if we divide 36 by 9 we obtain 4 and 4^2 = 16 which is our UnUn transformation ratioAs for the coax loop, sincerely I don't like it so much and I don't like the way it's connected to the coax, I'd probably use a tapped 1:1 transformer, say 5+5 turns with a tap at 3 turns on the secondary, the untapped winding would then go to the coax while the tapped one will be connected to the loop ends with the loop shield connected to the center tap, such a config would allow to mantain the loop balance; notice that you can do that with your NooElec balun, once you cut "R1" you just connect the coax loop braid to the center tap and you'll have exactly such a configBut again, just try the loop idea at my previous post, also since a random wire will probably be "too noisy" for your location

author: edy
author_rank: Super Contributor
timestamp: March 05, 2021, 05:37:14 pm
content: Thanks, I guess part of my confusion with the toroid construction is whether they are "isolation" or provide electrical continuity. Most of the toroid constructions show the wires wrapped around the toroid 3 times, and you basically "tap" off one of the windings that only goes around once. So you get a 1:3 voltage ratio and 1:9 impedance ratio. But if you put a continuity meter at one end of the first winding let's say (your antenna input) and one at the furthest other end of the entire set of windings (the one going to the shild of your coax) they are electrically connected. You are just "tapping" off from the 1/3rd way mark into the center of the coax. Technically you could just wrap one wire around the toroid and splice in a point 1/3rd way around it (at 0 and 120 degree mark apart) and use that connection.On the other hand, if you want to electrically isolate them (only magnetically couple) then I would have the wires never actually soldered to each other. One wire would wrap around the toroid 3 times, another wire would wrap around the same toroid 1 time. This would transform the voltage by a factor of 3, and the current by a factor of 1/3rd, so VI is same on both sides more or less. I'm not sure if this is the idea of the transformer used for radio antenna or not, and whether there is even enough "signal" strength to allow such a transformer to have enough magnetic coupling to even let a signal through. Perhaps for a transmitting situation, but for receiving it will probably be too low.So perhaps that's why I'm confused, and I should construct one that actually has electrical continuity and not isolating, like most of those 9:1 baluns show.

author: A.Z.
author_rank: Super Contributor
timestamp: March 05, 2021, 05:48:32 pm
content: why ? I mean, each design has advantages and disadvantages (set aside the difference between UnUn and BalUn), and sincerely, for some antennas (e.g. loops) I prefer using the "insulated design" (as you call it), possibly followed by a vanilla 1:1 guanella choke

author: cdev
author_rank: Super Contributor
timestamp: March 06, 2021, 02:00:43 am
content: And the improvement in signal is often really dramatic (or it appeared to me to really be when I tried one the first time. It was the design I posted the image of, implemented in enameled wire, on a diminutive FT-50-43 toroid ferrite core (shiny black) I still have it and it still performs very well with any old length of wire. its currently attached to my radiator for grounding. with a long wire going out my window to a tree in the back yard. Its my backup HF antenna.Another useful balun that I have now is made of two square binocular cores, its basically a copy of a popular Elecraft balun kit and its switchable from 1:1 to 4:1 with a toggle switch. It is wound using clear speaker wire, 18 gauge, and it works very well, always. With any balanced antenna. Yes, it works with loops. Its housed in a plastic box with vent holes on the side and banana plugs on the top. It uses a BNC jack for its connection. I built it in anticipation of getting a ham license and transmitting with it. It would probably handle 100 watts but not much more.Quote from: A.Z. on March 05, 2021, 05:48:32 pm

author: A.Z.
author_rank: Super Contributor
timestamp: March 06, 2021, 08:53:34 am
content: The elecraft is a good balun, it's a guanella with a switch allowing to connect the secondary windings either in parallel (1:1) or in serier (4:1), it can be easily built using a couple of toroids as shown herehttp://www.m0pzt.com/blog/4to1-current-balun/as for the unun, it's ok for an unbalanced antenna like an EFHW, a random and the like, but for sure not for balanced antennasand, in both cases the balun and the unun have almost no effect on common mode currents, so it will be a good idea adding a good guanella choke between the balun and the coaxor better said, the unun has no effect, the guanella in 1:1 config has good choking, the guanella in 4:1 config has about 1/2 of the 1:1 CMC impedance, so for both the unun and the 4:1 it will be a good idea adding a chokeForgot; if going to build that M0PZT design, use #43 material for the cores and increase the turns to 17; that is 16 for the toroid (8+8) plus one for the "crossing"