9:1 UnUn vs FLOATING ATU ANTENNA | Ham Radio

The 9:1 UnUn is a very popular option for random wire antennas. But it has its limitations and may not always be the best choice. Peter G3OJV. offers an alternative arrangement that has greater band flexibility and much lower VSWR.
LFG Z100-Plus with internal battery option.
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Icom IC-705 Transceiver 160m - 70cm
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RigExpert Antenna analyser for HF Antennas
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[@VE9ASN]

Remote tuners really are the way to go, virtually eliminates the huge losses in the coax.

[@_0815_]

I strongly recommend the LDG RT100 or its bigger brother the RT600. They are fully ATAS compatible, which means you can use them with any Yaesu rig that can control ATAS antennas. In ATAS mide the TRX puts out 12V DC on the coax and the tuner can sense the RF or go into the full tuning cycle with a push of a button on the mic. Tim, G5TM has put out some good Videos about it. I got one and I absolutely love it.

[@WECB640]

Peter, I've done this also with an AH-4 and my IC-706MKIIG. I would recommend that you choke the control cable at the ATU as it's probably connected shield to the case which is now floating, so there's RF on that control cable. I had to do this with the AH-4 and I also had to run the control cable away from the coax so it wouldn't couple to it. Great ideas! 73 OM

[@KD9ZHF]

The framing of the shot at 16:45 is great. Lighting was perfect. Great video content as well. You look great there though. You’re a natural. Also, your location must be very noise free - I’m jealous! I live in the city of Chicago and there is an apartment building close by, and I have to use a receive loop to null out all the electronic! Love watching your videos.

[@larrybarnette4795]

Sometimes a 4:1 unun will be better, that is easily made or simply by adding a tap to the 9:1 at the junction of the coils. Add an extra terminal to the unun (or switch) and note at which bands the match is closer to optimum. For a non- resonant wire, there will always be reactance to tune out even though the impedance may be close to 450 or 200 ohms. Before the 9:1 became the 'defacto standard' a few years ago, our transmitters with (vacuum tube finals, or valves in the UK, hi) used variable pi network output networks which would match a wide variation of antenna impedances. We never considered using a 9:1 unun to the antenna in those days. This is pretty much what is in those auto tuners only automated. So, the old is new again. For those of us with an AM broadcast background, there was always a matching network at the base of a series fed vertical tower, as the length was seldom an exact 1/4 wave in electrical length. Even if it was, the impedance would be closer to 30 ohms or so than 50 ohms. Efficiency of a high powered transmitter called for an exact match. 73 de KC4QI

[@zero_G.0]

Hi Peter, I’ve found the 9:1 works best with a longer wire 80ft+. The key to it working well is having at least 70ft of coax and a CMC at that distance prior to the transceiver, as it acts as part of the antenna counterpoise.

[@watersstanton]

Thats a massive coax length for many small gardens. Thanks for sharing.

[@almightyEsquilax]

Why not use a counterpoise?

[@zero_G.0]

@@almightyEsquilax you can add a counterpoise but I found it made no difference the coax feed is the counter poise and you can loose the length in a small garden. The longer non resonant length of wire the better.

[@halledwardb]

I have the AH705 tuner for the IC705, so I'll have to try something like this. Heard very good things about the ldg tunners as well.

[@briansalsbery9968]

The Sotabeams Bandspringer Midi uses this approach too. Radiator and counterpoise plug directly into tuner

[@TheMikeDarling]

Thanks for giving me some things to think about when operating portable with either a QRP or 100w rig. Dump the unun, and move the tuner to the antenna feed. Hmmm....

[@sinisabronic4309]

Nice idea to put battery operated ATU near antenna!

[@mikesmith5139]

Thank you for yet another useful video. Good ideas and explanations

[@migalito1955]

Nice idea. I have the AT-100 m that seems to be liked and I've liked so far. Not sure how much reflected power it can compensate for in terms of mismatch. I've also have had lousy luck with 9 to 1 baluns and would like to try one again for ideally 80 meters and hopefully 29 meters along with it, but this time I planned on using my nano vna to get a 450 ohm impedance at the wire to balun interface. Likely it would take several attempts or dozens to get the result aimed for. Now, I am not sure which route to go....

[@rogerlafrance6355]

A remote ATU is a good solution for a small garden or even mobile and more on the lower bands. One can load a vertical, odd wire, fence and even a whip. Matching at the antenna, reduces the RF in the shack as computers and such don't like it. Even my G90 matching a longwire in the shack makes RFI.

[@David-km8in]

Hi Peter, Interesting video. That antenna with tuner was the first antenna I used when I first got my foundation license. Unfortunately it never worked for me, maybe I was doing something wrong. Can you tell your viewers why you keep showing video of the Moonraker shop when your are advertising Water and Stanton. Nice holiday home. David M0DUU

[@FrankW650]

Hi Peter, you made the qso with me on the video (DL2GRF). At your experiment with the floating ATU antenna. You use an rf-choke at the begining of the coax at the ICOM IC-705 side. But in my opinion it is not floating, because your remote cable I don´t see a rf-choke as well. The remote cable is also working against ground. So RF coming back to the transceiver. That is in your case not a problem, because you use the battery inside the radio. So it is also floatend. In my opinion If you use power supply you have to put in additional rf-choke. What do you think?

[@watersstanton]

Yes you are correct in part and an RF choke on the PTT line would be a tidy solution. However, the PTT line does not stop the coax radiation as it is never at RF zero point. 73 Peter.

[@truhartwood3170]

I'm trying to understand how efficient this is compared to a dipole or EFHW. Some say the reflected power is turned into heat in the ATU, others say the ATU re-reflects it back to the antenna in-phase with the signal repeatedly until its fully radiated / lost as heat in the wire so its actually still like 95% efficient as long as you don't have a lossy transmission line (eg a long run of coax) between the ATU and antenna (low loss transmission like like ladder line or connecting the ATU straight to the antenna is fine). Others say that it's re-reflected by the ATU, but it could be out-of-phase with the signal and affect it destructively to some degree. I would love to see some kind of demonstration of any of this, proving once and for all what is actually happening. So far all I've seen are assertions and anecdotes, but anecdotally this setup seems to work just as well as resonant antennas in practice. So it doesn't sound like a big chunk of the transmitted energy is being reflected back to the ATU and simply lost as heat. We should be seeing signal strength drop by as much as 50% if this were the case and the ATU should get hot, which from what I've heard, it doesn't. Can anyone point me to some actual tests or demonstrations proving what's happening?

[@truhartwood3170]

Replying to myself just hours later - my search paid off! I found a pdf of the book "Reflections - Transmission lines and antennas" third edition, by M. Walter Maxwell, W2DU It explains, in 428 pages of detail, that reflected energy is just re-reflected by the ATU back to the antenna until it is dissipated through a combination of being radiated and being lost as heat through wire resistance. As long as you're using low-loss line or the antenna is connected directly to the tuner, almost all energy will be radiated. The myth that tuners, or SWR in general, are inefficient has numerous origins that are all covered in the book. Eg. if you're using higher-loss coax between the tuner and the antenna, it will be inefficient due to line attenuation as the signal is reflected back and forth repeatedly through it. Or if the SWR hits your radio, the radio will "feel it" and reduce output power proportionately, like if you're sending out 100W and 30W is reflected back, the radio will only send out 70W, but will "feel" (being super non-technical here) like it's pushing 100W still, since it has to overcome the 30W pushing back on it. This means you'll only be transmitting 50W, even though your radio is telling you it's pushing 100W. All of that 50W is radiated, you havent lost power to inefficiencies, but you'll certainly notice that you're sending out a weaker signal. A tuner will re-reflect that reflected energy back into the antenna so your radio doesn't feel it and so it will keep pushing out the full 100W. Anyway, look up the book and read it for way way way more detail! But basically, you can skip getting the $500 RigExpert and spending afternoons snipping away at wires trying to get them resonant, winding and testing endless toroids, etc. - just cut a wire to one of the random wire lengths, connect it to a tuner, stick as much counterpoise as you can on the grounding lug and away you go. You'll want to look at the radiation patterns of the various frequencies on the different random wire lengths to help you choose which length to go with, and choose inverted L or V, flat top, sloper, etc., but that's about it.

[@watersstanton]

There is basic coax loss at frequency, VSWR loss and UnUn loss. The first two can be accessed from web table, and the latter can be judged by heat generated. A rough guess is that UnUn loss is not mor than 1 dB which is not likely to be noticeable in practice.

[@truhartwood3170]

@@watersstanton I was looking at using an AH-705 with no unun, just directly connected to a random wire around 148' using the PL-259 binding post and a counterpoise. That way the SWR is just kept bouncing around in the antenna until it's radiated, without incurring transmission line losses. I can use the 6' of coax and control cable that come with the AH-705 I think, as the antenna can start just outside the window in front of my desk, and since the SWR wouldn't be reflecting back and forth in the coax, the line loss should be pretty minimal. If I'm understanding everything correctly that is.

[@JxH]

4:20 Missed a solder joint, white + yellow wires. Unless, somehow, that's intentional (?).

[@watersstanton]

eh?

[@mikesmith5139]

There doesn't appear to be any solder on the joint of the white and yellow wires, towards the front of the photo.

[@_0815_]

Hey Peter, ever thought of converting the 9:1 unun into a 'very off center fed dipole'? I converted my EZ Wire 9:1 random wire antenna into this contraption. 17m on the hot side, 3.5m "counterpoise" . It gives me 40, 20 and 12 without a tuner, and all the other bands above 40 with the internal one. Maybe an idea for another video.

[@watersstanton]

Thanks for that - interesting - when does an UnUn become a Balun?

[@_0815_]

@@watersstanton hehe, this could get truly philosophical 😂 The antenna behaves like a dipole so it's fair to say it's a 9:1 balun. But it has some real advantages, especially from a mechanical point of view. Feeding quite far on the side, further out than a classic Windom with a 4:1, but not being limited to the endfed halfwave scheme. It also provides lots of possiblities to mount it.

[@JxH]

10:15 The conceptual problem with the T2LT antenna is that it attempts to employ a current choke at a current null (voltage peak), i.e. at the lower 'end' of the lower driven element. Of course it'll still work (make contacts), but that's common with many flawed design concepts. I'm just here to point out that using a choke at a current null is not exactly an inspiring starting point for an antenna concept. Has anyone else noticed this ? Stands out to me.

[@watersstanton]

Line isolators are not effected by the point at which they are placed.