[Tech Minds] built one of those cheap automatic antenna tuners you see everywhere — this one scaled up to 350 watt capability. The kit is mostly built, but you do have to add the connectors and a few other stray bits. You can see how he did it in the video below.
What was very interesting, however, was that it wasn’t able to do a very good job tuning a wire antenna across the ham bands, and he asks for your help on what he should try to make things better.
It did seem to work in some cases, and changing the length of the wire changed the results, so we would guess some of it might be a resonance on the antenna wire. However, you would guess it could do a little better. It is well known that if a wire is one of a number of certain lengths, it will have extremely high impedence in multiple ham bands and be challenging to tune. So random wires need to not be exactly random. You have to avoid those lengths.
In addition, we were surprised there wasn’t more RF protection on the power lines. We would probably have suggested winding some coax to act as a shield choke, RF beads, and even extra bypass capacitors.
Another possible problem is that the diodes in these units are often not the best. [PU1OWL] talks about that in another video and bypasses some of the power lines against RF, too.
If you have any advice, we are sure he’d love to hear it. As [PU1OWL] points out, a tuner like this can’t be any better than its SWR measurement mechanism. Of course, all of these tuners take a few watts to light them up. You can, however, tune with virtually no power with a VNA.
This device is not as interesting as I thought it would be.
It turns out the operator manual is available online. The system has 7 channels, each of which selects one pre-tuned toroid and capacitor channel and adds them inline.
This device does not detect the SWR and insert appropriate reactance to cancel out reflections, it simply selects one from a number of channels and activates those relays (one for C, one for L).
Responding to his questions in the video, from the operator manual “antenna lead-in must not be longer than two feet” jumped out at me. That might be one source of his problem, especially since doubling the length of the lead in caused different channels to work/not work.
Sure about that? Sure you found the right manual?
This is yet another variant of the (in)famous and much-cloned N7DDC 7×7 tuner: It can tune far more than just 7 “channels”: Those toroid inductors and capacitors vary by a factor of two each, and the 7 relays select any combination, for 128 possible capacitance and 128 possible inductance values.
The last (15th) relay selects straight-through (no added reactance).
The forward and reverse powers are measured by the tandem match SWR bridge, at the top right of the board in the title image. The microprocessor selects the combination of L and C to minimize reflected power, and so finds the best SWR.
It’s definitely built to minimize cost, and there are better and more complicated designs, but these do work. Nice improvements are ones that can tune with lower input power, those can measure frequency and pick a 1st-iteration from a lookup table, and those you can pre-select the band with an auxiliary control input by CAT control or from the band select output of the transceiver.
I had wondered if it was an N7DDC clone, it seemed very likely.
When built properly they work rather well (assuming the antenna is tuneable)
Given that, the first thing I’d probably do if I suspected a problem with it would be to check the board against actual schematics, it wouldn’t be te first cheap radio/any product out of China that had wrong values or very basic PCB errors (those cloned directional couplers/SWR bridge all over eBay are a fine example)
I’d also want to try the antenna with another tuner, as another respndent says, some antennas are just damned hard to tune.
Correcting myself: the 15th relay is not for bypass in these designs. It selects whether the capacitor is ahead (‘CL’) or after (‘LC’) the inductor in the matching network. Sorry about that misinformation.
You’re right, I was wrong.
I was looking too hard at the manual, and not enough at the board.
On the bright side, I note that the comments all note my mistake, but don’t bother to explain how this tuner actually works.
TIL, hams are a surly bunch :-o
Literally explained by Paul in the first reply to you and Paul even corrected a mistake.
Maybe it’s you and not the hams?
It definely has SWR measurement.
This is basically same product as ATU-10, ATU-100 etc. – just with a beefier toroids.
All antennas are “wire antennas” but I figure what he meant by this was that he was trying to use a random wire antenna. These have to be sized so they don’t resonate at any frequency you want to use while being as long as possible (e.g. one size that springs to mind is 84′). Even so you’ll need something like a 9:1 balun to get something approximating to a 50 ohm match and the feed line needs to be treated as a counterpoise.
Since the tuner works by you putting low power R/F into it at the desired frequency and it adjusting the LC combination for the best measured SWR you’re ether going to have to go through this process every time you change band or you’re need to remember the setup for each band and signal this to the tuner from your transmitter. This is why people usually have the tuner near (or in) the transceiver. I have a built in tuner in my Xeigu G90 but people who use external tuners all seem to prefer the analog ones with the twin meter.
Tech Minds somehow doesn’t understand that the end of a half wave antenna has a VERY high impedance and expecting ANY tuner to handle it very well is completely unfounded. If you read the comments below his YouTube video you’ll see that lots of respondents tried to tell him that.
Techminds does seem to have some rather fundamental gaps in his knowledge and has demonstrated such many times, this seems to be another example..
I stopped watching his videos because he rarely if ever listened to or learned from advice in comments yet, somehow, he seems to have gained a reputation of ‘expert’ by people who know less.
I’ve started feeling that the YouTube algorithm rewards those who have mistakes in their videos, because it generates more comments which get counted as “engagement”.
Absolutely it does, there are content creators I respect and even admire who don’t, I believe, get the engagement they deserve, I guess because they don’t do clickbait, ‘sensational’ titles or controversy for engagement.
Ham examples, W2AEW, N2CQR, M0NTV, ZL2CTM and plenty more can be counted on for solid, accurate advice and when they do make mistakes, they correct or clarify.
Yes. The were several respondents who tried to educate him and the last I checked he hadn’t responded to any of them in spite of the fact that he had responded to other comments within the same time frame. I lost a lot of respect for his knowledge after that video.
“The system has 7 channels”
You don’t understand the tuner any better than the guy in the video.
Just wondering….
Has anybody made an antenna tuner with toroidal inductors and a stepper motor, just like in a variac?
It should not be very difficult to print some bracket to put a carbon brush in a bracket on a stepper motor axle.