If running qrp, you could use a 50 ohm bridge with an LED as a tuning indicator. QRP Guys sell them, but they are pretty easy to make...

I am a little confused on how these 50 ohm tuning circuits work. Is there a schematic available?
--
Colin - K6JTH?

Hi.
No, it could burn the output. That is the reason to use a simple linear output stage in some modified uSDX.
But you can resolve this problem installing an additional relay which will connect TRX output to load resistor 50 Ohm while tuning.
Needed control signal you can find at the rear panel, "EXTernal control" connector.

Hi OMs

i just acquired an “ATU-15” from a Chinese supplier on AliExpress and it seems to be working well with the QRP Labs QCX-mini I run into stealth antennas. However, I note some comments on the QRP labs forums that the simple BS170-based PAs?used on all QRP Labs products may be vulnerable to transient high VSWR while autotuners are doing their thing. I note that manual QRP tuners like the Emtech ZM-2 have a “tune” mode that makes sure a TX never sees a wildly bad VSWR while the match is being adjusted and I wonder if the N7DCC design includes anything like that? Maybe it’s not an issue in practice - would appreciate experienced and any suggestions on mitigating the risks.

I will attach a picture of the “ATU-15” as it seems to be an unusual model name. BTW the build quality looks excellent inside - none of the horror dodgy soldering I have seen in some YouTube videos of preassembled kits

Hi, Michael?
That is not a ferrite core, that is powdered iron core . They should to have high Q factor and minimum heating level unlike ferrite cores.?

Hmmm, I've been told that overheating a ferrite core ruins it.
I assume your tuner didn't suffer that fate.?

Hi Paul,?
for what they are they are a great little tuner, just supply it with RF and it tunes, the fault was me trying to match an swr of 5+.

Regards
M0DZO

Hi va3rr,

no my fault entirely the SWR was around 5, on 15m where the swr is around 1.3, it worked perfectly.
My G5RV needs sorting properly but it’s a bit cold at the moment, no need to touch the tuner it tuned up as soon as the RF hit it.

Regards?
M0DZO

Was it a low impedance you were trying to match? As long as your ATU-100 has decent caps & toroids, I wouldn't imagine it would heat up significantly with higher impedance loads...

73 de va3rr

Hi,
Just leaking smoke from my ATU100, fortunately it was just the toroids getting hot.

I must remember not to try to tune an antenna that’s too high swr.

Amanda M0DZO

Hi.
It is here

Hello, does anyone have the PCB file of this antenna tuner? I am sharing a clip link on YouTube. PCB Tech is used in it. I am looking for this PCB.

IDK that it is a fools errand.? It's a stepping stone. Every design is built off of previous knowledge.? There are a lot of good things that can be taken from the design and improved on.

Here is another design that is thought through:???

IMO, all of these ATU's are rated at best, 1/3 of what their stated power level is.

I have the ATU-1000 in service and it is reliable up to 1.5 KW depending on the matching conditions, mode, and duty cycle.? 2.5 KW probably not. The design is sound, however the components won't likely tolerate that power level very long.

One of the best couplers I have ever seen is the AN/URA-38? AKA RF-601? It is rated at 1KW continuous, no time limit, we would use them in RTTY running 1.5 KW 24/7/365.? You may want to copy a design like that.

That being said, the ATU-1000 is a good starting point.? A few things I would change in the design:
- Allow for RS-485 communications for full remote control head
- Use vacuum relays? in place of the simple SPDT signal relay (you could conceivably use multiple signal relays in parallel)
- Need larger cores or air cores and larger diameter wire for the inductors, this will make more loss
- thicker/bigger board traces, or ditch the board and use p-t-p wiring?
- add a 1:1 and 4:1 balun that can be switched in and out
- add memories for tune data?
- add a frequency counter to detect the tx frequency and look up stored match data

?

Al the bnc jumper is removed,the bnc jumper on the 320 links its internal tuner to the radio's pa,i am using the rf directly from the radio via the bnc,thus the radio's tuner is totaly seperate electricaly from the atu-100,i have the parts to repair my ft-707 now so will try the tuner with that if my avr board repair fixes it,fingers crossed.73 Paul m3vuv.

Paul

It's difficult to tell from the photo you provided, but it looks like you're feeding the ATU-100 from the ATU output of the PRC-320.? If so, that is going to create problems for you, as you need to tune two circuits simultaneously in order to succeed.

Although I haven't seen a PRC-320 in person, various photos indicate that there is a BNC jumper on the back of the radio.? This connects the RF in/out of the radio to the internal ATU.? What you need to do is disconnect this jumper and connect the radio directly to the ATU-100.? If your radio doesn't have this jumper, you'll need to find a way to create this connection.

Al

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At this power level I would go for something like this:

instead if relay switching if capacitors and inductors.
73 de oz9ny, niels