Portable 100w Auto-tuner

Or on the UK eBay site:

This tuner is available as a kit starting at around €25 (€35 with OLED) without case (case available for €20-25) but the kit has SMD components, so I was interested in the pre-assembled and cased options and I found these at anywhere from €61,88 (the one I have ordered) through over €150 (for similar units except the higher priced units are powered from a USB-C connection rather than just 10-15V and have a straight-thru option). There is also the option to buy the assembled board but without a case at anything between €53 and €80. In some cases the description states that it operates between 1.8MHz and 30 MHz in other cases up to 50MHz but apart from that the specifications of the various options are identical. Some adverts blatantly admit it’s the N7DDC design.

I thought some SOTA activators might be interested … It’ll be 6 weeks before mine arrives, I’ll post what I think of it when I have used it from a summit.

73 Ed.


I bought a kit for board and components. the board and components look ok.

I’ll get some help to solder the .05" spacing cpu chip, but the rest should be ok. The seller didn’t automatically send the instructions with the hardware, I had to chase them for the assembly instructions. The ad on ebay also said the chip has no programming but the box states it is programmed with v3 of the software/firmware. I may get to this kit some time this year.

Will be very interested to see your comments on performance.
73 Andrew vk1da/vk2uh

Hi Andrew,
I suspect you’ll get your kit before I receive my assembled model. Good look with building it. If it does work well, it’ll give portable ops a cheaper option to make that non-perfect antenna usable on some remote summit. Of course there’s nothing stopping it being used at home as well. It might be interesting to compare it’s performance against the MFJ tuner that I have here (which is too large for a summit trip).

73 Ed.

I noticed that ebay was suddenly filled with adverts for these kits etc. I couldn’t see if it used latching relays like some of the QRP portable designs use or if it needs powering all the time. However, looks interesting.

I don’t think it uses latching relays and hence needs power constantly.

Perhaps the N7DDC video would tell us that?

73 Ed.

I checked the parts list on one o these offers and googled the type of relay that was indicated. It’s not latching.

73 Jens HB9EKO

A group of us have built this ATU and it really does work. It needs powering full time to hold the relays but does remember where it was last tuned when you have powered it down and back up.
There are a miriad of options that can be programmed from press to tune to fully auto.

No doubt the spare boards with SMD components mounted will appear on a well know shopping site in the near future :smiley:

I built an ATU100 then after exhaustive testing cased same.
its specification claims:-

*Supply voltage of 10-15V dc,
PCB has a 5v regulator for both the switchcing transistors relays and PIC processor. My unit works from 8-14Vdc, my PSU max output is 14V

*Maximum current consumption 400mA.
During Tune mode all relays can be used, but not all are simulataneously used,
In test mode all relay driver devices (2n2002) are turned on, respective relays are energised. 15 Off relays plus 2n2002 devices and respective PIC outputs which is 400mA

  • Maximum working throughput of the standard 7x7 variant is 100W
    the relay contacts are only rated at 1.3A, therefore before entering tune mode the recommended power source is less than 10W. Once a tuned solution is found, the power can then be icreased to 100W.
    There are pads on the underside of PCB to wire connection to transceiver for tune initiate and from ATU100 to transceiver to initiate power reduction, provided the transceiver has these options.

  • Maximum possible measured power 150W
    I had an input of 118W through the unit, with no obvious signs of stress or damage, though with respect to relay contacts, 100W would be the limit.

*minimum power requoired to start tuning 5W
5w is default. This can be changed using a software / hardware option
it can go less than 5W, however the sense coil will require rewinding, there are details on internet showing how this is done.

  • Minimum possible measured power 0.1W. True

*Accuracy of power measurement 10%
My unit tracks a Bird 4413 with both 5 / 50 / 100W elements used

  • Typical consumtion 150 - 200mA
    Once tuned solution is found the current draw is low

  • Frequency range 3 - 54Mz
    My unit has been proven to work between 3.5 to 29MHz, not tried on 6m.
    Only tried with dummy load and off resonance dipoles (purposely lengthened and shortened dipole elements to give high SWR of 4:1)
    Unit found a tuned solution all bands 80-10m with exception of 30m had to reset and retry Tuned mode. Equipment Elecraft K2/100

Unit is not easy to build if you are not used to SMD components ranging in size from 1206 to 0603. Also uses air coils, single and double toroids.

Relays are made in Hong Kong, no equivalent in size or pinout, so expect usual delays for these. Relays are HK1400’s pinout does not conform to usual standards.
Most SMD’s are on rear of PCB, I was encasing mine, so soldered M2 nuts on bottom 4 pads for same on PCB, this protects components on underside from damage.
Relays are last to be installed. They are very susceptable to heat damage.

Also take care winding toroids they will only mount in PCB through holes if wound the correct way. I had to rewind all mine.

If your PIC is not programmed, then you will need a PICKIT 2 or 3 to program same, also need the PICKIT to change any parameters that includes display type and OLED size.

If you choose Autotune mode, then the power throughput must be less than 10W

In power down, the unit defaults to Bypass mode


Thanks for a very concise report Dave.

I have ordered the fully assembled and cased unit as I was afraid that I’d never manage the SMD work and more to the point would probably keep putting assembly off!.

73 Ed DD5LP

I have ordered one of these kits from Russia. Its been 90 days now in transit.
Dare say the ones from China would be quicker. Will report on component quality when (if) it turns up.
The intent is to build into a housing suitable to take out portable for when the extra power is warranted.


It’s arrived!
Scheduled to arrive sometime in September, it’s arrived today 15 days after shipping from HK (it was 10 days after the order before it was shipped, so I guess these may be being built to order).

There are no instructions at all with the unit. Of course there’s not a lot to it but a small downloadable instruction sheet would have been nice!

I’ll let you all know how it works.

73 Ed.

You can dig out the info from the guy who produced the design, it will be on his website.

Looks nice from that photo.

Not sure if this is from the original N7DDC guy or someone who has modified the open source firmware, but here’s a manual.


Once ICOM start selling their IC-705, I can see these becoming rare as everyone grabs one (the IC-705 has no built-in ATU).

73 Ed.

Nah you’d just buy a mAT-10 or the New mAT-705

I have one. Tried to buy from Russia but delivery failed to materialise after 3 months. Money back very promptly. Ordered from Hong Kong. Here in 10 days. Compared to my 125 W LDG auto tuner it looks like a 50 W rating. On the edge for 100 W. Definitely restrict power to 10 W when tuning.
Comparable with KX series of ATUs. I would be happy to run it at 50 W for SOTA if SWR <1.5 :1.

You could replace the capacitors with better RF rated ones and increase the diameter of the wire by 30% but the relay rating is always going to be a concern. Not adequate IMO and probably die if tuned at 100 W a few times. I’d like to see 2 A rated contacts as a minimum for 100 W preferably 3 or even 5 A. Remember RF is different from DC so needs derating.

However it is still good value for money. I expect to get many activations from mine.


Well, we’ll see how it copes over time. Most likely the most it’ll get is 5-10w for tuning and 70w PEP HF throughput when condx are bad on the summit.

If you are prepared to build it yourself and add the case yourself the kits start at €25! My built version at €62 is somewhat cheaper than the mAT-705 at UKL220 but I suppose for those willing to pay $200 for a rucksack for the IC-705 another 200 on top for the tuner won’t be an issue for them. I think your mAT-10 looks a lot better than the mAT-705 by the way John.

This is the mAT-705 image

And at nearly €1500 in Germany (https://www.wimo.com/en/ic-705) I wont be buying an IC-705 for some time - my guess would be that it’ll be down around €1100 in about a year - but I could be wrong …

73 Ed.

It’s an exceptionally good bit of kit and very robust and reasonably priced and works very well either directly with the 818 or manually with other radios For example I had a nice 80m SSB QSO the other day using it with the Mizuho and a ‘randomish’ wire…

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Used this ATU for the first time on a summit today. It “seemed” to work but made no difference on receive or transmit on my Aerial-51 404-UL (OCF) antenna which is resonant on 40m anyway!

I need to see what good it does matching to the antenna on a WARC band such as 17m.

73 Ed.

As Andy said in his first post on this thread, the relays are non latching in this cheap ATU. I have seen numbers as low as 25 mA per relay to 40 mA. I am not sure if it is the draw at 9 V vs 13.8 V. Whatever, latching relays are the way to go for portable operation. They are dearer and require slightly more complex programming.

Ed and ZL1JPS have pointed to a couple of ATUs that do have latching relays. Elecraft seem to have most things right and the KX2 is looking cheaper now the 705 is out there. Icons tuner will hopefully use latching relays but it won’t be cheap.

BTW N7DCC made everything available free. I don’t see any prohibition on commercial use.


As always - you pay your money and take your choice.

I was surprised to find a fully assembled automatic portable ATU for €65 and have been happy so far with what I have found.

Yes it does not have latching relays but it’s also a lot cheaper than those which do.

It doesn’t have a control “tune” interface control cable - it relies upon RF sensing (3-5w carrier seems sufficient with mine) to trigger a tune action if the SWR is higher than desired. It has connection points on the board where this can be added however.

This is a cheaper ATU than the manual ATUs that I was considering.

“You pays your money and takes your choice” - for the price I am quite impressed so far.

73 Ed.

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