Homebrew 144/28 MHz Transverter

As a suitable supplement to my new Elecraft KX2, I built myself a 10Watt 144/28 MHz transverter. Wolf, DK1HW gave me the tip to order the ready assembled board from www.transverters-store.com for
30 USD + 7 USD shipping. For the operation you need an ATTENUATOR BOARD for only 10 USD additional.

I have developed my own board with HF VOX and other helpful extras. In the housing, the transverter weighs only 160gr. The power supply is a clone of the KX2 Lithium Pack.

73 Chris



Yes - The transverter is fun!
I already used it a few times in SOTA activations. ( How to activate 2m SSB with low budget )
The frequency drift annoys a bit on longer runs, but I have the right tcxo already at home and will certainly install it this winter…
Hope to see you in a 2m s2s

73 Armin

Fine Armin, my first activation is still in front of me. Which tcxo do you suggest?

73 Chris

Hi Chris,
I also couldn’t resist and bought the “kit” i.e. set of boards and case about a month ago, to give me 2m capability again, now that I have got rid of my TS-2000 and just have the IC-7300 as the home station rig. Unfortunately I haven’t got around to building it yet. I am considering fitting the completed unit into an FA-AS antenna switcher case as there is support for RX only antenna and TXvrter in there (that unit I still have to order and assemble). A couple of “winter projects”.

I’ll be interested to hear how the transverter performs for you.

73 Ed.

Hi Chris

I got it from ebay

It was recommended on another website…

73 Armin

Thanks for the note, Armin. I just found this board in my craft box, hi.
I’ll give it a try and keep you up to date.
73 Chris

Chris , you’re an ANGEL !

I have also this transverter board, but not the attenuator board, and couldn’t decide how to connect it to my KX3, and make sure not to blow up the transverter from the first attempt.
So I delayed, and delayed …
Your circuit will help a lot, now if I only could find some time to work on this project …

A question @DL1CR : could you elaborate a bit on what settings you made, and what power you transmit on the KX2 (probably also applicable to a KX3)?

Thanks a lot !

Anybody besides me get a “403” error on the transverter store web site? I guess that is not quite as serious as a 404? :slight_smile:

If anyone is interested, I asked Serge, UT5JCW why his web site does not work for VK. He says it’s deliberately geo-blocked, as he is not interested in doing business with us. Our reputation precedes us, apparently :slight_smile:

Well, 404 is “not found” but 403 is “found but you aren’t allowed to look at it” which is fairly enticing…

It’s you John or it’s fixed. i.e. works for me.

I guess a typo created “HF vox” instead of “RF vox”, ie. RF actuated PTT?

Very nice transverter build.

73 Andrew VK1DA/VK2UH

I think it’s just the German for “RF vox”

Right Andy.

HF - HoeheFrequenz (High Frequency) often used when in English you could use RF Radio Frequency.

Another “False Friend” between the two languages in abreviations - KW can mean Kilowatt - bit it can also mean “Kuerzewelle” which in English is Short Wave.

73 Ed.

Hi Luc,
I set the power on my KX2 on 28MHz down to 0.5 Watt. After the 20dB attenuator it’s 5mW. That’s more then enough and therefore I set the tx gain on the transverter board to 50%. So I get the output power of 10W at 12.8V.

A rx signal of 5uV = S9 at 144Mhz produce a S8 on my KX2 at 28MHz.

I did not messure the rx noise level of the transverter yet.

73 Chris

Matching my transverter I put a rabbit ears dipole on a carbon fiber pole.

Legendary 0dbd gain and 2db coaxial loss according to my motto “Less power - more fun”

73 Chris

I measured the sensitivity of the transverter today. The following video shows the equipment and the process. DL1CR S/N test 10m 2m transverter - YouTube

With an input voltage of 0.05uV the signal-to-noise ratio is approx. 10dB (see picture).
The results could be somewhat worse with the usual measurement methods. In direct comparison with my Yaesu FT-817, the transverter was equivalent.

73 Chris

Love that little rotary attenuator :slight_smile:

Me too. It works up to 5Ghz.
A friend gave it to me on loan 4 years ago. I hope he doesn’t miss it.
73 Chris

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I converted the transverter to operate with a TCXO. The TXCO comes from a finished circuit board.
Armin made the suggestion.

I only used the 116 MHz chip and voltage regulator. The originally installed quartz can remain in the circuit. It is important that the 100p capacitor and the 220Ohm resistor are installed as close as possible to the transverter board. Here, SMD components are absolutely preferable (see picture).

73 Chris


73 Chris

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today I was able to compare the noise behavior of the transverter on the KX2 with the FT817 with CW filter. The beacon DBOTHE as a reference is approx. 100km away.

73 Chris
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