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Homebrew 144/28 MHz Transverter

Hey Chris

To me it sounds like there is more noise on the FT 817…
Why don’t you use the transverter mode on the KX2 to get displayed the correct frequency ?
What is your experience with the TCXO…has it improved a lot? I still haven’t installed mine - I’m just rebuilding my shack. So many projects … (for me it’s kind of typical for the Christmas season)

73 Armin

Yes Armin, the transverter seems to have less noise.

But I am not yet satisfied with the large signal behavior. I have provided two anti-parallel protection diodes at the 28mhz input of the converter because the RF VOX activates the attenuator after a few milliseconds delay. I will replace the diodes with 2 BA70-04 with 2 diodes each in series. This should improves the IM3.

You don’t have the problem if you use the PPT output of the KX2. But then you have to make a secure connection, otherwise you will destroy the FET from the preamplifier.

Since I am sometimes very excited when activating, I chose the safe solution with the RF Vox. The circuit itself has proven itself and the RF VOX is hardly noticeable: https://youtu.be/8dYwF_sNEew

The TCXO works very well. No noticeable drive and the offset is less the 10Hz. The offset of the original XO is -400Hz and drifting up to +100Hz, when the transverter warms up.

Good luck with the handicrafts.

73 Chris

Just an idea … I did not try this (yet).
Connect the microphone to the transverter and tap the PTT there, then connect to the KX2.
Put the KX2 in TX after a short delay, so making a “mini-sequencer”.
When the microphone gets broken or disconnected, you will be sure nothing will happen (unless of course, the connecting lead gets shorted somewhere and puts the TX in continous transmit …).
Attenuator should kick in instantly, but have a short delay switching off, because the tail of the TX could still cause some trouble …
Anyone tried it this way ?

Luc ON7DQ

Luc, that’s an interesting solution.
But you must consider that in the transverter the high level of the PTT circuit is 8V, of the KX2 3.3V.

73 Chris

I haven’t done that, but in essence It’s the “right” way to do it. Avoids hot switching anything. Without rf everything else can be switched over in almost any order and if the rf is last to go on and first to go off, the relays are protected. It’s the best option when using transverters, high power amplifiers and mast head amplifiers. The alternative is a complete sequencer driven by the microphone PTT.

The option often used, keying the driver radio and letting its rf switch everything else, provides less protection for hot switching relays.

Your suggested method only lacks a method of forming the transverter off after the rf from the kx2 has been terminated.

Ian White GM3SEK published an alternative two step sequencer in the RSGB handbook some years back. With revision to suit solid state voltages it is quite suitable for today’s needs.

73 Andrew VK1DA/VK2UH