[Elecraft] K3 and transverters

[Sebastian, W4AS]

With a K3 I use the XV144, XV222 and XV432 external transverters.

At first I was very disappointed with their frequency drift.  It was difficult to stay on frequency from a cold start, and it would continue to drift the more I transmitted.

Installing the $100 TCXOs helped but didn't really solve the issue.  To minimize frequency drift, the manual suggests to always have the local oscillator powered, easily accomplished by changing a jumper inside; note that requires 12 volts to always be present.

I checked the voltage on the 25 amp power supply I was using (a bit overkill on the current, yet it was what I had that wasn't being used) and made sure that it didn't deviate over time or while transmitting.

Frequency stability is very important to me as I often run meteor scatter contacts which are quite dependent on accurate frequency control, and demands a key down time of 30 seconds on and 30 seconds off.

I thought that perhaps by placing one transverter on top of each other as I had done, wasn't helping the cooling, so I made a little cabinet which offers approximately 3 inches of separation on all sides from the trio.  Again, that didn't help very much.

Frankly I was ready to go back to a TS-2000 for VHF/UHF as I hadn't been able to solve the drift issue, and it was embarrassing to talk to the locals on 2 meter SSB when I was drifting for the first few minutes.

Finally, the problem was solved rather easily.  After reading through similar stories from other hams, I found an old cooling fan for a 486 CPU processor which has almost the same dimensions as the small cooling holes on top of each transverter.  I applied double-sided tape to each corner of the fan, and placed it on top of the cooling holes.  As long as the little fan is on, the transverters will drift only a small amount, which is acceptable for the modes I use.

Note that my XV144 is the one I use the most often, and is setup to output only about 4 watts, which is enough to generate 50 watts from one amp (Mirage B108 capable of 80 watts), which is enough to fully drive my 300 watt amp (Mirage B5030G).  These amps and the XV144 are keyed using an external sequencer.  I'm not sure if the little fan would help if you were to use the full 25 watts output of the transverters.  I should also note that the K3 is driving them with very little power (I forget exactly how many milliwatts).

Don't use a large computer power supply fan, as the fan motor will be similar in size to the cooling holes, which means you would actually be covering them up and making the problem worse.

Finally, I haven't come up with a neat way of daisy chaining them.  Typically you would use BNC T connectors, but having three transverters close to each other, with six coaxial cables connected with six BNC T connectors creates quite a mess; in addition to the control cables, but that's just a minor issue.

73 de Sebastian, W4AS



On Sep 15, 2012, at 6:05 AM, Gary Gregory <garyvk4fd at gmail.com> wrote:

> *Has anyone got a K3 with the 2M and 70cm transverters got any comments
> plus or minus as to performance.
> 
> I don't have them myself but a VK is about to order his K3 and will be
> adding these transverters.
> 
> His interest is HF, 2 and 70cm and not 6M.
> 
> I thought I would ask here as I don't know what to tell him due to lack of
> experience in the higher bands.
> 
> Off list or On is OK as long as it doesn't flood the reflector with
> QRM.....:-)
> 
> 73
> *
> -- 
> *Gary*