I've got similar problems with the PHEMTs in the front-ends of the
144,222 and 432 Elecraft transverters (50 Mhz has a bandpass filter
and seems immune). I've not tried Dave's power meter idea (I will as
soon as it warms up!) but I'm pretty sure it's adjacent-band energy.
I'm in the process of moving T/R external to the transverter, and
using the unused relay to ground the gate on the unselected
transverters. Since we only use one of the 4 low bands at a time,
that's an easier solution for me .. and uses less room :)
de w1rt/john
On 2/16/07, David Olean <k1whs@metrocast.net> wrote:
> Hello Mike,
> The culprit is most likely rf from another band getting into the TS-2000
> and causing the problem. Best way to test is to get an HP or similar rf
> power meter and hook it to the 1296 antenna cable and SLOWLY run up the
> power on the other bands. I have had some serious problems at my QTH from
> such things. The hard part is that you have to rotate the antennas to peak
> each band up, and you cannot predict where the beam will peak up!
> Generally, once you find some rf at the lowest setting, you can then swing
> the other antenna around to see the peak. Levels can add from several bands
> too!! If you have a good spectrum analyzer, you could use that in place of
> the power meter. I have had to run filters on several bands where rf entry
> was a problem. I would suspect the 432 PA amp may be hitting 1296. There was
> an article in the NEWS newsletter on a good 3rd harmonic TX filter I built
> for a 432 KW amp. I saw over 100 dB of insertion loss at 1296.3, and it held
> up to 1500 watts at 432. It really knocked the be jeezus out of the 3rd
> harmonic, and now 432 and 1296 co exist at the same time. Can your 432
> system see the 1296 antenna, or are they vertically spaced on the same mast.
> Horizontal spacing is worse than vertical spacing. Signals are louder.
> Other bands may just cause out of band problems that can still damage or
> kill a front end. A good rx filter will work wonders for that problem.
> Levels near 0 dBm can start causing potential damage. If you see anything
> even near that level, you need filters real bad!
> 73
> Dave K1WHS
> ----- Original Message -----
> From: "MICHAEL SAPP" <wa3tts@verizon.net>
> To: "VHF TEST REFLTR" <vhfcontesting@contesting.com>
> Sent: Friday, February 16, 2007 8:38 PM
> Subject: [VHFcontesting] TS2000X question
>
>
> > Hi Folks: Are there any TS2000X owners out there that have had problems
> > losing the 2sk2685 HEMT front-end on 1.2 GHz? This is the third time I've
> > smoked one at W3KWH during a contest. I'm not sure if it is an ESD
> > problem or front end overload. I'm working on a bandpass filter solution
> > for the overload possibility but would appreciate any
> > comments/expereiences others may have. Thanks in advance. Mike WA3TTS
> > _______________________________________________
> > VHFcontesting mailing list
> > VHFcontesting@contesting.com
> > http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
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