[Elecraft] XV-50 LNA problems

[Timothy A. Raymer]

Gregory,

Not inexpensive, but works well:

http://www.dci.ca/

Specifically:

http://www.dci.ca/?Section=Amateur

We installed one of the 2M units on our repeater to eliminate bandpass and 
to give a DC ground to our preamp on our repeater system.  It was 
intolerant of the energy from Lightning.  One of these solved all our 
problems.  Looks like the specs say > -72dBm @ 135Mhz on the 2Mhz wide 
unit.  The 4Mhz wide unit is better documented, and shows > -89dBm @ 126 
Mhz. That should knock down any nastys that will get your 6m XV-50.

I will verture out on a limb, and recommend that you may want to turn off 
the Receive preamp in the Amp, if it has one.  The XV-50 has excellent 
performance, and you may be doing more harm than good if the Amp's preamp 
is on as well.  Others can probably give some counterpoint to this.

Hope this helps.

Tim Raymer
73 de KA0OUV
K2#1383

At 11:55 03/31/2005, Gregory P. Daly wrote:
>I plan to use the K2 and transverters, portable, for the June VHF contest. I
>use M2 “HO loops” for the “low gain” stack to allow quick setup when we get to
>a hill top. By the time we've gotten "the easy ones" worked with the low gain
>stack, the antenna monkeys have the "real" antennas up. The 50, 144, and 222
>loops are about 2 feet apart on a common mast. The plan is to use Mirage 160
>watt amps on each band.
>
>Much to my dismay, I discovered that with about 150 watts output, at 144.2,
>into the middle loop, the PHEMT GaAs FET, in the front end of the XV-50
>failed, gate to channel short. The first time, since my ESD discipline isn’t
>the best at home, I assumed it was static damage, and the FET was “wounded”
>and failed after a couple days of operation. I was able to get several samples
>of this PHEMT from Agilent, and replaced the damaged part. The second time, it
>was obvious what had happened, the large 144 MHz signal from the nearby
>antenna had coupled enough energy into the 50 MHz antenna to destroy the 
>LNA FET.
>This configuration has worked in the past, with other radios. My ICOM 551’s
>receiver has survived up to 500 watts in the 2 meter loop without damage.
>
>This problem is soon to be worse; the spring antenna project will be a 6
>element 6 meter yagi, on a common mast with the 2 meter and 1.25 meter
>yagis
.. and up to 1500 Watts on 2 meters.

>Any suggestions about protecting the GaAs FETs from VERY LOUD out of band
>signals, without causing nasty intermodulation products? It would be a shame
>to build a killer transverter and waste it’s excellent performance with
>clipper diodes in the front end.



>73 DE WB7RSG
>
>--
>Gregory P. Daly
>http://www.mitrek.com

Timothy A. Raymer
Missouri Department of Health
and Senior Services

<traymer[at]mail.state.mo.us>                        <RaymeT[at]dhss.mo.gov>
<KA0OUV[at]arrl.net>