Bob I have an HP435A power meter, I'll look at how much signal shows up on the 6 meter antenna tonight.... I expect it to be big, probably more than +20 dBm with +52 dBm comming out of the 2 meter amp. The 6 meter loop probably works pretty good close to 3X it's design frequency, and only a couple feet away.... I'll measure it tonight, and let you know.... it might be a good bit of info to have in the useful ham radio trivia collection
Greg Robert Friess <[EMAIL PROTECTED]> said: > Hi Greg, > > Because of the high power and close proximity of the antennas there is > probably considerable out of band power being applied to the LNA input. It > is difficult to suggest what is needed to alleviate the problem. Do you > have some means of measuring the power at the XV50 input when the other > bands are active? > > 73, > Bob, N6CM > > > ----- Original Message ----- > From: "Gregory P. Daly" <[EMAIL PROTECTED]> > To: <elecraft@mailman.qth.net> > Sent: Thursday, March 31, 2005 9:55 AM > Subject: [Elecraft] XV-50 LNA problems > > > > Now that I have my K2 fully stuffed with goodies... DSP, NB, ATU, Battery, > > SSB, 60M, 160M, IO... I got busy on transverters... and have all 3 > > working... > > but... > > > > 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. > > > > I've been thinking about bringing out band select signals, to switch loads > > onto the antenna ports of the unused transverters, but 12 volt coil coax > > relays are expensive. A shorted 1/4 wave stub might work, but it's close > > to > > 3/4 wave at 2 meters, so it may not be enough, an open 1/2 wave stub at 6 > > meters is getting rather long for running around in the field, the truck > > already has too much clutter on contest weekends ;-) > > > > Going back to the Icom receiver is not an option, after using the fully > > tricked out K2, listening to the 551 all weekend would be torture. > > > > > > 73 DE WB7RSG > > > > -- > > Gregory P. Daly > > http://www.mitrek.com > > > > > > _______________________________________________ > > Elecraft mailing list > > Post to: Elecraft@mailman.qth.net > > You must be a subscriber to post to the list. > > Subscriber Info (Addr. Change, sub, unsub etc.): > > http://mailman.qth.net/mailman/listinfo/elecraft > > > > Help: http://mailman.qth.net/subscribers.htm > > Elecraft web page: http://www.elecraft.com > > > > > > -- Gregory P. Daly http://www.mitrek.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com