XV-50 LNA problems

[Gregory P. Daly-2]

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


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[Robert Friess]

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" <[hidden email]>
To: <[hidden email]>
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: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com
>
>

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[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>

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[Gregory P. Daly-2]

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 <[hidden email]> 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" <[hidden email]>
> To: <[hidden email]>
> 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: [hidden email]
> > 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


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[Robert Friess]

Greg,

Once we know what we are dealing with then we can work out a solution.   It
could be as simple as an external lowpass filter.  That would be nice
because the loss would be very low.

Bob

----- Original Message -----
From: "Gregory P. Daly" <[hidden email]>
To: "Robert Friess" <[hidden email]>; <[hidden email]>;
<[hidden email]>
Cc: <eric@.SYNTAX-ERROR>; <UNEXPECTED_DATA_AFTER_ADDRESS@.SYNTAX-ERROR>
Sent: Thursday, March 31, 2005 12:53 PM
Subject: Re: [Elecraft] XV-50 LNA problems

> 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 <[hidden email]> 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" <[hidden email]>
>> To: <[hidden email]>
>> 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: [hidden email]
>> > 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
>
>
>
>

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[G3VVT]

 
In a message dated 31/03/05 19:42:07 GMT Daylight Time,  
[hidden email] writes:

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.



Have been using the DCI-145-2H, 4 section helical filter since 1999 on the  
local 2m repeater GB3LD which I hold the license. Without this we would be  
swamped by pagers in particular located on ours and adjacent masts. The normal  
bandpass and notches found in the repeater duplexer whilst they are efficient
in  preventing energy from it's own TX entering the RX, work relatively poorly  
in keeping out energy from external sources. Notch filters are only really  
successful when a single fixed frequency is involved.
 
The bandpass filter on the repeater worked so well that I ended up  buying
one for my shack when 153 MHz pagers were installed close to the home  location.
 
For these devices to work you need to have a bandpass filter of this type  on
the receiver that is being affected and not the TX that is causing the  
interference, unless the TX output purity is sufficiently poor to warrant  this. In
other words if the 6m receiver is being affected, a 6m bandpass filter  is
needed and not really much use in installing one on the 2m TX. Bandpass  filters
incur a penalty in that they are lossy and usually mean a  loss of about 1dB
in the case of the 2m unit and greater at UHF. If it is  installed in the
common antenna feed of the TX/RX mean the same loss on TX  power.
 
All too often the designers of normal every day amateur receivers for  
VHF/UHF skimp on the selectivity of the front end to achieve a better  sensitivity
and the price is blocking or even damage if the local field  strengths from
other sources are too high. By comparison commercial 2 way radios  by virtue of
performance regulations are far superior in the selectivity stakes,  quite
often using miniature helical filters at the front end to achieve the  performance.
 
Good bandpass filters are expensive, but if transmitters on other  
frequencies are causing a problems, are a necessary evil.
 
Bob G3VVT
Keeper GB3LD/GB3LF
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[Gregory P. Daly-2]

Bob:

     A simple low pass filter would be nice, but it might not cover all cases.
Eventually I'll be able to make max legal power on all bands, and I might find
myself in a situation where the lower frequency signal damages the higher
frequency transverter. At the moment, I'm only talking about 150 watts, but
eventually it will be 10 dB louder on all bands.


     I'm thinking external T/R relay is the smart move. If the relay is rigged
to rest in the transmit position, when the transverter is powered off, the out
of band signal will land in the PA output, I suspect the output of the PA
module is a big strong MOSFET or bipolar, that can take a few volts on it's
drain (or collector) when it's biased off. When I add a "real" amp, the plate
of an 8877 can take big voltage ;-).

     The Schottky diode in a small GaAs FET gate is pretty fragil to expose to
big bad high power transmitters at close range.

     I'm hoping somebody on the list will have a better idea. I don't mind
looking stupid to save a lot of effort ;-)

73 DE WB7RSG

Greg.


Robert Friess <[hidden email]> said:

> Greg,
>
> Once we know what we are dealing with then we can work out a solution.   It
> could be as simple as an external lowpass filter.  That would be nice
> because the loss would be very low.
>
> Bob
>
>
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[G3VVT]

 
In a message dated 31/03/05 23:06:29 GMT Daylight Time, [hidden email]  
writes:

I'm thinking external T/R relay is the smart move. If the relay is  rigged
to rest in the transmit position, when the transverter is powered  off, the
out
of band signal will land in the PA output, I suspect the  output of the PA
module is a big strong MOSFET or bipolar, that can take a  few volts on it's
drain (or collector) when it's biased off. When I add a  "real" amp, the plate
of an 8877 can take big voltage ;-)




------------------------------------------------------
 
External T/R relays to isolate the unused antenna feed and dump any  unwanted
energy into a dummy load with some form of interlock to prevent  transmission
until the feed is enabled would be the cheapest option by far to  resolve the
problems with damage to the XV-50 RX front end.
 
The commercial systems I worked on had ferrite isolators in the TX antenna  
feed to stop exactly what you talked about, i.e. TX power from another TX
coming  back down the feeder into the PA as this could generate unwanted RF  
products at the PA. The ferrite isolator works as a directional coupler,  allowing
TX power towards the antenna, but any energy coming back from the  antenna
towards the PA from another source is dumped into a dummy load. Not  normally
needed for ham equipment working in simplex, though essential with  systems on
busy sites working in duplex such as repeaters. Used universally  with
transmitter combiners into a single antenna.
 
Bob, G3VVT
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[VR2BrettGraham]

There are parallels here to two-radio operation for radiosport at lower
frequencies.

Bandpass filtering not only keeps dangerous energy from blowing
things up, but also makes it possible to operate on >1 band
simultaneously, not hear phase noise from the other rig, etc.

And unless VHF activity exploded in the Pacific NW since I left,
for those times one goes out on your own, you're then one radio away
from having a lot more fun than you would otherwise have.

Same filtering could also be moved over to the full-blown station in
the multi-op situation Greg described.

For the power levels & distances involved (in wavelengths), this should
be a piece of cake when at HF folks are pumping 1.5 kW into one
driver of a triband yagi whilst listening on another driver of the same
antenna on another band (separation being a dozen or two of
centimeters at most).

73, VR2BrettGraham

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[Bill Coleman-2]

On Mar 31, 2005, at 12:55 PM, Gregory P. Daly wrote:

> 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.

Coaxial stubs? LP / HP filters?

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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