Re: [Discuss-gnuradio] power amplifiers on TX

[madengr]

I'm running an N210 + LF TX/RX to 25W on HF, but also using separate RX and
TX antennas with adequate isolation ( https://www.qrz.com/db/KD4HSO ).  The
LF-TX is direct sampling so you don't have the issue of LO leakage when you
are not transmitting (i.e. zeros into sink).  With the I/Q conversion
devices you have LO leakage, and you must shut down the flow graph to kill
it.  If you offset-tune with an adequate filter then you could suppress the
leakage enough.  I have heard of using the LED on the N210 to trigger a
relay, but still would require stopping the flow.  Best method would be to
use user I/O to control it (assuming you have that on your hardware) via
messaging, but I have not gotten around to trying that.

Lou



Daniel Pocock wrote
> Based on the USRP specs (up to 100mW output power), I started looking
> around for amps that would get me up to a level comparable with other
> amateur rigs.  This is one of the first I found:
> 
> http://shop.kuhne-electronic.de/kuhne/en/shop/amateur/leistungsverstaerker/MKU+PA+2M-120W+HY+VHF+MOSFET-Power+Amplifier/?card=632
> 
> Specs mention a low-pass filter so harmonics shouldn't be amplified.
> 
> It takes 100mW in and puts out 120W on 2 meters.  It needs up to 21A
> when running, that probably means getting quite a serious DC power
> supply or just running it off a car battery.  It looks like it needs an
> external heatsink.
> 
> Has anybody else tried solutions like this with USRP or other SDR
> transmitters?
> 
> For simplex operation, if the application is not transmitting, will
> output power completely drop to zero when using something like this?
> 
> Can anybody comment on how to wire the USRP and a power amp for TX and
> RX through a single antenna?
> 
> Regards,
> 
> Daniel
> 
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