24 cms linear

One of my current projects is to build a couple of these
amplifiers and then combine them. I have received the
PCBs from DL2OCB and have removed some XRF286
devices from a pair of surplus Spectrian 2.3 GHz PA units
as sold by PyroJoseph on eBay. The 286's are in the package
that is soldered directly down to a copper heat spreader.
I removed them using a cooking hob. The devices came away
from the boards quite easily and seem to be in good condition.
The PCB's require some holes cut in them to take the XRF286
devices and the termination resistors, which I completed today.

I understand that when you solder the devices down onto
a heat spreader you need to be careful about not letting the
solder wick up and short the gate/source to the drain.

Talking about PyroJoseph I also bought one of his 30 watt
Class A 2.3 GHz amplifiers. A suitable heatsink with forced
air cooling was bought for a few pounds on eBay. So I should
have some power on 13 cms digital soon. As yet I don't have
any antennas for that band.

My upgraded USRP2 also covers the 3.4 Ghz band and
while I have a used loop yagi for 9 cms I don't have a PA yet.
As I doubt I will ever work anyone on 9cms DATV I am not
pushing that project forward at the moment. I do have some
cheap 3.4 GHz head units that will receive on 3.4 GHz which
I can loan out but first I will have to do some tests to see if
they will work for DATV reception. Unmodified they work at the
top of the band on receive and to modify them you need to
break the water tight seal which means water will
probably get into them when they are re-assembled.

Another little project on the go is to interface my Linux
DATV encoder app with a relay control board which I bought
to control the 6 way SMA relay I have. When a frequency is
selected the output of the USRP2 will be switched through
to the appropriate PA/antenna.

I saw GB3VX at Eastbourne for the first time this weekend.
It will be interesting to see if it is visible here when conditions
are flat.

I am no longer able to access GB3IV on the IOW mainly
because of a mixture of antenna changes (at both ends)
and strong radar QRM.

Now if I could only get GB3VR to add a digital input!
I am not sure what the clearance issues are as far as adding
extra input channels to an already established repeater.

One final comment, now that conditions are starting to pick
up there have been a number G/F QSOs on 70 cms DATV.
Not to miss out on the fun I will be adding a 70 cms yagi to
my mast in the next couple of weeks. So I hope to join in
down there soon. The only slight issue is that the French
use symbol rates below 2 MS/s and I don't have a reliable way
of receiving those yet.

I will post some pictures with my next rant.

MRFE6VP6300H

I have the MRFE6VP6300H in the AR305 circuit now.
I have had to change the input transformer from a 9:1
to a 4:1 and add some inductance to both the input and
output.

The amplifier oscillates at about 230 MHz and the only
way I can stop the oscillation is by placing a capacitor
across the output of the dual FET. This is not optimum.

So far I am getting about 150 watts out with around 27db

of gain at 70 MHz with a power supply of 48 volts and
drawing 6 amps, the device is biased on at 2 amps.

The input match appears quite good but the output match
is lousy. I would probably have been better off starting
with a fresh design and doing away with the ferrite loaded
output transformer which gets very hot (yes I managed to
burn my finger on it by accident). Still these Freescale
devices look to be the bees knees for modern amplifiers
up to 600 MHz.