Spectrian 180W Amplifier use on 13cm
I purchased a 180W 13cm amplifier some time back which I intend to use on 13cm for EME and probably on my tropo setup too when I get round to installing it!
The amplifier as standard comes with lots of parts which are not really needed by us, these will be removed and some minor re-wiring will be done to make it run on 28v/13.8v
There are other documents on the internet relating to this amplifier, see bottom of page..
I plan on using two separate 13.8V and 28V power supplies so the internal DC-DC converter can be removed along with the controller board this reduces the weight significantly!
My 13cm transverter output is around 400mW, this is not enough to drive the main three brick stage so instead I will leave the 25W driver board in place and attenuate my transverter output to around 10mW. The pre-driver board can be removed (whatever this does?!) and the transverter fed into the driver amplifier.
I have also removed the multi connector from the rear of the unit as this is no use without the matching plug!
This leaves us with a lot of free space where the DC-DC converter was to fit the control cables and RF connections.
The RF output connection has been replaced with a length of UT-141 and fed to an N socket on the rear.
The original semi-rigid that went from the rear socket input to the pre-driver board has been re-used between the driver input and an RF Input SMA socket on the rear, this now gives us the main RF In/Out connections for the amplifier on the rear and makes them a lot more accessable.
After some investigation I found that most of the required control/monitor lines were available on the power distribution board on the 40-way header, Forward/Reverse power monitoring is taken from the sensors on the output strip through the 8-way header.
I am assuming the blue multi-pin devices on the ends of the output coupling stripline are some sort of detector diode in a chip like package which feeds the opamps on the other part of the board. There is a spare one to be salvaged from the pre-driver board if you can remove it....
Here are the relevant connections on J4 40-way header:
The main PTT line first controls the biasing on the driver board, fortunately the driver board switches 13.8v on through the large transistor and this can be used as a 13.8v bias supply for the final boards so we get one Ground activated PTT line like any other amp to activate it.
Power supply currents with bias only (no RF) on my unit measured around 5.5A @ 13.8v rail and 3.8A @ 27v. On the three boards the gate bias on each device was measured at 4.0v
From reading Dave G4FRE website I found the pinout for the Output RF monitor circuit, see below:
Pin1 = Forward Power det (about 5V for 200W)
Pin2 = Reverse Power det
Pin3 = 8V supply to circuit
Pin4,5,6 = Ground
Also I found from Daves site that the circuit breaker built into the power switch is rated at about 37A.
This causes problems now we have modified the unit to run off 28V - about 2 times the current is drawn compared to the original 48V supply & dc-dc converter.
I found that the breaker trips at around 30-35A with ~150W CW signal through for a few seconds.
So far I have tested the amplifier (without the breaker) upto 45A DC input and seen about 4.7 volts on the forward detector which is probably somewhere around 170W. I have no meter for 13cm to handle that power so need to build a coupler and use the spectum analyser to measure the output more precisely.
The first tests that I did with my 3m dish, 150W and home brew septum feed indicated that 13cm EME is performig better than 23cm.
I was able to detect my echoes audibly all the time where as on 23cm with 130W it is very difficult to detect my echoes without the fft spectrum on the pc.
This 13cm setup was not optimised yet and to confirm this the sun noise only measured a litle over 5dB... quite poor for a 3m dish! The sun noise on 23cm was ~9dB if i remember correctly for an unactive sun!
I use an identical septum feed with no flare/ring on the front for both 23 and 13cm.
Both bands use a G4DDK low noise pre-amps, so my best guess of why I am more deaf on 23cm is desensing from local signals but I have yet to prove this.
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