[amsat-bb] ICOM AG-25, 2M Mast Mounted Preamplifier

Stan, W1LE stanw1le at verizon.net
Wed Mar 24 10:23:59 PDT 2010

Hello The Net:

I recently got in Bob's (W7LRD) preamp for testing, with the following 

144 MHz  G = 27 dB     NF = 1.3 dB
145          G = 27 dB     NF = 1.1 dB
146          G = 27 dB     NF = 0.9 dB
147          G = 26 dB     NF = 0.8 dB
148          G = 25 dB     NF = 0.9 dB

Performance is better than I expected, but lotsa gain.

DC voltage applied was 14 Vdc and lowered to 8 Vdc with no change in NF, 
but a 1 dB reduction in gain.
DC current was ~200 milliamperes at 14 V and 117 milliamperes at 8.0 
volts applied.
Below 8 Vdc, the gain decreases rapidly and the NF increases.
I like the wide operating voltage range.

The RF connectors are UHF type.
There is a larger screw with a plastic washer underneath,
but upon removal there is NO adjustment underneath for neither pass band 
tuning or gain reduction.

Reportedly there is a variable capacitor inside to allow tuning, but 
nothing externally accessible.

Has anyone found a adjustment for gain ?

Only choice I can think of is to reduce the RF gain on the transceiver
when the preamp is menu enabled.

If an attenuator is put in line, the TX power would also be attenuated.
 We do not want to just throw away RF power in an attenuator

Stan, W1LE       Cape Cod     FN41sr     Cape Cod


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