[amsat-bb] Re: ICOM AG-25, 2M Mast Mounted Preamplifier
w7lrd at comcast.net
Wed Mar 24 12:27:36 PDT 2010
The preamp is the Icom AG-25, which in the past has had questionable or unknown specs. Thanks to Stan now we know.
73 Bob W7LRD
----- Original Message -----
From: "W1LE Stan" <stanw1le at verizon.net>
To: amsat-bb at amsat.org
Sent: Wednesday, March 24, 2010 10:23:59 AM GMT -08:00 US/Canada Pacific
Subject: [amsat-bb] ICOM AG-25, 2M Mast Mounted Preamplifier
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
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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