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Need Schematic or information for a ICOM AG-25 and/or AG-35



Fant:
The AG25 and AG35 require that the transceivers they are used with have
internal sequencer circuitry. For example, I have an IC970 quadband
radio with the AG25, AG35 and AG1200 preamps connected. The IC970 puts
13 VDC up the coax to turn on the relays and to power the preamplifier
(ONLY) during receive. Upon transmitting, the IC970 drops the 13 VDC
PRIOR to transmitting RF up the cable. If this is sequence is not
followed, the preamplifier will be damaged.

I am also using an SSB Electronics SP13-O. The SSB preamps include
additional RF switching circuitry to protect the preamplifier when used
without a sequencer.

The ARRL handbook has diagrams for preamplifier sequencers. Be prepared
to build one if you are going to use the AG-XX series ICOM preamplifiers
with non-ICOM radios. You might find the SSB electronics preamps more
suitable for your application. In either event you will need a "bias T"
which is simply a circuit comprised of a DC blocking capacitor, and RF
choke and an RF bypass capacitor used to impose DC up the coax line and
to prevent DC from getting into the radio.

By the way, I can tell you from (bad) experience that the AG-25 uses a
3SK121Y GasFet. Hopefully for our mutual benefit, someone on the BB can
tell us what devices are used in the AG-35, and AG-1200 preamps and what
noise figure might be expected for these ICOM preamplifiers.

--
Joe Leikhim K4SAT
Jleikhim@nettally.com

Sky King, Sky King, do not answer.

"The Revolution will NOT be televised" -Gil Scott Heron

"Whats he building in there?"- Tom Waits


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