I use a comet duplexer CF-4160N to avoid desense issues. It acts as a bandpass filter with 60dB of rejection from your 2m TX. The dummy load is on there, because I read somewhere it acts better with one attached since it would expect to be connected to something vs open.



-Ant NU1U

On Tue, Feb 8, 2022 at 11:41 AM Dave Julian via AMSAT-BB <amsat-bb@amsat.org> wrote:

Just got a new SSB SP 70 preamplifier for my IC-9700 and having an issue with working 435 RX satellites like RS-44.

The amplifier works fine but I am getting terrible overloaad from the 2M TX signal. It causes the OVF light to come on and

very distorted audio. I have lowered the RX gain and TX power on the IC-9700 but by that time it kind of defeats the purpose

of a preamplifier. My set-up is an M2 2MCP22 with fixed polarity on 2m and a 436CP30 with the PS-70Cm polarity switch for UHF.

I have about a 200' run on LMR-400 to the base of the tower with lightning arrestors then about 40' of RG-213 to the antennas.

For testing I have the Sp 70 preamplifier temporarly installed at the base of the tower. No preamplifier for 2m.

Power to the preamplifier is over the coax from the IC-9700. I am looking any any suggestions on sorting this out.

I have removed the PS 70 at this point to avoid damage the radio or preamplifier.



Dave WB9YIG 


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