I also had bad interference to my IC-9700 while working sats & receiving on 435. I have SSB preamps installed at the antennas on both bands. My preamps power with separate injectors on the coax, not from the radio. The solution to the problem was to climb up on the roof and install the 2m/70cm diplexer on the input of my 70 cm preamp (as the AMSAT mode J tip page says).  I also installed a second diplexer in the shack on the 2 meter side between the radio and DC injector to minimize the 3rd harmonic interference.

I still get some very minor interference when pointed specific directions (toward other antennas on my roof), but the problem is gone 95% of the time. 

Ernie W8EH

On 2/8/2022 11:40 AM, Dave Julian via AMSAT-BB 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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