开云体育

I've just installed a YF-122s SSB filter in my FT-818, the audio certainly sounds much fuller but looking at the overall RF to audio spectrum there is considerable ripple and slope - amounting to nearly 4dB over 500Hz to 2.5kHz.? I checked the filter separately, correctly terminated, on a VNA and the response is beautifully flat (<0.7dB peak to peak).

I just wondered if anyone else in the group has seen this effect and dug into possible causes?

Many thanks

Simon
M0AZR

My initial guess? is mismatch to the filter.

What's the pass band look like without the filter installed? Or with another filter installed?
--
Oz (in DFW) N1OZ

Thanks Oz, I believe you are correct.? I replaced the mechanical filter with a "null" 10dB 2 kohm impedance attenuator in the SSB filter location (with suitable pin coding as per the actual SSB filter).

The ripple went completely, leaving a low-pass roll-off that tallies almost exactly with a simple LTspice model of the active audio filter that follows the product detector.? That is already down by 3.3dB at 2.5kHz.

All interesting and educational - but now to try and track down why the rig is not presenting the SSB filter with the correct impedance.

Simon
M0AZR