EMRFD Message Archive 15285

Message Date From Subject
15285 2019-05-24 14:23:10 mhadley157@gmail.... Compensating for xtal filter loss
I have a bargraph s meter operating from the agc line on my HyCas IF amp. Any idea's on the best way to correct the s meter reading when switching between crystal filters with different insertion losses without compromising performance? Filters are 8 pole 9.0 meg with bandwidths of 3.1 khz, 2.5 khz and 500 hz. Insertion loss is up to 6db.
I am using a SV1AFN H mode mixer on all bands from 1.8 to 50 meg.

Mike G4JXX
15286 2019-05-25 00:36:44 peter_dl8ov Re: Compensating for xtal filter loss
I faced the same problem when building my homebrew rig, but in my case it was accounting for the 10dB attenuator and 12dB preamp on the front end. So.........

1) Get yourself an analog MUX such as the 74HC4852 and connect the negative end of the meter to the common pin.

2) Wire a resistor between each of the selectable pins and ground using a different value for (in my case) 10dB attenuator, 12dB amplifier and straight through.

3) Switch the MUX pins using the same lines you use to select your front end mode.

In your case you would select MUX lines using the filter select signals.

Peter DL8OV
15287 2019-05-25 09:19:41 Mike Hadley Re: Compensating for xtal filter loss

I am using a bargraph led display with an lm3914 driver. I need to control the output of each crystal filter somehow without affecting the performance of the IF amplifier.

Sent from my Xperia™ by Sony smartphone



---- peter_dl8ov@yahoo.de [emrfd] wrote ----

 

I faced the same problem when building my homebrew rig, but in my case it was accounting for the 10dB attenuator and 12dB preamp on the front end. So.........

1) Get yourself an analog MUX such as the 74HC4852 and connect the negative end of the meter to the common pin.

2) Wire a resistor between each of the selectable pins and ground using a different value for (in my case) 10dB attenuator, 12dB amplifier and straight through.

3) Switch the MUX pins using the same lines you use to select your front end mode.

In your case you would select MUX lines using the filter select signals.

Peter DL8OV