Re: VK4PP uBitx LPF BANK add-on Board

Gordon Gibby <ggibby@...>

I decided to test the  little daughterboard system that I built to move the input filtering off theboard.

Everything connected:  80 metersignal (has to go thru three relays on the board and 3 relays off the board):  S9+30 dB in my apprxoimately 70db attenuation system.

Remove the wire from the soldered-to-the-trace input to just the 80 meter LPF, lay it a couple centimeters to the side....

Signal  dropped to barely hearable and S0.

30 db for  the portion above S9  (verified with attentuators)

18 db more toget to S7.5  (verified  with attentuators)

Unknown from S7.5 to S0 but likely at  least 6db/Sunit (sincethose above7 were 12dB perS unit measured) --42 db

Total isolation at 80 meters roughly 90 dB

​at the very least (down to the verified  S7.5 point) 48 dB + whatever it takes to go from 7.5 to0  


So the isolation at 80 meters seems good....probably declines with frequency 


From: <> on behalf of Glenn <glennp@...>
Sent: Friday, August 31, 2018 6:40 AM
Subject: Re: [BITX20] VK4PP uBitx LPF BANK add-on Board
All good points Warren.   I did some checks of isolation using a typical DIP relay, type HK19F. DPDT

I made a small jig to hold the relays and measure isolation across contacts etc.
Typically it was -34dB across open contacts,
-32dB from one set of contacts to the other. (common terminal)
-41dB from open terminals on each side
-39dB from common of one pole to open on the other pole.
-48db from common to coil.
 At 30MHz.  Better as freq drops of course.
That's without effects of a PCB and various other traces.


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