Re: VK4PP uBitx LPF BANK add-on Board

Gordon Gibby <ggibby@...>

The measurements that I made  for the daughterboard  bleed-through indicate that for the ENTIRE SYSTEM,  including the printed circuit board, connecting leads, relays, coils, coil wiring and all the RF wiring,  the bleed  through is almost NEGLIGIBLE. (lifted the bottom green wire in the accompanying photo and measured bleed through that had to go through ALL SIX RELAYS).    Far, far below the pass through the filter....  down to unmeasureable on the ICOM718..whereas properly filtered harmonics  were depressed into the S5 or S6 range from 30dB overS9  fundamental (as predicted by others' measurements indicating the FILTERS had acceptable performance)     Measurement performed at 3.5  MHz.  Presumably capacitive coupling would increase related to frequency, perhaps 10 times the amount would be expected at 30 MHz --- but that would only be 10dB more signal, perhaps reaching to S2   I don't want to risk my finals by doing  the experiment over and over.   The bleed through with a daughterboard --- even with unshielded wires --- is far far far below  the requirements to meet FCC specs.    (-43 dB being  somewhere around S7.5 in my tests).    Get the relays separated, get the things apart physically that need to NOT bleed into each other....and it isn't that difficult to fix the harmonics.  (The spurs are a different issue).   

From: <> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Friday, August 31, 2018 12:17 PM
Subject: Re: [BITX20] VK4PP uBitx LPF BANK add-on Board
I interpret this measurement from Glenn:
    "-32dB from one set of contacts to the other. (common terminal)"
as being from KT1 pin 14 to pin 16 as seen in the uBitx schematic.

Also, interpret his -39 and -41 dB numbers to be from one relay section to the other,
which I averaged as -40dB.    For example, KT1 pin 12 to pin 5.

I now suspect those assumptions are incorrect, but the analysis could easily be adjusted to for any change to those two numbers.


On Fri, Aug 31, 2018 at 03:40 AM, Glenn wrote:
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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