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: BITX20@groups.io <BITX20@groups.io> 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