Re: VK4PP uBitx LPF BANK add-on Board

Gordon Gibby <ggibby@...>

Hi, I get that.   I but Icannot measure it at all frequencies.  I don't have a spectrum analyzer, I have a RECEIVER and I've calibrated portions of its response in order to use it as a poor-mans spectrum analyzer.    Presumably the blow-by is capacitive for the most part, but not at all parts.   Lacking a spectrum analyzer, I measure the effective blow by at ONE frequency and then draw assumptions at others based on a model that it is primarily capacitve in nature (which has been the major point of discussion for weeks now......)

So if you know that capacitive reactance goes down by 10X when you increase the frequency by 10X, and in both cases you are feeding into a 50 ohm load.......the voltage you're going to get will go up on the order of 10X.    

​Thus you can make a prediction (based on the model) of what the bleed through might be at higher frequencies.   Or you can risk your rig by making other measurements if you don't have any other way to do it (which is me).   Does that make more sense?



From: <> on behalf of Warren Allgyer <allgyer@...>
Sent: Friday, August 31, 2018 1:50 PM
Subject: Re: [BITX20] VK4PP uBitx LPF BANK add-on Board


"Bleed through" or "blow by" at the operating frequency is not the issue. It is bleed through at the 5th and 7th harmonic that allows those harmonics to reach levels that are non-compliant.


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