[1000mp] CW Cap Mod and I.F. Mod not the Same - Over and Out

Wed, 1 May 2002 19:38:15 +0100

Hi Bill.
The problem is not agreeing or not agreeing with subjective opinions.
The problem are MDS, IMD, BDR tested with instruments.
I dont care much if the noise is more at first, second, third intermediate
frequency or at the audio amplifier.
I care that if I introduce an rf amplifier at higher-first IF the two
signals imd (2 or 5 khz spaced) will be damaged.
I care that if I introduce a steeper roll-over at audio frequency with K9AN
capacitor mod I improve MDS at -141dBM (and even better using the steeper
400Hz Inrad combo filters).
I agree that the problem can also be reduced using EDSP
demodulation-filtering.
But I dont like to use EDSP demodulation in CW or SSB (too narrow reception
impressions, tiring for the ears).
Anyway, go to W8JI web page to see FT1000MP tests and you can see that
perhaps it is better to improve MDS (without damaging imd performance) with
an audio filtering mod than introducing a rf amplifier at 70mhz if (wide
about 15khz so you amplifie all the signals within this window derating
FT1000MP imd).
73 es tks
Ian IK4EWX

----- Original Message -----
From: "WD8ARZ" <[email protected]>
To: <[email protected]>
Sent: Wednesday, May 01, 2002 8:07 PM
Subject: [1000mp] CW Cap Mod and I.F. Mod not the Same - Over and Out

> I.F. hiss due to insufficient previous stage gain to over come the
internal
> noise of the next stage, and audio high frequency response pass band at
> audio frequencies (cw or other wise) are two different topics..... and two
> different and unrelated mods.
>
> If the I.F. noise issue was being cured as you say by the cap mod in the
> audio circuit, why aren't the other audio paths that feed Ssb for example,
> also being modified to reduce the 'i.f. hiss'????
>
> The cap mod for the cw audio stage frequency response high end roll off is
> just that and nothing more. It doesn't reduce the I.F. stage noise one
iota
> .... only affects the audio frequency response.
>
> Too many folks here are using the term 'hiss' as a single source item, and
> it is not. Band noise 'hiss', rf amp noise 'hiss', i.f. noise 'hiss',
diode
> noise 'hiss', mixer noise 'hiss', audio frequency response 'hiss', etc etc
> are not the same and have to be treated individually. Noise that is passed
> from one stage to another can accumulate, but only if it is in frequency
> range of the stages that pass them and handle them, or the harmonics and
> distortion products inter relate. The audio stages do not handle i.f.
> frequencies.
>
> Put a noise analyzer in the I.F. stages, and put the CW cap mod in and out
> of the cw audio stage, and you will see ZERO effect in the I.F. stages.
> Period!
>
> You cant fix the effects of the I.F. at audio frequencies. You can mask
the
> effects of noise at the audio side, but that doesn't take care of the i.f.
> side. Signal to noise ratios, noise blanker performance, and dsp functions
> are all affected by what comes to it from the earlier i.f. stages, and are
> improved by the Inrad modifications. Not by the cap mod.
>
> This is also not a situation of agreeing with me or not on the CW cap mod.
> As I have said before. It is a user choice and I have made my choice and
you
> should make yours. The technical side of it has nothing to do with the
> agreeing with X Y or Z persons, so your best to leave the emotional side
out
> of it. Confusing sources of hiss, and mixing circuit effects is not
helping
> the situation either .....
>
> End of topic from me on this side. It is just a shame to see so many
> misleading statements put out, that are technically dis connected.
>
> 73 from Bill - WD8ARZ
> [email protected]
>
>
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