[1000mp] audio filters for the Mark V

[Garry Shapiro]

Yaesu's posture of denial re problems that are real and widespread has
convinced me that, when it comes time to buy the next radio, Yaesu is not in
my future.

Garry, NI6T

-----Original Message-----
From: 1000mp-bounces at mailman.qth.net
[mailto:1000mp-bounces at mailman.qth.net]On Behalf Of Ian White, G3SEK
Sent: Tuesday, June 01, 2004 12:47 AM
To: 1000mp at mailman.qth.net
Subject: Re: [1000mp] audio filters for the Mark V


J. Mc Laughlin wrote:
>    I do not know what "the hiss" is

Just to clarify this point: the "hiss" that everyone talks about is
noise at audio frequencies *above* the roll-off of the IF filters.

The noise originates in the IF stages after the filters... maybe in the
455kHz analog notch filter, which is never completely disabled, only
de-tuned.

It isn't a serious hindrance to communication, but it is quite
noticeable in unmodified FT-1000s, and also the FT-990.

Some people don't care about it, while others find it very irritating.
(I certainly do, because it's a constant reminder of another stupid
design error that Yaesu refuse to recognise, and that kind of thing bugs
me. YMMV, of course.)

The audio lowpass filters will kill the hiss completely, but you have to
adjust the audio cutoff frequency whenever you switch IF filters. The
Inrad IF amplifier mod masks the IF noise, but causes a permanent
degradation of close-in IMD performance.


--
73 from Ian G3SEK
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