Re: Sony SRF M37V image problem solved


huelbe_garcia@fastimap.com <huelbe_garcia@...>
 

Hi group,

yesterday I was playing with Redsun RP300. It has an odd behaviour, if
you tune 10-20KHz away from a string, local station, you can still
listen to a demodulated and readable audio a little bit more 'trebly'.
It's like a 'leakage' between the RF/AF stages. I would consider it
normal if it was, say, 1-3KHz... but 20KHz is too much!

On the other hand E100 works just as one expect, if you tune about 5-7
KHz (or more) away from a local station you heard the splatter, kind of
noise non-readable.

For a moment, I thought the filter replacement could be fix some kind of
'signal leakage'.

--hg

----- Original message -----
From: "Stephan Grossklass" <sgrossklass@yahoo.de>
To: ultralightdx@yahoogroups.com
Date: Fri, 08 Aug 2008 10:31:52 -0000
Subject: [ultralightdx] Re: Sony SRF M37V image problem solved

--- In ultralightdx@yahoogroups.com, "dhsatyadhana" <satya@...> wrote:

Hi all:

Jim Kenny and I were talking on the phone and each pulled out our
M37V
with a 4.5 khz retrofitted filter installed. Both of us realized
that,
unlike the stock M37V, there were no images from strong locals (i.e.,
phantom 680 signal from local 1590, etc.). I then turned on my Sony
7600GR, and the images from my strong locals were blanketing the
dial, but nothing on the M37V!
Do keep in mind that the '7600GR with its wideband MW/LW
frontend will be more easily overloaded by strong AM
locals than a set with frontend tuning. (Its image
rejection is no greater than on shortwave, i.e. an
estimated 30..40 dB, for the same reason.)

But in any case, improved image rejection with a better
IF filter is a puzzler. Image rejection should be a
function solely of the frontend, i.e. RF tuning and mixer
(or, for most sets, RF tuning only, as regular mixers
have no inherent image rejection).

(A 680 kHz response from 1590 definitely is an image
if we're looking at a single conversion set with the LO
running above the tuned frequency - as it's normally the
case - and an IF of 455 kHz.)

Depending on achieved Q (and thus ultimately parts
quality), image rejection near the bottom end of MW for
sets with a single tuned IF circuit is about 30 to 50 dB.
It drops quite a bit towards the high end, but as there
are no strong signals directly above the band, this is
not an issue.

Anyway, I fail to see how the IF filter would play in
here. It can't really be spurious responses either.

Hmm. *scratches head*

Stephan


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