[R-390] Image problem solved - Not.

[Jim M.]

I don't know about the Collins (never aligned the IF), but I did align the
SW's IF, but not staggered tuned.  Regardless, I don't think that IF
alignment would cause these images.  I think there may be a stage in the RF
front end that is running too "hot" in terms of gain, or in need of more AGC
control.  I don't have the energy now to take them out of their cabinets now
to do any A-B comparisons.  

For what its worth, I just turned on the Icom 775DSP to the inverted vee and
tuned to the same image frequencies I saw on the 390a, and I do indeed hear
the same images (!), but not as intelligible and quite a bit closer to the
noise floor.  On the 775, the images are all between about S-6 about S-8,
and seem to decrease normally (following the noise floor) as I add
attenuation, using the 775's built in attenuator.  The 2480 image sounds
like a "beat" between two modulated carriers close in frequency, with a beat
rate of about 4 per second.  The 2800 image is hearable but right at the S-6
noise floor.  The 3120 image (from the 1560 oldies station) is S-9 but
distorted.

I wouldn't expect the 775DSP to have a bad image or overload problem,
especially with the built in attenuator.  So now it looks like these image
signals are really coming in on the antenna to some degree.  Maybe produced
by some external mixing phenomenon.  

Now back to square one.

Jim N4BE

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Barry
Sent: Friday, October 26, 2007 2:19 PM
To: r-390 at mailman.qth.net
Subject: RE: [R-390] Image problem solved - Not.

>So.... This Collins 390a (with Collins RF deck) is hopping with images from
>AM broadcasters, I just never bothered to notice them before.  But
>apparently not the Stewart Warner.  When I get the chance, I am going to
>connect the SW to the outdoor antenna for another comparison.  It is
unknown
>what the differences between the two RF decks could be, however I have
>noticed that the Collins does tend to be a much "hotter" receiver than the
>SW, good AGC action... but tending to pop up the noise floor when no
signals
>are present.  Maybe too hot.
>
>Jim M.

Jim,

This may not have anything to do with it, but do you know if both IF decks
are stagger-tuned?

Barry - N4BUQ
_____________________________________________________________
R-390 mailing list
Home: http://mailman.qth.net/mailman/listinfo/r-390
Help: http://mailman.qth.net/faq.htm
Post: mailto:R-390 at mailman.qth.net
Unsubscribe: http://mailman.qth.net/mailman/options/r-390