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 Post subject: AM station on two places on the dial
PostPosted: Feb Tue 06, 2018 5:27 pm 
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Location: New Castle, IN
So, after my first stab at radio alignment on Super Sunday, my stations seem to come in better than ever...maybe too good. My local station (1550) now also comes in around 640 (although, not as strong). I assume this has something to do with the IF being 455, and this is 910 below the original signal. The short question is, did I screw up my alignment somehow? I apologize if this has been answered before; I tried to search but didn't have luck.


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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Tue 06, 2018 6:02 pm 
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Location: San Jose, CA USA
The usual cause of this behavior is that the antenna circuit is not tuned. Does this radio have a loop antenna? If so, make sure both sides are properly connected. If it uses a wire antenna, make sure the antenna coil tuned circuit is connected properly, and that the coil has continuity (particularly the winding across the tuning capacitor).

One of the jobs of the antenna tuned circuit is to block "image" reception, which is precisely what you have here -- the station coming in 910 kHz below where it is supposed to be on the dial.

If the station is extremely strong, sometimes a very weak image gets through, even if everything is functioning normally. For example, here I can get a little whistle while tuning a moderately weak station at 610 kHz from the image of a very strong station at 1500 kHz. This image is slightly offset, since the two are not exactly 910 kHz apart.

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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Tue 06, 2018 6:08 pm 
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Location: Annapolis, MD
Your assumption is correct....it is called an "image". The IF gets a signal when the LO is either above or below the incoming signal. The only thing that stops or minimizes this is the tuning of the front end RF and/or antenna stages.

Other fixes include changing the IF frequency or installing a trap tuned to the strong station.

What is the make and model of the set?

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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Tue 06, 2018 6:22 pm 
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Location: New Castle, IN
Thanks! Yes, this does have a loop antenna. I'll go over that part of the alignment and see what I messed up. It is a pretty strong signal (only 3 miles from my house). Thanks for letting me know where to check! This is a Firestone Air Chief Sonata (S-7393-1).


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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Wed 07, 2018 2:08 am 
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johnnyreece wrote:
Thanks! Yes, this does have a loop antenna. I'll go over that part of the alignment and see what I messed up. It is a pretty strong signal (only 3 miles from my house). Thanks for letting me know where to check! This is a Firestone Air Chief Sonata (S-7393-1).

It may not be a curable situation. Back in the old days the FCC would not allocate two stations in the same area 910kc apart for that exact reason.
But do try to tweak the antenna tuning section.

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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Wed 07, 2018 4:25 am 
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Location: Leo, IN or Zellwood, FL
johnnyreece wrote:
Thanks! Yes, this does have a loop antenna. I'll go over that part of the alignment and see what I messed up. It is a pretty strong signal (only 3 miles from my house). Thanks for letting me know where to check! This is a Firestone Air Chief Sonata (S-7393-1).


I doubt you ever eliminate this issue with this radio. I spent a few winters in Ocoee, FL where I had an AM radio station that was about 1/4 mile from the place we stayed in. That tower had two radio stations transmitting on the same tower. One on 1600 the other on 1680. With radios that had the first tube a mixer there was no way of keeping those radios from hearing the image freq 910 below the either 1600 or 1680. Radios that also had an RF tuned stage and tuning of the input into second stage mixer it was never a problem for those radios.
John k9uwa

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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Wed 07, 2018 4:45 am 
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Yep I have same issue with untuned RF sets... Locally there are 1600 & 1650 approx two miles away that have images...

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 Post subject: Re: AM station on two places on the dial
PostPosted: Feb Wed 07, 2018 6:00 am 
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Joined: Mar Sun 01, 2009 10:27 pm
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Location: Ann Arbor, MI
Hmm... Most old radios can not tune above 1600. Some have problems going even that high. So if I had local stations on 1650 or 1680, I would have to hope that I could tune in the image if I wanted to listen to them.

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