960 AM San Antonio

[Robert Douglas]

San Antonio has a low power daytime only AM station on 960 that duplicates 760 KTKR.

1. Is it a pirate, or what?
2. It seems to be emanating from the south tower of KONO 860. Maybe 50 watts or so. It dies by the time you get to New Braunfels.
3. KONO is a Cox station, KTKR is an I Heart station. These are COMPETITORS in San Antonio.

Who can solve this radio mystery?

 

[Mediafrog+]

Are you hearing this on multiple receivers? I am suspecting a leapfrog mix of the 760 and 860 signals which are 100 kHz apart, thus a receiver image 100 kHz above 860. The lack of a signal at night might be due to the low night power of both stations. Some radios are susceptible to such images, depending on circuit design. Just my $0.02.

 

[Robert Douglas]

Yes, hearing it on any car, any portable. Can you explain a "leapfrog mix" ? I know I.F. is at 455 kHz, but don't understand how 100 kHz could be relevant. Thanks.

 

[Mediafrog+]

Yes, hearing it on any car, any portable. Can you explain a "leapfrog mix" ? I know I.F. is at 455 kHz, but don't understand how 100 kHz could be relevant. Thanks.

When two different RF signals are mixed, you get products that are the difference of the two as well as the sum (this is of course the basis of a superheterodyne receiver.) For 760 and 860, the difference is 100 kHz, while the sum would be 1620 kHz. Are you hearing anything on 1620?

I’m sure someone else would have a better explanation, but the 960 product or image might be due to the resultant 100 kHz difference signal mixing again with 860 which would give a sum of 960. The difference of this would be on 760 which would be masked by the fundamental KTKR frequency.

I’ve heard of such leapfrog products being created at shortwave transmission sites where multiple frequencies are in use. If the transmitters are not sufficiently isolated/filtered from each other, leapfrog products may occur.