Topband: The Forbidden Frequency

[brianboschma]

Bob Tellefsen wrote:

>Charles
>There is another possibility, at least mathematically.
>That is A+B=C, in this case 1830 kHz.  For example
>610 + 1220 = 1830.  This is a classic intermod
>product.  It would require both sources to be near
>enough to some kind of junction to create the IM
>product, and the whole thing would have to be
>near enough to you for you to hear it.
>73, Bob N6WG
>_______________________________________________
>Topband mailing list
>Topband at contesting.com
>http://lists.contesting.com/mailman/listinfo/topband
>
>
>  
>
Mixing products are not formed in free space. Some type of non linearity 
needs to act to create the resulting mixed products. This could be due 
to heavy overload at the front end of the rcvr or something in or near 
the antenna system that creates the sum/difference products. To rule out 
the rcvr try turning off the preamp and inserting attenuation. If the 
products are gone it is likely your rcvr's front end and this could be 
solved by adding traps to your antenna system to do a more complete job 
of AM BC suppression.  It could also be a junction of sometype in the 
antenna system that is acting as a non linearity (diode effect ?). I 
have had this occur where I joined disimilar metals in the antenna 
element. In my case I had used a cheap steel crimp lug to join the 2nd 
half of my vertical with the bottom copper pipe. When the rains came I 
started hearing BC interference on 160. Replacing the lug with a tinned 
copper lug solved that issue.

I suppose a nearby steel wire fence or other poor connections could 
generate enough energy to create the carrier, however the BC stations  
would have to be fairly close, maybe less than 10 miles ?

Regards,

Brian
N6IZ