[AMRadio] Antennas


Larry Szendrei ne1s at securespeed.us
Tue Jun 22 19:57:23 EDT 2010


Bernie Doran wrote:
> Hi Larry:  what a dinosaur!!! you might even be older that I am. I 
> have not heard an 80 AM station since 1950s. but that sure qualifies 
> for a few feet. I wonder if anyone ever thought there was something 
> wrong with their xmtr. bet you could tell them that you are setting it 
> for side band the way TV does!!   Bernie
Hi Bernie!

Yep, vestigial sideband.

Nope, you're older, but I probably have older gear!

The first time I got a report like that I didn't think much of it. The 
second time it was from I a guy whose technical expertise I knew and 
trusted, so I took it as accurate. At first I couldn't think what might 
make a classic plate-modulated class C transmitter have asymmetric 
sidebands, and wasn't coming up with anything for a satisfying 
explanation (mobile transmitter was/is an Elmac A-54H, class C 807 
modulated by pair of 5881s). Then I though about how sharp the antenna 
tuned, and I came to the conclusion the antenna was acting as a sideband 
filter - albeit not a terribly effective one (assuming you wanted SSB - 
but who would want that? ;-))

73 and hope to talk to you on the air again this fall/winter,
-Larry/NE1S

> ----- Original Message ----- From: "Larry Szendrei" <ne1s at securespeed.us>
> To: "Discussion of AM Radio in the Amateur Service" 
> <amradio at mailman.qth.net>
> Sent: Tuesday, June 22, 2010 12:19 PM
> Subject: Re: [AMRadio] Antennas
>
>
>>> There have been some interesting cases with short loaded antennas
>>> in the BC band, the bandwidth has occasionally been so narrow that 
>>> the AM
>>> sidebands become attenuated!  Not going to see that effect in the 
>>> amateur
>>> bands unless someone is running an antenna only a few feet long!!
>>
>> Correct. This has been observed on my 75M AM mobile signal, with reports
>> of one sideband being attenuated relative to the other. Antenna is a
>> Webster bandpanner ("a few feet long").
>>
>> 73,
>> -Larry/NE1S 
>



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