On 8/14/2010 1:53 AM, hanslg@aol.com wrote:
> I realized made an error describing the product of cross-modulation:
>
> If you have only two signals present you will find cross-modulation products
> that are related to the harmonics and mixing of the two signals.
>
With diode mixing which you would have with poor connections you'd
likely have mixing products from all the frequencies within the
passband...IE all audio frequencies which would also make for a broad
signal with lots of splatter, particularly for those close by.
OTOH with a roof like that, rust and all, it's probably going to have
enough mechanical connections to work well. Fences would likely be far
worse. Chain link followed by the "woven wire" type.
73
Roger (K8RI)
> Say you have two (about equally strong) signals, one at 20 MHz and one at
> 20.010MHz. You will find the harmonics 40 MHz and 40.020MHz, the sum of the
> two signals at 40.010MHz and the difference 10 Khz. You will, further find
> mixing products of these signals, most important the mixing products of the
> 10 kHz products. You will, on your spectrum analyzer see signals at 19.990
> MHz, 20.02 MHz etc signal that are caused the the rectifying action of the
> (in this case) the il-conducting joints between the metal sheets.
>
> Chances that the 10 kHz product will cause any problem is minimal as it will
> require a rather large roof to be an efficient antenna for that frequency but
> the other products may cause interference in adjacent stations. When you
> experience this phenomena in amplifiers the biggest problem are the products
> that are close to the signals you want to detect as they are too close to be
> easily filtered out.
>
> Sorry for my prior mistake and miscalculation.
>
> Hans - N2JFS
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: Grant Saviers<grants2@pacbell.net>
> To: Tower Talk List<towertalk@contesting.com>
> Sent: Fri, Aug 13, 2010 6:48 pm
> Subject: Re: [TowerTalk] Fwd: Multi-Band Vertical Question
>
>
>
>
> re: metal roof problems: If I look on a spectrum analyzer connected to
>
> a separate antenna, what should I see? Where should I look re the
>
> transmit frequency? Is cross modulation the problem or is it
>
> intermodulation products? What kind of signals am I looking for?
>
>
>
> Grant
>
> KZ1W
>
>
>
>
>> It's your (ham) neighbors who would hear it. :)
>>
>
>>
>
>> 73, Jim K9YC
>>
>
>>
>
>>
>>
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