[TowerTalk] Fwd: : Multi-Band Vertical Question

[hanslg at aol.com]

 I dealt with two signals only, just to make it simple. If you add modulation, other signals etc. you end up with CM products from ALL the different signals. That makes an almost continuous band of signals usually.

Regarding metal connections; my (and many with me) experience is that you have diode mixing in ALL metal connections exposed to outside air (rain exhaust fumes etc). Rust is not a good connector ever. I would think that a chain-linked fence would make an excellent cross-modulation device. It is usually of extended length so it makes a good antenna too (to receive what's needed for the cross-modulation that is).

Imagine you put a relay outside without a cover. How long would that make good connections?

Hans - N2JFS

 


 

 

-----Original Message-----
From: Roger (K8RI) <k8ri-on-towertalk at tm.net>
To: towertalk at contesting.com
Sent: Sat, Aug 14, 2010 2:27 am
Subject: Re: [TowerTalk] Fwd: Correction Fwd: Multi-Band Vertical Question


On 8/14/2010 1:53 AM, hanslg at 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 at pacbell.net>

> To: Tower Talk List<towertalk at 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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