Topband: How Close is Too Close?

[Michael Tope]

Michael Tope wrote:

>I was looking at a 160 meter operating site which looks really 
>promising. The only downside for this site is that its only about 2 
>miles from another very active topband station. I realize the degree to 
>which two stations can coexist in close physical proximity is radio 
>dependent, but in general is 2 miles too close to operate the same 160 
>contest without incurring a significant handicap (clicks, phase-noise, 
>blocking)? The terrain is flat in this area.
>
>Thanks,
>
>Mike W4EF.............
>
>  
>
Thanks to all for the replies. Great information. Sounds like the answer 
to my questions is that 2 mile separation can work, but its a dicey 
proposition (I would have to listen through him to hear Europe and 
CONUS). I have some other site options that would afford much wider 
separation (15 to 20 miles) with the incumbent. I am going to focus on 
those sites first and keep the site which is close to the incumbent as a 
backup option of last resort (for his sake and mine).

By the way, I did a quick back of the envelope calculation assuming 
monopoles at both ends of a link with 2 mile separation. Using the 2 MHz 
ground attenuation curve in N6PL's vertical book (~40mV/meter at 2 miles 
w/1KW transmit power), I got +9dBm at the other receiver. Seems like 
that's doable, but in the category of "very challenging".

A related question - how close is too close to large high-voltage 
transmission lines (i.e. the big metal towers that handle hundreds of 
KVs). A number of my candidate sites are within 2 to 3 miles of these 
sorts of high-voltage lines.

Thanks,

Mike W4EF.............................