[Tech-Assist] STL problem now critical

[RADIO DOCTOR]

On Tue, 27 Mar 2012, Jerry Mathis wrote:

> I took an STL transmitter to the receive site, after the coax jumper 
> was replaced, and hooked it to the receive antenna with a directional 
> wattmeter. Forward power was 6.3 watts, and reflected power was 0.15 
> watts.

With the antenna 370' up the tower, I'd be concerned about that much 
reflected.  Your SWR probably wouldn't look too bad if the cable was 
virtually shorted at the antenna.

Are the radomes on the driven elements upward or downward?  If downward, 
they are known to fill up with water over time, but I suppose the upward 
ones could also fill up if they developed a crack near the top and the 
gasket was still good.

> Coincidentally, we happen to have in storage an RF feed for an STL 
> dish. The label on it says it is for a Mark Antenna P-9A96GN dish. Its 
> length is exactly 3 feet from the mounting flange on the feed to the 
> radiating element at the end (not the reflector at the *very* end). 
> The only odd thing about this RF feed assembly is that it has an 
> additional flange added to it, exactly one foot down from the main 
> mounting flange. This second flange has 3 holes in it. I can't figure 
> its purpose on one of our STL dishes.

The P-9A96GN driven element is for an 8' grid dish and has an N 
connector on it.  Some 8' and all 10' Anixter-Mark dishes I've seen have 
three 'guys or struts' to hold the driven element in place in heavy 
icing or big winds.  Seems that is what the extra flange would be for.

FMeXtra...Digital on FM without the expense and interference
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Lyle Henry, CPBE  THE RADIO DOCTOR  K9DKW/K7OO  Silver Lake/Los Angeles
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