[Tech-Assist] STL problem now critical

[Mike McCarthy]

First, let's make sure the TX end is operating properly.  Did you check 
the frequency of the carrier?  I've seen TX's drift over time and only 
to be misconstrued as a failing signal in general. Put back on center 
channel and all was well again.  Check power into the dummy load.  If 
the power is significantly different than into the antenna.....

Of note...make sure the center pin on the N connector going into the 
antenna is properly located and the feed point female is completely 
intact.  If the male sticks out long even 1/32", you will split the 
center pin of the feed point. Might the existing feed point or any 
connector be suffering this problem?  The same is true for the Heliax 
connectors as well.

I will say the N connector is repairable, but a PIA to do so if you 
don't have a panel mount N connector lying around.  In my case, 
necessity required I drill out the center and extended the foam and 
center of the 3/8" Heliax jumper right into the shaft and completely 
eliminate the whole inner part of the N connector assembly.  The N 
female outer frame and Heliax connector body were left for mechanical 
reasons.  But the line went all the way into the antenna's shaft and the 
much bigger 7/8" EIA bullet type sleeve connection in the feed point 
shaft. It was a perfect fit!!!!

This is but one reason I will not use N for mission critical exterior 
connections.  DIN 7/16 for me these days folks.

Your comment about the feed point being short could be telling. First 
test or sweep the "found" feed point measuring the VSWR on the ground.  
No reason to install a defective feed point.  Once confirmed, swap that 
as well confirming first that ***is*** the correct feed point for the 
dish.  Then remeasure the whole antenna system at the ground to verify a 
good match.

I would then take a dummy load up the TX tower and measure the TX power 
of everything before the antenna into the load. Then bring the meter up 
to verify all the power is getting to the antenna as calculated. 
Anything more than 1dB off from calculated is to be considered suspect.  
Pat Roberts mentioned changing the cable length to verify there are no 
standing waves at the meter. I concur or use a trombone section to vary 
the length.

Once you're really satisfied the TX end is where it belongs, repeat at 
the RX end, but reverse the TX and RX path to test everything at the RX 
end under power and call back to the studio for a meter reading.  Just 
be really careful of TX'g on a high peak the wrong direction.  Make the 
transmissions short.  No reason to take out a co-channel user 100 miles 
away.

MM

Once you are satisfied the TX end is as good as it can be, see if you 
see a signal on the ground at about a mile with only the old feed point..

On 3/27/2012 8:23 PM, Jerry Mathis wrote:
> OK, here's an update, and an urgent request for some knowledge and suggestions.
>
> One of my stations started experiencing STL dropouts this spring. At first I thought we had suddenly experienced a massive drop in our received signal strength. We had a tower climber go up the STL receive tower, re-aim the dish, and replace the coax jumper which appeared to be bad.
>
> Problem not solved.
>