[TowerTalk] RFI Broadcast Station Mixing in Crank-Up tower?

[Roger (K8RI) on TT]

There are a lot of possible spots where the  mixing can happen.

This brings up the question:  Mixing with what?  Nearby AM stations, ham 
bands, and why every 10 KHz?  What is the primary station, or stations 
and their frequencies?

"Any section" making poor contact with those above or below, making 
contact with coax braid, tension causing poor contact in connectors.

It's pretty certain it's related to cranking the tower up, but is it due 
to poor contact in that position, or that it picks up more signal?

I assume the mixing is gone during the raising and lowering process.  If 
not, does it just get weaker as the tower is lowered?
I'd be surprised that it's not strong near the full extension while moving.

Places to start::  If the mixing is only present at full extension, 
check for tension on the coax at the antennas, rotator loops, and at the 
cable stand offs.  Check the cable jackets, particularly where they pass 
through the stand offs.  Check cable jackets where they can move against 
each other.

Use a VNA to check all coax at full and partial extension.  Don't ignore 
rotator cables and connectors  either
If you don't have one, beg, borrow, or purchase one.  With the tower 
fully extended on a windy day, watch the traces for changes.  Have you 
tried a spectrum analyzer? Even the ones in the newer rigs can be 
helpful, but you need to look between the bands as well.

Check the places on the tower sections where the skids/pads contact 
adjacent sections for excessive wear and or missing galvanizing,

When the local repeater was here, I could block a 50W mobile a mile or 
two distant simply by rubbing a 10" screwdriver against any of the 
galvanized guy wires which were broken up with insulators.  I had a TB3 
tribander just below the repeater antenna @ 90 feet.  Legal limit on 10, 
15, or 20 did not bother the repeater.

73

Roger  (K8RI)



On 10/19/2015 10:03 PM, Rich Hallman - N7TR wrote:
> Has anyone had any problems with intermittent mixing from a close broadcast station with a Crank-Up tower?  I think I may have an issue with one of my towers.   Cranked up I hear mixing all over 80 meters (Every 10 KC).....Cranked down its gone.  I already eliminated the antennas.  Mixing gets very intermittent in wind as the tower moves around.
>
> Thoughts about grounding the top section to the bottom when fully extended?  Was thinking of grounding the coax at the top and bottom of the tower?
>
> Thanks....
>
>
> Rich N7TR
> ex KI3V, N3AMK, WB3JOV
> www.n7tr.com<http://www.n7tr.com>
> http://www.qrz.com/db/N7TR
> Telnet: dxc.n7tr.com N7TR DXCluster
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk


-- 

73

Roger (K8RI)


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus