Topband: Rotator creating spur on 1820

[Tim Duffy]

Hi Lloyd:

I would not recommend using braid to connect the mast to the tower. The
braid will take on water quickly and become less effective. A large flexible
insulated cable is the best way to go.

There are several ways to do what you describe. I think the bypass is very
good practice to eliminate noise and RFI. I have all of my rotors and
bearings bypassed. We actually put a kit of parts together here at DXE to do
just that. 

Most guys have enough stuff in their spare parts area to roll their own
bearing/rotor bypass cable, but the photos and drawings on the link below
will give you the idea.

https://www.dxengineering.com/parts/dxe-bbgk-2-25-p

73
Tim K3LR


-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Lloyd -
N9LB
Sent: Thursday, November 02, 2017 1:12 PM
To: topband at contesting.com
Subject: Re: Topband: Rotator creating spur on 1820

Do you have a heavy gauge flexible strap jumpering the mast pipe to the top
of the tower?

The mast pipe must be at the same electrical potential as the tower.  The
thrust bearing and rotor motor probably is not a low impedance path.

I use the commonly available 1 inch wide woven braid / ground strap material
to connect my mast pipe to the top of the tower.  It runs parallel to my
coax rotor loop at tower top ( about 24 inches long ).

73

Lloyd - N9LB
 
> ----- Original Message -----
>
> From: "K4SAV" <RadioXX at charter.net>
> To: topband at contesting.com
> Sent: Thursday, November 2, 2017 2:40:49 PM
> Subject: Topband: Rotator creating spur on 1820
>
> I have a problem for which someone on this forum has the solution. I 
> know that because I have seen that message sometime in the past.
>
> The problem is that my rotator is rectifying a couple of AM station 
> signals and creating a spur on 1820. It's normally pretty weak on my 
> receiving antennas but sometimes it's a problem. I found that if I 
> listen on my XM-240 near that rotator it can be very loud. As soon as 
> I move the rotator it causes the spur to go away, or become weak. A 
> few minutes later it is back again. It pops in and out.
>
> So who had the problem and how did you fix it?
>
> Note that my XM-240 actually shows a low SWR on 160. That's because 
> the
> XM-240 balun doesn't work well on 160 and the common mode currents on 
> the feedline couple to the tower and the tower becomes the real 
> antenna on 160. So in this case the tower is the antenna and it has 
> that rotator cable against it picking up max signal from that cable 
> (also radiating it to my other antennas). No, the XM-240 is not used 
> on 160 (except to find the source of this problem).
>
> The rotator is a Yaesu G-2800DXA.
>
> Jerry, K4SAV
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