[NLRS] Elevation rotators for small stuff

[Dr. Gerald N. Johnson]

U100 and U110 were the common models. Some had a simple meter, some were 
clackers where a switch in the rotor caused a solenoid to move the 
indicator and the clackers were automatic. I have a couple and parts, 
one is in use on my roof tripod. One time I wished for a full 1.500 inch 
hole so I took one apart and put the shaft in my lathe. Boring was going 
along fine until chips began to fall through the remaining wall. Had I 
checked the OD I'd have found it was 1.499. So to rotate the 
polarization of a 2m beam, I inserted a boom section smaller diameter 
and it worked decently. For vertical I'd peak it on the local repeater 
and it would be close enough. For horizontal I'd point it at the local 
repeater and spin the antenna for a null. The S meter (on FM they tend 
to be very generous) showed a 40 dB null which put the antenna very 
close to horizontal. Which was overkill, within +/- 20 degrees won't 
affect the signal strength which varies as the cosine of the antenna 
polarization error unless there is need to null the cross polarized 
signal. But that's another topic. a yagi tilted 30 degreess from 
horizontal looses maybe 10$ of the preferred polarization with the right 
angled polariztion is down less than 10 dB which for a longer yagi is 
still a useful signal without the need for two antennas or the 
polarization rotor.

Doing a couple searches, RS shows two rotors, neither in stock on line 
possible in stock in some stores. Searching Amazon turned up 116 hits, 
probably 15 actual rotors (search terms antenna rotator). Reviews veried 
from junk to good stuff for the same parts.

The digital TV and lower power digital transmitters has caused a renewed 
need for outdoor TV antennas and rotors so they do exist.

I bought one a few years ago on line from Solid Signal. Solid Signal 
doesn't stop sending e-mail but the junk collection on Thunderbird is 
happily keeping their e-mails from bothering me. This one uses a run of 
RG-59 or 6 as the control and signal cable. The control box and the 
rotor box each have two T connectors, one for the cable between them and 
the other on the rotor to go to the antenna and the the receiver. Its 
not rated to handle transmitted power. It claims to rotate in 1 degree 
increments. It also optionally supplies DC at the antenna for preamp 
power. It does not tolerate a unbalanced antenna, it has relatively low 
torque and I don't know what its really made for, it radiates broad band 
noise from its switching supply and digital controls at least 50 through 
433 MHz. It would be horrible around a TV receiver cutting sensitivity 
except that digital TV doesn't show noise, only lack of S/N.

I was at an information meeting about a HVDC power line a couple weeks 
ago. A gal representing one of the contractors announced that corona 
noise wouldn't be heard on an FM receiver even under the line. I made a 
loud protest that yes it was the nature of FM and digital TV to not HEAR 
or SEE the noise but that noise drastically restricted received signals 
and in the country could prevent farmers using GPS correction signals on 
FM or two way on FM near the line. They didn't like to hear that. I'll 
plan to appear at the utility regulatory board with similar comments.

I suspect that the rotator with coax could be run from a DC supply of 15 
to 24 volts. It quit working, I replaced all the coax runs, it still 
wouldn't run. I took it down, found a home made control box for a 
metered Alliance U series rotor and the rotor I had used for elevation 
some time ago and changed rotors and control cables. The coax cable 
rotor works fine on the bench with no antenna. I'm not pleased with 
having the change it or with the noise. Essentially I had to unplug its 
power cord to hear signals on VHF and then resynchronize it or remember 
where I last pointed it and move it relative to that direction. It may 
have been that the rotor was sensitive to RF, or that it can't handle 
the offset load of a rear mounted 5 element 2m yagi or the total load of 
that yagi and a K2RIW 19 element for 432 up a couple feet.

Years ago ARRL did some strength tests of the two styles of rotor U 
series vs CDR Ham-x series. In bending strength the U series was several 
times stronger than the Ham-M, but the Ham-M was had more torque IIRC 
but for microwave its poor because of the 15 degree increments for the 
brake.

73, Jerry, K0CQ

On 9/5/2013 9:45 AM, Russ Ramirez wrote:
>
>
> In a PM to Jon yesterday I described a rotor I spec'd in the '70s for Hams
> and CBer's for elevation and polarity made by Alliance - then 10 mins ago
> did a Google on the U100 and saw that this indeed was the same rotor. I
> don't feel too bad for not remembering that model number after nearly 40
> years :-) Other than Norm's Rotor Service, where they want $189 for a NOS
> unit, where can one find these now?
>
> Russ
> K0WFS
>