[TowerTalk] Antenna shift, VHF/UHF matching unit burning out

Roger (K8RI) on TT K8RI-on-TowerTalk at tm.net
Mon Apr 21 09:08:24 EDT 2014

On 4/21/2014 6:18 AM, Scott wrote:
> My suggestion is throw the Diamond antenna off the tower and put 
> something up worthwhile. Those things are useless imo.

I've found the 21' tall, collinear to work very well as I did the Comet. 
Both are limited to around 200 watts.  Until recently I never had a 
problem.  I have to be careful as there is one repeater that is right at 
the limit, or even closer than it should be and even though it's not 
line-of-sight, I hear them often and they use the same PL we do.  I did 
have to replace the Comet when it took a direct lightning strike.  The 
top looked like an exploded cigar. The brass element was melted back 3 
or 4 inches. The Diamond replacement has been in the same position for a 
good 10 years.  The tower has taken many strikes, but non to the 
antenna, half way down.

Simplex, I could work nearly as far (FM) most days as I could with the 
stacked 12L Yagis.  I've had very good luck with their mobile antenna as 
well.  There is one problem with the big mobile, duo band collinear on 
the SUV though.  Because of the height and accentuated rocking, after a 
few years they become loose and you can hear them rocking in the mount. 
I have to take the base apart and lap the connection for a tight fit and 
they are good for a few more years. I can work the regional repeater for 
about 40 - 50 miles.  The quadrant was greater than 60 miles.  With the 
car in the parking lots at MSU I could reliably work the pleasant valley 
machine on 12/72

I use them with the mag mount.  In the winter you make sure it's where 
you want it, because in cold temps they are there to stay, unless it 
goes into a heated garage.


Roger (K8RI)

> Scott
> N1CX
> At 10:23 PM 4/20/2014, Roger (K8RI) on TT wrote:
>> I think that I've lost a ground.  The SWR has gone sky high on the 
>> Diamond 144/440 repeater antenna. As the antenna is only rated at 200 
>> watts the matching network is pretty light duty.  Also, the AV640 
>> which originally was very easy to match, is now difficult to find the 
>> resonant points.
>> I believe this is due to a DC bias through the matching transformers 
>> putting the cores into, or near saturation.
>> I keep using, I think and I believe as I really don't know, but it 
>> sounds logical.
>> The new AV840 just arrived and I need to work on the Diamond antenna, 
>> so I need to find the problem before going any farther with the 
>> antennas.
>> I had been talking to N8ERF on the repeater when he mentioned I was 
>> getting noisy.  I immediately stopped transmitting, came in, got the 
>> SWR bridge, took it to the shop and put it in the line. The SWR had 
>> gone from 1.2:1, to off scale.  I think the finals are OK.  I 
>> certainly hope so.
>> So tomorrow, I'm going to add one of those grounding plates that tie 
>> everything together and to the station ground. The space behind the 
>> desk out there is a mass of wire, that could be neatened up, so I can 
>> see at a glance what is connected to what.
>> That and all the projects need to be finished up so I have an 
>> organized shop in which to work.
>> Any thoughts on the grounding would be appreciated
>> 73
>> Roger (K8RI)
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