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Author Topic: New installation and SWR observations  (Read 954 times)

Posts: 751

« on: June 25, 2009, 04:57:33 PM »

Hi. I FINALLY got both of the 95' towers up. Last weekend (missing the VHF contest by a week, natch), I connected the antennas and feedlines on tower #1.

This is all 'for what it's worth', so if you are not interested, please don't flame me!

Tower #1: 6 meters
Modified M2 6M7JHV at 100'. I used new 9913F7 to go from the antenna's N connector to just below the rotor. Here, a N male/female junction was made using a homemade adaptor to Commscope 7/8" CATV hardline.
Why the CATV stuff? 'Cause I have thousands of feet of it, brand new, still on the spools. It has low loss and will not asorb water. It ia also easy to work with, and light....
Anyway, at the bottom, I drilled holes in the house and brought the hardline into the shack. At this end, I also used my connector and an N female. From there to the radios, I use coax (to be discussed in a minute).

Same tower: 2 Meters
Carefully rebuilt KLM 16 LBX at 115'. (one QTH had a pair of these stacked).
Again, new 9913F7 to just below the rotor. There I have a THP mast mounted Preamp. The THP mounts directly to another run of the CATV stuss via a 'double male N.
Same jumper scenario in the shack.

Soooo, today I did this simple test:
(first of all, I am NOT a worshiper of 1:1 SWR. I'll leave that to the CBers. ha ha)
I took 2 pieces of coax , random length, already made up, but long enough to go from the CATV bulkhead to the main operating table. One piece was a section of older 9913 and the other was RG-11, both Belden.

First I looked at the 6 Meter SWR with my MFJ 259B.....

Using the 9913, the lowest SWR on the JHV was 1.4:1 at 49.7 MHz.
OK, I have had that reading at one of the last QTHs..
So, I looked at the SWR at 50.125. It was 2.2:1.
Next, I put the RG-11 in place (you know, 50 Ohm radio to 75 Ohm feedline to 50 Ohm antenna, you get the picture.....)
Lowest SWR freq changed slightly to 49.82, but still 1.4:1. Next, I measured the SWR at 50.125...2.2:1.

On 2 Meters, the results were more dramatic:

RG-11 Jumper: Lowest SWR (2 nodes) 142.5 / 146 MHz = 1.1:1.
SWR at 144.200 4.3:1 ouch!
9913 jumper: Lowest SWR (2 nodes) 141.1 / 148.7 MHz =
SWR at 144.200 2.1:1.

Believe me I KNOW I could prune the jumpers to get a 1.1:1, but it ain't worth it.

On 6, my TR-6 will load into a wet noodle and the auto tuner in my 756 PRO instantly knocks the SWR to 1:1.

On 2M, my SS amp should be quite happy with the 2.1:1 SWR......

I just wanted to share these results with you fine folks.

At one time, I thought about using sections of transmission line as imp transformers, but I figgered ALL those connections are just an invitation to losses and moisture ingress. After all, I am in the "Sunshine State" ha ha

I do not believe that an amateur on either end could 'detect' the difference of a 3:1 or 1:1 SWR.

thanks fer the bandwidth!

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