There was a sub-thread going here about using openwire vs: hardline on 6M to reduce losses. I axed a coupla of well known VHF/UHF friends their opinions on this. One friend, Steve, K1FO is well known for his years of VHF/UHF moonbounce, ham line of antennas, and amplifier construction and company. I've posted his response below (with his permission) regarding using open wire for a 600' run.... I also have another question in to him regarding the loss of using a PVC jacket on the openwire - awaiting response.
T
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FROM STEVE, K1FO:
A couple comments Tom.
Yes I am using open wire phasing lines on my 432 array.
The open wire is made from #8 enameled wire spaced .35" which makes
200 ohm line. It is not affected by rain. Ice is another story, but it
doesn't matter since the Yagis themselves are useless with ice on them.
I would advise against 3" spacing and bare copper.
Bare copper will oxidize and greatly increase losses. You should go
with double enameled wire. Useful life in our climate will be about 10 years before the enamel will be gone from UV and errosion.
3" spacing is too far apart. I estimate it to be 460 ohms, which will be
affected by rain and things near the line. I would recommend a maximum of 300 ohm line which would be about 3/4" spacing with #10 wire. I also recommend Teflon spacers. Teflon is ultraviolet tolerant and low loss.
However losses willstill be significant with a 600' run. The best I was able
to measure on a 50' section of my 200 ohm line was that at 432 losses were similar to 7/8" Andrew LDF (LDF5-50). Which makes the open wire line well worth it for phasing lines, but if questionable value for transmission line especially when the loss of open wire to coax matching sections are included.
I can't find the reference right now, but somewhere I did find how to calculate the loss of open wire line. If I remember right the calculated losses were lower than my measured losses, but the 2 numbers were in the ballpark. Calculated maybe something like 20% lower than measured, but I can't exactly remember.
If it were me, I would go with 1-5/8 or 1-1/4" Andrew LDF. There are incredible quantities of this cable in the surplus market and you can usually by 1-5/8" LDF surplus for less than you can buy 7/8 cable. Loss of 600' will be only .64 dB which I'm sure is lower than you will be able to do with open wire. Plus you don't have the problem of supporting the 600' run of open wire line. I have seen 500' rolls of 1-5/8 sell for under $1,000.
Steve, K1FO
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Tom,
Yes you can post my response.
3/4" aluminum jacket coax should be about 0.4 dB loss / 100' @ 50 MHz, your 0.5 dB measurement is in the ballpark.
Low density foam copper jacket is significantly lower loss for the same size. Even LDF5-50, Andrew 7/8" is only 0.26 dB / 100' at 50 MHz. But again, you will most likely find that 1-1/4" and 1-5/8" will sell for less than 7/8" surplus as most hams are afraid of the real big coax.
Steve
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My Intitial eMail to Steve:
Hi Steve,
I'm not sure if you remember me, but I stopped by your QTH back in 1974 with Bob, N1KW and took a look at your moonbounce station. I remember some HB 8877 amplifiers and a nice antenna H frame built from Hatry's tower parts... :-)
Anyway, I am designing up a big H frame for 6M using four, homebrew, 48' boom Yagis. Three of the Yagis are already built and working on the tower as a temporary stack at 110', 80' and 50' with a Stackmatch.
Here's a picture:
http://home.comcast.net/~k1jj/wsb/media/254120/site1062.jpgI understand that you used open line for interconnecting one of your UHF
Yagi arrays.
Here's the problem:
The feedline run to the tower is about 600'. The loss is too high for me
even using hardline. I was considering using open wire for the run.
I don't want to use a preamp or use a remote controlled 8877 amplifier at the tower to eliminate the TX/RX 3db loss from hardline
I planned on inter-connecting the Yagis with 50 ohm hardline, (having a
180/0 switch for top/ bottom high/low angle) and then tapping the openwire with a balun at the 50 ohm point using a stub.
The 600' of openwire would then run back to the shack where a reverse tap would bring it back to 50 ohm coax.
I figured on maybe 3" open wire spreader spacing with #10 bare wire.
What's you opinion on doing this? Is 3" spacing too much and how much does the WX affect yours?
Any suggestions will be much appreciated before I proceed.
73,
Tom, K1JJ
Marlborough, CT