Hi,

I currently have my antennas around 100ft from my shack but I am exploring the idea of moving all to a location about 1000ft+ away. Visual impact in the area will be reduced and the overall ground elevation could be increased say @200ft or so. I am looking for ideas as to how to feed these antennas with a single feedline from the shack to antenna site. The ldf 450,550etc is a very expensive option. I have been told I could use open wire feeder, but I have no experience with it. Can I make it myself or would it be better to buy? I would like to have a run of coax to the feedline and then the same at the antenna end. Will I need a transformer of some description at both ends to bring back to 50hms. Just an idea at the moment so would be glad to hear any thoughts.

thats not a run thats a marathon im not sure what antennas you want to feed but open wire feeder is very simple to make and 1000ft its going to be cheaper than buying commercial stuff which is too stiff for my liking anyway..

going off the the way you explain it coax /ladderline /coax and then needing to be at 50 ohms at the shack end i presume they are 50 ohm unbalanced feed antennas .

billy

Yes, that's perfectly feasible - the matched loss of 1000ft of 600 ohm open-wire feed-line is only 1dB at 28MHz.

But you need to make sure it is open-wire line, not the 450 ohm or 300 ohm commercial ladder line. Then you will need a 12:1 balun at either end to transition to the 50 ohm coax.

Note the antenna(s) will have to be a reasonable 50 ohm match.

73,
Steve G3TXQ

Thanks for the replies. I am planning to move my 5 band quad to this site, and put up a new 40m yagi. Also maybe a four square on 80m, have the comtek box here for a year so maybe this summer verticals may go up. What sort of wire for the feeder would be best and what spacing should I use. I was thinking 4 inches. Regarding the 12:1 balun should i try and make my own and if so is there any drawings/details I could obtain or is there a uk supplier where I could source them. Another issue I may have is getting a power source to the site for switching antennas. Any thoughts on this anyone. Everything just at planning stage yet but if these main issues i have can be sorted I can then progress. Thanks again for the help.

MI0JAT

Joe

Joe,

When I was doing something similar I used this idea for spacers

http://www.trueladderline.com/ladder/runtower.jpg

And put some together using the smae idea with B&Q pvc pipe as the spacer.

http://www.trueladderline.com/ladder/ladder.html
http://www.trueladderline.com/ladder/spacer1.jpg

also have some nice pics.

In my example the feedline and elements are made from a single piece of wire so no joints = less weak points not sure you could do that with a 300m run.
73,
Steve

Joe,

There are commercial 12:1 baluns available, but I've not seen a DIY design. Alternatively you could make it 450 ohm open-wire line which would then require a 9:1 transformer. Losses would be slightly higher but still acceptable. I think you will find a 9:1 DIY design more easily. But don't be tempted to buy commercial 450 ohm "window" line.

You can't just use any old wire and spacing - the wire diameter and spacing determine the characteristic impedance. Here's the formula:
Zo = 120 Ln( 2*b/a)
where a is the wire diameter and b is the centre-to-centre spacing.

For 600 ohm b/a needs to be 74 and for 450 ohm b/a needs to be 21

73,
Steve G3TXQ

Thanks for the replys regarding the formula for the wire. I'm not sure about my understanding of the equation. B/a is 74 for 600 ohm (which I think i will aim for by the way) but I,m confused as to the unit of measurement , should use mm, inches etc. Maybe you can brake the equation down a bit for me. Could I use something like 6mm stranded earth wire of would single strand be best. I done a rough measure from shack to site one evening past and its looking like @500m of a run. Is this workable? Site is great and very high asl so I would hope I can get this sorted. I see Dx enginneering, Array solutions can do a 12:1 balun so that can be sorted easily. Any thoughts also on getting power to the site to switch antennas etc.

Joe

MI0JAT

Joe,

The units don't matter because b/a is a ratio. So, whatever units you measure the conductor diameter, the spacing needs to be 74 times that (for 600 ohm) using the same units

If you use 1mm wire the spacing needs to be 74mm
If you use 0.01" wire the spacing needs to be 0.74"
If you use 6mm wire the spacing needs to be 444mm

Did you really mean 6mm diameter wire - that's massive?

Steve G3TXQ

Thanks Steve. I don't think I'll be using 6mm wire . I had a few rolls of that handy so thought I could use it. What size wire/ spacing in your opinion would be best Steve. Will insulated wire cause a problem long term with sun etc. I am determined to stay away from the commerical 450 ladderline as you suggest. Steve i have a sheep wire fence running up to the site on both sides so could I utilize the posts to mount the feeder?

Joe

MI0JAT