Hi all,

I'd like to make a 80 to 10 multiband delta loop which will be installed horizontally in my garden.

From my research i believe the length of wire should be around 280 feet, i think.

What i'm wondering is should i use a length of 75ohm coax for matching, or should i use a 4:1 balun and feed the balun with 50ohm coax?

I think if i use 75 ohm, then it will really be a mono bander but if i use a balun i can use an atu to tune the other bands.

Has any one got any other ideas?

Thanks
Matt

Matt,

You're right that the quarter-wave 75 Ohm matching section essentially turns it into a monobander.

The loop's feedpoint resistance varies anywhere from 90 Ohms to 300 Ohms on the various resonant bands, so a 4:1 balun covering the frequency range should limit the SWR on 50 Ohm coax to about 2.2:1.

280ft is about right for bare wire; if it's insulated it will need to be a few % shorter.

73,
Steve G3TXQ

Thankyou for the reply Steve.

Ive also read that i should use 450 ohm ladder line between the tuner and the 4:1 balun to minimise mismatch loss, do you think there would be much difference if i fed the balun with coax instead?

Cheers

If you want improved efficiency, feed the loop with 450 ohm ladder line to a properly balanced ATU and do not use a 4:1 balun. There is plenty of information on how to build balanced ATU's on the internet.

73's Vince G3TKN / ZL1VL

A lot depends on which bands you intend to use it.

If it's just the bands where it is resonant, a 4:1 current balun at the feedpoint plus coax is fine. But if you intend to use it on all bands, the ladderline option is better.

A single-ended tuner, together with a properly-designed balun will do just fine.

Steve G3TXQ

Thank you very much for replying...

One other thing that I have read about is the orientation. I was planning on having the loop "flat" in a delta or quad, but from what I gather this will make the loop not so good for long distance DX, but good for NVIS. I'm really after long distance DX rather than NVIS so I suppose I would have to try and mount it vertical?

What's a recommended height above ground for flat or vertical (i use the work flat because I am not talking about polarisation) for the install ?

Thanks,

Matt

PS. I love experimenting with antennas, normally I just suck it and see, but Delta loops are a bit new to me. :-)

Matt,

There's no simple answer to your question if you intend to use it as a multiband loop.

In the "flat" configuration, if you want good DX performance on 80m, you need it as high as you can get it! As you go up in frequency, the height becomes less important. In this respect it's no different than a horizontal dipole.

If you erect it as a vertical delta (apex up) it becomes poorer as a DX antenna as you go up in frequency. In that configuration it would be OK as an 80m DX antenna with the base wire only 5ft off the ground - but do you realise the apex would be at 90ft?

Steve G3TXQ