Dear all,
I got hold of 240 Ohm twin lead feeder, the type which has been used for TV installations in the 70’s before coax became common place. I want to use it to fed a wire dipole. This antenna should be tuneable with a Z-match on 80, 40, 30, 20 and 10m.
Does someone have experience in what dipole length/feeder length will work? I know that I must avoid having a voltage maximum at the feed point. Before doing the math I wonder if someone has the optimum length found by trial and error.
73 Heinz
PS: I will be activating a nearby summit tomorrow, not decided which one. If I get this antenna done this evening, I will include 80m, else it will be 40 and 30m (as usuall).
In reply to OE5EEP:
Hello Heinz.
When you don’t have an experience, I thing better will be to use any known antenna like G5RV. I use the type of the antenna and work well. When you use this type of the antenna you are able to tune it by twin lead line for one band only. On other bands you have to use antenna tuner. With multiband dipole is length not too sensitive. It only must not be shorter than 3/8 lambda on the lowest band. I thing a good idea is check the antenna by program like MMANA http://mmhamsoft.amateur-radio.ca/ before you start cut the wire. There is a lot of the antenna examples too.
Other problem is install the antenna on the SOTA. It is rather difficult to elevate the antenna up to 10 or 20 meters. I use 12 m laminated telescopic rod for support of the antenna and more often I use the wire GP antenna because the installation is easier. But I don’t have 80 m.
I will be very delighted at your 80m antenna, because on 40 m is not good condition for short distances. I’m looking forward contact on 80m.
73 Jirka OK1DDQ
In reply to OK1DDQ:
Dear Jirka,
I already have the Z-match antenna tuner, so tuning the dipole to several bands should not be a problem, provided I the feedpoint impedance is not at the extremes.
I have now a dipole with 2x10 m wire and 15 m of feeder. This will be raised with a 7m telescoping fiberglass pole in inverted V fashion. I hope this will work, there is no time now to give it a try. Tomorrows activiation will indeed be a field test for this antenna.
I will be QRV tomorrow about 0700 UTC around 3575 kHz, summit to be announced. I will work 40m and eventually 30m afterwards. Hope to hear you Jirka!
73 Heinz, OE5EEP
In reply to OE5EEP:
I found in a shop, selling mostly cheap garbage 100 feet of loudspeaker cable 2 by 1.5 mm2 (0.0023 sq in), very cheap. I cut off 50 feet and saved the remaining for further antenna projects. Then I stripped the 2 conductors and of 28 feet made a ladder line, roughly 40 mm wide, and the remaining 22 feet became the dipole legs, same lengths as the NorCal Doublet.
Finally a homebrew 4:1 balun meeting the coax to my tuner and rig, but i think the core should be larger, so i will make a new one. The antenna works guite good but sometimes i feel that a vertical is a better choice, to get “more DX”. Both can be supported by a 12 metre spiderbeam glassfibre mast och just use a tree where the branches is high enough.
Dear all,
Well the new antenna technically worked. I could bag 6 QSO’s on 80m (3xDL, 2xS5, 1xOK). The “caller intensity” was much less than what I get to see on 40m. The antenna did also work on 40m, 30m and 10m, other bands I did not try. I will experiment with shorter feeders, I simply did not know what to do with the excess feedline. I run it in a big “U”, away from the mast and back to me.
I have received a spreadsheet calculation off the list, which shows that thew dipole could be longer for optimum feedpoint impedance on 80m… (Still plenty of room for optimization).
73, Heinz, OE5EEP