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Trying 80m


#41

There’s nothing wrong with using an ATU - at home I have a doublet with a manual ATU. I also agree that it’s not more lossy than a matching transformer - in fact I suspect that at 80m my transformer is more lossy. It’s more about convenience when on a hilltop. Obviously an auto ATU would be ideal but the xyl thinks I’ve already spent too much over the last year getting back into this hobby.

A dipole is resonant at all harmonics but only low impedance on odd harmonics. My EFHW is high impedance and matchable by a transformer at all harmonics.


#42

I have and like two tri-band EFHWs and use them a lot - it’s good to experiment with different antenna types. I ‘grew up’ with manual ATUs so am spoilt now having a ‘press one button and it’s tuned in seconds’ auto ATU (ideal for cold winter activations). I’m still repaying the debt to my kind wife for the KX2 best ever birthday present.


#43

However it is matched to the transmitter, I think there is merit in getting a decent length of wire (eg a half wave length or more) as high as possible.

I find my Elecraft T1 really usefull, but although it will match my old wire doublet on 80m, the few times that I have tried it have not resulted in any contacts.

The old doublet is resonant a bit below 7MHz, and works fairly well on 30m / 40m / 60m, as in I have made a few contacts on each band without too much of a struggle. I have never measured its length, it just evolved - it started out as a 30m dipole, then one day, on a summit, I cut my spare length of wire in half, and added a bit to each end, to improve the chances of an S2S on 40m. At some later date, I split the “figure of 8” flex that I use as feeder, and stretched the span a bit more, to improve the chances of an S2S on 60m. That also shortened the feeder, of course, leading to potentially lower losses :wink:

I’ve been using it for years, because it just works - but I’ve had it in mind to try something a bit better, and I will persevere with the new linked dipole to see how I get on. I’ll probably still take the T1, though, to compensate for frequency changes, wire fences, shorter support poles etc.


#44

That’s been my experience. Before I gave it away to a friend getting back into the hobby I had for many years a windom-80 at home, and, like the new half-wave 80m dipole, it worked great on 80 as you would expect. But, in between I experimented with a random long wire configured as an inverted L (22m flat plus 4m sloping to a 9:1 UnUn on a ground stake). It worked great on 60m and higher but less well on 80m. Maybe, I just chose a bad random length, but it seems you can’t beat a half wavelength or longer.

As for height (above ground), I guess we activators will mostly have to compromise on that.


#45

I have been using a ZS6BKW doublet with success on 80m. At about 28m it is a bit shorter than a G5RV and a lot shorter than a full size dipole. This makes a big difference to its wind load, weight, space required for erection, etc. No doubt a full size dipole at the same height (6.5m) would radiate slightly better, but this antenna has allowed multiple activations to succeed when 40m was simply useless.

There are plenty of posts about it on the internet. Beware of some articles which reveal some misunderstandings about feedline length (should be 0.62 wavelength on 20m, with correction for VF where needed).

Here is one link: http://www.nc4fb.org/wordpress/zs6bkw-multi-band-antenna/

FWIW I don’t use 450 ohm open wire line, but 300 ohm tv ribbon. Again, the open wire line would possibly work a little better especially when wet. But rain seems to be rare in vk at present so that has not been a problem. The adjusted length of this ribbon is 11.2m but that’s due to the VF of this particular ribbon, so don’t copy that.

I feed it with the ATU in the IC703 and I don’t use a balun, it would be better to use a choke on the line connecting the feed to the radio.

I have also used it successfully with the FT817 via an LDG tuner, which allows it to be used on 10 and 21 mhz.

Worth considering by anyone offput by the length or unwieldiness of a full size 80m dipole. Oh, and another plus: it is so nice to move between bands without leaving the radio.

73 Andrew VK1DA/VK2UH


#46

I have had a lot of contacts on 160 metres using a G5RV wired as a doublet (300 ohm window line all the way to the tuner) and it is very effective on 80 metres.

As you say, it is so nice to move between the bands without leaving the radio, this is especially so when the summit is rugged or covered on rubble, and this virtue also applies to my W3EDP antenna!


#47

Also use a ZS6BKW at the home QTH and it seems to perform reasonably well on 80/40/20/17, its a bit less well on 60 and 15. On 80 it has a narrow bandwidth (Needs an ATU on 80,60,15) but is a good match on the other bands. I have used a choke balun ( 10 turns on a large torroid at the end of the balanced feeder) to get rid of noise otherwise the coax seems to pick up electrical gremlins as it approaches the house. Also experimented with an 80m inverted L ( 1/4 wave ) which tunes nicely but is always significantly down on the ZS6BKW - apart from DX - wonder if this is linked to polarisation? On summits I use a full length linked dipole (Currently 40/60/80) and have always been very suprised how well it performs with some european day time contacts - some of it will be the lack of electrical noise on the hill so I can hear the stations!

Antennas at home are a bit of a compromise as they are draped between / on trees in the neighbouring land and need to have a low visual impact and somehow fit between the overhead telephone cables ( which are better that they were with only one neighbour having ADSL - we have fibre to the premesis!) overhead mains and the 11KV supply cables.