22 Apr 2013

23cms omni-directional horizontal antennas?

At the moment I'm still pondering the bands to try at my new QTH in a few months from now.  One possibility is 23cms, a band I have never used on TX.

One consideration at the new QTH is antenna (non) visibility and I am anxious to go for "neighbour acceptable" solutions on all bands. For 2m SSB/CW/data I am still minded to use a couple of stacked big-wheel antennas giving around 5dBd horizontal gain. Up above the apex of the roof, this should soon be lost being not that much bigger than a TV yagi. The partly vertical feeder to this will load up on the HF bands as a nice stealth antenna: I have used the coax to my 10m halo as a very effective HF antenna, even on 472kHz despite being only a few metres long.

But what about 23cms?  Maybe to just get on the band simply and with an unobtrusive antenna the Alford slot is worth a try? If I understand correctly, these give an omnidirectional horizontally polarized signal with around 10dBd gain. Placed at the top of the mast, maybe above the big-wheel and inside a PVC pipe as a radome, and fed with low loss coax (or with the transverter up near the antenna) this might be enough to work the locals during UKAC contests.  Alford slots are popular for 23cm beacons and ATV, so why not for local 23cm SSB/CW activity or for weak signal data modes?

Another possibility would be a big-wheel (or should it be tiny wheel?) on 23cms. This would be about 12cms across only!

The photo above was from an eBay item which sold for around £130 back in April. Is anyone aware of commercially available 23cms horizontal omni-directional antenna?

10 comments:

Martin - G8JNJ said...

Hi Roger,

Personally I wouldn't bother with Omni's for 2m, 70cm and especially 23cm. They just don't offer enough gain to be useful.

If you need low profile antennas I found that a HB9CV for 2m and a couple of medium size Yagis for 70cm & 23cm offer a better alternative. They will fit on a small chimney mounted rotator and look similar in size to FM & TV antennas.

I think that you will find that most of the time you will only use them in one favoured direction anyway.

The alternative is something like one of the Create log-periodics. 100MHz to 1300MHz with about 6 to 8dB gain. Also useful for FM radio, DAB, TV, Mil Air, Sats and general VHF / UHF monitoring.

For HF, use something like a thin 20m long end fed wire with auto tuner, or a 9:1 Unun and remote tuner. Attach one end to chimney. Run multiple radial wires across roof to guttering. This reduces EMI in house and noise on RX.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com




Martin - G8JNJ said...

Almost forgot. The Moxon is another compact antenna for 2m which is comparable to the HB9CV.

Martin - G8JNJ said...

http://www.readbag.com/zs6wr-za-antennas-super-moxon

Roger G3XBM said...

2 stacked big wheels on 2m will give MORE horizontal gain than a Moxon or HB9CV Martin. Also, it eliminates the need for a rotator. Same also on 70cm. Guess it depends how much gain one is prepared to sacrifice for simplicity and ease of operating.

On 23cm though I agree that the forward gain of even a modest Yagi may be very beneficial but I'd be surprised not to be able to work most 23cm locals with an Alford slot on the roof.

Martin - G8JNJ said...

Hi Roger,

Yes stacked big wheels should give more gain. But my experience is that they don't. They are also quite big. Two with the correct spacing on 2m would not be inconspicuous. Mine certainly weren't :-(

Regards,

Martin - G8JNJ

www.g8jnj.webs.com




G0FTD said...

Moxon's on 23cm - why ?

You must have a serious real estate
problem if you asre having to reduce the size of a 23cm 2 ele Yagi ;-)

73 de Andy

Roger G3XBM said...

Andy, what I'm thinking over is my whole antenna set-up from VLF to 481THz. On top of a local "hill" for the first time, simple omni horizontal VHF-SHF antennas are appealing as they have lower visual impact on neighbours than beams and avoid need for rotators.

Agreed that even 4 x 55el array is tiny on 23cm! Basically I am more a VHF tinkerer than serious DXer, so looking for solutions that better match my needs. It might be nice to have a REAL large VHF-SHF antenna up, but somehow it ain't me, HI.

Graham Boor said...

Stuart G6NHG use to do some at reasonable prices when I dabbled in ATV Roger, not sure if he still does might be worth a email.
http://freespace.virgin.net/stuart.marshall37/index.html

Graham G8NWC

Steve Bunting said...

Building an Alford slot isn't too hard at 23cm, but I'd still look at a short yagi. When G3XDY or another local is on they could flatten you if you don't have any F/B. One of DK7ZB's or wa5vjb's "cheap yagi" designs would work a treat 'vjb even covers up to 1296. 73 Steve

G0FTD said...

Just found some time to reply Roger.

I've only got a simple FM handheld
for 23cm, Alinco G7 which I've done
some tests on.

I was surprised at how much hairier it was to use than 70cm.

And boy does not screwing the connectors up tight or puitting
connectors on poorly make a difference to losses !

I've tried some hilltopping but
found zero activity outside a few
local stations that followed me up
to 23cms.

I've got a 23 ele yagi that I've played with, and a double quad loop
plus reflector (about 10db gain).

The latter is very compact, offers
useful gain and useable bandwidth.

Some friends have some multimode
kits and high power. Alas we only
find ourselves to talk to.

Hardly worth the expense. We could
do the same with our £25 Baofengs !

But as always, it's RF and it's
always fun to push the boundaries.