VK Logger Ham Radio Forum Archive

I wonder what others are using for high gain on 23CM I am looking at ~50 el loop or A double rhombic
Have both ants started The loop ant is going to take a lot of work to finish!!
The double rhombic has only one problem What type of resistors do I use for the terminations
Power levels contemplated 18W initially up to max legal
Regards
Wal

Hi Wal

I was initially using a 35 ele M2 yagi on 23cm. It was quite Ok. Depends what you want to do though. But I sold that to VK3HV and am now running a 12 ft dish. Which is easier and better in some ways and not in others. For general tropo I think a single yagi is fine.

Gudday Leigh Have a 3m Dish will be one hell of a lot work to get up and running was wondering if anybody has had any experience with Double rhombic less than 2m long quoted gain ridiculous "27dBD" with quarter of that I would be happy!!
Regards
Wal

Interesting. A detailed analysis of the dual rhomboid antenna appears here: http://www.cebik.com/vhf/rh.html

It appears that the gain is more like 16dBi - about equivalent to a 16-element yagi. There may be issues with having to mount it well clear of anything metallic (e.g. tower) and supporting the matching and terminating resistor (+ heatsink) might be a bit challenging.

I run a 54-element DL6WU, which seems to work fine and is no trouble to mount on a mast and rotate. However, cutting all the elements was a bit of a job.

Regards,
Dave.

for portable a doublequad works similarly to a 16 el yagi, at home a 4.6m dish for eme experiments, a 3m dish on the mountain for long haul terrestrial , and a 1.8 solid dish underway for ute mounted portable mounted off the side of the tray. feeds on the dishes are right and left circ plate feed on the 4.6, doublequad on the 3 and a ve horn on the 1.8 which i will ditch and go to a doublequad. the ve horns are too big and heavy, mine being copper
73

Double diamond == 16 element yagi ?
Most definately not.
A double diamond offers only about 6dBi, where as a 16 element yagi you can expect about 16dBi gain.
A double diamond does have an excellent front to back ratio, but if a similar reflector is used on the yagi, the F/B performance is similar.

they were tested side by side Ash, from canberra to canobolas, fair dinkum
gain 11db, on page358 ,E.4.6 figure 459, uhf compendium, k.weiner dj9ho. they designed them and tested them in the aerial measuring contest in the uhf group of munich
they seem pretty good and heaps easier to build than a yagi, i use them for dish feeds too !
73's

My corner reflector is ok for portable work bit I need to get serious about 23CM at the home station and put up a decent antenna. A dish on my tower might not be a good idea in a cyclone prone area. Does anyone know anything about the 36 el slot-fed antenna produced by Com-an-tenna? Good choice? Or should I have a go at home-brewing something with a bit more gain?

Cheers

Wayne

Directive Systems out of the US will ship just about any of their loop yagi antennas as an element kit (minus the boom material), which is a very easy way to put together an effective 23cm antenna. I've used a DS 40el loop yagi on field days and it's performed very well, from the back yard I've measured 0.25db of sun noise with this antenna and my 23cm transverter setup, the calculations suggest around 19.5dbi gain. One issue with loop yagis is they are reasonably flimsy, and brass is typically used in the driven element, which in seaside locations would likely cause longevity problems... not so easy to stack either, as they should be mounted at the extremity of the support pole. However the DS folks in the US were easy to deal with and saved me an eternity cutting aluminium...

73 - Ted

Hi Ted

That sounds like a great idea. I will give them a call.

73
Wayne

VK2JDS wrote:they were tested side by side Ash, from canberra to canobolas, fair dinkum
gain 11db, on page358 ,E.4.6 figure 459, uhf compendium

You'e right. Now I'm thinking there's something wrong with the ones I built or the calculations on gain.
Now I have to dig them up and measure them again to make sure I'm not having a lend of myself.

Wayne,

For a very detailed look at building 23cm yagis...

If you've not visited Jim's website, worth taking a look at his article on "Building UHF Antennas" that appeared in QST some time ago - http://www.w6pql.com/antennas.htm. Jim has quite a lot of useful material on 23cm and above...

73, Ted

vk1bl wrote:Wayne,

For a very detailed look at building 23cm yagis...

If you've not visited Jim's website, worth taking a look at his article on "Building UHF Antennas" that appeared in QST some time ago - http://www.w6pql.com/antennas.htm. Jim has quite a lot of useful material on 23cm and above...

73, Ted

Hi Ted,

There is a lot of useful information in Jim's article.

I have reservations about his method of securing the elements, it does not look like it gives a reliable low resistance connection to the boom. As you know, a popular approach to solving this problem is to insulate the elements from the metallic boom.

Jim cites the VK5DJ design tool for DL6WU yagis, but as far as I understand it, that implements the David Tanner variation on the DL6WU design. (When is a DL6WU antenna not a DL6WU design?)

Jim's feed construction is certainly simple, but I wonder about its robustness. (I am thinking here of the damage of birds landing on the structure, and longer term wind fatigue of the inner conductor of the UT-141 that supports one end of the folded dipole.) Some of the designs using a plastic box and cable entry glands look more robust, especially for lower bands.

Another good site for useful info and links is Ian White's at http://www.ifwtech.co.uk/g3sek/diy-yagi/index.htm . (Ian has an index to the DL6WU design tools that are the closest fit to Guenter Hoch's design concepts.)

Wayne, it is worth Googling for some ideas, there are some beaut articles available.

Owen

vk1bl wrote:Directive Systems out of the US will ship just about any of their loop yagi antennas as an element kit (minus the boom material), which is a very easy way to put together an effective 23cm antenna. I've used a DS 40el loop yagi on field days and it's performed very well, from the back yard I've measured 0.25db of sun noise with this antenna and my 23cm transverter setup, the calculations suggest around 19.5dbi gain. One issue with loop yagis is they are reasonably flimsy, and brass is typically used in the driven element, which in seaside locations would likely cause longevity problems... not so easy to stack either, as they should be mounted at the extremity of the support pole. However the DS folks in the US were easy to deal with and saved me an eternity cutting aluminium...

I took delivery of a 45 element loop yagi kit from Directive Systems last week. I ordered the antenna with the boom which Dave (owner) cut into 4 pieces instead of 2. Put the antenna together in an afternoon. All the parts were there and it went together quite easily. The antenna looks well made, but I may have to put a couple of boom supports on the antenna as it does seem to sag a bit, but this is probably attributable to the 4 piece boom. Unfortunately though, no time and/or DX so far to give it a test.

Antenna took about 6 weeks to be made and posted to VK6. Price for the antenna posted was about $220.00.

Regards,

Rob...
VK6JRC

Hello
I noted Wayne's (VK4) post last December about the Melbourne antenna made by Com-antenna. While his post was answered with another suggestion I wonder whether anyone has tried the 23cm antenna made locally. I noted the suggestion of importing the kit from the USA, but with our dollar only buying about 65 cents US that is no longer a feasible option. I have a small Chinese made antenna (quite good) but really inadequate for a developing home station.

I will await with interest.

73

John Dawes
VK5BJE

Can anyone provide a link or details on how to make the feed for gridpack antennas? I see they seem to be commercially available from a company in SA - the gridpack that jaycar sell is also a cast aluminium reflector and it looks like it might be possible to change or modify the existing feed. Ideas and suggestions appreciated.
Paul vk4apn

Looking into 23cm antenna options myself at the moment, and I was made aware of Spectrum Antennas, located in Stawell, VIC;
http://www.vk3jwc.ballaratcomputers.com.au/

There isn't much information about his two 23cm loop yagi models, just pictures in fact, so I am hoping he can reply to my email query with sufficient detail.

Directive Systems in the USA can be found here;
http://www.directivesystems.com/

I have been told that Coman makes 23cm antennas and that he advertises in AR.
I don't see AR, and he doesn't have a website either.
How on earth do these guys run a business this day and age without an internet presence?
It isn't 1980 anymore!

My only concern with a loop yagi, is they might be too flimsy and intolerant of rough treatment with portable operation.
Maybe this isn't any real concern at all?

As much as I would like a 35 element M2, the landed $AU price is out of the question.

VK4CP wrote:Looking into 23cm antenna options myself at the moment, and I was made aware of Spectrum Antennas, located in Stawell, VIC;
http://www.vk3jwc.ballaratcomputers.com.au/

There isn't much information about his two 23cm loop yagi models, just pictures in fact, so I am hoping he can reply to my email query with sufficient detail.

There isn't much information about any of his antennas, and the information provided raises more questions than it answers. The pics looked like DL6WU (or variant) Yagis for 2m, and the 23cm loop Yagi looks similar (as far as the picture detail allows) to the DS one.

The loop Yagi is probably tougher than you think. VK1BL has a DS one, bought as a boomless kit so freight on an envelope of flat straps and the feed unit is much cheaper than sending a boom. Ted isn't very kind to the antenna in my view, it seems to survive being strapped on the roof racks against other antennas quite well... whereas the 2m Yagi is more inclined to be bent in transit.

Speaking about DL6WU Yagis...
Click on image for a full size view.

Why do people build 10 element and 12 element designs, when a 'sweet' length for a short DL6WU Yagi from a VSWR point of view is 11 (or 16) elements?

Owen

Owen