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Slot Antenna for 23cm


#1

Does anyone have experience with a high gain slot antenna for 23cm? It seems like a dream to mount and could be high gain at reasonable size and very rugged compared to a yagi with similar gain.

As a vertically oriented but horizontally polarized antenna it seems unique.

I would like a setup where I can put up something like this with a voice keyer and SSB for random contacts when tropo ducting exists while I work other bands with another setup.


#2

Nice idea, what material are you thinking would be suitable? The circumference needs to be a half wave i think?


#3

Well I was thinking about something about 1 meter long, rigid (aluminum?), with an SMA connector. I don’t want anything that could deform or be damaged as I don’t have a good way to really test the antenna. I thought perhaps I could stick the antenna on a mast top or on its own spike or something depending on the surrounding foliage conditions for a horizontal signal with a vertical mounting. Perhaps if the surroundings were right I could even hang it from something vertically, something that would work better with a rigid antenna with a bit of weight to it I think. I guess it could also be used on a rope between trees suspended horizontally and become a vertical for FM, perhaps with a rig or transverter mounted to the antenna as well. If I were to hang my yagi between trees along its boom on a rope it would be pointing at a tree, but the slot antenna would be focused broad side of course. I have an M2 yagi ( 23CM22EZA) but it does put stress on a mast and you really have to know who you want to work, and it seems a bit fragile but it has grabbed a nice contact for me and it is very light. I think the M2 would have been a better design with a mid mast boom mounting point of some sort.

I don’t know yet exactly how much gain a slot antenna of 1m long can get me, but it seems like it doesn’t take much length to get reasonable gain and it seems like a durable antenna.

I am not nuts about trying myself to get the measurements dead on for a microwave band, and I don’t have a good 1.2ghz analyzer so I am thinking about buying a slot antenna ready made. The only SWR indicator I have for 1.2ghz is the SG labs indicator light on the transverter.

The ARRL handbook says that tropo is more common at 23cm than at 2m, so I have hopes that some random TX might get me something when I was not expecting it…but I don’t have much 23cm experience right now.

I was really eyeing something from this guy:

http://www.pe1rki.com/23cm-13cm-9cm-6cm-3cm-10ghz-24ghz-slotantennas.html


#4

Tom,

A slotted waveguide antenna for 23 cm is getting to be a reasonable size, mainly due to the waveguide itself: inside dimensions typically around 10 cm x 20 cm. Gain will depend on the number of slots, but I would guess at least 80 cm long for reasonable gain. Even built with Al. rectangular tubing, the mass will start to be significant - much more than a Yagi. Others used double-quad radiator with a reflector sheet.

For moderate gain, you might try an Alford Slot. See the W1GHZ microwave antenna book at https://www.qsl.net/n1bwt/ch7_part4.pdf

The M2 23CM22EZA at 70 inch boom length is pretty long, so I am not surprised that it is stressing your mast.

You could try building a shorter Yagi yourself. See Andrew VK1AD’s blog. Andrew uses a timber boom and Al. elements. You can design a suitable Yagi using the VK5DJ Yagi design calculator, which is simple to use. All that is required is care with measuring, drilling and cutting. A 10-element Yagi would give around 11.7 dBd gain and be only a bit over 550 mm long - and much easier to handle for SOTA than the M2.

Good luck,

Peter VK3PF


#5

Some interesting ideas here
http://lea.hamradio.si/~s51kq/ANTENNA.HTM
will give you some options and an idea of finished sizes.
Have you thought about stacked Big Wheel antennas for 360 deg coverage?


#6

Hi Tom,
The SG Labs transverter also provides an analogue output for forward and reverse power.

I put together some parts from the junk box - meter / switch / pot and a lead with a suitable header, which plugs in to the transverter. You have to keep the cover off during use, so it wouldn’t be great as a permanent attachment, but I found it invaluable whilst tweaking the Yagi I made using the VK5DJ calculator.


Mine is 15 element using aluminium rod and a plastic pipe boom. The tolerances sound a bit daunting, but all you are doing is cutting aluminium rod, and then filing to length if necessary. Start with the longest element, then if you cut too deep, you can use the remains for the next element! Purchase a good steel ruler, if you don’t have one.

Anyway, let us know what you do, it’s all interesting stuff.

73
Adrian
G4AZS