VK Logger Ham Radio Forum Archive

VK2DAG wrote:
Before I was using 5 separate dishes and it just wasn't working!!

Matt, what problem did you have with separate dishes for each band? I would have thought that was a better arrangement than swapping feeds.

I have two of these, both steel and modified with fine brass mesh. This takes the upper freq to, theoretically, 10GHz as the spacing is less than 1/10 wavelength.

I have succesfully used them at 5.7GHz.

VK2TRF wrote:I have two of these, both steel and modified with fine brass mesh. This takes the upper freq to, theoretically, 10GHz as the spacing is less than 1/10 wavelength.
I have succesfully used them at 5.7GHz.

Where do you guys obtain this fine brass mesh from, and how much is it?
What widths does it come in?
How do you affix it to the gridpack skeleton, whilst maintaining an accurate reflector form?

I just measured the spacing between reflector "ribs" on my 24dBi gridpack, and it's 19mm.
Using this 1/10th rule, that would mean my 2.4GHz (13cm) antenna actually has an upper frequency of 19cm.
ie; 1.6Ghz only.

?

The mesh I used can be purchased at

http://www.metalmesh.com.au/cfm/index.cfm

Look for woven wire mesh, brass. It comes in different apertures as well. I used 3mm from memory.
On the 1st and larger gridpak, as ties, I used very fine single strand wire left over from a wire wrapping project. It took 2 days and lots of small holes in my fingers to finish. Start at one end and press the mesh into the grid at small intervals, tying off with the wire as you go. Only do a small area at a time! The more ties you use, the closer the mesh will form to the grid. The black stuff around the edge of the dish is cable tidy stuff from Jaycar. It is a split tube into which cables can be pushed. It is perfect to cover the hundreds of sharp ends of the mesh!
The 2nd dish uses cable ties. You need to make the apeture a little larger to force the tie through, but it is MUCH quicker.
The mesh is expensive. I seem to recall is took about $150 to do both antennas. Since the alternative is a solid dish, it was a fun experiment that did yield good results.

If you are interested, have a look what Dan VK2GG and I did on a John Moyle a few years back with this antenna.

http://www.vk2bv.org/wars-files/vk2trf-article-3.pdf


Jack

http://www.radiospecialists.com.au/ante ... 20yagi.htm.

I have one of these i want to modify for 23cm anyone done this

I have one on 23 can put up dimensions butvit looks like what you have there
they have 15-18 dbi and I have worked out 500 k under good conditions with 15= watts

VK3ZAZ wrote:I have one on 23 can put up dimensions butvit looks like what you have there
they have 15-18 dbi and I have worked out 500 k under good conditions with 15= watts

Thanks any info or pics would be greatly appreciated

Andy,

Have a look at the image at the base of that web page to see the 23cm gridpack. They do have a different feed arrangement to that used on the 2.4GHz item. They are 900x600mm.

I also have one and they work a treat. I have used it portable with an SG Labs transverter. At home, I have a 30-el yagi that I built using the design generated by the VK5DJ software.

Regards
Bernard

Andy,

There appears to be some confusion regarding the grid pack that you are asking about.

That grid pack is designed for 2.4 Ghz - the similar sized grid pack that Radio Specialists used to sell for 1.2 Ghz is a quite different feed.

A couple of points that you should note from the discussion (this topic goes back to 2010):

(1) Given that most microwave ops use horizontal polarisation, you will need to run the grid pack in such an orientation that the grids are horizontal

(2) The grid spacing is sufficient to work well above 2.4Ghz, but if you ever decided to try 5.7Ghz, you would need to reduce the grid spacing (most use a bronze style mesh)

There are all sorts of feeds that you could try for 1.2Ghz that will work once you find the correct focus position, which is roughly where the existing feed for 2.4 Ghz is.

I have seen the following types of feeds used successfully:

(1) Bow tie

(2) Quad

(3) Dipole

(4) Log periodic.

The log periodic feed is interesting - provided you don't run too much power. Have a look at https://www.wa5vjb.com/pcb-pdfs/LP8565.pdf and https://www.wa5vjb.com/pcb-pdfs/Yagi1250.pdf

Kent produces some really interesting printed circuit board antennas at a most reasonable price.

The 850 to 6500 LP is very useful as the feed is at the front of the LP, which means that you can mount it onto the existing feed of the Grid pack you have, with a suitable coaxial socket mounted on the end of the aluminium square section.

That will give you a pretty useful 4 band grid pack antenna for 1.2, 2.4, 3.4 and 5.7 although you would need to add extra mesh for 5.7Ghz to the grid.

Some food for thought Andy.

If you want to talk off forum, you can find my address in the callbook and find a matching phone number in the good old white pages!

Cheers

Peter VK3QI