Which feed for f/D 0.25?

Hi folks,

I have tried to improve my uplink with a 120cm dish. This is an old commercial dish with a low f/D 0.25.

Now I am using linear polarised WiFi grid antenna PW 24 dBi,

Due the low f/D I have choose K3TZ patch feed. I was calculating with a gain of 3dB for circular polarisation and 6dB for mechanical dimensions.

Test shows only +3dB.

I can confirm that th feed was placed correctly in focal point and SWR was not bad (indication on LZ5HP's XVRT), The reason why I did not reach the estimated gain is probably that the feed has not so wide radiation angle as I need for f/D 0.25.

To imagine that 120cm dish has 30.8cm depth and focal point is 29.2cm from it depth.

Has anybody an idea for circular feed for this parabolic dish, please let me know.

@dk0kp Hello Heiner, yes, the screews can impact to the patchfeed but I don't think that they make -6dB.

Studying materials about the feeds as SM6FHZ comparsion or W1GHz. It seems that with f/D 0.25 have patchfeed low effeciency. The most suitable f/D is 0.4.

PA1EW Hi Ed, thanks for suggestions! You have rights, the N-connector body stands off the reflector a little bit. Good point!

It is small picture - the black material is 3mm drill used for correct spacing. There is nothing, the plate is soldered and holded by the live pin of the N-connector.

Probably this type of feed is not suitable for f/D 0.25, the parabolic dish effeciency is only 50% depending on the study:

[Blocked Image: http://2ingandlin.se/432_MHz_ES5PC_patch_feed_in_dish.gif]

Probably the dish was designed originaly to feed with a dipole and rod reflector spaced 0.24 lambda or so. There is teoretical effeciency more than 70%

http://www.w1ghz.org/antbook/chap6-2.pdf

I rather changed my plans and order 100cm TV dish with higher f/D and will try helix. Think that it should work.

Thanks!

Unfortunately the dish was damaged in transport. But Santa (in June, hi) brings me a present - D6 analyser. Not calibrated yet, but it helps me a lot.

There are 2 screens, one is before aligment, second after. It was tuned toho high.

Did anybody try to Fred deep dish with a moxon? Or 2 moxons phased fór circular polarisation?

PA3FYM Yes, K3TZ patch. Will do that