Parabolic Dish Illumination

I am still having a problem with my parabolic dish, but I think I know what it is.
I am getting a perfect receive signal of around -30dbm but my send signal is miles off what is should be.

I believe the problem is to do with receiving all of the signal, but only illuminating part of the dish with the transmit signal due to a high gain can.

Anyone had this problem?

-John

I am going to attempt to correct this problem by using a Chaparral feed. This is basically a ring around the cantenna which affects the transmission angle - in my case, will increase the angle so that as much of the dish as possible (without transmitting around the sides of it) is fed with the signal.

I have cut my 'liquorice' can down to 181mm long which is apparently close to the optimal length - not sure why as it shoudl be an odd number of 1/4 waves long, but I'll try anything to get these dishes working..after all, the dishes were free and I'm having fun working it all out......

Will report back soon, In the meantime I need to go can shopping again for a 127mm diamtere can (at least 40mm high) - any ideas?

More information on chaparral feeds is available from http://www.qsl.net/ki7cx/wgfeed.htm

Regards
John

if you mean 5 inches then the freq range it will cover would be to low
between 1383.45 and 1806.97 won't it ?

check the little calc on this page half way down
http://www.turnpoint.net/wireless/cantennahowto.html

The feed can is still based around that formula, its the feed ring around the can which I am talking about using a 5 inch can for.
Check out the link in my previous post to see what I mean.

From what I can find on these feeds, the size of the chapperal feed is not too important. It is moved backwards and forwards for best illumination, then fixed in place.

It is used to disrupt the feed from the can to make the transmitted signal less directional, or in this case, to completely illuminate the dish.

sorry John my bad, Didn't read the post carefully
I see what ya doing now.

If interested I have a couple of the tins i made my cantenna out off left if you want them
They are 3.25" by around 13" and are aluminium and are open at both ends but they are the excact same size as the perserving jar lids ya get from the supermarket which you can just glue on

let me know if interested john

Hi!

Have you made the Chaparral feed?

I earlier made one of these stand alone "cantennas", D 100mm with a 31mm probe positioned 44mm from the back wall. It is working just fine as a standalone antenna.
www.saunalahti.fi/elepal/antenna2.html

Currently I'm experimenting with a 60 offset dish to establish a long distance 2,4 GHz WLAN connection.

When attaching my cantenna to the focal point of a 65cm offset satellite dish the received signal strength is increased remarkably as expected, but during the actual WLAN traffic the received packets dropped almost to zero. Throughput of the link went down. Maybe it's because of poor SWR of the combined system, or my can is not illuminating the dish as a proper feed horn. www.smw.se/qa/qa10.htm

So, now I'm thinking to redo the whole feed and add a scalar ring around the feed to better illuminate the offset.


What would be the optimum length / diameter of the feed and how is it’s diameter related to the scalar rings and general how to properly illuminate an offset dish?

Best regards, Christer

Hi!

Have you made the Chaparral feed?

I earlier made one of these stand alone "cantennas", D 100mm with a 31mm probe positioned 44mm from the back wall. It is working just fine as a standalone antenna.
www.saunalahti.fi/elepal/antenna2.html

Currently I'm experimenting with a 60 offset dish to establish a long distance 2,4 GHz WLAN connection.

When attaching my cantenna to the focal point of a 65cm offset satellite dish the received signal strength is increased remarkably as expected, but during the actual WLAN traffic the received packets dropped almost to zero. Throughput of the link went down. Maybe it's because of poor SWR of the combined system, or my can is not illuminating the dish as a proper feed horn. www.smw.se/qa/qa10.htm

So, now I'm thinking to redo the whole feed and add a scalar ring around the feed to better illuminate the offset.


What would be the optimum length / diameter of the feed and how is it’s diameter related to the scalar rings and general how to properly illuminate an offset dish?

Best regards, Christer