Last year I got hold of a so-called Cassegrain TV antenna. The Cassegrain principle has the advantage, that by a secondary convex reflector in front of the primary reflector the focal length is extended. Thereby the antenna is very compact.
The antenna I aquired is made by the company Gibertini and is called Cassegrain CP 60. For some reason it seems that the manufacturing has been discontinued but if you search the net you still can find some companies selling them.
This antenna has the big advantage that it has a radom covering the entire antenna, thereby protecting the LNB. The diameter of this antenna is 62cm. Due to the radom it can be easily transported and I took it to a few trips , for example to Denmark, where I was QRV as 5P8KW last September . The downlink antenna is the lower of the two antennas.
At that time I still used a SSB-Electronic 2.4GHz antenna called Airlink 60 (the upper antenna). It has a similar radom but it is not a Cassegrain but a prime focus dish.
I experimented with both, helical antennas and patch feeds, which led me to be a fan of the helical feed.
I came accross a dual band design by Bernd, DH1ND, who simply printed a holder for a 3 1/4 turns helix with a 3D printer. The reflector of the helix has a hole where the LNB is peeping through.
According to Bernd, the loss of the LNB signal by the reduction of the free sight of the LNB is about 1.5dB. I can confirm that the loss is not very high and with the signal strength of the satellitle inside a 62cm antenna, it is affordable.
I purchased a kit from Bernd to test it in my setup. Note that in a Cassagrain antenna with two reflectors the helical antenna has to be wound right hand wise (RHCP)!
Here is a look inside the antenna before the modification.
The secondary reflector has a diameter of 14cm.
Here is the complete setup with LNB and helix.
During practical tests with my portable station in my garden showed, that I was unable to detect any attenuation of the received signal from QO-100.
I tested the the uplink system and compared it to a 60cm prime focus dish with linear vertical polarization (the Airlink 60). The signal of the modified Cassegrain is about 2 to 3dB stronger than the linear polarized antenna (as expected ).
Now I only need to load one antenna into the trunk of my car for portable operation.
Holger 'Geri', DK8KW