HamTV Status

[G4IMO-TV]

Hi John, check your email.

For anyone else interested, the Horn dimensions were 83mm diameter and 230mm long. The 1/4 wave probe is 70mm from the back.

Nick
G4IMO

[radiogareth]

Nice, any details on the dielectric plate??
Gareth

[G4IMO-TV]

Hi Gareth
The best material to use for the Dielectric Plate is PTFE but it’s expensive. A cheaper alternative is Teflon. I actually ordered my material from Satellite Super Store who sell small plates for C Band. They can be glued together to make a bigger plate using a suitable low loss glue – Super glue works well.

Nick
G4IMO

[Basil]

Is Teflon not a DuPont trade name for PTFE?

[radiogareth]

Thanks Nick & Basil, yes, my understanding was that too, Teflon/PTFE the same. By a chance, I have large amounts of PTFE sheet and thinking back, probably two similar things that came with the Titanium C band LNB's I bought...got a feeling I chucked them out......
So dimensions and combined thickness/position would be great. I have well over a sq metre of 1.6mm and some big blocks, plus large diameter rods of the stuff. I knew it would come in useful sometime
Thanks
Gareth

[G4IMO-TV]

Hi Gareth,
When I made a polariser for C Band many years ago using tuning screws in a piece of 2 inch copper pipe, the theory suggested it needed to be 1 wavelength long. Assuming that applies to the dielectric plate then that would be the same. The width of mine is 5mm, and is flush with the rim of the Horn. It has been suggested by someone, may have been Steve Birkill, that tapering the front of the plate to a point improves it, but I've not tried that yet. As we are using a dish, and trying to receive a RHCP signal, then if my memory serves me correctly, with the probe at the top then the plate needs to be rotated cw so as to slope NE/SW. If you wanted LHCP then rotate the plate CCW so as to slope NW/SE. The plate must be at 45 degrees to the probe. Hope that makes sense. If I'm wrong then it's a case of the Brits doing another Telstar!

Good Luck

73 Nick
G4IMO

[PA3CRX]

Some years ago, for C-band (9 cm) satellite reception I used a piece of acrylic glass (Plexiglas) as polarizer. It worked very well and could probably be obtained more easily then Teflon.

To check if the polarizer functions: signal strength should improve if the material is placed ( and the polarisation of the other station is circular). While placing the material 90 degrees rotated the signal should drop (-20 dB or so) caused by wrong polarisation.

Just try!

Chris PA3CRX

plexiglas acrylic glass polariser.JPG (233.66 KiB) Viewed 2111 times

[G7JTT]

Hi Nick just seen this post, I haven't had any emails from you and yes I've checked the junk folders which account did you send it to ?

Hi John, check your email.

For anyone else interested, the Horn dimensions were 83mm diameter and 230mm long. The 1/4 wave probe is 70mm from the back.

Nick
G4IMO