Posts: 49
Threads: 6
Joined: Sep 2016
Greetings,
I was wondering if anyone has got some info on homebrewing notch/pass cavities for 23cm, rather than me trying to scale them off some 70cm ones.
The project is to add 23cm onto an existing dual band repeater here in the central west. Its already got separate transmit and receive huts interlinked by power and audio cables, so it wont need much in the way of a set of cans to get the required isolation.
any suggestions appreciated
73 Dave vk2jds
Hi Dave,
You can use 70cm cavities in 3/4 wave mode for 23cm, you will have to reduce the loop size and depending on your separation between sites maybe you can get away with notch cavities in the receive leg not much rf floating around on 23cm.
We where lucky to pickup up a Sinclair Labs 6 cavity bandpass/reject 3/4 wave cavity duplexer 10 years ago when no body wanted them for $200 Canadian for the Newcastle repeater. I noticed that most of the TX/RX (now owned by Bird) 23cm units are 3/4 wave.
Maybe single loop and Tee pieces on each three cavities will give you the rejection you need, food for thought.
Cheers Peter VK2ZTV
I've got one of these:
RFS CP1800-142-RME, Specified for 1710 - 1910 MHz,
It was aquired for the Chatswood 23cm repeater in Sydney. Ended up getting what we needed pretuned etc with the repeater so this was never used.
I have no idea if it can be convinced to go to what ever frequency you want to use it on but you are welcome to try.
Can email you the tuning instructions, test certificate etc etc if you want.
Posts: 49
Threads: 6
Joined: Sep 2016
Thats a good idea Peter, the thought hadnt crossed my mind !
I will pursue that path now. Thanks for the post, and Compton for your offer !
I will try modifying the loops on the 70cm cans i have here.
Have a transmitter and PA now, so next is getting the most out of the rx, with a LNA.
73 Dave
Posts: 153
Threads: 16
Joined: Feb 2017
Hi Dave,
I also have the same, RFS CP1800-142-RME designed for 1700 - 1910 MHz.
Noting, all the tuning screws are well out so should tune down quite a way.
Also, the line rods could be lengthened simply with copper washers.
Lotza 3mm brass screws.
My pocketVNA or my Wiltron 640 will help tuning it.
Wouldn't your septum feed, do the job?
Alan VK2ZIW
