Cavity filters

[gm0mzb]

Hi all

My work has agreed to sell us the cavity filters required for our repeater :chee. I will do my best to collect them over the next week or so.
I have been chatting with a fellow repeater keeper from England, and a few years ago he gave me details of how to modify similar filters for a better notch :scratch hopefully somewhere in the region of 30dB a filter instead of the 20dB at the moment. I have enclosed a pic of the modification. I will see if I can scrounge the parts and modify one of them to see if it makes a difference.

[GM8GAX]

If you can not get hold of an Oxley trimmer, I have some Mullard ones you could use to try out the mod.

Peter

[gm0hzi]

i,m due a baby cow in a fortnights time so i can help with the filters if needed :scratch

[GM1BSG]

Wullie

I still think I can make the filters more effective by making the existing filters in the radio more efficient or adding a nice SMT strip filter.

The RX/TX paths are seperate right? so a notch would be a lot easier inside the radio.

We can simulate the performance before build and make a few protos and actually test.

I was considering suggesting a pre-amp inside on the RX path for this anyway just to compensate a little for the insertion losses.

Its useful to think outside the box, but this time i think inside would be better ;-)

BR, John

[gm4vgr]

Thats great news Wullie :bigg

[gm0mzb]

Had a look at some of them onthe sweep generator today.

[GM0FSV]

Knowing you Wullie you could get a piece at anybody's door, keep on scrounging :pira

[GM1BSG]

Wullie

As we spoke about, I will bring the Anritsu network analyser down Thurdsday along with the 2955B and we can have a play. I think an internal cleanup might squeeze a bit more out of them.

I will also bring down the polystyrene slabs and some extrusions so we can build them into a small frame for mounting in the box area now cleared.

BR, John

[gm0mzb]

I will do my best to get some of them down by Thursday.
Depending on what I have onthe cards in the way of work this week, I will get the isolators re-housed and re-configured as Circulators, found some nice boxes at work that will do the trick :bigg.

Had a look at some of the specs for some of the Commercial Duplexers they are quoting about 88dB ish at -600kHz.
With the circulator in use I reckon we can get to that if not better, possibly 92dBish but we will have to keep an eye on the insertion loss :sad:

[gm0mzb]

Came accross this on e-bay but the seller does not ship into Europe :cry:

This is what I had in mind for some of the filters :idea


Will have to wait and see if I win the auction for the Oxley caps :twis


Wullie

[gm0mzb]

I have the Oxley caps and have received them during the weekend.

I convinced the seller on e-bay to send one of the Hi-Q coupling links to Scotland so hopefully it will be here soon :chee


Wullie

[gm0mzb]

Hi all.


With the new antenna, Heliax and Circulator being installed, I thought I would spend some time today and make up the correct phasing harness for the filters using some RG223 (mil spec cable).

With the remaining cavities having being modified for Bp/Br thanks to Peter GM8GAX, I tuned them up using the new harness made from the RG223.

Hopefully over the weekend I will get a chance to swap them over with the filter installed on the repeater.

With the correct harness, I can get 98dB of rejection with only 3 filters, for 1.5dB insertion loss, see pics below.

[gm0hzi]

i think i`m free this weekend if you need hand ...
but only one as i have blisters on 4 fingers on my right hand :cry:

[BILL HARDIE]

NEIL

I'M NOT EVEN GOING TO ASK !

BILL

GM6RGY

[gm0hzi]

jam up on the bars bottle line :frown:
these things are damn hot 145c

[gm4vgr]

OUCH Neil that had to hurt :eek: