5760 MHz filter


bart_ghz <shf2@...>
 

Hello,

The system I used during the last contest(sepperate feeds in an
offset dish) worked fine.But I also have a homemade wb5lau dual band
feed in a prime focus dish.I would like to live test this setup and
compare it with the offset dish.
But the isolation from 3cm to the 6 cm port is not realy good (about
17 dB).I was planning to use the same setup as with the contest
(switching both coax relais).But even then there will be 20 dBm
going into the 6cm pa.

Therefore I was thinking of building a low pass or bandpass filter.
I know that you can build a lowpass filter direct on the 6cm probe
(read in Hyper Nr 129).
But I was thinking of something easier to build.
Pipecap filter are not that difficult but I was wondering if it can
handle 40 dBm of power on 6cm.

Other suggestions are also welcome.


John Quarmby
 

Hi Bart

I use the LUA dual band feed and had the same problem of low isolation, so I added an extra relay on the output of the 5.7GHz PA. When on Tx on 10GHz, the 5.7GHz PA is switched to a small dummy load and the 5.7GHz feed sees a short circuit so that any power is reflected back out to the feed, although the phase is unknown. At -17dB it won't make a big difference to the main beam pattern.

73

John G3XDY

----- Original Message -----
From: "bart_ghz" <shf2@telenet.be>
To: <ukmicrowaves@yahoogroups.com>
Sent: Sunday, October 12, 2008 4:48 PM
Subject: [ukmicrowaves] 5760 MHz filter


Hello,

The system I used during the last contest(sepperate feeds in an
offset dish) worked fine.But I also have a homemade wb5lau dual band
feed in a prime focus dish.I would like to live test this setup and
compare it with the offset dish.
But the isolation from 3cm to the 6 cm port is not realy good (about
17 dB).I was planning to use the same setup as with the contest
(switching both coax relais).But even then there will be 20 dBm
going into the 6cm pa.

Therefore I was thinking of building a low pass or bandpass filter.
I know that you can build a lowpass filter direct on the 6cm probe
(read in Hyper Nr 129).
But I was thinking of something easier to build.
Pipecap filter are not that difficult but I was wondering if it can
handle 40 dBm of power on 6cm.

Other suggestions are also welcome.






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gw3tkh@...
 

In a message dated 12/10/2008 16:49:18 GMT Standard Time, shf2@... writes:
But I was thinking of something easier to build.
Pipecap filter are not that difficult but I was wondering if it can
handle 40 dBm of power on 6cm.
I use a pipecap filter on the same set-up with no problem at +40dBm.
 
73 Keith GW3TKH




bart_ghz <shf2@...>
 

Thanks for the replies.I'll go for the pipecap filter first.
I have some silver plated tubing and end pieces here (old stuff from
my job)
I'm cerious about the insertion loss.I hope it will be around 1 dB.
I can ofcourse use an extra relay as John suggested (with an insertion
loss off about 0.5 dB).

73 de on7bv
Bart