Date: Fri, 25 Apr 2014 21:49:47 +0000
From: Benedikt Sveinsson <benedikt@ok.is>
To: Amps <amps@contesting.com>
Subject: [Amps] low pass filter fail ;)
I have been building a 2M SSPA - final part in the puzzle has been the low pass
filter.
After building this filter, copied the design from W6PQL - but I have limited
resources here in TF land, so I don't have access to good PCB materials. But
the filter was measured using a mini VNA Pro analyser with good results. 1:1.2
SWR on the operating frequency and cuttoff starts around 150Mhz
well, after transmitting about 10s I noticed a drop in output power, I took the
cover off and aimed the camera while transmitting
This is what happened on youtube: https://www.youtube.com/watch?v=9lU3I3BgmkE
I suspect there is something else wrong, as this happened very fast 10-15s -
and solder melts!
Guess I will go and find teflon sheets and make my own capacitors with copper ;)
73, Benni TF3CY
## Do you really require a LP filter ? You could also use a .25 wave long
coax stub..with far end shorted. You can also add additional stubs etc.
Paralleling caps is the real answer to your exploding cap problem. 2-4 caps in
parallel would be the ideal ticket. Your typ 2m ant will only be resonant on
its 3 and 5th harmonic. You can make stubs that will kill odd harmonics if I
remember correctly. W2VJN has a good book on stubs.
## Parallel some caps..and you wont have any more issues. I have used the
teflon sheeting sandwiched between 2 aluminum plates,,and that works superb...
provided it is constructed correctly.
## I like the idea of a LP filter......... then it kills everything beyond the
cutoff freq. A bandpass filter would even be better. You could also use a
LP filter
for TX....and a low power bandpass filter...for RX only.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|