EMRFD Message Archive 1056
Message Date From Subject 1056 2007-09-27 01:54:29 Ed Almos Do I Need to Use Diplexers?
at 45MHz to the second I.F. at 4.9152MHz in a prototype receiver. As
these frequencies are fixed do I need to use a diplexer on the RF and
IF ports or can I just use a 3dB resistive attenuator to ensure a
reasonable match?
The schematic I am using is as follows:
http://www.qrp.pops.net/images/dipl1c.gif
Edward Almos HA6SST1057 2007-09-27 02:27:50 Baruch Zilbershat... Re: Do I Need to Use Diplexers? 1065 2007-09-27 21:25:13 jr_dakota Re: Do I Need to Use Diplexers?
a pad on the output will do the trick, I've noticed Wes uses those in
a lot of his designs, the downside is they aren't for low power
battery designs as they need to use a fair amount of current to get
the max performance out of them .... Since you usually have a crystal
filter after the 1st mixer the amp/pad combination make for a better
wideband match for the mixer which is hard do do with a diplexer only
... Of course you could use both a diplexer and an amp/pad between the
mixer and xtal filter, lots of room for experimentation here
To me the main advantage of the diplexer is it's filtering effect
making it act as a (not very steep) roofing filter ... I believe that
is why KK7B uses them in his direct conversi1067 2007-09-28 05:58:40 Allison Parent Re: Do I Need to Use Diplexers? 1069 2007-09-28 10:36:35 Kevin Purcell Re: Do I Need to Use Diplexers?
> Some people like the diplexer but the real pro's use a fet at commonIs there a reason a grounded base JFET (with or without a diplexer)
> gate like the j-310 or best cp-643 biased to about 30ma .gets you
> about 10db gain Rin 50Ohms and flat to more then 150 Mhz .
> its the best there is.
> 4z4rb Baruch
is not so common as a post-mixer amp in amateur designs? The reverse
isolation would be useful.
--
73 DE N7WIM / G8UDP
Kevin Purcell
kevinpurcell@pobox.com1070 2007-09-28 11:32:26 Leon Re: Do I Need to Use Diplexers?
1071 2007-09-28 13:22:03 Allison Parent Re: Do I Need to Use Diplexers? 1072 2007-09-28 14:36:31 Baruch Zilbershat... Re: Do I Need to Use Diplexers? 1073 2007-09-28 18:30:07 Allison Parent Re: Do I Need to Use Diplexers?