[amsat-bb] Filter out 3rd harmonic of 145MHz
matthew at mrstevens.net
Wed Mar 29 03:35:52 UTC 2017
FWIW, I have operated my FT-817 reciever/FT-857 transmitter using the MFJ
duplexer (with the 70cm side unterminated ) as a 2m BPF successfully.
Once I tuned my arrow for a good 50ohm match, I have also used the same
setup with no duplexer at all - tested at up to 30w with no interference
between rigs on either mode J or B. I'm not necessarily recommending you do
it that way, just saying it's worth experimenting for yourself (as Mike
did) to find out what works best to solve a problem in your particular
On Tue, Mar 28, 2017 at 11:20 PM, Mike Diehl <diehl.mike.a at gmail.com> wrote:
> I too have an MJF I use with my Elk and it performs well. More recently
> I've been using an arrow with my FT-1634 and had no real problems with
> desense on Mode J. However, on Mode B I had all sorts of problems. FM
> wasn't so bad but on AO-7 it was practically useless unless I ran <1 watt.
> As a test I just threw on the arrow diplexer as an LPF and it gave marginal
> results. I tried many things to get rid of the problem going so far as to
> convert my 817's to N type rear connectors, hand built and sweeped a set of
> jumpers, you name it same problem. Eventually I decided to try a terminated
> diplexer. Not having anything on hand I desoldered the 70cm pigtail on the
> arrow diplexer and soldered (2) 100 ohm carbon film resistors in its place.
> Next AO-7 I gave it a shot and it worked like magic even when I was QRO at
> 5 watts.
> With this lesson learned I believe the need for termination may be poorly
> represented by a bench test. I think that much of the UHF I was trying to
> block was actually making its way back through the BNC because of its
> proximity to the radiator. I now have it sealed and wire tied to the boom
> of my arrow and it works better than I ever expected the arrow diplexer
> Mike Diehl
> > On Mar 28, 2017, at 7:19 PM, Douglas Tabor <dtabor at estesvalley.net>
> > Thanks for that info Bob. Like Patrick, I also use the MFJ Diplexer (and
> spellcheck likes duplexer too) and have had good success with it. I will be
> ordering a terminator to correct my laziness (and maybe get a dB or two).
> > Appreciate your reply,
> > Doug, N6UA
> >> On Mar 28, 2017, at 16:51 , Bob <WB4SON at gmail.com> wrote:
> >> I actually dug up a Comet CF-4160J Diplexer (both Comet and Diamond
> call them "Duplexers") and swept its response with my Spectrum Analyzer,
> using the Low-Frequency and Common Port. I was also curious to find out if
> it mattered if the High-Frequency Port was terminated or not.
> >> The bottom line is that this particular Diplexer would reduce the
> 2-meter 3rd harmonic by 55 dB, and had an insertion loss of 0.12 dB. And I
> confirmed that there was a small reduction performance if the
> High-Frequency Port was not terminated.
> >> I would expect the performance of Diamond models would be similar and I
> will test one when I find one.
> >> The actual report can be found here: http://wb4son.com/wpblog/?p=2828
> (if the link is blocked, try WB4SON dot com and search for CF4160)
> >> 73, Bob, WB4SON
> > Douglas Tabor
> > dtabor at estesvalley.net
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