[amsat-bb] Filter out 3rd harmonic of 145MHz

[Mike Diehl]

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 could. 

73

Mike Diehl
AI6GS 

> On Mar 28, 2017, at 7:19 PM, Douglas Tabor <dtabor at estesvalley.net> wrote:
> 
> 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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