I rarely use my Arrow and 2 dual band HTs, but, dragged them out this week because I'm scheduled to do a high school demo in 2 weeks and thought I better start practicing my technique again, update the KEPS in my Palm PocketSat+ and get the battery packs charged.
So this discussion in the last couple of days is very relevant to me and here's my 2 cents...
The only compliant I have about the Arrow is that it looses it's speckles and the plastic tips fad to white when used outdoor for long periods :-) Several years ago I ran it for a full year on the roof with a hygain TV rotator and fixed EL of about 30 degrees. The arrows are now plain aluminium.
First I view all anecdotal comparisons of before and after results with some caution. A diplexer change from the OEM to another cannot account for the improvement in one pass with fades to the next pass with no fades IHMO. It is so, please tell me the science behind this. If a defective diplexer was acting as an attenuator then I sure can see there would be an improvement in signal. In my location, 2 low passes with the same max elevation on the same satellite can be quite different depending on which part of the horizon is below the pass - open prairie vs the noise floor of city. Sometimes there are fades and sometimes there aren't any. Satellites tumble. Sometimes to your advantage and some times they work against you.
Now, as to the Arrow OEM diplexer; with the 2 HT's I don't use it except as a mode J filter, see
http://www.amsat.org/amsat-new/articles/Mode-J/ to reduce desense, and, a mini UHF preamp
http://www.hsmicrowave.com/html/amateur_lna.htm , and, anecdotally I can tell you that I can see the increase in bars on S-PO Meter and these old ears can hear the difference when the preamp is switched on and off.
For those of you who want to use an external diplexer such as a Comet, you can still use the OEM diplexer at the same time as a filter.
BTW yesterday I just practiced listening and heard a monstrous booming signal from ISS, got to hear 4 or 5 answers to questions during the Ottawa ARISS with the Arrow and a max 10 degrees pass, no preamp needed, LOS just under 5 degrees. Also AO-27 max 20 degrees over Eastern NOAM until it went digital - ever notice it goes digital just as it hits the 49th parallel? Is that an anti-Canadian thing?
73, Alan VE4YZ EN19kv AMSAT LM 2352 http://www.wincube.ca