[amsat-bb] Diplexer recommendation

Wed Jan 10 00:31:34 UTC 2018

I use Comet CF-4160Ns in the VT ground station.  A while back (June of 
2016) I measured the insertion loss and isolation for a single diplexer 
with a calibrated Rhode and Schwarz network analyzer 'on the bench' and 
the numbers are close to the spec (with a 50 Ohm termination on the 
'unused' port for the two port measurements of a three port device).

The claimed numbers are 0.1dB for VHF insertion loss, 0.2dB for UHF 
insertion loss, and a blanket '60 dB' for isolation.  In that controlled 
measurement situation, for the COM to VHF port path (with a 50 
termination on the UHF port) I got 0.048 dB of insertion loss at VHF and 
59.695 dB of UHF isolation.  For the COM to UHF port path (50 ohm 
termination on the VHF port) I got 0.100 dB of insertion loss at UHF and 
73.812 dB of VHF isolation.

So technically the measured performance did better than the claimed 
performance on everything except the UHF isolation from the VHF port 
which only missed the claimed spec by about .3 dB (assuming I didn't 
screw up the cal process).

All of that though, was for a /single/ diplexer.

I'd have to think more about the ganging of two diplexers on either end 
of the cable and whether or not you'd actually get the full 'double 
isolation'.  Something about that first diplexer and internal coupling 
or reflected UHF energy if the there is any mismatch causing UHF energy 
(from say a VHF third harmonic) leaking back into the UHF radio.  Maybe 
not if you have a good match.....but then coupling at the antennas and 
an LNA with gain in the mix.........interesting problem to fully think 
through and sort out the details........

On the surface though, if you had two diplexers, one on either side of 
the cable, and inserted a UHF signal into the VHF port on one side and 
then measured the UHF signal power on the VHF port of the diplexer on 
the other side, there would be about 120dB or so of loss in that path (2 
times the isolation plus the cable's insertion loss).......just not sure 
thats an appropriate test considering that's not quite how the actual 
system is installed when antennas and LNAs and radios are all in the mix 
and matches aren't all perfect.

Fun stuff to think about though!

-Zach, KJ4QLP

Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 1/9/2018 2:18 PM, Robert McGwier wrote:
> Since I don't believe the isolation numbers, are they measured or claimed?
>
> Bob
> N4HY
>
>
> On Tue, Jan 9, 2018 at 12:10 PM, Floyd Rodgers <kc5qbc at swbell.net> wrote:
>
>>   I use diamond mx72n pair to allow a 100 ft run from shack to antennas
>> using 7/8" hardline. .1db loss and plenty of power at 400/250w fm.
>> isolation of the units back to back is 120db uhf/vhf which is plenty to run
>> satellite with two radios and two antennas.
>>
>>      On Tuesday, January 9, 2018 10:22 AM, Paul Stoetzer <n8hm at arrl.net>
>> wrote:
>>
>>
>>   Page 10 of PA1IVO's presentation at the 2011 AMSAT-UK Colloquium
>> includes measurements of the Wimo Diplexer. It appears to have very
>> good specs in general, though it looks like losses were measured at
>> 1.45 dB at 436 MHz, which is a bit high.
>>
>> https://ivok.home.xs4all.nl/pa1ivo/doc/AmsatColloquium2011.pdf
>>
>> 73,
>>
>> Paul, N8HM
>>
>> On Tue, Jan 9, 2018 at 11:16 AM, Rico van Genugten
>> <rico.van.genugten at gmail.com> wrote:
>>> Hi all,
>>>
>>> Thanks for the recommendation Patrick, I have contacted MFJ and hope they
>>> will ship a couple of them to the Netherlands. I have also contacted WiMo
>>> for some specs on their diplexers as they aren't available on their
>>> website, I will share them on this list when I receive them.
>>>
>>> 73,
>>> Rico PA3RVG
>>>
>>> On Tue, Jan 9, 2018 at 4:57 PM, Patrick STODDARD (WD9EWK/VA7EWK) <
>>> amsat-bb at wd9ewk.net> wrote:
>>>
>>>> Rico,
>>>>
>>>> I had used either Comet or Diamond diplexers in the past, until I
>>>> found the MFJ diplexers were about half the price of the Comet and
>>>> Diamond units, with what I saw as comparable performance. WiMo in
>>>> the US is like your description of MFJ in Europe; I've never seen
>>>> or tried WiMo diplexers.
>>>>
>>>> One review I saw a while back actually showed the MFJ-916B to be
>>>> much better than Diamond's MX-72:
>>>>
>>>> http://www.w4gso.org/news/comparing-duplexers-mfj-vs-diamond/
>>>>
>>>> The pictures and screenshots aren't in this article, but the text
>>>> tells the story of this comparison.
>>>>
>>>> 73!
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Patrick WD9EWK/VA7EWK
>>>> http://www.wd9ewk.net/
>>>> Twitter: @WD9EWK or http://twitter.com/WD9EWK
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Tue, Jan 9, 2018 at 9:42 AM, Rico van Genugten <
>>>> rico.van.genugten at gmail.com> wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I'm using an FT-897D for TX (non-duplex), and an Airspy and computer
>> for
>>>>> RX. Good idea to use four switches Greg, in fact that's what I'm
>> currently
>>>>> doing. With four switches you always use one antenna for RX and the
>> other
>>>>> for TX though, I want to be able to use the same antenna for RX and TX
>>>>> when
>>>>> that works better with the current satellite orientation. Using two
>>>>> switches and two diplexers I would be able to independently select
>> which
>>>>> antenna to use for RX, and which one to use for TX. I posted the
>>>>> connection
>>>>> scheme on twitter (warning, mspaint ahead):
>>>>> https://twitter.com/PA3RVG/status/950649511935905792
>>>>>
>>>>> But we are drifting from the original question: which diplexers? I have
>>>>> heard good stories about the MFJ-916, but its availability is not
>> great in
>>>>> Europe. What about Comet, Diamond or Wimo? Are they any good?
>>>>>
>>>>> Regards,
>>>>> Rico
>>>>>
>>>>>
>>>>>
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>> expressed
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>
>