[amsat-bb] Diplexer recommendation

Wed Jan 10 13:36:33 UTC 2018

Hi all,

Thanks for the link to the article Adrian, that's a very good comparison.
It seems that the differences between the Comet, MFJ and Diamond are minor
and they all meet their specs, with the exception of UHF isolation on the
VHF port, which is in the 55-60 dB range for all units. This is in
agreement with the measurements done by Zach on the Comet. According to the
QST article the Comet's input SWR is a bit higher on the VHF port (1.3:1)
and the Diamond and MFJ's input SWR is a bit higher on the UHF port (1.4:1
and 1.3:1), but nothing too shocking.

I ended up ordering a set of MFJ-916BN's from MFJ directly. Shipping to the
Netherlands is 29 dollars. Not too bad considered the unit price and the
current dollar to euro rate.

Thanks all, I will let you know how they perform when I get them. As stated
before, I will not be using them back to back as in Floyd's situation, but
rather run two feedlines and connect a diplexer to each of them.

73,
Rico
PA3RVG

On Wed, Jan 10, 2018 at 1:31 AM, Zach Leffke <zleffke at vt.edu> wrote:

> 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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