[amsat-bb] AO-92 L/V with an Alinco DJ-G7T full-duplex (long)

Tue Mar 5 23:23:06 UTC 2019

Hi!

I have written a bit about the Alinco DJ-G7T and using it on satellites on
this list over the years. I wrote about using it on AO-92 in both U/V and
L/V modes last year:

http://amsat.org/pipermail/amsat-bb/2018-February/066923.html

Until the past weekend, I had always worked AO-92 L/V with two radios -
transmitting on 1.2 GHz from the DJ-G7T, and receiving the 2m downlink
with my Kenwood TH-D74 (which can also record the downlink). I have used a
couple of different antennas, but have wondered if the DJ-G7T could work
the L/V mode full-duplex like it can work U/V (with some caveats) full-
duplex. Now, I have tried this for myself, and will ask the question...

Can the Alinco DJ-G7T work AO-92's L/V mode full-duplex? Yes.

Before the past week or so, I was aware of the triplexers offered by
Diamond that included a 1.2 GHz port. Those are noticeably larger than the
diplexers from Diamond and other manufacturers, and a larger price tag as
well. I saw something online that mentioned the Diamond MX-37 diplexer,
having one port for HF through 470 MHz, and the other port for 800-1300
MHz. Physically, the MX-37 diplexer is similarly sized with other
diplexers, and it has two coax pigtails for those two ports - coax with an
N connector for the 1.2 GHz port, and a PL-259 on the other pigtail for
use with the lower frequencies. The common port is an N socket. After I
received this diplexer in the mail, I was ready to fit it into my portable
AO-92 L/V station.

I have been using a 10-element 1.2 GHz Yagi for AO-92 L/V in the past few
weeks, and I tie that to the PVC handle of my Elk log periodic. I decided
to tie the MX-37 diplexer to the PVC handle behind the antennas. This
allowed me to connect the 1.2 GHz side of the diplexer directly to the coax
pigtail from the Yagi's driven element. I used a 3-foot/1m length of coax
from the PL-259 connector on the other side of the diplexer to the Elk's
coax feedpoint. From the common port on the diplexer, I ran another
3-foot/1m length of coax to the DJ-G7T.

To keep from causing audio feedback while transmitting, an earpiece or
something like that needs to be plugged into the DJ-G7T. The DJ-G7T uses
a single 4-conductor 3.5mm jack for speaker/mics. To split out the speaker
jack so I can use an earpiece and an audio recorder, an adapter is needed.
I use Alinco's EDS-10 adapter, which provides a 3.5mm speaker jack and a
2.5mm microphone jack (don't need anything in the smaller jack for this).
Alinco also has an EDS-14 adapter, which looks very similar to Yaesu's
CT-91 adapter used with a few HTs (VX-6R and VX-7R, among others) - where
the two jacks are on short pigtails from the 3.5mm plug. The Yaesu CT-91
adapter works fine with the DJ-G7T.

The DJ-G7T only allows transmitting from VFO A, the upper VFO on the HT's
display. I put the 1267 MHz uplink frequency in this VFO, along with
encoding the 67.0 Hz CTCSS tone. I use 5 kHz tuning steps on this radio for
1.2 GHz. I set the volume for this VFO to 0, and tightened the squelch to
the maximum. For the lower VFO (B), I put 145.880 MHz with the squelch left
wide open, and adjusted the volume to a reasonable level using my earpiece.

I used this setup for 3 passes over the weekend. The antennas were a little
heavier with the diplexer on the handle, but I could still control them
with one hand. I held the DJ-G7T, along with the splitter and patch cable
to my audio recorder. I could still adjust the knob for the transmit VFO,
and made some contacts on those 3 passes. It was fun to be able to use just
one HT for AO-92 L/V.

There are some tradeoffs when going from a two-HT setup for AO-92 L/V to
just the DJ-G7T. The 2m receiver isn't as good as with other HTs, certainly
not as good as the TH-D74 I have normally used when working L/V. I heard
some other signals mixing with the AO-92 downlink on parts of a couple of
passes. Of course, the DJ-G7T does not come with a built-in recorder like
the TH-D74. There may have been a little less power going to the 1.2 GHz
Yagi, passing through the coax to the diplexer's common port and then out
from the diplexer to the Yagi, but I still got through. During one of the
L/V passes, I was still able to get through AO-92 transmitting at low power
from the DJ-G7T (rated at 300mW for 1.2 GHz).

I posted some pictures of this setup on the QRZ satellite forum, in a long-
running thread "Where's AO-92???", starting at:

https://forums.qrz.com/index.php?threads/wheres-ao
-92.614536/page-34#post-4986044

Audio from my recorder on the 3 passes I worked last weekend with this
setup is in the "Satellite_Audio-2019" folder in my Dropbox space:

http://dropbox.wd9ewk.net/

The direct link for the pass I worked Saturday evening, where the recording
started at 0537 UTC Sunday (3 March), is:

https://www.dropbox
.com/sh/v3byggtuqw33fkk/AAA_gyTts4RpjT3jZa8GJI5ha/Satellite_Audio-2019/20190303-0537UTC-AO92-DM43bl.mp3?
dl=0

Audio from the 1709 UTC pass Sunday morning is at:

https://www.dropbox.com/sh/v3byggtuqw33fkk/AACeV6R0Bjh-RRPXTrNpblAca
/Satellite_Audio-2019/20190303-1709UTC-AO92-DM43bl.mp3?dl=0

and the late-morning pass at 1843 UTC Sunday:

https://www.dropbox.com/sh/v3byggtuqw33fkk/AADmbAfFYtHARDfULAR
_J5eSa/Satellite_Audio-2019/20190303-1843UTC-AO92-DM43bl.mp3?dl=0

It is nice to see that the DJ-G7T is capable of L/V full-duplex operation,
just as it is capable of U/V full-duplex operation, in line with Alinco's
advertising for the radio - with some caveats. I can now alternate between
a one-radio setup and a two-radio setup for AO-92 L/V. More fun with
radios... :-)

73!

Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/
Twitter: @WD9EWK or http://twitter.com/WD9EWK