[amsat-bb] DJ-G7T and full-duplex satellite operating - the 2018 sequel

Wed Feb 14 15:58:19 UTC 2018

Hi!

After dusting off my old Alinco DJ-G7T for use with AO-92's L/V
configuration, I have been using it for AO-92's U/V mode and on
other satellites. I wanted to see how it would do with U/V
satellites in particular, given how it performed with V/U
satellites like AO-27 and AO-51 when I bought the radio in 2009.
I have also seen some recent comments online stating that this
radio is good for satellite work. It can be, but only in certain
situations.

Back in 2009, I was able to make the DJ-G7T work full-duplex with
AO-51, with a post titled "DJ-G7T and full-duplex satellite
operating":

http://amsat.org/pipermail/amsat-bb/2009-May/019177.html

I turned off the extended (non-ham) receive coverage in my DJ-G7T,
and it worked. I remember that, even at the city park I used for
much of my operating then, the radio would be very sensitive to
other signals way outside the 70cm band when working the U/V FM
satellites of that time. I never was able to work SO-50 full-duplex
then, with its weaker downlink compared to AO-51 and AO-27. After
almost 9 years, nothing has changed there. I just tried to work
SO-50 this morning with the DJ-G7T and Elk log periodic, yet I
never even heard the downlink once during a 39-degree pass. The
downlink VFO's S-meter was pegged for most of the pass, probably
from some other RF the radio was receiving. Even using the clock-
shift menu setting didn't improve things. I won't bother using my
DJ-G7T with SO-50 in the future, unless I have another radio for
the downlink.

In the past couple of years, we have had some U/V FM satellites
(AO-85, AO-91, AO-92) that we never had back in 2009. Simply switching
the uplink and downlink bands has been a cure for receiver desense in
other radios like the Icom IC-W32 or Wouxun KG-UV9D when trying to work
full-duplex, but it's not so simple with the DJ-G7T. Depending on the
pass and the antenna I'm using, I can still have receiver desense on
2m while transmitting on 70cm to any of these satellites. When I am
able to overcome the receiver desense on 2m, the DJ-G7T works fine for
the U/V FM satellites. This normally means I am using my Elk, and not
other antennas like the MFJ-1717 long duckie I have used with a few
other HTs. For higher passes, I am able to use the DJ-G7T with the
MFJ-1717 and hear myself while transmitting through AO-91 or AO-92,
but not near AOS or LOS when the receiver desense covers up the
downlink.

If I am only receiving the 2m downlinks from the 3 current Fox-1
satellites, and not trying to transmit to the satellite, the DJ-G7T can
be a good receiver. All of this is dependent on the surrounding RF that
the DJ-G7T might pick up, of course. What works in one location, may
not work the same in another location. I demonstrated this with two
videos I recently posted on YouTube. Here is an AO-91 pass from 6
February:

https://www.youtube.com/watch?v=jSK_v3L_RHk

And an AO-92 pass, earlier on the same day:

https://www.youtube.com/watch?v=E3nfO4tKEAI

I have also posted some audio recordings and pictures of the DJ-G7T used
with these two antennas on AO-91 and AO-92 passes in my Dropbox space.
Go to http://dropbox.wd9ewk.net/ and look for the "DJ-G7T" folder. In
there, I have subfolders for different passes I have worked with this
radio. Some of the U/V passes were worked with the Elk as the antenna,
and some with the MFJ-1717.

As an uplink radio, the DJ-G7T has performed well with the U/V FM
satellites and for AO-92's L-band uplink. I had to increase the mic
gain from 3 to 4 (maximum), and I have only received good reports on
my transmitted audio. My signals may be down a bit on 1.2 GHz if my
tuning isn't keeping up with the Doppler and AO-92's uplink AFC is
having to work, but I have been getting through with this HT (1W on
1.2 GHz) and an old 5-band Yagi mounted on the antenna connector.
I have not tried using this radio for the uplink with SO-50, but I
am confident that using a DJ-G7T with a different radio for the
downlink would also be acceptable for SO-50.

I went back and read through the QST review of this radio from April
2010. The review mentioned trying this radio on AO-27. The reviewer
mentioned hearing slight interference when working full-duplex. That
must have been done from a very RF-quiet location, and on a very high
pass. When I heard any non-ham intermod on 70cm, that would tend to
cover up the downlinks from AO-27 or AO-51.

I have liked my DJ-G7T for non-satellite uses, as it is a neat little
radio which includes 1.2 GHz. This HT, along with the 5-element Yagi I
have had for a long time, has been my uplink setup for AO-92's L/V
configuration over the past couple of weekends. For satellite use, I
think it would be great as an uplink radio for the 3 bands, and might
be useful for full-duplex operation on the U/V satellites, but comes
up way short with the only V/U FM satellite we currently have (SO-50).
I don't have an antenna that would let me see if the DJ-G7T could work
AO-92's L/V configuration full-duplex, but that would be interesting
to see. I won't sell my DJ-G7T, and will continue to recommend the
TH-D72 for anyone looking for an HT currently in production to work
V/U and U/V FM satellites full-duplex. Otherwise, there are many HTs
that can work V/U and U/V FM satellites that have been out of
production, or there is always the option of using two radios.

73!

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