[amsat-bb] AO-85 and TH-D72A, full-duplex? Yes, of course!

Sat Nov 28 05:24:49 UTC 2015

Hi!

I have been trying some Chinese-made dual-band HTs, seeing how well they
work with AO-85 full-duplex. I have tried 4 of those radios recently, and
have posted my observations in a series of messages here on the AMSAT-BB
list. Earlier this afternoon, I did the same with a non-Chinese HT, the
Kenwood TH-D72A. I had no concerns about this radio's ability to work AO-85
full-duplex, but I wanted to try it and confirm this for myself.

I have had my TH-D72A since it went on sale at the local HRO store in late
2010. Over the past (almost) 5 years, I have upgraded its firmware, used it
to make QSOs on various FM and packet/APRS satellites, and used it for APRS
on my road trips. It's a great radio, although it is among the most
expensive 2m/70cm FM HTs in current production. This was a reason why I
have been interested in trying other HTs, seeing if there were any
alternatives to the TH-D72A for full-duplex operation on AO-85 and the
other upcoming Fox-1 satellites - and especially if they cost less than the
TH-D72A.

OK, the obligatory question and answer. Can the TH-D72A work AO-85 full-
duplex?

YES!

Unlike with the Chinese-made HTs, the TH-D72A does not have the 2.5 kHz
tuning step. Since the TH-D72A doesn't appear to have the sharp receive
filtering I have seen with the Chinese-made HTs, this is not an issue. I
can leave the TH-D72A's downlink VFO on 145.980 MHz for almost the entire
pass, with a quick change to the next lower tuning step (145.975 MHz) for
the last few minutes of the pass. I did not use narrow FM on either VFO
for this pass. Based on what I saw with the other HTs, I would only
consider using narrow FM on the downlink VFO if the receive audio sounded
bad. The downlink audio sounded OK in "normal" FM today. Another difference
from the Chinese-made HTs is that the uplink VFO must be VFO B (the lower
VFO) on the TH-D72A. This is the only way to activate the DUP function,
which allows the HT to receive on VFO A while transmitting on VFO B, when
these frequencies are in different bands.

Other commonly used settings like transmitting the 67.0 Hz CTCSS tone from
VFO B, tighten the squelch on VFO B while opening the squelch on VFO A,
and balancing the audio so you only hear VFO A (menu 120) made it easy to
know I am only hearing audio from the downlink VFO (VFO A). If needed, I
could have set the downlink VFO (VFO A) to receive in narrow FM (NFM) with
menu setting 131, while transmitting from VFO B in "normal" FM (FM).

I used an audio splitter in the TH-D72A's speaker jack, feeding audio to an
earpiece and my Sony audio recorder. This recording is an MP3 file, which I
put in my Dropbox space along with a larger WAV file (RF recording from
HDSDR) and other files related to this pass. These files are available from
my Dropbox space at http://dropbox.wd9ewk.net/ (look for the folder named
"20151127-AO85_Fox1A-DM43"). This way, anyone can compare the recordings
from this radio against the other recordings I've posted from testing the
other Chinese-made HTs.

The AO-85 pass this afternoon around 2226-2240 UTC had a series of resets,
but I was able to complete 3 QSOs - AA5PK in west Texas, K8YSE/7 not far
from me in the Phoenix area, and VE6SMI in Alberta. I had no problems
hearing myself while transmitting, and my transmit audio sounded good -
from the TH-D72A, and from my SDR receive setup I had in my yard (SDRplay
SDR receiver, HDSDR on an 8-inch Windows 10 tablet, AMSAT-UK VHF crossed
dipole on an 8-foot mast and tripod).

The fact I could use a TH-D72A to work AO-85 is no surprise to me. Even
with having to quickly switch VFOs to adjust the downlink frequency, then
switching back to the uplink VFO before transmitting, is not a problem.
None of the HTs I have tested recently have separate knobs for volume,
squelch, and tuning for each VFO. This radio would be number 1 on my list
of HTs I have used to work AO-85 full-duplex, going on top of all of the
Chinese-made HTs I have tried in the past few weeks.

With the TH-D72A, I have a radio capable of working V/U and U/V FM
satellites full-duplex. I also have a radio capable of packet and APRS, and
I have used mine to make packet QSOs through the ISS, NO-44, and NO-84 when
its packet/APRS digipeater was active earlier this year. It is nice to have
at least two options for HTs in current production that can work AO-85
full-duplex (TH-D72A, Wouxun KG-UV9D), along with many other HTs that
aren't in production but are also capable of working satellites like AO-85
full-duplex.

Now, it's time to find my old Icom IC-W32A in my garage, and maybe even an
Alinco DJ-G7T I think I still have. I'm not worried about the IC-W32A and
its ability to work AO-85 full-duplex, as it handled the ISS cross-band
U/V repeater fine in the mid- to late-2000s. It would be interesting to
try the DJ-G7T on AO-85. The DJ-G7T was a very poor performer when I tried
to use it to work AO-27 and AO-51 full-duplex, satellites with stronger
downlinks than SO-50. If I find these radios and can try them on AO-85
passes, I'll post reports for each of them.

73!

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