[amsat-bb] more about the TH-D72A for satellites

[Patrick STODDARD (WD9EWK/VA7EWK)]

Hi!

I wavered on whether I was going to get this radio straight away, after 
the fiasco (related to FM satellite operation) the Alinco DJ-G7T was 
last year.  I didn't want to get bitten by a radio that was supposed to 
be capable of full-duplex operation, but fall short like with the DJ-G7T.
After some thought, and after yesterday's hamfest, I drove over to the 
local HRO store to see if they had any in stock.  At mid-afternoon, HRO
still had 3 on the shelf at this store. I decided that, if the TH-D72 is 
the true successor to the TH-D7 including the cross-band full-duplex 
capability for FM voice satellite operation, I'd take the plunge.  I 
bought the radio and the only option they had for it in the store 
(cigarette-lighter cable, compatible with several other Kenwood HTs 
including the TH-F6A I purchased a few weeks ago).  

I charged the battery last night, and cleared some time this afternoon to
go out to my favorite city park to try it out.  Not having used a Kenwood
HT on the satellites except for the TH-F6A as a receiver, I read through
the manual to make sure I had it set up for FM satellite work.  I looked 
at a few parameters I felt would be useful:

1. Transmit with VFO B, receive with VFO A.  VFO A has better sensitivity 
than VFO B, so why not go with that?  There is no restriction on which VFO
can be the transmitter for this radio.  

2. Audio balance.  I set that all the way to VFO A, since I wasn't 
interested in hearing VFO B.  I could see with the S-meter if anyone else 
was transmitting on the satellite uplink, and then rebalance the audio if 
necessary to hear it.

3. Squelch.  Open all the way on VFO A, tight on VFO B.

4. "DUP".  This was a new one for me, not being familiar with the TH-D7 in
the past.  Once I figured this out, turning it on for my transmit VFO (VFO
B), I was able to hear audio from VFO A whether or not I was transmitting
on VFO B.  

I had to get a plug adapter to use my normal audio cable/splitter setup 
for an earpiece and my audio recorder with a Kenwood HT and its smaller 
speaker jack.  I already had one for my TH-F6A, and it worked fine with 
the TH-D72A.  I made sure tuning steps on both bands for both VFOs were 
at the smallest step (5 kHz), and that I had VFO B set for high power 
(5W).  

I started with the AO-27 pass at 2102 UTC.  A very high pass here, with 
maximum elevation of 80 degrees.  I worked 7 stations in 7 minutes, and 
received good reports on my audio through the satellite with the new 
radio.  The only issue I had in hearing the downlink wasn't due to the 
radio - I had to move the antenna around as it passed over my head, and 
there was a moment or two where the downlink audio was less than ideal.  
I had to switch VFOs when tuning the receive VFO, something I don't have 
to deal with on my IC-2820H mobile radio or when I use memory channels in
a non-full-duplex radio, but that was not a problem.  

The second pass I attempted with the TH-D72A was on AO-51 around 2322 
UTC.  This was also a high pass, with maximum elevation of 63 degrees out 
here.  I had a little bit of difficulty hearing the satellite in the first 
minute or so of the pass while transmitting, which could have been related 
to how I was holding the antenna (Elk log periodic).  I found during this 
pass that I had to twist the antenna to clear up any receive issues while 
transmitting.  I think I might have heard the slightest desensing during a
couple of my transmissions, but that could have been related to how my 
antenna was oriented toward the satellite.  I logged 10 QSOs on the AO-51
pass, which wasn't bad for all the activity on there.  

As I posted earlier and said on the air, the TH-D72A is the real deal as 
a dual-band HT for full-duplex FM satellite operation.  It does what the 
DJ-G7T could not do, and I didn't even have to use the expanded manual on 
the CD that came with the radio to get it set up for satellite work.  I 
also set it up to work on APRS, which took little time to do.  I have not 
tried it with a computer, to see if it will work as N8MH asked earlier.  
Packet is actually something I was not very interested in for this radio - 
FM satellites first, APRS next.  The radio's GPS took only a few minutes 
to pick up signals when I first activated it.  

I do not have test equipment to quantify how well the TH-D72A's receiver
is and how it compares to other radios.  From playing with it last night 
and today, I know the receiver is on par with the IC-2820H I usually run 
on FM birds.  Excluding transmitter power, the only thing the 2820 has
over the TH-D72A is its separate knobs for each VFO.  It also compares 
favorably with the sensitivity of my IC-T7H HT - the radio I've used on 
satellites from outside Hara Arena in Dayton (my other radios' receivers 
get swamped with intermod there, but not the IC-T7H).  I will have to 
test it in a high-RF area like that at Dayton, to see if intermod plays 
havoc with the weak satellite downlinks.  

I'll work with this radio more, to get more familiar with it and possibly
work it into my demonstrations.  I will eventually get around to hooking
it up to a computer, and seeing what I can do with packet and APRS.  If 
I'm not careful, I might even go as far as having an all-Kenwood HT 
station for the OSCAR Straight Key Night in a few weeks (TH-D72A as CW 
transmitter, TH-F6A as receiver).  

73!







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