[aprssig] Kenwood D700/D710 RF Problems

Herb Gerhardt hgerhardt at wavecable.com
Wed Jul 21 17:42:44 CDT 2010

Since we are discussing noise issues, this might be a good time to bring up
my problem with a D700 radio.  I am also changing the title to Kenwood
D700/D710 RF Problems.

I am using a Kenwood D700 up on a mountain top as an APRS digipeater.  Here
in the Pacific Northwest we are experimenting with 9600 baud APRS on several
bands.  Well I am supporting both the traditional APRS on 144.390 at 1200
baud on the right side of the radio using a KPC3+ TNC (Vers 9.1) and on the
left side of the radio I am running 9600 baud APRS on 144.350 using the
internal TNC.  The beauty of this set up is that one Kenwood radio and only
one antenna, can operate both digipeaters.

Yes, we are experimenting with this set up at a number of locations around
Western WA using both D700 and D710 radios and have not had any equipment
problems until now.  As soon as I installed this equipment at our site on
South Mtn and the radio transmitted on either side on high power, the Astron
SS-25 switching power supply tripps off the line.  Turning the output power
down to 5 watts (low), seemed to keep the power supply from tripping.  This
dual digi worked fine for about a week and then the 9600 baud side
disappeared off my screen.  I had to wait until I had time to make another
trip up the mountain about a month later.  The 144.390 digi side continued
to work fine, so that proved that the power supply had not tripped and the
radio's right side was still operating fine with its external TNC.

What I found when I went back up there was that the D700 internal TNC had
completely reset itself to parade rest but the radio's memory channels were
still as programmed.  I brought another power supply and D700 with me, so I
replaced both the power supply with an identical one and a different D700
radio.  Well, we experienced the same power supply tripping problem as
before on high power and  also on medium power.  We did lots of head
scratching and investigating and it appears that the problem is an RF
problem of when the radio transmits on high or medium power, it trips the
Astron SS-25 power supply off line.

I had one torride  core with me and installed it on the head cable with one
additional wrap through the core.  That helped.  We then moved the D700
control head around in our enclosure to get it as far away from the power
supply as possible but that is still less than 6 inches and wrapped the head
with some aluminum foil that my sandwich was wrapped in.  We also rolled up
the head cable and put a steel plate over the top of it.  We then set the
power level to low power on both sides of the radio and so far, so good.

So the question is:  has anyone ever experienced similar problems with their
D700 or D710.  If so, how did you resolve the problem?  Keep in mind that
the mic is not connected to the radio.  

Like I said, so far, so good but being on a mountain top is not the ideal
place to have equipment which might randomly trip off line especially since
this site is not accessible during the winter months.  Any help or
suggestions are welcome.....  BTW, the 9600 baud experimentation on VHF, UHF
and 220 works great.  In my area with VSOMTN (144.35 APRS @9600 baud) on the
air, it works better than the traditional SOMTN (144.39 APRS @ 1200 baud),
so that is what I am running in my trackers......


Herb, KB7UVC
NW APRS Group, West Sound Coordinator
Our WEB Site:  http://www.nwaprs.info 

> -----Original Message-----
> From: TM-D710_TM-V71 at yahoogroups.com [mailto:TM-D710_TM-
> V71 at yahoogroups.com] On Behalf Of michael_r_mcmaster
> Sent: Wednesday, July 21, 2010 2:55 PM
> To: TM-D710_TM-V71 at yahoogroups.com
> Subject: [TM-D710_TM-V71] Re: Honda Civic Hybrid and TMD710 ...
> Geoffrey-
> I can still make the extension cables, yes.  I took the online store
"offline" since I've
> been extremely busy with my career work and family duties... I just
haven't been
> able to be responsive to the orders/emails as they come in.  If
interested, send me
> an email through the "contact us" web form on the greenlightlabs.com
store.  I'll
> reply as soon as I can... usually over the weekend if I'm available.
> To answer the question about the noise, yes, the "woodpecker" sound is a
> signal coming from *inside* the cable... no amount of outer shielding will
> any difference.  The twisted pairs of the Ethernet cable make no
difference either...
> the signals in the Kenwood design are not a differential pair.  The issue
seems to
> be an over sensitive microphone element; owners that sent their radios in
> service reported that the fix was replacement of the transducer element in
> microphone.  Searching the forum history on the topic should bring up
quite a few
> hits.
> I analyzed the Kenwood cable design when I made the GPS-710... it's quite
> ingenious.  The white wire carries the analog audio, and it is wrapped
with many
> individual strands of wire which are twisted together at the RJ45 plug to
> the ground wire.  These uninsulated wires also serve as a drain wire to
the cable's
> outer foil shield.  The GPS-710 cable follows a similar design, with a few
> to aid manufacture and improve durability... they measurably  outperform
> (already good) Kenwood design.  I run a 20 foot cable on my personal
> with no problems, but my microphone never produced the woodpecker noise.
> -Michael KC0VIN

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