[aprssig] Kenwood TH-D7 GPS connector grounding

Greg D. ko6th_greg at hotmail.com
Fri Sep 19 01:14:38 CDT 2008

Hi all,

An update...  I've removed the separate battery pack, and wired in a 78L05 3-pin miniature regulator.  I'm picking up power from the Batteries America BT-11h pack by drilling a small hole in the side, and snaking a wire down to the bottom of the first battery string.  At the bottom of the pack is a metal contact for the positive terminal, and it's got a hole in the middle.  So, I stuck the bared end of the wire into the hole, and pushed the first battery down the slot, holding it in place and making contact with both the battery and contact point.  Ground comes from the GPS serial connector.  

I'm still working on the mounting, but for now I just lashed the board to the back of the belt clip.  Picture at:  http://home.wavecable.com/~ko6th/IMG_0235b.jpg.  The regulator is that little black thing behind the 1uf input capacitor, right above the big black wire that heads to the back of the board.  I've had no issue with RF interfering with the GPS, even though the GPS is right next to the transmit antenna.

The issue about the efficiency of the power system has turned out to be kind of a "don't care".  It doesn't show up well in the picture, but the radio and GPS are turned on.  I turned them on around 07:45 am today, and it's now about 10:45 pm.  The radio has been on continually all day, sending a beacon every 5 minutes at high power, and it's still running.  (Pack voltage is down to 7.05v right now.)  Batteries are Sanyo 2700 mAh AA cells, charged in a Powerex MH-C9000 charger.  I think the D7's "high power" with a 7.2v nominal voltage means about 2.5 watts, right?  I certainly would like more, but 15+ hours of base operating time, with the GPS running, is REALLY nice.  And I don't think the 3db reduction from full power makes much difference, especially with an extended whip antenna attached.

Greg  KO6TH

> Date: Sat, 13 Sep 2008 00:01:17 -0700
> From: wa8lmf2 at aol.com
> To: aprssig at lists.tapr.org
> Subject: Re: [aprssig] Kenwood TH-D7 GPS connector grounding
> Greg D. wrote:
>> Hi all - Dave, Bob, Patrick, Steve,
>> Wow, this is a bit more complicated than I thought it would be.  A couple of items:
>> 3.  So, that diode (D3) also prevents any juice from the battery from being available at the power plug.  But, I think this means that if I can get a wire to the positive side of the battery pack (way down deep inside), I can get juice from either the battery or external power (through the battery pack connection to the radio, since they're always connected), and I can pick up the ground side from the ground side of the GPS plug (NOT the battery pack!).  Yes?  And, at that voltage, I'll need a 5v regulator; a simple 3-terminal one should do.
> The standard 3-terminal regulator is horribly inefficient.  When you 
> drop 12VDC to 5VDC with the standard 3-terminal analog regulator (i.e. 
> 78xx-type) you will be dissipating more power than you use. [7 VDC at 
> 75mA = .525 watts wasted while 5 VDC at 75mA = .375 watts delivered to 
> load.  
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