[MRCA] [armyradios] 4 pin power connectors...foiled yet again!

[W2HX]

Thanks, Sean for the thoughts. I think the cable is ok. But there is definitely a difference between the pinouts of the Harris power supply and the pinouts of the sincgars base (not sure how the PRC-74 got into this discussion, I might have missed it originally).  I guess I would be interested to take "a few radios" that use this MW 4-pin style connector and see what they use for pin outs.  I wonder if there is a "general consensus" on what pins carried positive and negative poles.

If the Harris is the "odd man out" and does not conform to the "majority" of pin outs used out there, it just seems strange. If their power supply was not meant to be able to be used with other equipment sharing the same connector, then why use the same connector? Why not just use some MS series connector where you can be sure that someone isn't plugging something into your power supply that is potentially dangerously incompatible?  Seems like an unfathomable design decision, but I defer to Harris' extremely capable design engineers (who have surely forgotten more than I'll ever know about design!)

I have chosen to take the advice of K4CHE and cut one of the cable in half and rewire to do what I need.  This is one bear of cable! I have never experienced a cable quite like this. First, it is about 0.5" in diameter. Next, look at its construction (see picture below). A very thick rubber jacket. Then, not only does it have a braided shield that would stop a bullet, but it has an inner conduit that the conducts pass through! This is not just another insulator, the wires are free to move inside this conduit. Strange (to me). Just cutting through this thing was a challenge!  
http://www.w2hx.com/x/RXMTProject/cable.jpg

One mystery solved - why only three out of 4 pins connect through - there are only 3 conductors. I addition, two of the three are of a larger AWG than the third! Amazing. I can only imagine what this cost the government.

Tomorrow, I will attempt to re-solder up the cable and try it out again. 
 
73 Eugene W2HX
 
From: armyradios at yahoogroups.com [mailto:armyradios at yahoogroups.com] On Behalf Of Sean Kelly
Sent: Thursday, September 13, 2012 11:01 PM
To: armyradios at yahoogroups.com; xraydeltaone at hotmail.com
Subject: RE: [armyradios] 4 pin power connectors...foiled yet again!

  

>Arrghhh! Why can't things as simple as +24V and ground be simple! 

Eugene,


Armed with the knowledge that I've been rated as an "armchair expert" in the past, here is what I can offer.


The PRC-74 uses a power connector that has two pins positive and two pins negative. I think it is to carry the whole 4.5 amps that the radio can consume during key down. The wires are small, the pins are small. It looks like just one of each wouldn't be enough.


Perhaps your radio or your cable was designed with another, parallel purpose in mind, besides its original application. Perhaps both purposes were created at the same time, or the cable was created by a manufacturer that wanted to capture an additional contract for a radio (or other piece of equipment) that would require higher current at a later time, and wanted to use an off-the-shelf item for the future gear.


Umm, you can tell I can't remember exactly what you said about which wire went where by now, right? Yup, I've forgotten. But you get the jist of my theme: there's a reason for the mismatch, we just don't know what it is. Oh, final attempt: It could be a SNAFU (Situation Normal, All Fauled Up) - your cable got made wrong.



Sean
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