Kenwood: Yet another TM-D710G mic extension cable question

[joltman]

First post from an amateur radio newbie:

I have mounted my 710G behind my second row seats. I need a mic extension cable that can run to the driver's side doors and under their sill plates up to under the dash and finally come out above my info screen. This will be about 15-20 ft. I know that the Kenwood's mic has a crazy pinout. If I were to use a standard CAT5e/6/6a/7/8 cable, the mic line and the DTMF's GND would be shared and would result in the 10Hz "woodpecker" sound. I thought I'd be smart and make my own cable. I got a 25' long CAT8 cable, RJ45 crimping tool, and CAT6 shielded RJ45 jacks. I used the CAT8 cable because each pair of wires is individually foil wrapped. I trimmed the ends off and crimped the RJ45 with the following pinout:

1. BLUE (foil pair 1)
2. BLUE WHITE (foil pair 1)
3. BROWN (foil pair 2)
4. BROWN WHITE (foil pair 2)
5. GREEN (foil pair 3)
6. GREEN WHITE (foil pair 3)
7. ORANGE (foil pair 4)
8. ORANGE WHITE (foil pair 4)

This is if you're looking at the bottom side of the RJ45 (pin side). I also used the pinout from the Kenwood Manuals I found online where 8 is Keypad serial data and 5/6 are mic gnd/mic respectively. I thought that this would be sufficient to mask the clock that DTMF uses. In order to hook the mic's male RJ45 up, I used an RJ45 panel mount coupler. I tested this setup last night. I did not uncoil the 25' of CAT8. I still got the clock signal on the TX. It was actually quite loud. at this point, I'm not really sure where to go. I could try to find a CAT6a panel mount, or I could try to punch down to a standard keystone wall jack. I'm curious what others have done in this situation. I've Google searched, but I've never come across an actual solution, save for the vendor who stopped selling extensions. Any help would be appreciated. Thanks!

 

[AK9R]

No answers, just guesses. I'd look at the crimp connectors to make sure the IDC contacts are clean and straight before crimping, make sure the wires are straight where they are crimped, make sure the open terminals on the plug are clean, make sure the terminals in the RJ45 jack are clean, make sure there's no physical stress on the cables on either side of the jacks.

I'm sure you've seen this, but I copied it from the service manual just in case.

 

[joltman]

@AK9R thanks for the response! I forgot to mention a couple things.

1. The mic is actually an MC-62. I would think the pin out would be the same, but I've not been able to find specific images confirming that. There is no RJ45 jack inside the mic body. I've already checked.
2. I plugged the MC-62 directly into the body and tested TX again. No clock noise. This makes me think that the head's pins are clean. But I could try cleaning the connectors on the new cable.

I was wondering if the short run of the coupler in question could be introducing that noise. It's just an RJ45 on one end, and then an inverted (upside down) RJ45 on the other. Both soldered to a small PCB with straight traces.

The other thing I'm going to try is just a normal patch cable.

 

[joltman]

Whelp. I tried a bunch of things.

• TEST: Plugged in a CAT 8 cable, unmodified
  • RESULT: LOUD, FAST clock noise on RX end.
• TEST: Plugged in short CAT 6 cable, unmodified.
  • RESULT: LOUD, FAST clock noise on RX end.
• TEST: Snipped end off of modified CAT8 cable and punched down to CAT6 jack in correct order, noting that Kenwoods RJ45 pin numbering is opposite of standard RJ45 pin numbering.
  • RESULT: LOUD, FAST clock noise on RX end.
• TEST: Removed standard RJ45 wire to pin 1. This corresponds to Kenwood's DTMF signal.
  • RESULT: SOFT, SLOW clock noise on RX end.

I have no idea where this leaves me now. I have seen the video about fabbing a biscuit jack that has a switch on it to turn off DTMF, but my test above shows that the noise is still present, albeit quieter and for some reason slower.

 

[mmckenna]

How do you have the shield/foil grounded?

 

[joltman]

How do you have the shield/foil grounded?

That's a good question. I'm not. I didn't even think about it. I thought the foil would simply block the EM from coming in. I guess the question is, which pair should I ground, then how? Ground the DTMF pair (which I believe is DTMF and NO CONNECTION)? And then ground it to the GND that's _not_ MIC ground? Maybe strip some of the non-MIC GND and solder the foil to that GND?

 

[ramal121]

Kenwood mics have two grounds. One labled "E" (earth) and the other "ME" (mic earth). Both must be utilized to make the mic operate (they are combined back inside the radio). "E" is return for PTT and other logic signals and "ME" is return for the mic element only.

If you were to dissect a mic cable you would find the mic line only (MI) has a shielding braid around it and connected to ME. This is to reduce induced noise and "cross talk" from the other logic lines.

Using CAT cable, even the overall shielded cable, does not prevent induced noise. Since Kenwood uses dynamic mics that operate in the
10 mV range it is very easy to get a few clams to show up on your transmit.

 

[dfb8085]

First post from an amateur radio newbie:

I have mounted my 710G behind my second row seats. I need a mic extension cable that can run to the driver's side doors and under their sill plates up to under the dash and finally come out above my info screen. This will be about 15-20 ft. I know that the Kenwood's mic has a crazy pinout. If I were to use a standard CAT5e/6/6a/7/8 cable, the mic line and the DTMF's GND would be shared and would result in the 10Hz "woodpecker" sound. I thought I'd be smart and make my own cable. I got a 25' long CAT8 cable, RJ45 crimping tool, and CAT6 shielded RJ45 jacks. I used the CAT8 cable because each pair of wires is individually foil wrapped. I trimmed the ends off and crimped the RJ45 with the following pinout:

1. BLUE (foil pair 1)
2. BLUE WHITE (foil pair 1)
3. BROWN (foil pair 2)
4. BROWN WHITE (foil pair 2)
5. GREEN (foil pair 3)
6. GREEN WHITE (foil pair 3)
7. ORANGE (foil pair 4)
8. ORANGE WHITE (foil pair 4)

This is if you're looking at the bottom side of the RJ45 (pin side). I also used the pinout from the Kenwood Manuals I found online where 8 is Keypad serial data and 5/6 are mic gnd/mic respectively. I thought that this would be sufficient to mask the clock that DTMF uses. In order to hook the mic's male RJ45 up, I used an RJ45 panel mount coupler. I tested this setup last night. I did not uncoil the 25' of CAT8. I still got the clock signal on the TX. It was actually quite loud. at this point, I'm not really sure where to go. I could try to find a CAT6a panel mount, or I could try to punch down to a standard keystone wall jack. I'm curious what others have done in this situation. I've Google searched, but I've never come across an actual solution, save for the vendor who stopped selling extensions. Any help would be appreciated. Thanks!

Joltman this be an easy project. It seems to me that you may be over thinking this thing. I have used several different radios over the years and have extended the head and body lots of times.

Do this by 2 ways...either incorporate the kenwood cable and buy you a "Straight Thru" double female inline coupler and just get a long enough cat6 with rj45 plugs already on it making sure it "Straight Thru" also. Dont get connectors that are over because then everything flipped and your really screwed. Very easy just plug and go.


2nd way......just buy the best "Straight Thru" cat cable with rj45 jacks on it that is long enough to do the complete run and be done with it.

 

[kayn1n32008]

I'm not.

Ding ding.