Kenwood: Mic Extension TM-71

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KK4JUG

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I have a TM-71 mounted under the front passenger seat of my '16 Sorento with the head mounted on the side of the console. The mic cord plugs into the unit under the seat but the coiled cord is too stiff to be convenient to use from the driver's seat. The mic plug appears to be an RJ-45. Would a standard short RJ-45 extension cord work as an extension cord?
 

wrath

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Yes a standard cat 5 cable with a duplex connector works like a charm on the 71 and the 710g it's older sibling , if you ever want or need to extend the head same deal and your Good to go.

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Thunderknight

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Yes, I'll confirm this as well. I did that for about 6 or 7 years....to get the mic from under the rear cargo floor to the front.
 

KK4JUG

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Thanks, guys. Wrath, you talk about extending the head distance but I may want to shorten the connection because the distance from the head to the radio is only about 18".
 

wrath

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Yeah it is a rather generous length out of the box , but you never know when your going to pick up that Greyhound bus you have had your eye on (lol).I made the mistake of buying the cable extension kit myself.

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bharvey2

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A word of caution: While a CAT 5 or 6 cable is electrically correct. Using one will more than likely introduce a choppy "helicopter" like sound into your transmission. In the OEM mic extension cable, the MIC conductors are shielded within the cable. No reason it has to be inside the cable though. I rolled my own but used a separate, small diameter coax specifically for the MIC conductors then encased the two cables in a length of wire loom. No noise.
 

KK4JUG

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bharvey2, I'm gonna try it without the shielding first. It's a relatively new vehicle with Bluetooth, etc. so some of the noise may already be shielded. If that doesn't work, I'll do it your way.
 

bharvey2

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bharvey2, I'm gonna try it without the shielding first. It's a relatively new vehicle with Bluetooth, etc. so some of the noise may already be shielded. If that doesn't work, I'll do it your way.
I'm not sure the noise is necessary picked up from external sources. It might be clock pulse of some sort being generated by the radio itself. Nothing wrong with trying however. Just keep the extension cable as short as possible and route using good installation practices. Also be sure to request a few radio/audio checks. From your side of the radio there is no indication that there's a problem.

Good luck my friend.
 

cmdrwill

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It is NOT the shielding on the cable, but mic and data signals wind up on the same pair right next to each other and you wind up with clicking in the mic audio. So you need a different wiring to avoid signal crossover and transmitted 'noise'.

Kenwood does NOT follow the standards for pins either..
 

bharvey2

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It is NOT the shielding on the cable, but mic and data signals wind up on the same pair right next to each other and you wind up with clicking in the mic audio. So you need a different wiring to avoid signal crossover and transmitted 'noise'.

Kenwood does NOT follow the standards for pins either..
I may have been mistaken about the CAT5 wiring but I recall terminating my own CAT6 cable following Kenwood's wiring diagram. I had noise show up during transmit. When I used used CAT6 but lifted the MIC conductors and wiring in the shielded/coax, the noise went away. I'll see if I can find the information about the shielding of the MIC conductors.
 

bharvey2

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Hoping this works: I'm trying to attach a PDF of the TM-V71A service manual showing the mic cable and shielding. It should be page 90 out of the service manual
 

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wrath

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I have been using standard cat5 on my mic for my home instalation of my 710g and no noise what so ever , if it helps any ,I do have ferrite chokes on the cable though .

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W9BU

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As the service manual snippet in bharvey's post shows, the Mic Audio is on pin 6 and the ground for the mic audio (MIC E) is on pin 5. The OEM Kenwood cable has a shield around the wire used for Mic Audio only. The OEM Kenwood cable lands that shield on pin 5. There are other lines in the cable that carry a clock signal from the radio to the microphone (believed to be used for the DTMF generator in the mic). Because of the proximity of the clock signal and the mic audio, that clock signal radiates into the mic audio. Kenwood went to a lot of trouble to keep that clock signal out of the mic audio, hence the special cable they use.

Ferrites on the cable may knock down RF on the cable, but do nothing to keep the clock signal out of the mic audio.

Overall shielded network cable just traps the clock signal inside the cable with the mic audio.

CAT5 vs CAT6 changes the rate of twist of the wires in the cable, but the clock signal is still there and can still radiate into the mic audio.

Changing what wire you use in the cable doesn't really address the close proximity of the clock signal to the mic audio. Telephone cables (aka twisted pair) work because twisting the two lines in the pair tends to reduce the common mode interference. Even if you put the mic audio and MIC E on two lines of a twisted pair, the clock signal is still there and the twist may not have any impact.

Your best solution is to buy the Kenwood mic extension kit. But, it's expensive and hams are cheap. There was a guy (Green Light Labs) who obtained a supply of cable just like what Kenwood uses and was building aftermarket extension cables, but he's moved on and I don't believe he is building cables anymore. His web site is still up and you can try contacting him, but you may not get a positive response.

All of the above suggested fixes may nor may not work to eliminate the ticking in your transmitted audio. If they work, great! If they don't, well at least you understand the problem.

There are two more fixes not mentioned may also solve the problem. The RJ-45 connector is susceptible to losing contact if the cable is stressed causing the connector to be pulled one way or the other. You can try re-positioning your cable to see if less stress is put on the connector. That might make the problem go away. You can also try a little bit of contact cleaner to see if that knocks the oxidation off of the connector thus improving the signal.

This is an old problem that has haunted users of the TM-V71 and TM-D710 since the beginning.
 

KK4JUG

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Thank, guys.

RE: Green Light Labs--"Due to personal time constraints, I'm unable to accept orders on these cables at this time. This product will be reported as "out of stock" if added to your cart."

I may either relocate the radio so that the mic cord doesn't have to extend as far as it does or spring for a $20.00 extension. I think I'll try those....in that order,
 

WD8NUP

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Amazon Has Just What We Need

https://www.amazon.com/Ethernet-Cable-Internet-Shielded-Snagless/dp/B00GBBSWAC

All twisted pairs are individually shielded and then the entire cable is also shielded.
It is referred to as Cat 7 cable. I am not sure if all Cat 7 cable is made this way or not.
All you need to do is add a RJ45 coupler at the end to plug your microphone into.
A 15' cable is $9.00.
I see they are offered in different lengths too.
 

W9BU

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Not so fast.

In Cat 7 cable, each of the four pairs are individually shielded plus there is an overall shield for the bundle of four pairs. In the Kenwood mic cable, the Mic Audio is on pin 6 and the Ground for the mic audio (MIC E) is on pin 5. In TIA/EIA T568A or T568B cable pairing, pins 4 and 5 are a pair and pins 6 and 3 are a pair. So, my assumption is that in the referenced Cat 7 jumper cable, the Mic Audio and the Ground would still be in separate pairs. I don't think Cat 7 cable solves the issue with the design of the Kenwood mic cable.

Here is the mic cable wiring diagram from the service manual:
 

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WD8NUP

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If that is the case I would just cut the ends off and put new connectors on making sure that I use the shielded pairs where needed.
 

FKimble

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Just checked the cable pinout in my owners manual, slightly different from above:

1- no connection
2- DC 8V, 100mA max
3- GND
4- PTT
5- GND (MIC)
6- Mic, 600 impedance
7- No Connection
8- Keypad serial data

Read on the Yahoo group for the 71A that a flat cable would put more separation between the serial line and the mic line and would help reduce/eliminate the motorboating. Seems to work on mine. Radio mounted in front of console in my ranger. Mic cord was obviously not gonna last long as much as it was getting stretched(also pulling on connector). An 18 inch piece of flat CAT5 secured midway to eliminate pulling on connector also provided just enough extra to make mic cord long enough. 3 fixes in one, not pulling on connector, added link and separated the critical wires. It seems to have worked on mine. Funny thing, I had the radio a year before it started motorboating.


Frank KK4YTM
 
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