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Message |
    
Vanillagorilla
Member
Username: Vanillagorilla
Post Number: 85
Registered: 4-2005
| | Posted on Saturday, July 16, 2005 - 11:44 am: | 
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I sold my Superstar3900HP Gold to a friend and am currently testing out another friends 2000GTL for possible purchase...PERFECT and LOUD with one small problem (?)
If I connect a Cobra/Uniden 4pin to 5 pin "adapter" so I can run my 4 pin mics I seem to have a receive issue with the D-104 lollipop and/or Piezo mic. When I plug those mics in (without keying up) I hear a static/light squeal in my receive that sounds like the guy I'm talking to is off freq....here's the wierd part...with these two mics only mind you...I have to turn down the dyna-mic to 12-1 O'clock and they clear right up!
I can use other 4 pin power mics with no problem (even the M6C 4pin) except being told the radio is too loud  ..shouldn't we all have that problem
Only thing I know is that the 2 mics in question are my LOUDEST mics. Even with either of those mics set at 12:00 and dyna-mic at 1 O'clock the reports are very loud and clear but please turn it down. Any clues as to why a mic should effect recieve that way? Is it just the way it is? If I rewire either of these to 5pin I wonder if it'll have the same problem? My friend ran this rig with a silver eagle and did not have this problem. My mics work fine on any other radio of mine...(GrantXL...148GTL ect..)
One last thing..even turning down these mics to "0" produces the same thing unless I turn the radios "dyna" down as mentioned....there you have it...any ideas or explainations?
Hank '905 |
Vanillagorilla
Member
Username: Vanillagorilla
Post Number: 86
Registered: 4-2005
| | Posted on Sunday, July 17, 2005 - 3:22 pm: |
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..as a side note..just noticed the same thing happens on the Grant in the mobile using the HiPo Piezo mic (and 4 to 5 adapter)...any tech's on duty?
Have since decided to pass on the 2000 anyway..$200 ain't bad at all for this sweet and LOUD rig but I'm more of a mobile unit guy anyway...too big for my bench!
Still like to know what causes that receive issue though..for future ref ya know?!
Hank '905 |
Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 558
Registered: 6-2004
| | Posted on Sunday, July 17, 2005 - 6:24 pm: |
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the microphones could be wired incorrectly or there could be something wrong with the adapter. Without looking it's difficult to say. You'd be surprized how many microphones will work even if they're wired incorrectly according to the manufacturer - especially if they were made to work with relay switched radios and not diode switched radios. |
Vanillagorilla
Member
Username: Vanillagorilla
Post Number: 87
Registered: 4-2005
| | Posted on Monday, July 18, 2005 - 4:56 pm: |
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Hmmmm...wired both up myself to cobra/uniden specs...I know what yer saying though. I had the adapter apart and all looks well inside. Perhaps I need to omit one wire from inside the adapter? Like where the shield and ground are now wired together? Hmmmmm...
Hank '905 |
2600
Advanced Member
Username: 2600
Post Number: 571
Registered: 7-2002
| | Posted on Tuesday, July 19, 2005 - 1:41 am: |
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Aw man, not this one again. The "Four-wire mike on a Five-pin radio" problem.
The extra pin on the 5-pin radio is to provide TWO (separate) ground circuits. Pin 2 is the ground for ONLY the mike's audio current. Pin 4 is the (second) ground for JUST the transmit/receive switch hooked to pins 3 and 5. Keeps the current flow into the T/R switching circuits from also flowing into the audio circuit.
That's why the Astatic and Turner mikes have six wires. The shield (audio ground) and the blue (on Astatic) get tied together for a 4-pin radio. That one has ONLY one ground, on pin 1, so the two grounds inside the mike get combined on one pin.
On a 5-pin radio, that adapter comes down to three choices.
1) Hook both ground pins on the radio side together.
2) ONLY connect the pin 2 (audio) ground.
3) ONLY connect the pin 4 (T/R keying) ground.
Typically one of these three choices will be the least annoying. Combining the two ground circuits by jumping pin 2 to pin 4 tends to make the odd receiver noises worst. Using just one of the two ground pins tends to make transmit feedback noises worst.
The only way I know to get around this problem is to change the radio itself to a 4-pin socket. It requires putting a relay inside the radio. The relay hooks to the "Pin 4 ground" wire, keeping the two ground circuits separate.
A commercial "Roger Beep" board (the one with a relay on it) will also do this, but only if you cut the circuit-board trace to the relay's 'ground' pin. The "pin 4" wire goes there. This separates it from the beep board's ground circuit that's connected to the black wire on the beep board.
And if you discover a simpler solution that doesn't create "weird audio noise" problems, that would be cool.
A mike with only one ground wire just doesn't agree with a radio needing two separate 'ground' wires.
You could try hooking JUST to pin 4 or JUST to pin 2 with the wire from Pin 1 on the 4-pin side. My experience is that you'll just trade funny receiver noises for funny transmitter noises.
73
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Hollowpoint445
Advanced Member
Username: Hollowpoint445
Post Number: 565
Registered: 6-2004
| | Posted on Tuesday, July 19, 2005 - 5:08 pm: |
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I've never encountered or heard of this problem. I read in a newsletter from the 80s that what's necessary to replace the 5 pin jack with a 4 pin jack on a Cobra 2000 is to wire the 4 pin jack parallel to the existing 5 pin jack, but use only the audio ground - don't connect the switching ground. So if you want to experiment, you can try removing the ground connection to pin 4.
Giving this a little thought, the switching ground is DC while the audio ground is AC. If you put a resistor inline to the switching ground, and connect a capacitor just before the resistor and then to the audio ground, it should ground any audio to the right pin and the switching current to the right pin.
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Vanillagorilla
Member
Username: Vanillagorilla
Post Number: 88
Registered: 4-2005
| | Posted on Thursday, July 21, 2005 - 2:36 pm: |
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Sheesh! Alrighty then..I'll consider this "explained" thanks both for your wisdom!
Learning every day.
Hank (Gave up on the adapter and use 4 pin mikes only on 4 pin radios. ) |
