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Speed Air helmet connection to PMR


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Has anyone had problems with their "Speed Air" helmet radio connection?

I added an extension cable to change the two (Twin) pin plug to a single 2.5m so that it would work with my Cobra MT 975.

As I have two extension cables I tried them both and one just receives but does not allow to transmit and the other doesnt do anything?

Any sugestions?

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Hi Duncan,

I'm sure this can be made to work but the configuration of the stereo 2.5mm jack on the Cobra is in question.

I have worked out a few of the anomalies of different 446 radios and unfortunately they don't all follow a 'standard'.

Are you at all technical, do you have a multimeter and a spare 2.5mm stereo plug?

Alan

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Hi Alan,

The short version is .... NO

I, stupidly, assumed that it would be as easy as 1...2....3 to add a converter cable from a twin pin (2.5mm and 3.5mm) to a single 2.5mm pin.

Today I was made aware that the twin pins vary in size and distance from each other depending on the radio manufacturer. I was also told that some pins have one, two or even three rings.

I have emailed "Speed Air" asking if they sell a special cable to adapt to a Cobra MT-975 but am doubtful.

As I'm not very technical I am assuming that I will have to change radios (which I dont want to do) but if I do then I will most probably go for the Intek MT-5050 which is compatible.

I'm open to sugestions but dont want to strip cables, headset or radios to achieve success.

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OK Duncan we can try a couple of simple things to try to identify the configuration.

I'm assuming you have bought one of the aftermarket twin pin to 2.5mm adapters.

Usually the 3.5mm pin on the headset is the receive (phones) connection. Turn the twin pin connector around so only the 3.5mm plug goes into your adapter with the 2.5mm pin in free space. Does the headset work on receive?

Now plug just the 2.5mm pin into the adapter, push it in slowly and see if the radio goes into transmit mode briefly as the plug is pushed in.

Once fully in push the PTT button, does the radio transmit? With sound or without?

Cheers,

Alan

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Some Cobra radios use an unusually long 2.5mm jack. I believe the wiring is standard but if you don't use the long jack the connections won't meet properly. IIRC there is an adapter available from Maplin that takes the standard 2 pin into a long single 2.5mm pin that should sort you out.

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OK!

The receive (RX) is the 2.5mm! Yes it works when I just plug that in my twin pin to 2.5mm adapter.

Now plug just the 2.5mm pin into the adapter, push it in slowly and see if the radio goes into transmit mode briefly as the plug is pushed in.

No!

Once fully in push the PTT button, does the radio transmit? With sound or without?

NO!

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OK some extra info!

The extreemly long 2.5mm adapter which fanman was talking about. When this is insirted fully the radio shows a constant (TX) and other radio shows constant (RX) but no sound eitherway (Except RX radio has soft static sound) + PTT does not work.

When removing 2.5mm jack the roger sound goes on (RX) radio

Does this help?

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OK!

The receive (RX) is the 2.5mm! Yes it works when I just plug that in my twin pin to 2.5mm adapter.

Now plug just the 2.5mm pin into the adapter, push it in slowly and see if the radio goes into transmit mode briefly as the plug is pushed in.

No!

Once fully in push the PTT button, does the radio transmit? With sound or without?

NO!

I'll number these points so we (I) don't get confused :? Use with the normal length adapter.

1. This could be slightly awkward. The 'standard' is the 3.5mm being the phones (RX). Area you certain it's the 2.5 for the RX? At least one half works.

2. If the 2.5 is RX then slowly inserting the 2.5 won't give TX. Try slowly inserting the 3.5, any TX?

The fact that the extra length adapter put the radio into continuous TX shows external PTT is possible.

I have one radio where the only way to PTT from the headset is to set the radio into VOX mode.

I've sent you a PM, cheers,

Alan

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Hi Alan

I received a reply from Cobra (see below)

For models that use a single jack:

Plug size: 2.5mm (3/32”) stereo plug

Microphone Type: Electret

− The tip is the speaker

− The middle connector is the microphone

− The shaft is ground

The PTT switch is wired in series with the microphone element.

If the PTT function does not work or is unreliable, place a 2.7K ohm resistor across the

microphone element.

Not sure if this is any help .... probably not!

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Hi Duncan,

If the PTT function does not work or is unreliable, place a 2.7K ohm resistor across the microphone element.

That's exactly what I expected.

If you can modify your microphone , or find someone to do it I don't know, but there could be another way for it to work.

Set the radio into VOX mode, press the PTT and talk and the radio should transmit.

Let me know, cheers,

Alan

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Hi Alan,

I just switched the VOX mode on and tried but without success!

It works fine without the headset but the same results as before with headset. So no joy!

I have compared both my 2.5mm pins with the diagram and both seem to be the same but as mentioned before only one of these receives sound and both don’t transmit.

I'm puzzled as to why this is!

Who would be able to modify something like this? I wouldn’t know where to start looking!

Duncan

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