Tecpro AD913 PMR Wiring

[AnthonyHunt]

Hi all,

Wonder if anyone can help. I'm in the process of making a wiring loom for PMR's to interface with the comms. I have all the correct components.... I think, but I'm not getting where I want to be. I'm wiring for Baofeng 888's.

As far as I can tell the wiring on the Canford XLR should be:

• Pin 1 to 3.5mm sleeve - mic gnd
• Pin 2 to 3.5mm ring - mic +
• Pin 3 to 2.5mm sleeve - speaker gnd
• Pin 4 to 2.5mm tip - speaker +

When connected I get a lot of hum and noisey RX radio. If I disconnect the mic lead from the radio I get pure signal. Note I don't have any putt from the Tecpro yet. I believe this should be working by the AD913 making the mic gnd and speaker gnd connection on holding the Tecpro call button. This is all working as expected on my Motorola Cobra units but they use a single 2.5mm 4-pole connector.

If anyone has this working, or the genuine Canford cable, please could you share the wiring?

Thanks,

Ant.

[sunray]

Pin 2 is mic + for the Tecpro therefore it needs to come from the radio loudspeaker via a resistive attenuator.

Pin 4 is the headphone output from the Tecpro therefore it needs to go to radio mic via a resistive attenuator.

Pins 1 and 3 are both GND without any sort of switching.

 

The way I have done it is to use an IEM system from pin 4 rather than the transmitter part of a 2 way radio which makes the system work full duplex, just like the rest of the system.

I happen to have used a 'HS121' for the interface rather than a beltpack but can't imagine the XLR will be wired any differently.

[timsabre]

It's probably the dc bias on the mic line, put a dc blocking capacitor in the mic line 1uf with positive towards the tecpro pack.

[paulears]

I'm not sure which way around you are having the problem - the hum and noise - is this heard on the radio, from the loop system or do you mean the radio receive INTO the loop system is clean but only when the mic input to the radio is removed? The Baofengs are a bit leaky - and connecting external sources to them often seems to then couple the RF output when they go into transmit back up the spout, so to speak. I second the need to drop the audio down quite a bit before feeding to to the radio.

 

Could we have a bit more into on exactly what happens - transmit ok, but receive not or vice versa or both - and how disconnecting things clean it up?

[AnthonyHunt]

Hi folks,

Thanks for your reply’s. I’ve had all of those issues that you mention in terms of wiring this via headset packs etc. Note that I’m using the Canford Tecpro AD913 Radio Interface. This should provide me with everything mentioned. I’m pretty sure the problem is with the wiring of the adapter cable as, like I said, my official PMR JNR cable is working fine.

What I said in the previous post is still relevant. With both mic and speaker cables attached to the radio there is constant noisy output from the radio with or without transmission. With the speaker only cable connected I have no noise when not receiving and clean output on receive. I have no transmit from Tecpro to the pmr so can’t tell you what the Tecpro output is doing.

Thanks,

Anthony.

[timsabre]

Sorry failed to read the post title, assumed you were using a beltpack.

 

Where are you hearing this radio noise, on the comms loop?

 

This diagram appears to suggest that if you connect mic gnd / sleeve to spk gnd / sleeve, which the canford unit may well do as a common ground, it will put the radio into PTT mode - might this be what is happening?

 

http://www.miklor.com/COM/images/dualplug.jpg

[sunray]

Sorry failed to read the post title, assumed you were using a beltpack.

Sorry so did I as this is the only way I have interfaced radio and Tecpro. Ignore my previous suggestions on the 913 connexions as I have no experience with them.

img src="http://www.miklor.com/COM/images/dualplug.jpg"

This is fairly typical of the wiring for a handheld radio's speaker mic but they do vary between makes. In this version the 'mic gnd' will have DC volts on it in receive mode.

My guess for this mic plug layout and please bear in mind I don't have experience of this:

Pin 1 and 5 - LS GND 2.5 tip

Pin 2       - LS +   2.5 sleeve

Pin 3 and 6 - Mic GND 3.5 sleeve

Pin 4 - Mic + 3.5 tip

 

So do I read it correctly that the call button on the wired station speaking will put this into TX?

 

And I second the blocking capacitor.

[AnthonyHunt]

Thanks again for the reply's.

That was actually the same diagram I was working to, plus a very odd looking Canford diagram.

https://www.canford....20Issue%205.pdf see page 4 fig 1 & Page 2 fig 1.

As far as I could work out pins 5&6 were empty? Maybe I should be looking at a different configuration on the Canford diagram? Hence why I was looking for the wiring of the official lead. I'm pretty sure it doesn't have any capacitors in as my official jnr lead is just cable.

The "static" does come over the comms system. I know the system to be good and silent when there are no mics live. And as I said, the comms is clear without the 3.5mm mic lead in.

In terms of the ptt, I've also connected the grounds which didn't change anything.

Yes, you're correct. Pressing the Tecpro call button for longer than 2 seconds is supposed to press the ptt until the call button is released. Meaning you have at least some control over what goes over radio.

[sunray]

I also used this same website version of the document to glean the connexions but sadly some of the lines have not scanned properly.

I have attempted to come up with a prototype from this document and the mic in Tims post but I don't know if Tims is the correct version for your radio.

P4 fig1 may not be correct for your radio, I know Wouxun and Yaesu are different and my first guess would be that Wouxun and Baofeng are more likely to match.

 

I have worked with radios interfaced onto 3 systems now:

1st was with a moto HH radio and all commercial cables. I was on the radio and for half the time had no idea what was going on as I only heard when someone pushed the button.

 

Second time, I 'built' the system using a belt pack and a collection of HH radios, Connected to 'headphone out' was a VHF radio in permanent transmit, Connected to 'mic in' was a UHF receiver. Operators carried 2 radios, one for talking and one for listening, so the radio user could hear permanently just like wired stations.

The complication was radio operators tended to forget to release the PTT while chatting, which was OK as long as they weren't trying to chat to another radio operator. So I added further receiver so both radio operators had their own talk channel.

Third system which has just come out of a panto run, I used an IEM system for base transmit which was very successful.

[AnthonyHunt]

Hi sunray,

Thanks for the info. I'm interested in how you got the iem working?

I've tried this all again this evening starting from scratch. What I can confirm so far:

• Pin 1 to 3.5mm sleeve - alleged mic gnd
• Pin 2 to 3.5mm ring - alleged mic +
• Pin 3 to 2.5mm sleeve - speaker gnd (as diagrams)
• Pin 4 to 2.5mm tip - speaker + (as diagram)
• Pin 5 to pin 1 (as diagram)
• Pin 6 to pin 6 (as diagram)

This has given me ptt when pressing the call button as described. And audio from the radio side being transferred onto the comms circuit. I still don't appear to have any comms sound going to the radio though? And I still have a constant buzz from the radio side entering the comms circuit.

I checked the voltage across pins 1 and 2 when the radio transmits and it pin 2 goes positive. However, when not transmitting pin 2 is negative by about 1.3v? And, here's the real catch; when releasing the ptt after a transmission the noise on comms vanishes momentarily. I'm going to guess that this is where the voltage on pin 2 goes to zero before becoming negative? Worth putting a diode across pin 2? Is it worth my swapping pin 1 and 2?

Thanks for your thoughts.

Ant.

[sunray]

First I stress again that I don't know this product at all but from the Canford sheet you have linked to, I think you are barking up the wrong tree.

 

The Sheet describes  1&2 as RX, The sheet shows 1&2 going to the INPUT of an amplifier stage,

The sheet shows 1&2 being connected to the 2.5mm plug.

 

You describe 1&2 being connected to the 3.5mm plug.

 

IF your radio requires the sleeves of both plugs to be connected together for PTT then you have correctly wired that part.

 

It is quite possible that that the 'loud' LS circuit may leak into the 'sensitive' input of the 913 and potentially with noise and/or distortion if you have the I/p & o/p confused.

 

Can I suggest you LISTEN on the 913s and the radios connectors [with the aid of an amplifier if required] to actually find out where the sound comes out of and then by deduction where the sound has to go into.

 

My scheme for the IEM was simple,I used a standard belt pack and connected the Tecpro headphone output to an isolating transformer and 10Kohm volume control then to the IEM base station input [and additionally to a Canford powered speaker].I connected the LS output of a Motorola mobile radio [used as RX only] to a 4:1 transformer to step the voltage down as well as isolation then a 10Kohm volume control and 1uF non electrolytic to the mic input of the Tecpro.

The transformers may not have been required but I just included them 'in case' as I wasn't going to be in attendance.

[sunray]

Good old Cut and paste... this last job with IEM was customers own Baofeng HH for the receiver.

[AnthonyHunt]

Buy the man a cigar... in fact buy him the whole box!

I seriously owe you beers!

I went all out and went for a straight swap over without testing. After all, I can only blow it up once.... right?

Turns out you were spot on. So, the wiring layout on pg 2 fig 1 is correct and so is fig 2. The misleading diagram was pg 4 fig 1. Which shows the 2.5mm and 3.5mm connectors the wrong way around.

So the correct wiring is:

• Pin 1 to 2.5mm sleeve - speaker gnd
• Pin 2 to 2.5mm tip - speaker +
• Pin 3 to 3.5mm sleeve - mic gnd
• Pin 4 to 3.5mm ring - mic +
• Pin 5 to pin 1
• Pin 6 to pin 3

This has given me crystal clear comms on both sides. The call button ptt is instantaneous and doesn’t have the 2 second delay previously expected from documentation. A bonus. Side note, turn power saving off on the connected radio as it pips.

From your previous iem solution, I guess that the radio connected crew had both a radio and iem pack?

 

[sunray]

I guess that the radio connected crew had both a radio and iem pack?

 

Glad to have been of assistance, it's actually quite a common problem that inputs and outputs get mixed up, usually due to confusing descriptions.

 

I've had this issue a few times, especially for interface equipment. Example: a hired in OEM TBU with male XLR labelled 'input' and female labelled 'output', it had been wired into the mixer using standard XLR cables and 2 gender benders so o/p of mixer went to 'input' and I/p to mixer came from 'output'. It didn't work but wiring input to I/p and o/p to 'output' worked fine. I also find 'REC IN' and 'REC OUT' are often confusing.

 

 

The first time I used a radio on a Tecpro type system [I was the portable station] I missed a lot of the useful messages as the speaker didn't 'push the button', so when I installed a system some time later with a couple of radios I went for the full duplex approach with permanent base transmit. That way the radio user becomes a 'clone' of belt pack users. See the other recent thread too.

 

Worth remembering that not all radios use 2.5 plug for speaker and 3.5 for mic, Example the old Icom IC2E style radios.

 

See radio and comms interaction.

[AnthonyHunt]

I've just been looking back at your breakout circuit. It sounds like a really neat option. Have you considered marketing it? Especially as Maplin's are likely to close the components could be going cheap?