Batboard

I have a motorcycle A4 rotary Spectra that I would like to use with a helmet (in a car). Of all of these motorcycle radios that were produced for police departments, surely someone has come up with a economical helmet kit or interface that is compatible with the Spectra.

Question #1 is: What is out there that is economical? IE, I don't want to drop $200 on a purpose-built something when I can modify an off-the-shelf FRS type headset and build an interface for $50.

Next question is: I had the radio on the bench last night and was experimenting with the 15pin connector on the rear of the radio. The PTT circuit is fairly straightforward; I can put the radio in to TX mode by connecting the PTT line to digital ground. What is strange is that the MIC HI line has no effect. I don't get a pop or a click when the radio is in the TX mode. I tried using Digital Ground as MIC HI return and nothing. I do see around 8v on MIC HI referenced to Ground.

Any suggestions are appreciated!

Some Spectras do not have the correct jumpers on the command board to support MIC Hi in the 15 pin ACCy connector.
Did you measure about 9 volts on the MIC Hi pin? That would indicate the jumpers are in the correct places.

Any helmet mic, for use with a Spectra, would need the mic preamp in it, AKA carbon mic circuit.
Headsets for portable radios and FRS do NOT have the preamp.
A DC blocking capacitor and series resistor can be used to provide audio to the ear piece without over driving it or
shorting out the audio amplifier in the Spectra radio.

I measured around 8 volts from MIC HI to digital ground. I don't know where it should be referenced. Seems like there should be an analog MIC LO return like on the control head?

Regards,
Steve
KW5CQ

Steve,

In the control head, MIC Lo is tied to analog ground on a separate lead back to the radio's command board. On the ACCy jack, Mic Lo is connected to the DIG ground pin. The DIG ground is very short and goes to the command board ground common.

Thanks for the clarification, Wil. I will check that out.

The plan is right now is to strip out a Spectra palm microphone, use it's PCB/amplifier and remote mount the mic element in the helmet. The PTT is simple, I can simply remote mount the PTT switch on the belt harness. It will be really nice to bring all of the signals out of the radio via the 15 pin accessory connector. That will keep the installation clean and simple.

Best Regards,
Steve Kent
KW5CQ

There are a couple of surface mount zero Ohm jumpers that normally have to be moved to provide for
an external mic and external PTT from the rear accessory connector. You will have to fully remove
the control board from the chassis to gain access to the jumpers that are on the bottom side.
Some are on the top and some are on the bottom.

Jim

2n2222 wrote:I have a motorcycle A4 rotary Spectra that I would like to use with a helmet (in a car). Of all of these motorcycle radios that were produced for police departments, surely someone has come up with a economical helmet kit or interface that is compatible with the Spectra.

Question #1 is: What is out there that is economical? IE, I don't want to drop $200 on a purpose-built something when I can modify an off-the-shelf FRS type headset and build an interface for $50.

Next question is: I had the radio on the bench last night and was experimenting with the 15pin connector on the rear of the radio. The PTT circuit is fairly straightforward; I can put the radio in to TX mode by connecting the PTT line to digital ground. What is strange is that the MIC HI line has no effect. I don't get a pop or a click when the radio is in the TX mode. I tried using Digital Ground as MIC HI return and nothing. I do see around 8v on MIC HI referenced to Ground.

Any suggestions are appreciated!

Jim,

From what 2N2222 says, the 'jumpers' are already in his Spectra.

Jim202 wrote:There are a couple of surface mount zero Ohm jumpers that normally have to be moved to provide for
an external mic and external PTT from the rear accessory connector.
Jim

Good news...

I prototyped it tonight on the bench and it all works!

The only thing that I don't like is that 5 of the wires on the 15 pin acc'y connector go to my mic/headset/ptt interface box, but I have that one wire that has to go to the ignition. Is there a jumper that will eliminate the need to have a switched 12v on the ignition termnal of the 15 pin acc'y connector?

I could make the jump internally, but I'd rather not do that...

Thank you for the help.

Best Regards,
Steve Kent
KW5CQ

2n2222 wrote:Good news...

I prototyped it tonight on the bench and it all works!

The only thing that I don't like is that 5 of the wires on the 15 pin acc'y connector go to my mic/headset/ptt interface box, but I have that one wire that has to go to the ignition. Is there a jumper that will eliminate the need to have a switched 12v on the ignition termnal of the 15 pin acc'y connector?

I could make the jump internally, but I'd rather not do that...

Thank you for the help.

Best Regards,
Steve Kent
KW5CQ

Steve,

Yes there is a 'jumper' on the control head circuit board in the A4, A5 & A7 model radios. It is actually a zero ohm surface mounted resistor. marked "000", that can be unsoldered and relocated to another set of pads. This will eliminate need for the 12v Ignition lead on the 15 pin accy connector. There is a photo of the 'jumper' somewhere here on BatBoard.

CAUTION.... MAX fuse size for ALL Spectra IGN leads is 5 amps, one or two amps is a much better choice. The one or two amp fuse will prevent burning up the control head circuit board in case of other component failures in the radio or head.

A properly operating A4, A5 or A7 Spectra will draw no more than 1/2 amp on the IGN lead.

We get lots of Spectras in here for repairs and see the results of over fusing the IGN lead. There are a few Spectras here including two Astro Spectras that have the command board completely destroyed by fire because someone had the IGN lead grounded without a fuse and the 'jumper in the control head set to not have to use the IGN lead.

B + To Ground, Over!
There is a photo of the jumper here on the BatBoard (somewhere).