latched output with accessory port on Maxtrac/Radius

[eportel6607]

Hi guys,
First post here. Thanks to the admins to fixing the "register" link to sign up.

My first question is a question about the Motorola Radius and Maxtracs with a 16 pin logic board. I made a bunch of mobile extenders out of P110. These units have a 16 pin accessory plug on a 24" cable that plugs in to the back of the radio. All the necessary components are installed into the P110 case to make this work without any "controller". The two things that need to be changed on the default configuration of the Radius/Maxtrac is that pin 14 needs to be programed to PL/COR detect and the internal jumper JU505 (I think) To make a nice neat finished product I would like to be able to switch on and off this mobile extender (3.2 amps max on TX) by the front panel controls of the Maxtrac/Radius. Is there a way to configure the features and accessory connector to have a latched output (either high or low to trigger a reed relay if necessary) to switch the power on and off for this mobile extender? Maybe like a PA options..or some other feature that I'm not aware of?

Thanks guys,
Chris

[eportel6607]

Sorry guys. Just noticed some type errors and can't find a way to edit the post.
The title was suppose to read "latched output with accessory port on Maxtrac/Radius"

[Bill_G]

No. Not that I'm aware of. Nothing in the accy settings allow a front panel button to change the state of an i/o.

[eportel6607]

Ok Bill...that's what I thought but before I designed an external way of switching the extender on and off I wanted to see if I could do it with the front panel controls.
Thanks for the reply.
Chris

[kcbooboo]

Pin 13 of the ACC Jack has switched B+ on it. When you turn the radio on via the VOL control, the resulting B+ is also fed to pin 13. It is only good for perhaps 1/2 amp, so use this to activate some other power-handling device (relay or transistor).

Bob M.

[eportel6607]

Hi Bob,
Hey thanks for the input. I'm using pin13 for the extender itself...although it could also be used for more than one function if properly isolated.
If I did use pin 13 for switching the extender transiever it would mean that the extender would be on when the mobile was powered up. This would cause a huge issue when more than on unit was on scene. Only one extender can be on (on the same link channel) at a time. The rule is the first unit arriving on scene will call out and indicate the link channel that is being used and then every unit arriving thereafter will switch their portables over to the first arriving unit's link channel. There is only 3 link channel available for mobile operating...so we have to limit the amount of extender that are activated. I do really appreciate the input though...but I did consider using pin 13 until I thought of the consequences.
When I initially wired up the extender's transceiver (P110) I thought everything was working fine...until I shut the mobile (Radius/Maxtrac) off. When I did the active low output (pin14) rather than floating, it goes to ground which makes the extender's transceiver (P110) transmit constantly. So I used pin 13 to trigger a transistor with pull up resistor to switch the output of pin 14. So now when the mobile is on the transistor is activated, closing the circuit of pin 14 to the mobile extender's (P110) transceiver PTT line. This of course makes it possible for the extender to transmit when the mobile radio receives valid PL decoded signal and it then gets rebroadcast over the extended radio. When the mobile is shut off the transistor that I added on pin 13 disconnects continuity on pin14 and all works fine.

[Bill_G]

Yep. Commercial products worked out those contention problems. They did it with busy channel detectors and random timers so that one unit, usually the first on scene, would be the master, and all others would remain quiet.

[eportel6607]

Yep. Commercial products worked out those contention problems. They did it with busy channel detectors and random timers so that one unit, usually the first on scene, would be the master, and all others would remain quiet.

Ah yeah like the Pyrimid unit...huge money and waaaay more than we need. The Motorola PAC-RT works like that...but it does a few things that make it "smart" like. It samples (like a priority in a scanner) continuously the portable frequency to see if there is a transmission coming from the portable user and if so, it allows the portable users transmissions to have priority over the receiving signal from the mobile radio. This is helpful if the repeater has a long tail. If this is the case..without the priority sampling the portable users would have to wait until the tail of the repeater was finished before he/she would be heard. Otherwise the transmission from their portable wouldn't be herd at all because the mobile extender transceiver would be busy transmitting (the received signal from the mobile) to the portable user.

I have found that there is two ways to fix this issue. 1) Use an extender that has this "priority" logic control...like we just talked about...or 2) Use a gated PL on the repeater. With this configuration the repeater only transmits the PL tone when it "sees" or receive a PL tone. Another words it only transmits a PL when it receives a users transmission...so the tail, IDs and other transmissions that originate from the repeater itself doesn't cause the mobile extender to rebroadcast the transmission to the portable user. Which means that as soon as the a user un-keys the extender stops rebroadcasting and that also means that the portable user can immediately transmit.

I was told by a personal friend that is a Motorola tech that the Pyramid and Motorola PAC-RT systems actually work not as the first on scene, but the last on scene. When the last unit arrives on scene and pulls the portable from it's charger or turns on the extender system the extender sends out a tone burst that shuts off any other extender on the same frequency (channel) within range...this ensures that only one extender is on at any given time. But with some minor training and a Gated PL on the repeater we can achieve the same results for far cheaper.

Thanks Bill. I love this stuff!
Chris

[d119]

I was told by a personal friend that is a Motorola tech that the Pyramid and Motorola PAC-RT systems actually work not as the first on scene, but the last on scene. When the last unit arrives on scene and pulls the portable from it's charger or turns on the extender system the extender sends out a tone burst that shuts off any other extender on the same frequency (channel) within range...this ensures that only one extender is on at any given time.

That is 100% correct. It's a reverse-hierarchy. Last unit to power up takes over. The issues with not using a sampling system is that if you are using this in a public safety configuration, regardless of what's going on with the dispatcher, if the extender is not sampling for portable activity during a transmission and a unit keys up over the dispatcher with emergency traffic while the dispatcher is talking, the unit will not be heard.

In most public safety systems, the dispatcher has full duplex capability (console priority). If the dispatcher is talking and a unit keys up during the dispatchers transmission, the dispatcher is still heard on the transmitter, but the dispatcher can hear the unit while the dispatcher is keyed down.

If your extenders don't support sampling, this doesn't work and can become a safety issue. Of course, if you aren't a public safety agency and/or this doesn't apply to you, it doesn't matter.

Pyramid SVR 200 series mobile repeaters are all over eBay, often for under $200. I don't think they are narrow band compliant though, of course with proper tuning and set up, they can be made to conform with narrow band specs, even though they are not type accepted.

[Bill_G]

Thanks Bill. I love this stuff!
Chris

Me too Chris. I'm glad to see some bright techs out there willing to work the problem, and come up with their own solution. It might not be perfect, but you learn a lot in the process, and it makes you appreciate well crafted commercial and DIY engineering.

PS - I had forgotten about reverse hierarchy. Thanks!

[eportel6607]

Ahh yeah I did remember that most public safety systems are full duplex. Actually most dispatch public safety systems if I remember correctly are either remote base's or the base station itself IS the repeater. So of course if you key the transmitter of the base the transmitter IS the repeater transmitter and it's receiver will always be able to receive regardless of if it's transmitting or not. Our system is a low band repeater (with VHF hi extenders)...but the bases work just like mobiles. So with our system even if we had a sampling mobile repeaters there is no advantage to it because there is no duplex radio (other than the repeater itself) to take advantage of the safety of the sampling mobile repeater. We are involved with public safety but we are not a police or fire department so although the transmissions could be important..they aren't critical...even if they were, the dispatcher would need to be either have a full duplex remote base to the repeater or the dispatcher would have to be using the repeater as the base to take full advantage of the sampling mobile repeater. So I guess in our case this little mobile repeater system works very very well. If you consider the fact that I built these little gems for under $40 this is a no brainer. Now I'm concerned about the narrow band mandate...we have always used GP300s for our portables...I LOVE this radio but it's not narrow band compliant...I know there is a kit but is it worth it?? I guess this is another topic though.

Bill. Yeah I love work stuff like this out. I don't think that anybody in our group understood what these extenders would REALLY do until I showed them in person. We have to have coverage in the whole state of RI..not just a little city or county..so in band portables where not an options. The extenders can't be beat for the money. As long as we are under a mile and a half away from the extender we will get into the main repeater full quiting. Oh I'm not a tech Bill...just somebody who loves to show the local and state police how a system that cost about 2 million dollars less then there's can have better coverage in every way!
Thanks guys again for the feed back and great conversation. I have some other questions that I'll be tossing out very soon.
Thanks again,
Chris