Multiple CTCSS tones TXed at the same time?

[aaknitt]

I'm wondering if it's feasible to transmit more than one CTCSS tone at the same time on the same frequency and still get proper decoding in receiving radios. I know that it can work because I've tried it, but I'm not sure it worked properly or as well as it would have if only one tone were being sent. Here's my situation and what I'm considering.

Right now we have a VHF remote base with a UHF link to a dispatch center. Users operate in carrier squelch mode on the VHF frequency, except when they want to talk to dispatch. When they talk to dispatch they transmit a CTCSS tone on the VHF frequency, which activates the UHF link. I'd like to move to a VHF repeater instead of simplex, but still maintain the current method of operation. So far I've thought of two ways of doing this:

1) Users transmit CTCSS tone "A" for normal communications and tone "B" for communications intended for dispatch. The repeater keys up for both tones and always transmits tone "A" on the output. When tone "B" is received, the repeater controller keys the UHF link. In this scenario, all communications with dispatch would be via the UHF link. User radios would be set to decode tone "A".

2) Users transmit CTCSS tone "A" for normal communications and tone "B" for communications intended for dispatch. The repeater keys up for both tones and always transmits tone "A" on the output. When tone "B" is received, the repeater transmits tone "B" in addition to tone "A". In this scenario, the dispatch radio would be on VHF, but set to decode tone "B". User radios would be set to decode tone "A".

Option 2 eliminates the UHF link, which reduces complexity. However, it eliminates the ability of dispatch to definitively preempt transmissions. I'm wondering if option 2 is even a possibility. Like I said, I know it works sometimes, but does it work reliably all the time with no performance degredation? Any thoughts are welcome.

Thanks in advance,

Andy

[nmfire10]

Most decent repeaters allow MPL operations (Multi PL). You can give it a whole list of PL's to accept. However, I doubt you would be able to use that to control an auxiliary device. You could use a multi-coupler on the RX side of the duplexor to feed another radio with only the other PL. Use a COR from that to drive the link.

[aaknitt]

I was thinking a separate PL decoder board tied to the discriminator output of the receiver would do the trick. I have a shared tone panel, but that's not what I need. Those are for different PL tones by different users. What I'm wondering about is transmitting two PL tones at the same frequency at the same time. For example, if I had two PL encoders on a single transmitter, one for 114.8 Hz and one for 127.3 Hz, and both active at the same time, would user radios set to each of those tones decode properly?

Andy

[nmfire10]

OOOH. How would you even make a radio do that? It would be much easier to allow the infrastructure to operate in MPL.

[HumHead]

I have an installation running now that is doing pretty much exactly what you are looking for. Here is the setup:

-VHF repeater (MTR2000) linked to dispatch on a separate simplex channel via a low-power CDM-750.
-The MTR2000 is run in base station mode, using a Zetron Model 38 controller, with the auxiliary relay option. The Model 38 is interfaced to the main system connector on the MTR2000 using Zetron's custom interface cable.
-The CDM750 link radio is interfaced to the MRTI port on the MTR2000, except that...
-The PTT on the link radio is derived from the auxiliary relay on the Zetron Model 38, not from the MRTI connector.
-Two tone sets are enabled on the Model 38- set one is tone "A" in, tone "A" out. The second set is tone "B" in, and tone "A" out, with the auxiliary relay enabled.
-Dispatch audio is always re-broadcast over the repeater.
-For a number of reasons, we have the audio priority on the MTR2000 set to give our users priority over dispatch, however, the audio priority can be easily re-ordered on the MTR2000 to give dispatch audio priority instead.
-When a user transmits on the "Us & Dispatch" channel on their radio, they transmit tone "B" This causes the Model 38 to key the repeater, as well as the auxiliary relay. This transmits the audio on both the repeater and the link.
-When a user transmits on the "Us only" channel, they transmit tone "A". This causes the Model 38 to key the repeater, but not the auxiliary relay for the link, so they are only heard on the repeater.

It has been working like a champ for a number of years now, and gives the agency exactly what they want.

[aaknitt]

OOOH. How would you even make a radio do that? It would be much easier to allow the infrastructure to operate in MPL.

Yeah, but that's not quite what I'm after. I want some (user) radios to hear all transmissions from the repeater (without using CSQ), while other radios (dispatch radio) only hears some transmissions (those intended for dispatch).

HumHead's setup is pretty much exactly what I was thinking for my "option 1". "Option 2" tries to do away with the extra link radio, but I'm not sure it's a good idea...that's what I need some feedback on.

Andy

[aaknitt]

I have an installation running now that is doing pretty much exactly what you are looking for. Here is the setup:

-VHF repeater (MTR2000) linked to dispatch on a separate simplex channel via a low-power CDM-750.
-The MTR2000 is run in base station mode, using a Zetron Model 38 controller, with the auxiliary relay option. The Model 38 is interfaced to the main system connector on the MTR2000 using Zetron's custom interface cable.
-The CDM750 link radio is interfaced to the MRTI port on the MTR2000, except that...
-The PTT on the link radio is derived from the auxiliary relay on the Zetron Model 38, not from the MRTI connector.
-Two tone sets are enabled on the Model 38- set one is tone "A" in, tone "A" out. The second set is tone "B" in, and tone "A" out, with the auxiliary relay enabled.
-Dispatch audio is always re-broadcast over the repeater.
-For a number of reasons, we have the audio priority on the MTR2000 set to give our users priority over dispatch, however, the audio priority can be easily re-ordered on the MTR2000 to give dispatch audio priority instead.
-When a user transmits on the "Us & Dispatch" channel on their radio, they transmit tone "B" This causes the Model 38 to key the repeater, as well as the auxiliary relay. This transmits the audio on both the repeater and the link.
-When a user transmits on the "Us only" channel, they transmit tone "A". This causes the Model 38 to key the repeater, but not the auxiliary relay for the link, so they are only heard on the repeater.

It has been working like a champ for a number of years now, and gives the agency exactly what they want.

HumHead,

Would the Zetron 38 allow you to assign different courtesy beeps depending on the input PL? I'm thinking it would be necessary to have some kind of feedback to let the user know whether they're talking to dispatch or not.

Andy

[RKG]

How about this (assuming a Quantar operating in "in cabinet" mode (i.e., not using a voting system)):

Program for MPL:

Active tones are:
1) Input: tone A; output: tone B.
2) Input: tone B; output: tone B.

Now, run the Rx line on the wireline side through a DPDT relay, and power the relay coil via an Aux Output on the Quantar.

In the Wildcard screen, create a wildcard table that, on condition MPL user 2, activate the Aux Output, else deactivate it.

As a result:

All subscriber traffic is repeated using Tone B on the output.

When a subscriber transmits sending Tone A on the input, the wireline to the dispatch console is connected; otherwise it is not.

If you're using a station other than a Quantar, then you might have to go to an external repeater controller. The Zetron 38 Max has the capacity to decode multiple tones, to activate an external relay based on some tones (but not others), and the ability to designate which tone is generated by a wireline key. Be sure to order the optional relay kit, though, which must be factory installed.

[HumHead]

The courtesy beep is an on/off option on the Model 38. You either have the beep, or not, on a tone by tone basis. So, you could leave the beep on for the local tone, but off for the dispatch channel. Personally, I would keep any courtesy beep to the local tone pair. It would probably not be long before Dispatch got tired of hearing it.

Another standard that we have adopted, instead of beeps etc., is to use our full four digit identifier (agency+individual unit) when transmitting on the dispatch tone, and only use a two digit unit ID when talking locally. That lets you know in a hurry who is calling who on which tone.

Regarding your "B" option, you obviously can't mix DPL at all. You could theoretically mix two CTCSS tones, but you will generate mixing products and beat notes in the process that may cause havoc to yourself or other co-channel users.

If this is for any kind of public safety application, I would only consider the option of doing it properly with a link radio and appropriate repeater controller. Trying to jury-rig a tone mixing setup is only going to cause problems at the worst possible moment.

[aaknitt]

Ok, now to throw in some new requirements and somewhat hijack my own thread.

This system would also ideally be able to locally monitor the output frequency of the repeater for talkaround operations from units in the field. I think I have figured out a way to do that by using a second receiver and operating the repeater in "simplex" mode, as shown in this diagram:

http://radioetcetera.googlepages.com/Re ... ption1.pdf

I'm a little unsure as to whether the remote connector on an IC-F3000 would work as I'm hoping it would. The thing I haven't really figured out is how to have a local mic that can key the repeater only or both the repeater and UHF link. I'm thinking I could parallel the mic audio and PTT to the mic inputs of both the repeater and the UHF radio, and then have a selector switch in the PTT line to select transmissions to "local only" or "local and dispatch". Would this be ok?

This would be a lot easier if the repeater were at a remote site, but if this actually happens, it won't be. Any thoughts?

Thanks in advance,

Andy

[psapengineer]

This may be a little bit "out there" but it's worth mentioning. In decades past they used to do this kind of thing using RA/RT control. The outbound UHF link was set up to pass console keying, function tones, and LLGT. The console had a very long HLGT before function tone to allow the link time to get on the air. The repeater, at the far end, was a "wireline" controlled repeater. The UHF Rx was attached to the wireline input. The repeater was set for wireline priority over squelch gate (repeated) audio. This gave the system console audio priority. I know its not directly related to the thread but if it helps....

Regards, Bob

[Dan562]

Hello Andy,

I think Bob's idea will work as a RA / RT repeater configuration and I believe when you order the MTR2000 Base Station / Repeater from Motorola include the AUX I/O (Wildcard) Option, the C540 Option, the Standard Tx / Rx Antenna Relay Option, the International Wire Line Board Option (which allows you to configure the Wire Line Board for High Impedence) and the Instruction Manual. In the back of the current manuals there should be a section for programming the Wildcard for the RA / RT configuration.

There's also a MTR2000 Optional T2-R2 Talk-Around DLNxxxx Kit with it's own Instruction Manual and Hardware included available through the Schaumburg's factory's Marketing / Sales Group. You'll need to purchase a separate MTR2000 Second Receiver or use a Subscriber Mobile as a Second Receiver. Using a mobile as a Second Receiver, you will be required to find the external line input connections to Mute the receiver's recovered audio any time the MTR2000 repeater keys-up and transmits. Using this T2-R2 configuration the repeater's receiver always has P1 Priority.

I'm a bit concerned about transmitting 2 PL tones simultaneously from the Subscriber and/or the Base Station / Repeater. Generally the Tone PL transmits between 500 Hz & 750 Hz for being considered Sub-Audiable. Transmitting 2 PL Tones simultaneously could change the picture completely allowing the tones to be heard as a low frequency noise and there's also a possibility to create a combination third tone which probably would not be filtered out of the recovered audio.

Dan

[aaknitt]

Thanks for the info, very helpful. I happened to stumble across the Bridgecom CS-540 repeater, which I think would do what I'm looking for quite readily. It's set up to be a community repeater, and its COR output can be programmed to go active on only one designated user, which I could used to PTT a UHF link radio. Talkaround receive would come from a second receive-only radio whose audio would be muted when the repeater is TXing. The TA RX radio would share the antenna with the transmitter and be switched with a coaxial relay. The overall picture of what I'd need is starting to come together pretty nicely...it will change slightly depending on what repeater we end up getting, but I think it can be made to work with a number of different repeaters. Here's the setup with the Bridgecom repeater:

http://radioetcetera.googlepages.com/Re ... ption2.pdf

Andy