Simoco Talk Through for MR and Raynet

[Rob_Brookes]

There's insufficient room here to fully document this one. It's by no means as complicated as it appears here and if anyone wants it set out in a separate document in greater detail I'm more than happy to do that.

This one might possibly be of interest to both mountain Rescue teams and the amateur radio, Raynet, organisation. I've not gone into any great detail as regards the assembly and housing of the two radios involved as this is a matter of personal taste quite often and as Simoco SRM9030 radios are already housed in more than adequate cases, they can be merely bolted down onto a wooden board if that's all that's needed.

In this particular case I needed them to be all in one place and not dangling by their cables as they normally are when needed for use or demonstration. As such both SRMs are mounted in the same unit along with a single control head which operates both radios. All the actual work is done by the configuration blown into the radios. In all other respects they are perfectly standard apart from one of them having been fitted with a Dmap accessory card. More on this later.

The housing I used is based upon the standard Simoco desktop power supply and all that I've done is scrounged a spare bottom box section and bolted the two together. Both boxes contain their own speaker so nothing external to what you see is required in order for it to work. The TSX2000 (I think there's a newer model now) has the capability to charge an external backup battery if required and the switched mode PSU mounted on top of the assembly is more than capable of powering both radios as it's not possible to have both transmit at the same time. Control of the various functions is handled entirely by the Dmap board.

Housing.jpg

There's no need to be delving into the innards of the radios used, all the functions are handled by the configuration file loaded into each radio.

I've not included any config files with this post as most who can program these sets in the first place will know how to arrange that which is required in this configuration but if anyone needs them then I can send them on to you. As the frequency requirements of mountain rescue and Raynet are different, there's no 'generic' config unfortunately. The original guidance document on which this is based has been attached and should give sufficient information on how to do this without going into frequency details etc.

A9k-821_Dual_Transceivers[1].pdf

In my case I used a low band (E0) SRM fitted with a Dmap board. This was due to the immediate use to which the device was going to be put. A second high band (AC) SRM was fitted to the bottom box.

The most difficult bit of the whole thing was actually splicing two power leads together so that both radios could use the same, fitted, PSU. You could use a choc-block connector if you can accept it being a rough way of doing things.

At all times one of the radios is the 'Primary' set and the other is always secondary. At switch on the primary SRM is the one fitted with the Dmap board and it's this set that is displayed when power is applied. Only the primary SRM will transmit if the PTT is pressed but both SRMs receive any signal on either the E0 or AC channels they are tuned to. The 9030 control head will switch to display whichever radio is currently receiving but again, if the secondary set is receiving a signal then unless this radio has been selected by pressing the button marked "RADIO", it won't transmit. Either radio can be selected and either radio can transmit once selected but only one at a time. You're not going to be blowing any fuses because both radios transmit together.

Control Head.jpg

The same control head and fist microphone works with both radios, all you need to do is to press the button marked "RADIO" to switch between them.

There's no particular reason for using low band for one of the SRMs, it could just as easily have been UHF. To the radio amateurs this equates to me currently using 2 and 4 metres but 70cm and 4m or 70cm and 2m is equally feasible. Whatever you need to use. Mountain rescue in the UK uses both low and high bands which is why we have the setup shown here.

In the old days of Raynet, there used to be a temporary 'Talk-Through Permit' that needed to be obtained from RSGB I think it was. These were time-limited licences and over the years I built a lot of talk-throughs for various groups. With the system described here, this function is built in and by pressing the button marked 'REPEAT' any transmission received on either of the SRMs will be re-transmitted on the other. This is a two-way function which mountain rescue calls rebroadcast but radio amateurs know as 'Talk-through' or two frequency simplex. All the same thing as we have it configured here.

One slightly annoying characteristic of this setup is that whilst operating a individual radios, the audio output of each is controlled by the normal volume control. When switched to 'Repeat' however, the volume is controlled by a programmable value in the configuration file. This needs to be at around 15-18 in order to get adequate levels of cross-over audio but these values represent a fairly loud output when sat listening to the device. Some method of disconnecting the speakers would be needed when using the rebroadcast/talk-through function although one of the TSX2000 boxes I've seen does actually have a rocker switch specifically for this purpose. Pulling the plug on the internal speakers is the easiest way to achieve this of course.

In operation with a mountain rescue team where GPS tracking of team members on the hill is required then it depends on where this device is to be operated as to which SRM should contain the Dmap board. If used as a base that has a fixed low band uplink to a remote site on a hill somewhere then use the setup I have here. If it's to be used in a vehicle to provide enhanced comms into an otherwise bad area then the Dmap board is possibly best fitted to the high band SRM.

The reason for this is that the same vehicle can also plug a laptop into one of the three available ports, only two are used here, on the Dmap SRM. This allows use of MRMap but as your hill party will be on high band, the Dmap board needs to be in the high band set. The secondary SRM has no accessory board fitted so it's main RJ45 socket is taken up with the required cross-connection cable. I used a short CAT5 extension lead to bring the RJ45 port to the outside of the case as otherwise you need to dismantle the thing each time you need to re program. The control head and the other end of the cross-over cable go into the two ports on the Dmap board. This leaves the main SRM RJ45 socket free for use with a computer and MRMap. Another reason to do it this way is that the radios can't be programmed via the Dmap ports and so to avoid unnecessary plugging and unplugging of leads each time you need to reprogram, use the main RJ45 for the computer connection.

In use in a forward control vehicle for example, the base would be operating on the low band side and the hill party on high band. The vehicle can speak to either base or hill merely by selecting the correct radio with the "RADIO" button. It goes without saying but some thought needs to go into what the display says for each radio as putting say "Kendal" on both of them is only going to lead to pain. Better to use something like 'Base' on the low band SRM and 'TWC' (Team working channel) on the other. Obvious really but heat of the moment and all......

Once in position and able to satisfactorily communicate with both the base and the hill party then the operator presses the button marked "REPEAT" and connects the base to the hill party directly. By using a portable radio on the same channel as the hill party, the forward control vehicle operator can still hear and be heard but they can use the fist mic on the SRM device at any time and speak on whichever is selected as the primary set.

If the 'REPEAT' button isn't pressed then the whole thing operates as a normal vehicle-mounted radio on whichever of the two has been selected as the primary set. All normal channels are available on the high band set and the base, on low band, can be patched through to anyone using any of the available high band frequencies so base can talk to Coastguard or helicopter merely by the vehicle operator selecting the appropriate high band channel and pressing "REPEAT" (Remember to press it again to switch it off when it's no longer needed!!)

The system described has been tested over many years in my car and has been shown to work well. The FFSK GPS signals are passed straight through as they would be with any rebro but they can also be intercepted at the vehicle itself which can then be used to provide full forward control including monitoring the whereabouts of team members on the hill.

One thing I haven't tried yet is in order to use the system as an MRMap monitor for forward control, you need the high band radio programmed with the appropriate own data address etc. For a base, which is what the FCV becomes, the ODA will be 1. However if the vehicle itself needs to be tracked then a GPS board can now be fitted to the low band SRM as we've now worked out how to have both GPS and a second control head (or computer in our case) when using the MA-ASIGF accessory board. As far as I know, the functioning of the rebroadcast device isn't affected by the two SRMs having differing own data addresses which in turn cause them to have different functions. It should still work as a rebroadcast but now, the vehicle will receive GPS signals from the hill party and plot them on MRMap running in the vehicle, the team base will also get these signals as they'll be passed through the rebroadcast vehicle. At the same time the base will have the whereabouts of the forward control vehicle displayed on the map via the low band GPS link.

I might get around to trying that one some day unless someone else wants a go. I can provide details of how it would be done.

The only real proviso with this system really only concerns any radio amateurs using it. The radios are PMR and their heat sinking reflects this. They have a duty cycle that's strictly 90:5:5 and so long overs are not recommended. The sets will auto-protect by reducing the transmitted power until they shut down altogether.

Added by author on a point raised:
The device described here will also operate as a semi-duplex repeater on the various channels used by Mountain Rescue for this purpose. However a diplexer is then needed to keep the two radios apart and as these are very tightly tuned, some means of switching it out of circuit would be needed if more than the repeater channels were in use. Under these circumstances both radios would be high band (AC). Manually switching a co-axial aerial relay in and out of circuit is easy to arrange but the device was really conceived for use as a cross-band talk-through unit. In the case of the amateur 2 metre frequencies they are too closely spaced to allow simple filtering but in principle it would work.