TK-880 Simplex Repeater?

[DeoVindice]

I've been brainstorming solutions for a mobile local range extension system. A full duplex repeater using two mobiles has been considered, but bulk, complexity, and power consumption don't have me too enthused about it.

 

The specific application would be for intergroup communication between groups also utilizing handhelds for intragroup communication, primarily for family hikes and possible SAR. My future in-laws purchased a house in an area I frequently hike and prospect in, with little to no cell service, and I'd like to be able to relay signals through my truck to their house in town. It's not particularly long distance, but terrain obstruction is a real issue and I tend to park the truck below and outside of whichever gulch we're hiking on a given day.

 

This has me thinking on a simplex repeater. I've nearly finished a TK-880 mobile install on my truck. The idea would be to program a channel into the 880 with a repeater input as its RX channel, and a repeater output as its TX channel. A simplex repeater box would be plugged into the 880's mic port via an RJ45-RJ45 cable. Normal intragroup operation would be on the extender's output frequency. The simplex repeater unit would have courtesy tones enabled, so that any intergroup transmission going over the extender could be identified. Activating the repeater would require the user to either turn off talkaround or switch to a dedicated channel with the repeater input programmed.

 

Aside from the size, weight, complexity, energy, and cost advantages, eliminating the duplexer would also seem to make the system frequency-agile since no tuning is required. This appears to be a real advantage if in an area with a GMRS repeater, since deconfliction is just a matter of changing channels.

 

Has anyone else tried something like this?

[WRAK968]

I have built a repeater out of two TK880's. The solution is simple, but not as simple as plugging in an RJ45 jumper.

I used a surecom repeater controller with an adapter. They make them specifically for the TK880 series radio. The surcom plugs into the RX radios ext speaker port on the back, and plugs into the TX radios mic port on the front. No soldering needed, all plug and play. Personally I wouldn't use any radio thats hard wired to your POV as it could kill the battery if operated for too long. I bought a 130Ah deep cycle battery meant for trolling motors and that ran the repeater for 4 days of use. Of course you will need a duplexer that can do a majority of the 462/467 span. Those types of duplexers typically have de-sense with any power levels over 25 watts so youll want to use the standard 25W unit over the 40W "H" model. The nice thing about that is if you go to an area and there is heavy traffic on your channel, you can change the channel at the push of a couple buttons to any of the 8 repeater pairs. By using the "OST" option, you can have control over tone pairs, even using split tones if you wish.

Finally, Kenwood mobiles have a duty cycle of 20%. I believe this extends to about 40% on low power which I have set at 10W.  If you wish I can send you pictures of the completed project and a list of parts I used. Message me your e-mail address and I'll send it over.

[gortex2]

So in theory yes it would work and I have done similar for SAR work. In actual use it didn't work well at all. Most simplex repeater modules receive the audio, record it then re-transmit the audio. The issue we ran into is that delay time. If in an area where others can't hear the input of one use they don't know you are talking and you don't know if they are due to delays. While it did work ok for general messages "CREWS REPORT TO COMMAND" it was almost useless for routine conversations and use. At the end of the day we built a small pelican case 5 watt repeater that does what we needed. 

 

Guess it really depends on your needs. If you plan to have conversations I don't think its efficient. If its for a "i need help" scenario then its probably going to be OK. The other possible solution would be to put a small but efficient repeater at your future in laws house. Done right its not going to look bad and would work well. 

[WRAK968]

So in theory yes it would work and I have done similar for SAR work. In actual use it didn't work well at all. Most simplex repeater modules receive the audio, record it then re-transmit the audio. The issue we ran into is that delay time. If in an area where others can't hear the input of one use they don't know you are talking and you don't know if they are due to delays. While it did work ok for general messages "CREWS REPORT TO COMMAND" it was almost useless for routine conversations and use. At the end of the day we built a small pelican case 5 watt repeater that does what we needed. 

 

Guess it really depends on your needs. If you plan to have conversations I don't think its efficient. If its for a "i need help" scenario then its probably going to be OK. The other possible solution would be to put a small but efficient repeater at your future in laws house. Done right its not going to look bad and would work well. 

I missed the part where he was using store and forward comms >.< though he does talk about using repeater input and output so its a little confusing. I still feel a semi-duplex system would be better (One RX radio and one TX radio) for what he wants.

[gortex2]

This has me thinking on a simplex repeater. 

This is a store-forward unit.

[DeoVindice]

This is a store-forward unit.

Different terminology describing the exact same thing.

[RCM]

Different terminology describing the exact same thing.

 

Exactly. The point is that it's illegal.

[DeoVindice]

Exactly. The point is that it's illegal.

Based on what, exactly?

[WRAF213]

Based on what, exactly?

 

47 CFR 95.303:

 

Repeater station. A station in a fixed location used to extend the communications range of mobile stations, hand-held portable units and control stations by receiving their signals on one channel (the input channel) and simultaneously re-transmitting these signals on another channel (the output channel), typically with higher transmitting power from a favorable antenna location (typically high above the surrounding terrain).

 

GMRS does not explicitly state a prohibition on store-and-forward operation, since store-and-forward operation is a packet radio mode.

[RCM]

Based on what, exactly?

I might be mistaken. I just looked in Part 95 and couldn't find it.

[DeoVindice]

I might be mistaken. I just looked in Part 95 and couldn't find it.

Okay, no worries. I know that store-and-forward is prohibited on MURS, but haven't found anything for GMRS.

[RCM]

Okay, no worries. I know that store-and-forward is prohibited on MURS, but haven't found anything for GMRS.

Yeah, I think I was conflating MURS rules with GMRS rules. Or vice versa.

[WRVR263]

What Deo is asking is similar to my concerns.  Here's the situation.

Evac scenario.  Teams have GMRS licenses and radios (mostly handhelds) however with the terrain they won't always reach the CP via either a fixed or portable repeater.  Mission critical issues include their ability to communicate with each other whether or not they can hit the repeater but also communicate with the CP, typically at a sheltering facility or at the Staging Area.  If the field units are operating simplex in a general area, they should be able to communicate with each other.  If we could rig a kind of relay repeater (simplex tactical frequency on one side - link frequency to CP on the other side) the units could communicate directly with one another, the CP could monitor and also receive calls or give assignments or safety warnings back to the field units.  Additionally, if for any reason field units couldn't copy each other but were in range of the relay repeater, the CP could forward the message back over the repeater.

This concept is similar to what we use in the fire service for remote radio sites, with a radio uplink to the site from dispatch, but transmitting and receiving on a simplex channel on the "field" side of the system.

Store-forward can get pretty crazy if multiple units in the field are generating "real time" traffic with critical details such as access / egress instructions, critical exchanges of safety details, etc.  (Can you imagine the chaos if forward units were exchanging critical messages rapid-fire with the store-forward repeater walking on top of them?)

Open to creative ideas (if any are legal) and thanks in advance.