My GMRS Repeater in Ammo Can

nayr · Feb 1, 2012

Ive been slowly building this for the last month or so, I finally got it together and online today so I thought I'd share.

Its not finished yet, I am thinking I can get a pre-amp to fit in there somehow then I'll make a cover plate with fuses, switches and plugs to hide the "internals"

End Results sound great, I need to build a better antenna and get it up higher but I am starting field/range tests this week.

Who knows how much I have into this, its probably around the cost of a used repeater off ebay but thats including 6 handhelds I refurbished, antenna, coax, mast, plus alot of knowledge gained.

its a Kenwood TK-860 receiver wired to a TK-860H 35w transmitter through an ID-o-Matic II with a 20w ebay duplexer. Ive got six Kenwood TK-350Gs to use with this system.

Cheers,
-R

Thetoulman · Feb 1, 2012

Nice build.

How did that eBay duplexer work out for you? I've been eyeing them myself.

How do you plan to power it in the field?

Nice work.

nayr · Feb 1, 2012

the eBay duplexer seems to be working great, I am pushing 35w through a 20w model due to space limitations. I dont have a UHF SWR power meter (yet) so dont know whats coming out of the duplexer.

With 2 handhelds and the radios unlinked i was able to transmit full power to one handheld while the other was transmitting full power to the receiver very nearby with no discernable noise added when one side or the other was keyed up or both at same time.. I guess a preamp will see how well it works, I am thinking I may need some filters for receiver.

In the field it will be battery powered, either by my camper-van's system or a standalone battery I toss into another ammo can. Here are the handhelds in there own ammo can:

One of the big to-do's on this radio is wire up a relay & cap to that blower fan so it kicks on when the transmitter is keyed and runs for a few moments after it's unkeyed. After that I am thinking of building a version of the 70cm Collinear antenna for GMRS this spring.

-R

Rt169Radio · Feb 1, 2012

Looks quite interesting.

prcguy · Feb 2, 2012

Nice build but I might make some comments. Loose the adapters on the duplexer and get some good short double shielded cables from the radios to the duplexer like RG-142B/U. Mount and electrically bond the duplexer to the metal case.

Generally the small mobile duplexer you have barely provides enough isolation for a low power repeater and will not support using a preamp. Whatever your tx/rx isolation is now will appear worse by whatever the gain of the preamp is. Adding a preselector cavity in front of the preamp can offset the problem but would not fit in the box. Just my 2c.
prcguy

62Truck · Feb 2, 2012

That's pretty cool!! I can't wait to see the end result!

KD8PVX · Feb 2, 2012

Sometimes the knowledge gained is worth its weight in gold. Keep working at it and the main thing enjoy it

- William

Sent from my SCH-I800 using Tapatalk

nayr · Feb 2, 2012

Thanks guys, the duplexer is going to be mounted & grounded instead of sitting loose like that.. I just dont have the hardware to secure it where I want yet.. The feed-line and adapters are going to stay, really the loss is minimal and im not shooting for a wide coverage mountain top system... I am talking to just handhelds here and I could spend that effort & money on the antenna with better results.

I am just glad that all the surrounding neighborhoods, parks and schools are well covered from my handhelds with little to no deadspots... If I wanted a repeater to cover the greater metro area I think I'll build another, with no space limitations to fit in my rack cabinets in the basement.. which I wont rule out but first I need the city to leme put up a tower/mast.

yeah at this point im not convinced on spending money for pre-amp, and with me being in middle of metro area I know the noise floor is pretty high.. was just a thought and If I found a suitable one used for cheap I might get it just to see if I can make it work.. It might just be better to find a slightly more sensitive receiver.

The goal of this was mainly to be a badass portable base station, not a crappy repeater.. Here in colorado I have alot of hobbies and activities that take place where reliable comms means getting everyone HAM licensed.. that wasent going to happen so this is what I came up with.. dont need 20 mile coverage..
I am completely happy if I can get it setup to do 5miles well around my deployment site without much fuss.

-R

nayr · Feb 2, 2012

I do have a question since I have attracted some attention on this, right now I am using the speaker output as audio source because the controller has a de-emphasis circuit.. Should I remove the de-emphasis and take the discriminator output from the receiver? It would require some changes that would be pita to reverse and right now I am finding I NEED to set the volume on the receiver and controller to get it sounding ok.. If i use the discriminator output the receiver volume wont have any effect and I am afraid I'll loose some tuning ability..

For example I turn receiver volume to minimum and set the pot so it just barely unmutes the receiver.. volume level is low being transmitted but if I nudge the pot a little louder its too loud and there's alot of background noise, so I turn up receiver to about 4-5 and everything sounds great.. nice audible transmission with handhelds at about 1/3rd volume and when they cranked all the way up there's not really an increase in noise.

RIght now it works, and sounds fine.. but I kinda want that audio output for a local speaker, if I tap into it as it is I couldn't change the speaker volume w/out effecting its "tune". I am thinking the pot is so sensitive because of the de-emphasis, but if not then damn it'll be hard to get it sounding this good w/out the ability to fine tune.. I guess I could just measure and replace the pot with a narrower one for this setup

-R

prcguy · Feb 2, 2012

You should use discriminator audio and not the speaker. Using a signal generator with ext modulation input or a service monitor and sweeping 300 to 3000Hz audio spectrum will tell you if the de-emphasis will need to be in or out of the circuit.

You can also set the generator deviation to say 3KHz using a 1KHz tone with no PL then set the repeat audio to 3KHz with no PL so you have a reasonable 1:1 repeat audio, then set PL level separately.

Using discriminator audio you will set the repeat levels once and not have to worry every time you mess with the volume.
prcguy

nayr said:
I do have a question since I have attracted some attention on this, right now I am using the speaker output as audio source because the controller has a de-emphasis circuit.. Should I remove the de-emphasis and take the discriminator output from the receiver? It would require some changes that would be pita to reverse and right now I am finding I NEED to set the volume on the receiver and controller to get it sounding ok.. If i use the discriminator output the receiver volume wont have any effect and I am afraid I'll loose some tuning ability..

For example I turn receiver volume to minimum and set the pot so it just barely unmutes the receiver.. volume level is low being transmitted but if I nudge the pot a little louder its too loud and there's alot of background noise, so I turn up receiver to about 4-5 and everything sounds great.. nice audible transmission with handhelds at about 1/3rd volume and when they cranked all the way up there's not really an increase in noise.

RIght now it works, and sounds fine.. but I kinda want that audio output for a local speaker, if I tap into it as it is I couldn't change the speaker volume w/out effecting its "tune". I am thinking the pot is so sensitive because of the de-emphasis, but if not then damn it'll be hard to get it sounding this good w/out the ability to fine tune.. I guess I could just measure and replace the pot with a narrower one for this setup

-R

nayr · Feb 4, 2012

it must be effecting my range as well, I did some range tests as its setup and I could key the repeater 5 miles away and hear the curtsey tone and ID loud and clear but no repeated audio coming out.. at the edge of the hand helds range (~2mi) the voice was either coming in 100% perfect or nothing, cutting out like a cell phone instead of fading away.. I think the voltage from the speaker output is too low if the signal is not 100% that its being de-emphasized too much.

Im going to verify this with another test today, then rewire the rig for discriminator output.. I found a pair of 12 turn 10k trimmer pots I can replace the 1 turn pot with, that should make tuning the audio inputs/outputs much easier.

I figured I could use 2 handhelds with the volume set to about 1/4-1/2 hooked to a PC sound card, transmit a tone out one and tune the pot on the repeater until the levels match what's being received via software oscilloscope.. mebe not the best way but I can do it with the gear I have on hand.

-R

zachsradios · Feb 8, 2012

How far do can you talk on the handhelds to that repeater.

nayr · Feb 9, 2012

currently handheld range is just over 2 miles in all directions from repeater, in an urban environment with pretty much perfect audio

I am going to retune and test it this weekend, I should be able to get a little more range by allowing weaker signals to repeat..

A better antenna will be the key to getting to my 5 mile goal.. currently I am using a DB-J1 Dual Band J-Pole tuned for MURS/GMRS which I dont believe is giving me any gain.. it was very cheap and allowed me to get this project off the ground tho.

The repeater its self has no problems getting its signal out 5 miles, its making it sensitive enough to pickup the little handhelds thats the trick.

mrwilson706 · Feb 9, 2012

Very cool, thanks for sharing!

robertbennet · Apr 19, 2012

Wiring pinouts

verry nice setup iam trying to do the same with 2 tk-840's, i have 10 tk-370 that i use right now with a tkr repeater, my question for you is what pin out are you using for the tx and rx ? i want to make a cable to link them togeather but iam stuck on the pinouts this is what i come up with ..rx-pins 4-detect output, 6-gnd, 12-audio out. on the tx pins 8-ptt in, 6-gnd, 5-mic in, please let me know thanks

willgrah · Apr 20, 2012

I use the DBJ-1 J-Pole for my base antenna. It is about 30 ft. up and will transmit and communicate a solid 5 miles with my HT's. Ten miles or more base to base. I am putting out 25 Watts from my base, HT's are 4 watt. It has good ears for a $25 dollar antenna. The gain is said to be 2.1 Dbi, not much. My terrain is suburban, trees, two story houses, etc. I can hit a tall repeater 32 miles away, not full quieting but strong enough.

My only suggestion is to look at line loss and try to get the antenna up a bit higher. After that I would only go to a higher gain antenna. As far as the signal just dropping and not fading I have run into that. It was always the programmable squelch not being set just right.

popnokick · Apr 20, 2012

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The fact that you wrote you needed a preamp or more sensitive receiver has me thinking about your duplexer. Is it possible you're experiencing more RX desense than you should? Who tuned your duplexer, how, and with what instrument? My repeater didn't achieve its best RX sensitivity until I had the duplexer professionally tuned by a radio service shop using a network analyzer. And I have an eBay duplexer.

WX9EMS · Apr 20, 2012

Nice setup!

As far as your receive sensitivity, how did you tune your duplexer? Agreeing with popnokick, it needs proper alignment for peak efficiency...the slightest bit off will make a difference in range. They are not usually tuned right out of the box (unless specifically tuned before delivery), they need to be tuned to the operating frequencies. Sometimes even bumping them around and such affects the tuning.

Hirschkorn · May 20, 2012

May have to do this but up it to 50watt's..

RKG · May 21, 2012

nayr said:
it must be effecting my range as well, I did some range tests as its setup and I could key the repeater 5 miles away and hear the curtsey tone and ID loud and clear but no repeated audio coming out.. at the edge of the hand helds range (~2mi) the voice was either coming in 100% perfect or nothing, cutting out like a cell phone instead of fading away.. I think the voltage from the speaker output is too low if the signal is not 100% that its being de-emphasized too much.

Im going to verify this with another test today, then rewire the rig for discriminator output.. I found a pair of 12 turn 10k trimmer pots I can replace the 1 turn pot with, that should make tuning the audio inputs/outputs much easier.

I figured I could use 2 handhelds with the volume set to about 1/4-1/2 hooked to a PC sound card, transmit a tone out one and tune the pot on the repeater until the levels match what's being received via software oscilloscope.. mebe not the best way but I can do it with the gear I have on hand.

-R

The courtesy beep and CWID are sent by the transmitter with the receiver serving no function. When you try to repeat input voice, the receiver is important, because it supplies the audio to be repeated. If you hear the beep and CWID better than you hear input voice, that tells me that your receiver is being desensed by your transmitter, which tells me that your duplexer is either not tuned correctly or simply doesn't supply the necessary separation.

Edit: and if you do have a de-sense issue, adding a pre-amp is not going to help; it will make the problem worse.

My GMRS Repeater in Ammo Can

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