If you’ve wanted your own GMRS repeater but didn’t know where to begin, here’s the video you’ve been waiting for. This quick and easy tutorial shows you how to turn the Wouxun KG-1000G GMRS Base/Mobile Two Way Radio into a real, working, fully functional GMRS repeater!
Not referring to any specific rig, but definitely the scope to be able to create mobile and relatively cheap base repeaters, is a feature worth having - even if it’s never used.
Whilst dual receive TxCrs will have an internal duplexer anyway, radios equipped with a cross band or same band repeater mode tends to have a better Rx & Tx 'front end’s, which all around makes for a better performance of set.
The best ones allow you to cross mode any Rx selectable to any Tx selectable, but that comes with a bit of a price tag, but the more limited and more accessible stuff is more than what most would demand, so value wise - repeater mode equipped sets at no silly money prices are a bargain by default.
It’s also worth noting that in practise, repeaters need a better Rx and a more robust PA (higher duty cycle rated at one extreme), so whilst these bargain mobile RPTR equipped sets won’t be on permanent commercial RPTR grade modules level, the fundamental necessities a RPTR needs will be present and similarly the uprated module grades even if still downgrade vs commercial RPTR grade gear.
Well, if cross band RPTR mode on my UV-9 series handheld demonstrates anything, the RPTR spec KG series mobiles will be equipped with very usable and higher output RPTR modes that won’t be a lesser grade. Which is kind of what you’d expect.
How must distance do you need between the antennas? Why not sell a repeater package with everything needed to set up the repeater minus the tower of course?
There’s lots of possible answers to the antenna separation aspect, where on actual formal repeaters or cross linked separate transceivers do much the same.
As many half waves as feasible, if antennas are on the same horizontal plane. However, if stack them vertically (exactly which should sit highest is really site and pattern dependent and pattern dependency is more determined by the Rx antenna as this has to capture as much of the weaker SIG’s at many elevations, where a Tx antenna with a suitable radiation pattern has to emit the repeated content on a transmission that gives the best output spread and coverage. Really, there’s no absolute to v vs H sitting and spacing, just rule of thumb guidance you apply with site and coverage in mind.
In respect of on-rig repeater functions, they usually send and receive on one antenna using a internal inductive duplexer that allows both Rx & Tx modules (tuned suitably apart, 600khz+ minimum - more is always better such as the more normal 1Mhz + between Tx & Rx aka input and output/uplink and downlink frequencies.
The separation of frequencies is a necessary case on either kind of repeater, as the 3dB shift/attenuation between opposite polarisation won’t be a workable workaround as the Rx needs to see the repeater output (Tx) as near far below threshold as possible to prevent severe desense in the input’s Rx module.
Since we were talking dual radios, links and separate antennas etc, there’s really no generic fits-all combination to bundle and with that said, allowing for the potential of many radio services covered for RPTR use, it wouldn’t be feasible - it’s the sort of thing you figure out and package on a case by case basis. There’s also liabilities involved that can make it a right old minefields of iffy grade mines to navigate, a minefield laid by a drunk type hazardous.
I certainly wouldn’t attempt to prepackage a bundle of split radios based RPTR setup and I’m a challenge junkie. As for the in-topic unified type, if you wanted a mast to use for temporary transportable antenna sitting - if you’ve the sense to figure out if the RPTR function had use for you, you’re more than capable of choosing a suitable mast and grade of cable and fittings to suit the type of sitting.
To simplify it, and this goes for any paired rug set used as an extender or repeater -
Ideally you want as much separation between rigs as is feasible - so really two PSUs would be needed. Aside from running two DC feeds off of one PSU being a pain if say output rig is upstairs and antenna is roof/mast mounted, unless you seriously overrated the shared PSU, there’s a lot of scope where output rig will rob the Rx rig of current and a voltage drop if your output set is on a mid/high output setting.
So best practice is two PSU’s. With a minor DC side mod to each, it’s possible to add remote power control via wireless or wired control using a cheap microcontroller (not needed, but adds possibility for fine tuned flexible remote control via many means) or a simple switch system to trigger the control relays on the DC-OPT of the PSU’s. Not necessary, strictly speaking, but since most license provision use of repeater management require you can shut it down/isolate easily in the event of issues, it’s somewhere between good practise and potentially a requirement on a fixed setup and expected on temporary setups that you can isolate and/or kill the RPTR.
Radio separation is more about putting the equipment at ideally optimal locations relative to antennas and keeping coax runs as short as is manageable bearing all things. Using very high grade low loss coax is what sanely setup system employs.
Aside from wavelength based determination of spacing of antennas and using suitable radiation pattern based choices, to prevent stray RF migrating between radios in the chain, you need them spaced. Antenna wise, aside from the multiples of half wavelengths consideration of separation, they also ideally need to be spaced and positioned to keep out of each others radiation pattern - preferably existing within each others radiation pattern nulls.
Vertical vs Horizontal spacing of antennas is a bit of science I won’t go into any further, but ARRL, RSGB, and many professional tech references outlined it and issues quite well and saves me reinventing the wheel.
But to put some perspective on it at a simple practical level - if you look at manufacturers guidelines for their own marketed simplex/duplex DIY setup repeater/extender controllers aimed at dual radio based setups, they recommend a basic opposites extremes for radio and antenna siting.
So you could put one radio by front of building (boxed) at the base of the Rx antenna sited mast and say have the taller mast out back as far away as you can manage with as much height sep as you can effectively use and get away with.
But a note of overall caution - in many countries, there are prohibitions on use/setup of repeaters on domestic properties. Many exempt LPD hotspots because they are sub-watt ERP and unless you’re using a antennas beyond the usual helicals, best case is substantial RF levels won’t go beyond much past the extremes of your property at VHF/UHF - but in that context, using colineears etc to boost coverage will certainly takes LPD ‘repeater’ and gateway hotspots into higher effective ERP beyond the property boundaries and may breach the EMC requirements if power levels are boosted pre antenna.
I mention this, as 25W/50W upwards Tx output of the Tx half of the chain on external antennas (anything effectively resonant) will see an ERP of somewhere between 1/4-1/2 of input power if you are talking 1/4 through 1/2 wave antennas, more gain from 3/8ths through full wave and collinear usage will definitely be an issue. In fact, the same basic reasoning applies to why most countries I know of prohibit sitting even low power broadcast transmitters (RSL station levels upwards) on residential properties or even on an empty site within the confines of a residential zone/buildup.
Hence why permanent or long term temporary RPTR’s exist in the back of beyond relative to where they serve.
It’s a major responsibility, and that’s a fact. You would have to delve into the dark magic of propagation, EMC and filters use (including cavity filters) to do it right. I know having had to endure it, and even on my LPD grade hotspots (WiFi, DMR and C4FM), I’ve rebuilt them to incorporate proper filtering vs the SDR style barn door wide BPF’s usually employed best case.
How much you’ll need to incorporate/consider for temporary fixed or portable in your local is something you’ll need to explore.
Which ties in nicely to some of why pre-bundled plug-n-play kits are not generally made available or viable to many retailers.
But you’ll do what you see fit, irrespective of the complications and liabilities - I will just hope you employ sense and take responsibility regards of what level you undertake of running a RPTR.
Given there is often a need to separate the two rigs, at least when you aim to make it efficient and likewise protect the Rx front end from xxW of induced RF flooding from the Tx half of the pair (no, a few feet isn’t remotely close to how far you need) -
You’ll be needing a long interconnect, whether it’s a multiple set of cables (where audio and data/control/sync are broken out on diff connectors) or one carrying everything. So you’ll want to possibly use a low gain audio amp on Rx Audio Output to provide makeup gain to account for SIG level drop over a long coax run carrying the crosslink audio. You’ll also have to power it, so you’ll be potentially looking at poking DC up the cable as well if you want line power, but that’s not always a good move.
Regardless, you’ll want a good low-noise amp, and to put it bluntly, any amp RF or AF you use should be of low-noise characteristics, and it’s no less important for low voltage/current signals such as interconnects carry, it’s actually technically and practically desirable bordering on essential for a decent link.
You’ll want decent low loss coax on the RF and AF feeds, without a shadow of doubt. Now you may not appreciate why on the AF side, but since you’ll have spare coax left over from the RF feeders stuff, may as well use it on the AF side too - it’ll be a better grade than the expensive BS hyped brand stuff they brainwash audiophiles into buying.
I personally use the same stuff I used for DBS satellite connect from LNB to receiver. The fact I had a few hundred metres left over on a commercial size set of drums ensured it wasn’t gonna be left to corrode from no use.
An alternative audio pass through feed could be to seek out a audio Tx/Rx wireless pair and use those instead of a wire link.
In fact, with a bit of ingenuity, you could multiplex it all over a simple digital connection where you use relatively cheap modules to demux the sync/control SIG’s and audio from the multiplex.
Sounds a bit SF, I guess, but if you looked at how stuff gets routed these days, even in the pro repeater world, you’ll find some degree of a multiplex connection carrying two or more interleaved SIG’s.
It’s a very in-depth area really, to many it’s bordering on dark magic much like many see doing technical stuff at UHF/SHF is perceived as.
All I will say is, if you go beyond a simple temp mobile sited RPTR setup, you may want to give it serious thought first.
To close my thoughts - when it comes to anything beyond a simple lash up, which with no offense intended, is precisely what that setup demos in the video - for temporary setup, great for basic mobile/portable site ops and really not advisable without serious evaluation anywhere else and planning.
Without drawing this out any further, I’ll put this concept into the mix -
If repeater setup and optimised clean use of was as simple as lashing up two transceivers with audio and control umbilicals and there was all it took, everyone and their dog would have done so and VHF/UHF services ending up like 11m was at it’s peak. The QRM and subsequently occurring complaints and accusations (founded and unfounded) would have recreated the radio ‘Wild West’ 11m experienced.
About the only real difference is the cheap glut of equipment is, even at it’s shoddiest, is a massive step up the food chain from that used then and now on 11m.
It worth doing experiments. Find a frequency that is just listenable to, but pretty busy. Ideally one that has good readability but only tickles the meter, one with continuous hiss/noise. Then get a portable radio, and tune it to the repeater shift you want to use. Press the PTT and see what happens to that weak signal. Your repeater will need to be able to hear people who are not strong on the input. Just a few Watts of RF can make that weak signal vanish. It takes me quite a while to squeeze the best rejection out of cavity filters, and I note that now I have a proper analyser, some of the repeaters I have in use are NOT running at their best because the analyser let’s me squeeze every last dB out of the system. Pressing the PTT with less than a Watt can wipe out weak signals many channels away. In band repeaters without cavity filters are never going to be practical.