Building a GMRS repeater

[ThomasB3131]

Let me say up front that this is not meant to be argumentative.... Only for trying to understand what I might be missing....


If this is true, then explain to me why my 10 watt (as measured at the antenna RF port of the radio) repeater that is made from two midland 8 channel mobiles, with a duplexer, that's attached to one end of 50 feet of RG6, that the other end is attached to a homemade Ladder-line antenna that's encased in a 5 foot piece of PVC (one I made for use on GMRS), and that said antenna is mounted on top of a 20 foot section of conduit that's attached to the side of my motor home ---- is working solid 10-12 mile radius of my motor home using handhelds? Now grant you, where the motor home sits is on a hill with an elevation of 596 and the surrounding area is below that, in some cases way below, but still even so, according to your "personal experience" it should not be working worth a darn.

Also, the most expensive part of this build was the 25 bucks I gave a man for the duplexer. All total, I have around a max of $150.00 in this build.

Now I have built, installed and maintained many of these things I like to call "PVC Repeaters" over the years. These PVC Repeaters are generally nothing more than 2 portable radios (many of which are a max of 3 watts if I'm lucky), my own designed repeater controller (a simple switching transistor), with a 7ah battery, solar charge controller, solar panel, all usually installed within a piece of five foot PVC with end caps, that in most cases are usually thrown up into the tops of trees or mounted to a pole that is then raised to anywhere from 20 to 40 foot in the air and I've yet to have any complaints on how well they work. I've even had some of these mounted to pipes on top of tall buildings for use as a portable "weekend use" repeater for volunteers that do traffic control at parades and such and have gotten great verbal returns on said devices.


I guess that it's simply that I don't understand, after 30+ years within the RF field, why people are always pushing this idea that unless you spend thousands of dollars up front for equipment and then spend big time money each month for tower space that a 1-10 mile radius of coverage repeater system like I've suggested in the past or mentioned above just won't work.

I guess what I'm missing and maybe not accepting is what a person said earlier about how too many people put way too much thought into this stuff and make it way too complicated not only for themselves but for others.

What ever works for some may not work for others ---- I've been told.

AMEN

 

[WB9YBM]

Do you think it is possible to get 5-7 miles with a repeater that is only about 30-35 ft above average terrain? If it is that can probably get him going.

In the experiments I've done in ham radio (144 MHz & 220 MHz) a hand-held will reach about one mile per one watt of output power. (Plus/minus a bit for "ground clutter", antenna efficiency, etc.)

 

[gman1971]

Use your browser and find radio mobile online site, put your radio specs, antenna gain, height, etc... and that will give you a spot on coverage map of how far your radio will reach with any given power, etc. See how far 10 Watts UHF at 35 feet AGL gets you in the Madison, Wisconsin area... not very far. The GMRS repeater Madison 700 is like 229 feet AGL... and runs 50W with some high end hardware, and antenna.

Rules like 1 watt = 1 mile without any other context are just that, made up rules without context... devoid of any empirical science and a sampling of 1 (One) ... and if that was the case, I mean, if 1 W = 1 mile was any true, then how would you explain the result when I've strapped a 2W MURS Ritron walkie talkie to my large GPS controlled TREX700 helicopter, climbed up to ~1000 feet AGL and reached like 45-50 miles range? with just 2W, portable to portable...

G.

 

[mmckenna]

Rules like 1 watt = 1 mile without any other context are just that, made up rules without context...

I just have to shake my head and move on.

 

[gman1971]

haha, yep, move on...

 

[prcguy]

With 5w at around 300Mhz and a small 5dBi gain antenna you can get into satellites 23,000mi away just fine.

if that was the case, I mean, if 1 W = 1 mile was any true, then how would you explain the result when I've strapped a 2W MURS Ritron walkie talkie to my large GPS controlled TREX700 helicopter, climbed up to ~1000 feet AGL and reached like 45-50 miles range? with just 2W, portable to portable...

G.

 

[mmckenna]

With 5w at around 300Mhz and a small 5dBi gain antenna you can get into satellites 23,000mi away just fine.

I haven't been able to pick up a 50KW AM broadcast station from the east coast. By their theory, that station should be good for exactly 50,000 miles.

And someone probably needs to alert the US Coast Guard that their design premise for the Rescue 21 system using 1 watt hand held radios at 6 feet high is faulty. Not sure how it's been working all these years. Must be some sort of RF magic.

 

[gman1971]

@prcguy, I was being sarcastic; yes. I am aware that with 5W you can reach satellites and other things very far away...

@mmckenna, lol, RF magic... if you believe this is magic then that sums it all up...

G.

 

[KJ7GHU]

I came across this dialog and was instantly interested. There is a small "community" in eastern Washington where a few of my family reside. The service area would be under 10 miles and one of my cousins has a place on the side of a mountain about 200 feet from the valley floor. If I built a repeater at his place I think, based on a the terrain map, there would be no radio shadows for the rest of the community.

Currently I am a licensed HAM with my Tech license and found this to be an interesting problem. I would enjoy hearing from anyone who has built a GMRS repeater.

73,
Dale

 

[gman1971]

Hi there KJ7GHU, as you probably know, altitude is king. The hillier the area, the more elevation you'll need to cover everything without shadows/blind spots. Adding buildings into the mix requires even more altitude + antenna gain + good radiation pattern. The more power you have on the TX side the better your filtering/duplexer will need to be in order to keep the RX side from desensing. GMRS max legal is 50W, no limit on antenna gain.

200 feet AGL without knowing the terrain is kinda impossible to guess what kind of range.

This website will help you determine coverage for whatever kind of repeater you want to setup. It has worked wonders for me, and I know the repeater guys here in the linked GMRS midwest network group use it.
Radio Mobile Online


G.

 

[amphibian]

Currently I am a licensed HAM with my Tech license and found this to be an interesting problem. I would enjoy hearing from anyone who has built a GMRS repeater.

Building a GMRS repeater is no different than building a 70cm ham repeater ---- just remember to program it for the GMRS repeater frequencies and you can not go over 50 watts at the Transmitters RF port. Unlike ham, commercial, and PS, GMRS does not require a separate license and does not require co-ordination and/or application fees. Best practices are: 1: try to make sure you don't place one in operation that's on the same frequency as another GMRS repeater within 50 miles of where you want to place yours unless you have no other choice then make sure yours and the other one do not share the same CTCSS/DPL codes, 2: if there are already other GMRS repeaters in the area try first working with the owner of those before spending your hard earned money putting yours into operation, 3: remember that you are still responsible for all that happens on your repeater even though you give 1-100 others permission to use your repeater, and 4: like ham always try to obtain good clean and inexpensive working radio equipment and find the best location for the least amount of money (including monthly money) to put the antenna & repeater at. Tower site cost can get very expensive if you are not aware of the ins and outs of tower/building charges.

I've built, bought, sold somewhere in the area of over 300 repeaters over my career in the RF field. The ones I built ranged from a cost of 100 bucks (yes you can do a total build of a quality GMRS repeater along with the antenna for 100 bucks if you shop around and do a little trading here and there) up to thousands. Each and every one of them have had a challenge of their own. Some have been as simple as making eggs for breakfast and others ---- well there have been times I didn't have enough hair to pull out... If you are a licensed ham as you mentioned, then I would suggest getting with some of your local ham club members that have built a few repeaters and get suggestions and ideas from them first.

Good luck,

amphibian