PDA

View Full Version : GMRS question



bacpacker
03-06-2011, 01:45 AM
I have a question for the forum. I have been ask about how to put together a repeater for a GMRS system. I've dome ham radio for years, but have no clue about GMRS. Does anyone on here have any expereince with it? How if works with repeaters in particular?
Thanks for any help you can lend.

Robert96
09-21-2011, 06:46 PM
A GMRS repeater is simply a UHF machine, set up on one of the designated repeater pairs for GMRS. You're legally limited to 50 watts out to the antenna. They require no coordination, you just build the machine and put it up (assuming you already have a GMRS license from the FCC.)

Lots of information on GMRS out there on the web.

Paul AE5PB and
GMRS WQCX 344

izzyscout21
09-21-2011, 08:29 PM
My interest is peaked. Sounds like really cool option for comms.

Stormfeather
09-30-2011, 09:18 PM
Ok, so say I have Garmin Rhinos with the GMRS function/capabilities. . . is it possible to build one of these antennas and extend the range of my non-licensed garmin rhino? (hypothetically speaking of course, wouldnt want to run afoul of the FCC Police)

bacpacker
09-30-2011, 10:42 PM
I don't believe the Rhino is capable of being set up as a repeater. Does it have a removable antenna on it or is it fixed? If it's not removeable their wouldn't be any way to hook up another antenna. Also IIRC correctly the Rhino is a low power (5watts or less) unit.
I don't know much about GMRS (the guy I was going to help build a repeater ended up not setting it up, at least not yet) but I think a good brand to look at for setting up as a repeater would be a Motorola buisness band unit and set it up with the GMRS frequencies. The Motorola's can put out up to 50 watts depending on model. That paired with a good antenna placed in a good location such as a hill top or mountian would give you very good coverage in your area.

dragon5126
10-05-2011, 10:41 AM
OK a little misconception here... ALL GMRS radios require licensing to operate on GMRS frequencies. there are some that operate low power on shared (with frs) frequencies as well as have the FRS frequencies available to use. you do not need a license for the FRS frequencies but do for the shared and dedicated GMRS frequencies per the FCC (fcc.gov). Next not all GMRS radios are able to operate on repeaters as not all of them are capable of duplex operation. Some but not all GMRS hand helds can be connected to an external antenna. If it has any FRS capability it can not have the ability to use an external antenna as this is forbidden on ALL FRS radios (FRS is Family Radio Service, and are the cheap little hand helds. Radio shack sold one mobile that looked like it had an external antenna but it actually was the entire radio in the antenna base, with a remote control head, for a while)

Stormfeather
10-05-2011, 08:09 PM
OK, Ive got the Garmin Rhino 120's with scrambler technology incorporated in them. They do not have removable antennas, but they are both FRS and GMRS radios. Thats why I was asking if I would be able to access GMRS frequencies or be able to utilize a repeater with them. Are these worth it or no?

dragon5126
10-07-2011, 06:25 AM
OK, Ive got the Garmin Rhino 120's with scrambler technology incorporated in them. They do not have removable antennas, but they are both FRS and GMRS radios. Thats why I was asking if I would be able to access GMRS frequencies or be able to utilize a repeater with them. Are these worth it or no? OK Had to go to garmins site to double check a few things so here comes an edit... the scramble you refer to is only on the GPS transmit position function, not on voice transmission.

Yes the Gmrs frequencies are in the radio and are useable but you are SUPPOSED to fill out a license application and send it in and wait for the issuance of a licence and follow the proper regulations before using them. Current production US authorized Rhinos CAN use repeaters and are set up for it on the authorized repeater frequencies only. However those made for Canada (the ones I had experience with) have these frequencies blocked out since Canada does not allow repeaters for GMRS use.

While I was on the site I see they have extended the line considerably... I need to check it out !

dragon5126
10-07-2011, 06:33 AM
As for worth it, there arent any other GPS units out there that will send your GPS location directly to another GPS... so you are looking at apples and oranges. if you are talking about just a two way radio, in all honesty, they suck, any radio capable of FRS falls into that trap. Dedicated GMRS radios are far superior, and there are ham radios now that do what the rhinos do but require a ham license and are much more expensive. As for a GPS... it's the only one that has a radio, again with the exception of the ham rig. Yes they are valid and worth having, you just have to realize that they have limitations due to the compromise of the FRS side.

bacpacker
10-07-2011, 01:45 PM
With the ham radios Yeasu has a ht model# VX-8DR that has built in GPS capability and can been seen from other units, plus the full vhf/uhf bands. You do need the license and the radio runs $359-400, but gives you good capabilities.

Stormfeather
10-07-2011, 04:51 PM
Ahh, so basically, my units dont have enough ass to transmit the distance I want them to is what Im finding out. Apparently 0.5 FRS and 1.0 GMRS just doesnt make the range I need it to. So. . . Im thinking im going to put a few units up for sale and see about getting some of the new Rino 650's. Apparently they have 5x the transmit power on GMRS. 5 watts on gmrs sounds good if im reading this right. What do you guys think?

bacpacker
10-07-2011, 05:17 PM
5 watts vs 1 will help you out for sure, with any type radio. I do know from my time as a ham that your antenna is as important as the power your putting out. You can run 1000 watts thru a peice of crap and not be able talk very far, where 5 watts with a good antenna design will allow for great comms.

dragon5126
10-08-2011, 03:09 AM
OK here we go into teaching mode. Power is relatively irrelevant as BP has stated, all things being equal. what does matter is the antenna, it's position and the operating frequency. They try to claim 20 miles on the 5 watt units. the reality is that will only happen if you can see the other radio 20 miles away. These rigs are strictly line of sight and that means exactly what it sounds like. the frequency they operate on transmits in straight lines, the radio waves do not curve along the surface of the earth like lower frequencies do. so quite literally if the other radio is below the visual horizon of where you are using yours. you wont reach it. a better antenna will concentrate your transmitted power toward the horizon but will not over come this. a higher antenna may. Just like when you are up on the roof or in a tall building you can see further in the distance, because this changes your view of the horizon it does the same thing for radio waves. Also the type of antenna will concentrate the radio wave closer or farther to or from the horizon.

an Ideal antenna is referred to as an isotropic radiator. and while they really don't exist they are a model that is used to define antenna performance. An isotropic radiator would transmit it's energy in a perfect sphere, think of a beach ball, with the antenna going through the center. In the real world the radiation pattern is closer to a donut, flattened at the top and bottom. The better the antenna is the flatter the donut gets, so lets look at that beach ball again... push down on the top of it against the floor, the flatter it gets the wider it gets, the same thing with transmitter antennas. we want a nice flat donut for a radiating pattern. The problem is your hand, arm, head and body will affect the pattern and skew it so few antennas on the radio it self are very effective, but there are some tricks that can be used, like holding the radio up in the air and using a separate speaker mic, an antenna that isn't mounted on the radio, a device known as a tiger tail which is actually a part of the antenna the manufacturer didn't include because it is a dangling wire hanging off the radio (in specific the antenna's ground).

Now most people are used to using a term known as "s units" this comes from CB days. to give you an idea of how power relates to the received signal, S units are based on a scale from 1 to 9 and 9 plus (normally we would call it a scale of 1 to 10 but thats how it is referred to since anything over 9 is full scale and may actually be a signal stronger than ten but thats where the meter stops). if the person you are talking to is transmitting 1 watt and you are receiving them at a level of 1 they will have to increase their power by ten fold to make an increase of one unit at your position. Now they are transmitting 10 watts and you are receiving them at 2 units to increase it one more unit, they again have to increase their power by ten fold that means to make it up to 3 units at your end they need to xmit 100 watts, 4 units takes 1000 watts and so on, it is an exponential progression of power. So as you can see the single most important item is the antenna and it's position well beyond anything else.

Next we have to look at where you are, the terrain can physically block your signal. rock, concrete, metal and trees full of moisture, green wet vegetation all can block the signal as well. so really the only place you will get the full performance out of a hand held radio with an antenna directly connected to it is on a body of water with nothing in between the two radios ( the water acts as an improved ground plane, topic for another time). Dammit where did those paragraphs run off to???

bacpacker
10-09-2011, 02:03 AM
Very good discussion on antenna's. It is hard to describe, understandably, how they work. You did good.
Next you get to describe the various types of antenna's. :)

dragon5126
10-13-2011, 10:04 AM
heck thats easy! first there are antennas that stick up in the air, then there are antennas that lay side ways and then there are broken antennas... any questions? Seriously though... It'll have to wait til I have two eyes... got an infection in my right eye and am fighting the eyestrain which is why I've been absent as of late. but if everyone will come up with questions it will speed up the explanations, and the theory applies to all radio communications not just gmrs.