Just completed my first build of a portable GMRS band repeater (UHF 462/467 MHZ simple license band). GMRS radios are cheap and affordable in many retail electronic stores. They operate on FCC allocated UHF frequencies between 460-470 MHZ. Different from ham the license to operate is merely pay to purchace and no test required. There are many affordable chinese clone radios that can be programmed to operate on and within FCC specified limits for GMRS channels, as well as Ham radio frequencies or commercial frequencies.
Handheld radios sold in retail have all sorts of silly claims about how far their range is. These claims seem almost useless. In reality it's all about how high above the ground is your transmitter, how clear is your line of site of obstructions, how good is your antenna(does it have signal gain or does it attenuate the signal), and probably lastly how much power can you transmit. Normal handheld radio antennas aren't very good and power is normally 2-5 watts and often less with the minature FRS/GMRS combo radios sold in retail. Range handheld to handheld on flat wooded terrain tends to be less than 1 mile. Open terrain and clear line of site can increase this dramatically. Height and a good antenna are even better.
I chose to create a "simplex repeater" this uses a surecomm SR112 repeater controller box which cost about $40 and comes with a cable to plug into most handheld GMRS radios(and ham and chinese clones). When the radio receives a signal the surecomm SR112 records it and then spits it back to the radio to retransmit back out. In it's simplest form you can use a fishing rod to sling a sinker and line over a tall tree and then tie off to a handheld connect to the SR112 and you can create a 1.5-2 mile radius communication bubble. Anyone on the repeater channel can transmit and the repeater will receive and retrans on the same channel. If you are within range of the repeater you will hear your transmission played back to you and be sure that it has been retransmitted throughout the area. If not you will know you are out of range and can only and still communicate line of site to others near you.
In my setup I utilized a comet CA-712EFC omnidirectional 460-470mhz GMRS 9.5 DB gain base station antenna. This Antenna was a bit expensive at around $150 on Ebay. 6-7DB gain antennas are smaller, around half the price, and likely a better choice for a portable setup. For a radio I used a leixen note which is a very large chinese handheld with actual real power output as much as 25 watts that operates between 400-480MHZ. In my application it puts out about 5W on low 8-10W on medium and 17-19 W on high(per my wattmeter). I set it on medium for the repeater radio. I'm using a tuperware box and duct tape to house the radio and surecom SR112....................Of importance is the fact that the radio is suspended in the air under the antenna connected by less than 2ft of coax to the radio. I tested a setup with a 70ft transmission line leading to the antenna. The line loss of the long transmission line reduced the signal of received transmissions to the point that my range was cut by about 40%. ...................The radio and repeater box have internal batteries. I'm experimenting with a car battery connected to the radio with field telephone wire to trickle charge the radio battery keeping it going for several days at a time. There is issue with having both radio and repeater controller on the same DC battery/common ground. It messes up the PTT on the radio. (I will try diodes in the battery cables to fix this). ..................Antenna must be as far away from dense vegetation as possible for the signal to propagate with maximum effeciency. On my first try the antenna was within 3 feet of the main tree trunk and it had a serious negative effect on range. Second try a picked a hardwood tree and a branch 15 feet out from the main trunk and had a dramatic increas in range.
Currently I am getting 3.5-5+ mile range from handheld to the repeater. If you're in a open area and stand in the back of your truck with your handheld you can get a really long range to the repeater. In the woods standing on the ground it is much less as your signal has to propagate out through the trees and vegetation. Terrain here is flat and river bottom with 75% mature timber.
This is a great low cost setup you can cache on a hill top or in a tall tree to facilitate communications in lack of cellphone infrastucture for your family camping and off road adventure, club off road trip in rural area without cell signal, emergency communication in neighborhood or large area of town in power/network out situation.
Handheld radios sold in retail have all sorts of silly claims about how far their range is. These claims seem almost useless. In reality it's all about how high above the ground is your transmitter, how clear is your line of site of obstructions, how good is your antenna(does it have signal gain or does it attenuate the signal), and probably lastly how much power can you transmit. Normal handheld radio antennas aren't very good and power is normally 2-5 watts and often less with the minature FRS/GMRS combo radios sold in retail. Range handheld to handheld on flat wooded terrain tends to be less than 1 mile. Open terrain and clear line of site can increase this dramatically. Height and a good antenna are even better.
I chose to create a "simplex repeater" this uses a surecomm SR112 repeater controller box which cost about $40 and comes with a cable to plug into most handheld GMRS radios(and ham and chinese clones). When the radio receives a signal the surecomm SR112 records it and then spits it back to the radio to retransmit back out. In it's simplest form you can use a fishing rod to sling a sinker and line over a tall tree and then tie off to a handheld connect to the SR112 and you can create a 1.5-2 mile radius communication bubble. Anyone on the repeater channel can transmit and the repeater will receive and retrans on the same channel. If you are within range of the repeater you will hear your transmission played back to you and be sure that it has been retransmitted throughout the area. If not you will know you are out of range and can only and still communicate line of site to others near you.
In my setup I utilized a comet CA-712EFC omnidirectional 460-470mhz GMRS 9.5 DB gain base station antenna. This Antenna was a bit expensive at around $150 on Ebay. 6-7DB gain antennas are smaller, around half the price, and likely a better choice for a portable setup. For a radio I used a leixen note which is a very large chinese handheld with actual real power output as much as 25 watts that operates between 400-480MHZ. In my application it puts out about 5W on low 8-10W on medium and 17-19 W on high(per my wattmeter). I set it on medium for the repeater radio. I'm using a tuperware box and duct tape to house the radio and surecom SR112....................Of importance is the fact that the radio is suspended in the air under the antenna connected by less than 2ft of coax to the radio. I tested a setup with a 70ft transmission line leading to the antenna. The line loss of the long transmission line reduced the signal of received transmissions to the point that my range was cut by about 40%. ...................The radio and repeater box have internal batteries. I'm experimenting with a car battery connected to the radio with field telephone wire to trickle charge the radio battery keeping it going for several days at a time. There is issue with having both radio and repeater controller on the same DC battery/common ground. It messes up the PTT on the radio. (I will try diodes in the battery cables to fix this). ..................Antenna must be as far away from dense vegetation as possible for the signal to propagate with maximum effeciency. On my first try the antenna was within 3 feet of the main tree trunk and it had a serious negative effect on range. Second try a picked a hardwood tree and a branch 15 feet out from the main trunk and had a dramatic increas in range.
Currently I am getting 3.5-5+ mile range from handheld to the repeater. If you're in a open area and stand in the back of your truck with your handheld you can get a really long range to the repeater. In the woods standing on the ground it is much less as your signal has to propagate out through the trees and vegetation. Terrain here is flat and river bottom with 75% mature timber.
This is a great low cost setup you can cache on a hill top or in a tall tree to facilitate communications in lack of cellphone infrastucture for your family camping and off road adventure, club off road trip in rural area without cell signal, emergency communication in neighborhood or large area of town in power/network out situation.
