I have a dream of setting up a repeater on the top of my mountain which has not power

[MacJack]

I'm a newbie to GMRS and made a great connection with my local repeater guy and sent him a donation to keep it up.  His repeater is not that busy but I want to add my own on my hill (mountain).  No electric available, good solar view and need to hear how you guys did or would set up your repeater in waterproof Tupperware box... solar, battery, duplexing two radios (40 watts) with cables plus one antenna...  

 

Looking for low maintenance as I will not be going up the mountain that often...  hard hike carrying equipment up the mountain.  I should add the only one repeater in area and not a high traffic area and want to respect my new buddy repeater traffic and his history (friends etc).  

 

So I looked at RT97 https://shop.mygmrs.com/collections/featured-products/products/retevis-rt97-gmrs-repeater-5w  and found out it is not as advertised being 10 watts.  In fact I wanted 30-40 watts unit as using HT 4 watts.  

 

Thanks in advance for your help and if Admin needs to move this to another forum, great... 

 

Jack

WRJX754

[JohnE]

PM sent

[Radioguy7268]

Hopefully you've already read the thread on: "I just got my GMRS License and now I want my own repeater".

 

Solar and high power repeaters don't play so well together if your budget is less than NASA. If you've got a high elevation site, you can talk to everywhere you can "see" at relatively low power. Higher power margins just help to overcome background noise and decrease fading. I'd tell you that 10 watts going into an actual 6 dB antenna is an ERP of 40 watts - and probably overkill if you're using 4 watt portables to talk back. If you really want to make a repeater work better - a better receiver is worth much more than transmit power.

 

If you really do have the idea of "doing it once, and doing it right" you need to forget about Retevis for a mountaintop site, and you also need to forget about using tupperware. A NEMA style weatherized box can be placed outdoors, and will hold up well against the elements if you pay attention to properly sealing up any holes or bulkhead fittings. I've got outdoor sites that have held up for more than 15 years with a NEMA box on a pole - but I wasn't dealing with 8000+ ft elevations or extreme winds/icing.

 

You can buy a high end used commercial repeater like an MTR2000 for about the same cost as a new Retevis RT97 - and you're getting 10 times the quality. Most reputable sellers will even program it for you - saving you the expense of cables and software.

[gortex2]

For a solar setup the RT97 is ideal. If your only planning to use HT's to talk to it talking back at same power should work well. A 50 watt repeater does nothing more for a 4 watt radio trying to talk back. Buy a decent antenna (DB404 or other commercial UHF) and good cable and it will outperform your expectations. Go cheap on cable and antenna and you will loose interest quickly.

[MacJack]

Thank you guys for your comments...  keep them coming as it helping me turn dream to develop a plan...

[MacJack]

JohnE, I looked you up and your post and did not see it... please direct me to that.

 

Hopefully you've already read the thread on: "I just got my GMRS License and now I want my own repeater".

 

[wayoverthere]

JohnE, I looked you up and your post and did not see it... please direct me to that.

https://forums.mygmrs.com/topic/1402-you-just-got-your-gmrs-license-now-you-want-your-own-repeater/

[taco6513]

Get a DB420 for your antenna.

WRCW870

[jerrym58]

There are a lot of engineering details that go into setting up a repeater. I think if your friend’s repeater is serving your needs and you have an amicable working relationship that you are ahead just helping him maintain his repeater. But if you are going to forge ahead anyway here’s some things to think about. Mountain tops get hit by lightning frequently. You need to ground the antenna support structure and ground the coax to the same structure. Surge protection like a Polyphaser is also needed. All ground rods need to be connected with large diameter ground wire. Motorola’s R56 manual is the Bible for site grounding. I agree with another comment on the DB420 antenna but it is very high gain. When you increase the gain you narrow the vertical beam width. I think that antenna’s gain drops in half at about 5 or 6 degrees down so depending on how high your mountain is there may not be enough power and sensitivity left in the valley below. For sites lower to the ground I think the DB420 is the best UHF repeater antenna ever made. I have put many of these up for business repeaters. On a mountaintop site you may have to select a non-standard PL tone or DCS code to stay out of a neighboring repeater’s coverage area on the same frequency.

[WRKC935]

I have experienced a DB420 being used at too high of an elevation in Columbus, Oh.

Commercial repeater owned by a TV station. Had repeater and antenna mounted at 750 foot on a work deck. 

Repeater would talk to Indiana with no problems.  It however would not work at all within the 270 outer belt unless you were in the helicopter. 

Think of antenna gain from an omnidirectional antenna like this.  The pattern of the antenna is like a doughnut.  In order to get gain from it, you have to crush the doughnut.

So as you compress the doughnut, and it spreads out (directional gain) the bottom and teh top get pushed together.  You need to be IN the doughnut in order to talk and hear the signal.

If you raise the bottom of the doughnut above the ground, then you no longer have coverage. 

 

 

Now, on to solar powered repeaters.

Honestly the repeater / duplexer / antenna is the easy part. 

The amount of storage and charge capability of the panels, specifically what amount of each that you need, are the difficult part.

And this all hinges around the load.  The receive / not transmitting part is easy to figure out... you put a current meter on the radio and see what it's drawing at rest. 

Then you get a reading on what it's drawing when transmitting.   The hard part is figuring out how much transmitting the repeater will be doing in a 24 hour period. 

How many amps for how many hours.  And you need to be reasonable with transmitter power as well.  Is this going to be a public access repeater?  How many folks do you expect to be on it and for what length of time.

How many hours are there is a day during the winter where you are wanting to put the repeater?  Does this location have good views of the Southern sky? 

The reason for the winter day time is summer is easy.  Days are longer than the night and A couple 300 watt panels and a car battery will keep you going.  The winter, snow fall on the panels, possible lack of access (you did say mountain) is where you need to closely consider storage and charge capability.  If you are drawing 2000 watts or power out of the battery system per day and due to day length and other factors can only put 1500 watts of power back into the batteries during the course of a day, your battery plant will go dead. 

 

Couple things to know.

First is output power (RF) requirements aren't near what you think you need.  (Most will want 50 watts)

Case in point.  I have a system I manage that has 420's for transmit and receive through a combiner.  The antenna's are at 400 for receive and 380 for transmit. 

Base stations are set at 20 watts out.  They will not turn down further.  So 20 watts out the back, into an 8 port combiner that drops 3 db off the signal.  Then through 600 feet of 7/8 cable with a loss of 2.65 db per 100 feet. 

Calculator says that's 13.25 db of loss.  Now that is in addition to the 3 db from the combiner.  So 16.25 db of loss figured against 20 watts.  If we convert 20 watts to dbm... we get 43.0103 dbm.  Subtract 13.25 db and you get 29.76 dbm.  Now switch that back to watts and it's a antenna melting 912mW  or milliwatts.  Not even 1 watt at the base of the antenna and the thing talks from Columbus to London Ohio.  that's 40 some miles.  Granted the antenna has some gain.  But the system is still an alligator,,, big mouth,  out talks it's receive abilities. 

Point is that if you run 2 watts in to a db420 or even a 408 and have a duplexer with only 1 db or so of insert loss and a 30 foot run of cable, and not 500 feet, then you are gonna still talk at least as far as you hear. 

Once you are getting serious about this endeavor, go download and figure out a freeware software called Radiomobile.  It's a coverage mapping software.  Do coverage testings with low power levels of 30 or 33 dbm (1 or 2 watts)

Once you see that going from 30 dbm to 40 dbm or 50 dbm (1 watt to 10 watts to 100 watts) you will see that the coverage doesn't drastically change.  Of course the 100 watts is purely for seeing the difference as we are limited to 50 watts out on a repeater. There is some change, to be sure, but it's not a 10 mile circle vs a 100 mile circle.  And since the software takes into account frequency and topographical data for the area around the transmitter site, you may find that only 1 watt will sufficiently cover the area you wish to serve and beyond that the topography of the land stops the signal anyway. 

 

Lots of math involved in a solar setup to be sure. 

But if you are serious, I would be looking for a lower powered repeater that runs on 12 volts and not 24 and begin searching out solar panels. 

And be aware that panels will show the MAX output in direct sunlight.  Meaning that a 300 watt panel is only going to do 300 watts on a cloudless day at high noon when it's being fully hit by the sun directly and not at an angle.

What ever it says on the panel figure 1/4 to 1/2 will be the average output throughout the course of the day.

[gman1971]

For very high up places you're better off with a low gain, or unity if the altitude difference is too big.

 

G.

[n4gix]

I have experienced a DB420 being used at too high of an elevation in Columbus, Oh.

Commercial repeater owned by a TV station. Had repeater and antenna mounted at 750 foot on a work deck. 

Repeater would talk to Indiana with no problems.  It however would not work at all within the 270 outer belt unless you were in the helicopter. 

Think of antenna gain from an omnidirectional antenna like this.  The pattern of the antenna is like a doughnut.  In order to get gain from it, you have to crush the doughnut.

So as you compress the doughnut, and it spreads out (directional gain) the bottom and teh top get pushed together.  You need to be IN the doughnut in order to talk and hear the signal.

If you raise the bottom of the doughnut above the ground, then you no longer have coverage. 

 

Those antennas can be ordered with the amount of down tilt you need to offset the squished doughnut enough to regain the coverage needed.