Radioguy7268

Again, if you want to use DMR for Digital simplex, the FCC already offers you a service for this choice. Go get a part 90 license, talk on DMR simplex all day long. Make sure you license it as an MO6/FB6 Private Carrier, and then all your friends and family (plus anyone else you want to count as a 'subscriber' under your license) can join along for one 10 year term. As a bonus, you can use encryption, run a repeater, and even pump out more than 50 watts.
There are no GMRS  Part 95 radios that will do Digital today, so unless you want to wait for a possible rule change, wait for manufacturers to respond to the changes and build GMRS digital radios, you would end up using Part 90 equipment anyway.
I really don't understand the resistance to using what's already available today. If you want to use DMR, then use DMR - it wasn't like you were going to be using it to talk with existing analog GMRS users anyway.
 

Again, if you want to use DMR for Digital simplex, the FCC already offers you a service for this choice. Go get a part 90 license, talk on DMR simplex all day long. Make sure you license it as an MO6/FB6 Private Carrier, and then all your friends and family (plus anyone else you want to count as a 'subscriber' under your license) can join along for one 10 year term. As a bonus, you can use encryption, run a repeater, and even pump out more than 50 watts.
There are no GMRS  Part 95 radios that will do Digital today, so unless you want to wait for a possible rule change, wait for manufacturers to respond to the changes and build GMRS digital radios, you would end up using Part 90 equipment anyway.
I really don't understand the resistance to using what's already available today. If you want to use DMR, then use DMR - it wasn't like you were going to be using it to talk with existing analog GMRS users anyway.
 

You also have the issue that while DMR is a basic digital standard, every manufacturer has their own flavors that they have built on top of the standard to add features for their user base. So when one repeater owner decides to add Restricted Access for Security, and then another one wants to add enhanced Privacy/encryption, another will decide to implement GPS Location. Good luck trying to them all on board with your DMR dream.
As already mentioned before - go get yourself an FB6 Private Carrier license on Part 90 if you want to do DMR. If you're determined that it needs to be done on GMRS frequencies - then go write up a petition for rule change & wait around for 5 or 10 years to see if the FCC responds.
 
 

You also have the issue that while DMR is a basic digital standard, every manufacturer has their own flavors that they have built on top of the standard to add features for their user base. So when one repeater owner decides to add Restricted Access for Security, and then another one wants to add enhanced Privacy/encryption, another will decide to implement GPS Location. Good luck trying to them all on board with your DMR dream.
As already mentioned before - go get yourself an FB6 Private Carrier license on Part 90 if you want to do DMR. If you're determined that it needs to be done on GMRS frequencies - then go write up a petition for rule change & wait around for 5 or 10 years to see if the FCC responds.
 
 

You must be new here.  50% of the new posters in these forums cannot even figure out how to program an analog repeater into their new GMRS radio.  Do you seriously think that DMR will work for "every man"?
And before you ask, I am *very* familiar with programming a DMR repeater and DMR radios, both Motorola and other brands.  It's orders of magnitude more difficult than programming an offset and a tone or two for an analog repeater.

40 miles is quite a stretch for a 4 or 5 watt portable to reach back to the repeater in most real world situations. I'd question why you think you might need 50 watts in order to reach 40 miles out, but you're not worried about the other half of the path - the repeater's receive side. If you need lots of power to reach out, how's that 4 or 5 watt portable going to answer back?
If there's power in the building, it's probably 10 times easier to just use that. I don't think I've ever put a repeater cabinet outdoors on a building rooftop. Even if they didn't want to have us penetrate the roof, we could always find a way to wall mount the repeater inside & then sneak a coax cable out onto the roof. I have had to use non-penetrating sleds and find interesting ways to hide antennas so that the building architecture was not 'damaged' by the sight of an ugly exposed dipole. But solar power on top of a building that already had existing service? Nope.

Who are you talking to and what do they carry for a radio? I believe you said you've got relatives 15 miles away. If they carry portables - it is MUCH more important that your desired repeater can hear those 4 or 5 watt portables from 15 miles away than it is for your desired magic repeater to punch out 50 watts so you can reach them.
Pay more attention to how well your repeater can receive - and you'll end up with a better system.
Wouxun mobiles built into a repeater are twice as expensive and half as good as other solutions available. Search up the term desense, and you'll see what's going on.

Spurious emissions are like farting on the airplane: benign to you but a discomfort for the neighbors. Studies aren't needed. Keying your Baofeng will not bring Airbus or Boeing or Embraer down, it will simply stink up the joint.

Is it just me, or are the GMRS/FRS rules and regulations among the most convoluted, ill-conceived and poorly-written set of rules the FCC has ever come up with? It could be just me. Maybe not. It could be others too. Or just me, I don't know.

This was one of the first threads I delved into when I first got my GMRS license and joined this forum.  It should almost be required reading:
 

If you are talking to 4 watt portables - who cares how much power gets through the duplexer? A "tight" duplexer tuning that loses more dB is preferable to a sloppy duplexer tune job that gets more power/less dB loss.
Remember, you are using the duplexer to achieve isolation between the transmit and receive frequencies. Isolation is your key measurement - NOT power throughput.
On most of these rigs built with an inexpensive notch AKA compact duplexer and 2 mobile radios, turning DOWN the transmit power will result in better overall range, less desense, and longer equipment life. 
 
 

If you are talking to 4 watt portables - who cares how much power gets through the duplexer? A "tight" duplexer tuning that loses more dB is preferable to a sloppy duplexer tune job that gets more power/less dB loss.
Remember, you are using the duplexer to achieve isolation between the transmit and receive frequencies. Isolation is your key measurement - NOT power throughput.
On most of these rigs built with an inexpensive notch AKA compact duplexer and 2 mobile radios, turning DOWN the transmit power will result in better overall range, less desense, and longer equipment life. 
 
 

Radio waves don't know the direction in which they are heading - ie: being transmitted or received. The signal is the signal. The trouble you originally described would not be due to antenna height.
Why go through the trouble of raising up the antenna, but avoid doing a simple 5 minute troubleshooting test and report on the results?
 

Radio waves don't know the direction in which they are heading - ie: being transmitted or received. The signal is the signal. The trouble you originally described would not be due to antenna height.
Why go through the trouble of raising up the antenna, but avoid doing a simple 5 minute troubleshooting test and report on the results?
 

The main reason 90% of repeaters use a duplexer is because of ISOLATION, not because of power loss. As others here have said, yes you can work it with 2 antennas, but you will likely still need additional filtering. If all you can measure is wattage & SWR, you are never going to appreciate what true isolation and improved receive sensitivity (and selectivity) can do for your repeater.
How's that saying, when your only tool is a hammer, every problem looks like a nail?  I guess in the radio world, when all you have is a watt meter, every problem looks like a lack of power.
If you have enough RF power to reach out to whoever you want to talk with, but they can't reach you back because your repeater's receiver is being drowned out due to poor isolation (likely from your own transmitter)  - then what's the point?  You've now got a bunch of time and money invested in a one way paging system. The point of having mobile transmitters is to allow them to talk back.
I'd gladly give up 3 dB of transmit power in a duplexer if it offered 100dB of isolation. Most of the affordable compact notch duplexers will only give you about 65dB of isolation with a 5 MHz split. Add a tuned bandpass cavity or two to the receive side, you'll pick up even more isolation - and you'll still be ahead of the 45 or 55 dB isolation of a split antenna system with 20 or 25 ft. vertical spacing.
Oh yeah, and if you do a split antenna system, don't use braided cable for your coax. You'll leak somewhere around 6-10% of the signal with most decent brands - even worse with the cheap knockoffs that use a loose weave for the coaxial braiding. Think about where that 6-10% of your signal is going as it travels up the tower. Even the real Heliax hardline has some RF signal leakage, but it's about as good as you can get in an imperfect world.

^^^^^ Is 100% accurate. It baffles my mind when folks say they need a 50 watt repeater and all they have are 4 wat handhelds. We used to deal with this in the LMR world all the time. Balance of a system is not only good practice but can help reuse frequencies also. We had multiple factories in one city all using the same frequency. All of them were far enough apart the 5 watt TX repeaters did not interfere with the other sites. 
Our C-C SAR repeater on UHF is set for 10 watts at our antenna on TX. We only have UHF portables and no mobiles. Rarely does one who can talk to the site not hear the site. Even my testing with a mobile was great. When you can see the antenna from miles away no need to have a ton of power. 
In the GMRS world with limited repeater frequencies this is something all should remember. 

You need vertical separation for a dual antenna setup. Unless your doing a combiner and receive multi-coupler I don't see the value in the dual antenna setup. A good duplexer will have a small amount of loss and in the end work much better than the dual antenna setup. There is alot more to this discussion than just antenna. The repeater is another big item that needs to be figured out. A repeater made from cheap mobiles will be worse in a dual antenna setup than a purpose built LMR repeater. 
In the LMR world a lot of sites use dual antenna. My one SAR site uses a receive multi-coupler with a DB408 at 35' up a tower. The TX antenna is thru a TX combiner at 15' off the ground. With the filtering on both TX and RX I see no desense at all on 75 watt Quantars on GMRS and our SAR channels. Another site we have an ICOM FR4000 with a BPR duplexer. Out of the duplexer is a 30 watts into 1/2" LDF 150 up the tower. Again no desense at all and there is multiple LMR repeaters at this site. Both sites have great coverage for the area and both serve specific purposes. If I didn't have other SAR LMR frequencies at the first site we would have a duplexer. 
Normally the cost of feedline and antenna will be the same cost of the duplexer. 
 
 

The main reason 90% of repeaters use a duplexer is because of ISOLATION, not because of power loss. As others here have said, yes you can work it with 2 antennas, but you will likely still need additional filtering. If all you can measure is wattage & SWR, you are never going to appreciate what true isolation and improved receive sensitivity (and selectivity) can do for your repeater.
How's that saying, when your only tool is a hammer, every problem looks like a nail?  I guess in the radio world, when all you have is a watt meter, every problem looks like a lack of power.
If you have enough RF power to reach out to whoever you want to talk with, but they can't reach you back because your repeater's receiver is being drowned out due to poor isolation (likely from your own transmitter)  - then what's the point?  You've now got a bunch of time and money invested in a one way paging system. The point of having mobile transmitters is to allow them to talk back.
I'd gladly give up 3 dB of transmit power in a duplexer if it offered 100dB of isolation. Most of the affordable compact notch duplexers will only give you about 65dB of isolation with a 5 MHz split. Add a tuned bandpass cavity or two to the receive side, you'll pick up even more isolation - and you'll still be ahead of the 45 or 55 dB isolation of a split antenna system with 20 or 25 ft. vertical spacing.
Oh yeah, and if you do a split antenna system, don't use braided cable for your coax. You'll leak somewhere around 6-10% of the signal with most decent brands - even worse with the cheap knockoffs that use a loose weave for the coaxial braiding. Think about where that 6-10% of your signal is going as it travels up the tower. Even the real Heliax hardline has some RF signal leakage, but it's about as good as you can get in an imperfect world.

Or "Handie Talkie".  A portable handheld radio; what many call a "walkie talkie".

OK, now I understand a little better about what you're asking.
In my world, terminology of a "base" station means you are transmitting on the lower (462.x) frequency, and speaking in simplex to other people on the same 462.x channel.
A Control station is what you use to work a distant repeater, and those transmit on the higher 467.x frequencies. Then they receive on the 462.x   The appearance of a Base or Control station can be the same (a mobile radio on a desktop) but the programming and functionality would differ.
You're not going to work a distant repeater by transmitting on the Base (462.x) frequency. If you have a repeater using a duplexer, you're not going to be able to do what I suggested (plugging in a mic) to do what you want.
If you key your Control station on a 467.x frequency that's the same as your repeater, you're going to overpower the receive side of your repeater. Not recommended.

If the two radios are not keyed at the same time, they should not interfere with each other.
If the repeater and the base would be keyed at the same time, the stronger signal from the base would likely walk all over the repeater's output. Assuming you would be the one in control of the base radio, why would you knowingly create your own interference?
I guess my biggest question is "why?"  Other than being in love with the concept of a small 5 watt self contained repeater, you could just put in a larger and higher power repeater using the existing antenna & line that you've already got in place, and then plug a mic into the repeater so you could use it as a dispatch point. Pretty much every mid-range commercial repeater offers that option, especially if they're made from two mobile radios - like a CDR700 for example:
 
 
 

Microwaves were invented during Roman times - Emperor Nero cut off some dude's fingers & left him with only his thumbs. 
That same guy (Digitalis Minimus)  went on to invent the UHF PL-259 connector, for hams who were 'all thumbs'.  True story.

Double check your programming on both sides (repeater and mobile/portables). I'd think that it's more likely a fat-fingered typo than a problem with the antenna & line.  It's either that, or you're describing a de-sense issue in a unique way...
The suggestion of testing in simplex with another radio hooked up in place of the repeater is a real good test for basic troubleshooting. If a portable works just fine in simplex mode, then there's likely a problem with the repeater or duplexer. If you experience the same problem when testing with a portable - then you know you're looking at a coax/antenna issue.
 

I think you might have meant to say "relegated" to the dustbin of history, but over regulation will get you to the same place

Buy an antenna for the service you want. If your using GMRS buying a HAM antenna isn't going to be the best. As said above the TRAM is a good option for cheap antenna. Although for the price f both of these antennas you could have bought the Laird FG4505 and been done at once. Make sure you trim the TRAM per the instructions. Im not convinced the gains they show are remotely accurate but thats another discussion.