gortex2

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.

Well, if it's DC to daylight and beyond, then a Faraday Cage isn't what you are looking for.  It's one thing to block RF signals.  If we are talking about trying to attenuate Alpha, Beta and Gamma radiation then it's a whole different ball game.  ANd the truth is ONLY plate steel, and LOTS of earth are going to work.  So let's quit screwing around and get a go fund me together for a dozer and a BIG track hoe and most likely a portable concrete plant and start building AT&T style bunkers and skip the discussions of ammo and trash can's with aluminum tape around the seams and lids.  I mean if we are going to be ridiculous, lets just get to it and skip the silliness all together. 
Here's the problem.  If you are looking to block stuff that will kill you anyway, what's the point unless you have other means of protecting yourself for event's like you are referring to.  And if you DO have those means, they will certainly protect radios that are around you went it happens. 

GMRS is normally a bring your friends along service. If your here to find friends you may be disappointed. Yes there are some areas that are ham like but alot of areas gmrs is radio to radio or user groups that really wont answer another user....
 

GMRS is normally a bring your friends along service. If your here to find friends you may be disappointed. Yes there are some areas that are ham like but alot of areas gmrs is radio to radio or user groups that really wont answer another user....
 

I can 100% tell you through experience, if you don't use some serious filtering, like found in a duplexer, vertical separation isn't enough unless you plan on using very low power... like 5 watts.
 
I have a portable repeater system the doesn't use a duplexer. At 5 watts, it can have both antennas about 100 feet from each other and it works locally with limited issues. However, if I want to run 50w, or even 200w, I have to separate the two antennas by about 400 to 500 yards to avoid desense issues.
 
I also have a fixed repeater with a duplexer sharing 1 antenna. The duplexer cooks off about half the power, both transmitted and receive. However, antenna placement is going to impact performance more than transmitted and receive losses in the duplexer. You would have to cut your power 4 times to see a single s-unit of loss. 
 
Most people who don't run a duplexer, don't do it for performance benefits, mostly because it's not a noticeable benefit. It's done to save money or to provide rapid diversity in deployment and changing frequency or even bands without having to re-tune or replace the duplexer every time. Such as my portable field unit.

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. 
 
 

So, your CERT Net was going on and while it was going on when someone checked in you could occasionally hear someone else on the receive frequency.  In other words, when your receiver broke squelch because the repeater transmitted a tone, you could hear the folks in the background who were trying to talk on the simplex receive frequency, is that right?
Could anyone else on the CERT Net hear them, or were they local to you only?
Before you started the Net, did anyone listen with squelch off to hear if the channel was in use?
When you did hear them, did you transmit on 462.675 MHz and announce, politely, that the frequency was in use?
They could have been on GMRS or FRS.  Except during an emergency, they have as much right to be on the channel as your CERT Net.  We share the repeater receive frequencies with simplex users of both GMRS and FRS radios and while it would be ideal for each of us to listen with squelch turned off to hear if a frequency is in use before transmitting, there is no GMRS training that covers that.
It sounds like folks were just using their radios and it happened at the same time as the Net.  If they were using a different tone from you they might not have even heard you.
As far as it being “a violation”, no, it wasn’t, at least in my opinion.  No more than the Net operators were in violation for transmitting on a channel that was in use already by a couple of folks with their radios.
And since you liked seeing the actual regulation regarding emergency use, here’s the one that requires shared use:
§ 95.359 Sharing of channels.
Unless otherwise provided in the subparts governing the individual services, all channels designated for use in the Personal Radio Services are available for use on a shared basis, and are not assigned by the FCC for the exclusive use of any person or station. Operators of Personal Radio Service stations must cooperate in the selection and use of channels in order to avoid interference and make efficient use of these shared channels. 
   

It's difficult to say how much help a GMRS repeater would be in the situations that you state. The most common radios in any neighborhood will be FRS and they cannot access a repeater as they lack the input frequencies. GMRS requires an FCC license (well, you are supposed to have one) but those radios aren't in the bubble packs you see at the retailers. GMRS licenses can only be shared among family members and each team or group would have to have their own license or licenses. If you are going to put up a repeater, then one of the little 5W units connected to a Tram 1486 or Diamond X50 would cover the area your 40-foot tower has to its radio horizon. Using that small repeater also means the cost of providing battery backup is a lot lower as a $60 15AH battery could keep it running for a couple of days with moderate use.

I have 6 NMO mounts on the roof of my F150 (crew cab). All are hooked up to APX mobile radios. I see no noticeable issues. Really will depend on power and quality of radio. Cheap radios and high power don't go well together. 

I have 6 NMO mounts on the roof of my F150 (crew cab). All are hooked up to APX mobile radios. I see no noticeable issues. Really will depend on power and quality of radio. Cheap radios and high power don't go well together. 

I have 6 NMO mounts on the roof of my F150 (crew cab). All are hooked up to APX mobile radios. I see no noticeable issues. Really will depend on power and quality of radio. Cheap radios and high power don't go well together. 

I used the UV-5R for a while. It's an OKAY radio in my opinion, there's nothing that good about it. And there is nothing that bad about it, it is just okay. There's really nothing more to say about it in my opinion. 

I recently started getting into Motorola's that are tuned down to GMRS Frequencies, I use them often while working, and while doing shifts as a security officer, I found to my personal preference the baofengs just aren't big enough for me. I like larger radios that have a little weight in your hands but that's just personal preference

That's what Amateur Radio bands are for. 

Agree. I tell everyone to start with a 1/4 wave. IF you spend $10 on the whip its expensive and will outperform the pepper shaker all day long. Midland has a market as the overlanding crown will be all over the antenna. I looked them up a few years ago as they are used overseas alot but they were crazy costs for what it is. I think in the US there are multiple antenna vendors that provide quality LMR products. Go with a reputable manufacturer and you'll be happy. 

GMRS is not a "hobby" GMRS IS intended for people to bring their own audience (ie; your group while off-roading) GMRS is NOT for people that "want to make contacts" It seems you have been misinformed about what GMRS is for, and what its primary purpose is.  It sounds like amateur radio or the Grindr app are more of what you are looking for.

Agreed!  Once again, in a perfect GMRS world, with no linked or "networked" repeaters, this should be a minimal problem.  Absent garbage being constantly piped in from across the state or across the nation, most repeaters I have ever heard, have little traffic.  If you regularly operate on one repeater output for 50W simplex, and a repeater becomes active, you could switch to another 50W output and probably find it vacant.  Without linking, the chances that all eight are in use via an overpowering repeater in your area are kinda slim.  With so much linking, well, that can be a problem in some areas, especially when all eight 50W channels are blasting the same conversation out at the same time.

462.xxx5 (channels 1-7) are repeater-free. Perfectly adequate for local traffic between HTs or between HT and mobile. Local traffic between mobiles on 462.xxx0 at full power has a good chance to overpower repeater interference. The opposite happens only when mobiles are far and repeater is close. In this case use reserve frequency, according to your communication plan.

I am in a general area with two linked repeaters tied in to more.  Conversations entirely on the most distant one regularly tie up the two closer to me.  Another guy has put up a big repeater tied in to a big national network along with a couple of nodes and another guy still, felt it necessary to link his short range repeater into that network.
AFAIK, GMRS was not created so that people get to "enjoy" useless chatter from across the state or across the nation.  It was for families, friends, and others, to have reasonably reliable two-way radio comms in their local area.  I define "local" as how far a base, mobile, ht, or repeater, can reach to other devices in the area it is set up in, be it 5 miles or 100 miles, depending on terrain and gear used.  If dead air is so worrisome, there are options available without unnecessarily clogging the 8 existing repeater/50W Simplex channels with pointless noise.  Ideas include:
1) get your ham Tech license.  It really isn't that hard.  A little reading and study.  No more Morse Code test.  Hams have waay more repeater frequencies at VHF and UHF and can therefore better handle the linking.
2) If too lazy or whatever for #1, CB allows for talking and hearing skip from all over.  Unlike internet linking, which is really no different than VOIP phone calls, your radio, antenna, and location, come together to allow you to talk to a distant state (or country) using the airwaves, not a glorified phone network.
3) If your base, ht, or mobile, allows; program in some ham repeaters or other frequencies and listen to them.
4) Download a scanner app and listen to public safety and ham stuff from across the country.
5) call someone on your phone, in the next county or the other side of the country.  Be it a friend, relative, or a random desk clerk at a big chain motel; you can experience the same "thrill" of talking to distant places using the same (VOIP) technology that makes those trendy and kewel repeater linkups possible.  And you don't even have to remember to key or unkey a mic!

https://cdn.shopify.com/s/files/1/0531/2856/0817/t/10/assets/GXT1000-Owner-Manual.pdf?v=1621291161
they are in the manual on the website....
 
 

You should probably say something like this as a preface to your post.
"The information contained in this post is provided for informational purposes only, and should not be construed as legal advice on any subject matter. You should not act or refrain from acting on the basis of any content included in this post without seeking legal or other professional advice."

https://docs.fcc.gov/public/attachments/DOC-396533A1.pdf
 

If you use a low powered repeater in a box like the Retevis RT97S or Midland, the entire repeater is in a waterproof enclosure. 
Otherwise it’s going to depend on what repeater you use. There are NEMA enclosures that can be mounted on your tower or you can build something. 
Air circulation, even when the ambient temperature is 100° is still better than stagnant air that allows components to build up even greater heat. 
NEMA enclosures can be outfitted with air conditioners but everything you do that increases the energy requirements makes things more complicated. 
 

It's been said many a time here that GMRS and FRS are "bring your own contacts" services, meaning that you're not going to find a lot of people hanging out on either repeaters or simplex just waiting to conversate. Some folks here enjoy and highly recommend Grindr for that reason. I prefer amateur radio (VHF and UHF) for talking to my circle of friends either on the road or on the hiking trail, and HF for seeing how far I can toss my signal, and GMRS for occasionally conversating with my wife who has zero interest in an amateur radio license.

As far as I understand you cannot operate on CH19 and CH21 North of Line A. So, for me travel channel would be CH20.
https://www.fcc.gov/reports-research/maps/frequency-coordination-canada/
 

Recently a big GMRS youtuber posted a video about the repeater-jammer, callsign WRTD259 in Steelton PA that got busted by the FCC for jamming a repeater.  In that video the youtuber reads the public FCC violation notice and displays the FCC public notice of violation on the screen - you can see the full, public complaint against WRTD259 here:  https://www.fcc.gov/document/jonathan-gutierrez-licensee-station-wrtd259-steelton-pa
Now SOMEONE has filed a notice of privacy-violation against that video, demanding that all personal information about the jammer be removed from the video.. Of course, there is no way to know exactly who filed the notice.. 
But if we were to guess who filed the notice, hypothetically, it would seem funny that a jammer would demand everyones attention while jamming, but does not want any attention after he gets caught.