tdukes

Duplex means the radio is transmitting on one frequency (467.xxx MHz for GMRS) and receives on the corresponding frequency (462.xxx MHz). Simplex means the radio is transmitting and receiving on the same frequency in the 462 MHz range (except for the now-permissible 0.5W ERP NFM channels 8-14, which are 467 MHz).
I really abhor the FCC channel number scheme which treats the simplex main channels and repeater as /separate entities/. As seen in a number of threads on this forum, it just leads to confusion (in the old days, one had a button on the radio that toggled between simplex and duplex on a given channel, and the channel was commonly identified by the .xxx portion of the frequency [one's license only authorized TWO of the eight main channels, so your channels A&B might not be the same as my A&B).
Channels 15-22 and 23-30 (aka: rp15-rp22, 15r-22r, and other naming schemes) receive on the 462MHz, with the result that people with simplex only radios (FRS) or tuned to simplex 15-22 still receive the output from repeaters, but can not transmit to the repeater.
 
Most R-Pi configurations (I'm only accustomed to Amateur Pi-Star usage) are simplex from radio to Pi-Star -- only one side can transmit at a time (a true repeater is receiving on 467 and SIMULTANEOUSLY sending what it received back out on 462). If the R-Pi side is transmitting, it will not hear anything you try to send until the board goes silent (toggles to Listening mode). For Amateur, there ARE boards that support duplex mode -- they have two antenna on the board (not to be confused with dual-band boards, which can be configured for 2m or 70cm usage).
Take into account that these boards run VERY LOW power... <50mW is not uncommon, I don't think I've heard of any that gets as high as 100mW! Strangely, my radios can pick up my Pi-Star system from down the block (500 feet or so), but it won't receive my transmissions, even on high power. Probably evidence of how much more sensitive the Kenwood/Icom HTs are compared to an SoC radio chip on top of a potentially RF-noisy processor board.
Once your signal hits the internet, simplex/duplex is irrelevant -- it only applies to the link from radios to node and node to radios, and most R-Pi nodes are probably running simplex. If someone has managed to connect the R-Pi to an actual repeater, then it is duplex at that repeater. If it is linked to another simplex node, well -- it is again simplex.
 

I just got a 1486 last week and I cut it for 462 using a nano-VNA. 
The sections that need be to cut look like they are brass.  I cut them accurate and clean just using my scroll saw
So far performance is pretty good.  The chart was pretty accurate for me.. In the end my lengths were exactly what the chart suggested for 462. 
I have heard that many people found that the chart was off for them so be careful not to cut too short! 
It is easy to be off by a mm or so depending how you hold your ruler to the base of the coils. I measured with the butt of my zero clearance ruler touching the base of the coil.
 
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I have a Tram 1486 and i tuned mine because the instructions said I had to -  following the instructions to cut both the top and bottom sections, I tuned it to 467.700 because it is for a repeater... But when I checked the tune on 462.700, the SWR was still a very low -  dont remember exactly what it was, but under 3:1.

Never mind.  I'm a dumbass.
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I have a question... why are you going to try to tuning it?  It's a stacked 5 phase element high gain antenna with the center frequency being very close to GMRS frequencies.
 
Due to being a stacked phased element antenna (5-1/2l), if you cut the top or bottom, you are only adjusting one element and throwing the phasing completely out of whack, causing massive issues with receive and transmit, regardless of what the SWR meter says.  You can't even adjust all 5 elements because the LC network of the antenna is tuned for factory resonance. 
 
I would just leave it alone.

I'm on a repeater and was going to go with 465 but since SWR is for the TX, I wasn't sure. Didn't want to start cutting if I wasn't sure.
Thanks!!

You’re best off tuning it for your transmission frequency. If that is strictly in the 467 range then tune to that. If it is divided between 467 and 462 then tuning to 465 works. 

I had plans to have it be an open repeater but have been thinking about not doing that for reasons you just stated. I would like to know who's using it and that they are licensed to operate a GMRS radio. There are plenty of yahoos out there unlicensed. I heard some this past weekend burping and farting over the radio. Not going to tolarate that. Just not cool or even funny!

@KAF6045,  you must take all of the rules collectively into consideration.  Not just one half of one qualifier in one sub-part of a sub-section.  For example, § 95.1705 (f) allows for legal station sharing.  That is why owners setup clubs and/or have you request sharing access of the repeater in writing (via email or the web app here on MyGMRS.com, for example).  The request and approval become part of the station record.  The licensees who are sharing the repeater operate under their own license... therefore, no special ID system is required.
 
The only time a repeater requires an ID is if it is an open repeater... meaning it's not private or shared, but rather open to the public for any licensed operator, without written agreement or record.  If @tdukes plans on sharing, he's fine with no ID.  If he plans on providing an "open system", then it will need an ID.

Said user's must be under the repeater owner's license (and hence call sign). Other license holders ID'ing doesn't qualify -- the ID MUST be that of the repeater owner.
Does not say anyone with permission granted by the license holder, but are operating under the license of the holder... Which, given earlier regulations, means "immediate family" (I disregard the clause about allowing others to use the station under EMERGENCY situations -- That clause basically appears in every FCC service class and allows anyone to use pretty much any means to obtain aid, licensed or not).

So, two things come to mind.  One is, your repeater doesn't have to ID itself as long as the users are ID'ing.  If someone doesn't ID... tell them they are not allowed to use the machine.
 
The other being there are no part 95 certified amplifiers.  Repeater owners do occasionally get site visits from the FCC for inspection.  I doubt you would get more than a verbal to stop using it (if anyone actually came by), but in my opinion, the risk isn't worth the benefit.  Especially because there is almost no practical difference in rang or quality of communications between 15-20 watts and 50 watts.  Your money is much more well spent in buying a great antenna system and doing what it takes to reduce losses on the transmission line.
 
With that said, you can buy a proper/real type approved or grandfathered type 90 repeater for a touch more money than you are already planning on, but it will have the tech to support heavy use if needed.  Some are as cheap as $400... a great commercial grade might be around $1,500. 
 
I would recommend searching the forum and talking to some of the active repeater owners on the site to get a better idea of what to expect.  I have a 25w continuous duty repeater that was built from two transceivers.  It cost me about $1,000 for everything.

One... The ID requirement is not "every 15 minutes" but at least once in each 15 minute window in which the repeater has been activated. If no one is using the repeater, it doesn't have to ID. The timer starts when access is made (even a mere "kerchunk"), does NOT reset on accesses within that fifteen minute period, and expires at the end of the time, when the ID is emitted.
If the tones are not published (and you monitor the repeater to ensure someone doesn't sniff out the tones [some radios have "tone-search" functions]) but are set in radios used by you and immediate family operating under your callsign AND these users ID with your callsign, it is taken as sufficient to also ID the repeater.
Official regulations are https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-95/subpart-E cf:
95.1705 (c) (2) (definition of immediate family) 95.1751 (a) (1) & (2) (frequency of ID) 95.1751 (b) (valid forms for the ID) 95.1751 (c) (1) & (2) (repeater non-ID conditions) I tried to access the help file by downloading the ZIP archive -- but all that displays for me is the main topic menu... NO HELP TEXT! So you are on your own with regards to what is possible in DUPLEX mode.
 

Just remember, that as predicted in the proclamation video, "some people" will always and forever spew reasons why Ch19 (any channel, actually) is not "the right choice", and will argue about it as they have for years, accomplishing nothing.. Those people are not invited to join with the rest of us normal people on Ch19..  They can go talk to themselves on some other channel..
 
My name is Queen Randy and I approve this message.