So just an observation and kind of a question.

I put a gmrs repeater, and shortly after storms damaged what I thought was the transmitter, but turned out to be the duplexer. So I ordered a cheap fumei off Amazon and tuned it up. I had it setup correctly and was getting up to 84db attenuation, but then...

Everytime I transmit too it with a weak signal the transmitter desenses the receiver. Returned 4 different times and it just wasn't working well. So I did this:
Dummy load on antenna port, analyzer in on the low, out on the high. To my surprise my notches were off by 500khz, and only about 60db. So I left it configured this way and tuned each side narrowing my freq span until I got down to 1mhz span and a -80 to -85 db. Setup a weak signal from my signal generator, and if it's enough to break squelch on the receiver, the transmitter doesn't blind it. Pretty happy with it, but I've never even tried to tune a duplexer that way.

If you have some duplexer problems, this might help you. Anyone ever tried this way of tuning?

Sure. Start with tuning each side, then tune across the whole duplexer, always with a dummy load on the unused port. And actually if you want to get super precise about it, do a final check that way connected to the antenna instead of a dummy load, the slightly different impedance might shift the notches slightly. Notch only duplexers you have to get right on although I haven't dealt with them much. If you have high RF/other transmitters at your site that's probably not feasible, but then again if that's your site you need a bandpass/reject duplexer anyway.

100% accurate.

Tune one half, then the other.  
Load on Low, TM on antenna and high.  Capture that trace, then move to antenna and low, with load on high.
Are you talking about a good Bp/Br or a cheap-ass 4- or 6-cavity mobile duplexer?

What are you using to test it?  I've had issues with a Freedom not having enough dynamic range to actually get a good reject, the notch gets buried in the noise floor of the instrument.  Aeroflex and sitemaster do it nicely enough, sitemaster's just a painfully slow sweep.  
A good spec an with tracking signal gen (HP 8591) or VNA (HP 8753) are my weapons of choice if I'm building a repeater.

Everything I ever read, was told, or seen just tune the low/high, cable it up and your done. But mine was most def off. Ide say, 8 miles on a 5 watt handheld was the max. Was a little let down, but now it works great.

It a cheap ass 4 cavity fumei, not a good bp/br. I used a nano vna to tune it.

I've been looking at these duplexers on Amazon for over a year now.  I want to get one just to fiddle with it for the experience, but I don't really have a need.  I probably transmitted zero times in the last year on V/U bands.  Not to say it wouldn't be handy, and I do have a GMRS license in addition to amateur.  Just nobody to talk to.

It's good to see that a nano VNA can be used successfully for this application.

I spared some details for brevity, but the nano vna tuning isn't quite the end if it. After getting 80-85 down I put a radio on the antenna port set to 462.675 (tx freq) and then set the vna cw freq to 462.675 connected to the high port (rx port). It's VERY touchy tuning, and the first cavity (furthest from the antenna port) is the touchiest one. Some very delicate tuning until the 'high' port passes as little of the low freq as possible. Swap sides change frequency to high and repeat on the low port. Your kinda flying blind there but I got it pretty well. I'm sure there's some amount of desensing.

There's a newer vna called the saa2 with more dynamic range. It should be better, but still not as good as a commercial instrument. But thats essentially how I did it.

Yeah it's still pretty impressive for a device that costs less than a hundred dollars and fits in a shirt pocket.  Like you say, probably not perfect, but serviceable.

I don't think they have enough range (only ~50 dBm?)

I could be wrong.

An IFR 1200S works for me.

If you are anywhere near me or wanna do the shipping method.
I am located in Morris County - NJ & travel is somewhat impossible due to med issues (A.S.)

I'll break out my spectrum analyzer and tune it for you for only $1600.00 per cavity (Democrat price)
OR
$Free (2A / Arfcom / Republican / Conservative / Libertarian / Friend of GoatBoy pricing)    LO


I am serious btw.  
I have an Agilent (HP) 9340B SA with tracking generator and a cheapo desktop Rigol SA with TG (actually very nice and a fraction of what the Agilent cost me)

I have mostly dealt with public safety gear UHF 400-470Mhz  (+ "T-Band" 470-527MHz) , but did a few VHF and 800 a while back.

Happy 4th!

RBAD

BTW = My family has given up on GMRS - too busy. too many limitations (digital not permitted. so no P25 or DMR //  no encryption  // etc)
I also wanted a permanently installed repeater and my main intent is to use it for emergencies and family uses the repeater for comms with their kids on their farm.
(no cell phones allowed until they are 15 - a good policy!)
I went through the freq coordination and FCC licensing process ($1400 for 2x UHF FB2 freq pairs and mobiles / portables) + $250/10 years for the FCC license.
(each family group kicked in $$ to make it work)

BUT...
It's only around $250-275? for a 10-year FCC license for the IG ("business band") spectrum licensing.
There are "itinerant" frequencies available (several VHF / several UHF / 2 freq pairs for repeater use) that do NOT require the freq coordination/engineering process.
These freqs were intended for business use where they are not operating in a dedicated area.

MIGHT be a great ARFCOM COM idea?  we license all itinerants (VHF and UHF) and make them available to all members of the business called AR15.com
way more flexible than GMRS and not too much $$

Sorry.. Forgot..

A few Comm YouTubers checked multiple "alternate" methods of tuning a duplexer w/o a spectrum analyzer w/tracking generator on hand.
The NanoVNA, while an ultra cheap and awesome gadget, failed miserably/

I'll try to dig up links and post 'em.


RBAD
Site Admin in Exile  

Ar15.com could get nationwide freqs as a business. Keep in mind they will be the same dozen or so pairs that every nationwide business will also be on (98% is construction). You could also get statwide freqs that are less busy, but then would need a pile of different freqs.

Could be GMRS with a specific primay and secondary with a specific PL/DPL......

Or FM CB on a specifc channel (does CB have PL on the new FM radios?)

Or FRS freq/PL combination

Or get ham licensed

Or Freeband

All of the options. People hate radios.

TT

TT

Can you allow friends or family to use your nationwide itinerants like on a road trip or camping or whatever?

When Itinerant licensing got publicized on a bunch of prepper channels (including this website) FCC responded by really scutinizing applicants for Itinerant business licenses. At one time anyway they were almost refusing to issue "nationwide" licenses, and being more particular about business documentation.

My license got pushed back several times because I wanted to include Alaska, Hawaii and Puerto Rico in the license. Stepped it down eventually one at a time...would've liked to have gotten lower 48+PR but I ended up with just the lower 48.