WyoJoe

If you have a cable that works for the GM-30, it should also work for the KG-935G as long as it has the same kind of connector, which I believe it does (My KG-UV9G does). You shouldn't need a separate cable.

Generally speaking, you'll want to use the SWR meter to ensure the antenna is properly tuned, then remove the meter. As for the "jumper" cable, no, it does not need to be the same as your feed line. A short length (12 to 18 inches is typical) of 50 ohm coax with suitable connectors is sufficient. Because of the short length and temporary nature of the connection, the type of coax doesn't matter much.

This isn't entirely true. There are "closed" repeaters that are intended to be used only by club members or members of specific groups (such as Search and Rescue).
This seems to be the exception for the most part; many ham repeaters are "open" to all licensed hams to use freely. In fact, for most that I'm aware of, use of the repeater is encouraged, likely to increase traffic and give people someone else to talk to. Unlike many GMRS users, most hams I've met like to talk to others whenever the opportunity presents itself.

This isn't entirely true. There are "closed" repeaters that are intended to be used only by club members or members of specific groups (such as Search and Rescue).
This seems to be the exception for the most part; many ham repeaters are "open" to all licensed hams to use freely. In fact, for most that I'm aware of, use of the repeater is encouraged, likely to increase traffic and give people someone else to talk to. Unlike many GMRS users, most hams I've met like to talk to others whenever the opportunity presents itself.

Welcome aboard Ben,
Hopefully GMRS won't be disappointing for you. One thing you're likely to find is that there aren't a lot of people sitting around waiting to talk on GMRS. The way the service is licensed, many users have GMRS radios primarily for talking with family members either on simplex (radio to radio) or on private repeaters, and in many cases don't seem interested in talking with anyone outside their small group. This seems to be a fairly common experience shared by new GMRS users.
In some areas, however, there is a fairly active GMRS user base that tend to use mostly open (shared) repeaters, and will chat readily with others. The best way to find out if that's the case in your area is to monitor the repeater outputs in your area to "see" what you can hear. You might find that there is an active GMRS community using one or more repeaters in the area. If so, you should be able to get information on who to contact to use the repeater. Remember, permission to do so is granted by the repeater owner, except in the case of open repeaters.

Welcome aboard Ben,
Hopefully GMRS won't be disappointing for you. One thing you're likely to find is that there aren't a lot of people sitting around waiting to talk on GMRS. The way the service is licensed, many users have GMRS radios primarily for talking with family members either on simplex (radio to radio) or on private repeaters, and in many cases don't seem interested in talking with anyone outside their small group. This seems to be a fairly common experience shared by new GMRS users.
In some areas, however, there is a fairly active GMRS user base that tend to use mostly open (shared) repeaters, and will chat readily with others. The best way to find out if that's the case in your area is to monitor the repeater outputs in your area to "see" what you can hear. You might find that there is an active GMRS community using one or more repeaters in the area. If so, you should be able to get information on who to contact to use the repeater. Remember, permission to do so is granted by the repeater owner, except in the case of open repeaters.

I think the reference to 22 channels was taking into account that the repeater channels share the same output frequencies as channels 15 to 22. So yes, there are typically 30 channels, but 8 of them are duplicated, in a manner of speaking.

From the GM-30 specs: Rx Frequency Range: 65-108MHz, 136-174MHz, 400-470MHz
The specs for the DB-20G shows the same.
It looks like both radios receive the same frequencies. Of course 65-108MHz is the broadcast FM spectrum (~88-108 in the U.S.).
I suspect the tuner won't allow you to tune in anything outside of the specified range, although I haven't tried to do so.
As these radios are FM only, you won't pick up anything understandable on digital modes, although you may hear something when they're being used.

B=Base, R=Repeater, M=Mobile, F=Fixed, RM=Repeater + Mobile, etc.

I know I found the firmware update on their site in the past, but like you, I only saw the setup file this time. Perhaps an email to them would result in them sending the file?

B=Base, R=Repeater, M=Mobile, F=Fixed, RM=Repeater + Mobile, etc.

I've noticed quite a few "Hot" or "Nashville Hot" chicken places opening up recently. There's a local-ish chain called Angry Chickz or something like that with several locations in the L.A. area and even one in Bakersfield.
Anyway, we've strayed a bit from the original topic, so to bring this thread back a little bit...
Do you think you could reach your home base from Crazy Hot Chicken?

I'm not familiar with it! It's been a while since I went to Rattler's. I don't think Wicked Chicken was there the last time I went. Perhaps I'll have to give it a try.
Perhaps Papatree has tried it?

Here are the steps to set these particular options from the radio's keypad:
Select the channel you wish to change the options for.
Press MENU, then 2, to get to TXP (Transmit Power) option. Press MENU again to change the setting, then up/down arrow to select High or Low as preferred, then press MENU again to save, and finally, press EXIT to exit the menu.
For selecting Wide or Narrow, use the steps above, except pressing MENU then 5 (instead of 2) to access the WN (Wide/Narrow) function.
 
For PL tones, follow the steps above, but using the following menu options:
10 for R-DCS (to set the receive DCS code)
11 for R-CTCS (to set the receive CTCSS tone)
12 for T-DCS (to set the transmit DCS code)
13 for T-CTCS (to set the transmit CTCSS tone)
 
To summarize, regardless of which option you wish to program, the basic steps are:
Select the channel to be changed and tune the radio to it.
Press MENU (to enter programming menu)
Press option number (or use up/down arrows to select the correct option)
Press MENU again (to change selected option)
Use Up/Down arrows to select preferred value
Press MENU again (to save)
Press EXIT (to exit programming menu)
 
The step I miss most often is the third press of the MENU button. I have pressed EXIT at this step more times than I care to admit, and when I do that, my selection is not saved.
If you are following all the steps above and still having problems making the changes on your radio, it would most likely be due to having an early version of the firmware installed on the radio.
 
I hope this helps.

If the specs are correct, that looks to be an excellent antenna for GMRS. For VHF reception, having an SWR below 1.5 isn't a necessity. I suspect it will reasonably tune a much wider spectrum that what's stated. If you were wanting to transmit in the VHF range, however, you might want something different, depending on the part of the spectrum you wanted to transmit on.

If the specs are correct, that looks to be an excellent antenna for GMRS. For VHF reception, having an SWR below 1.5 isn't a necessity. I suspect it will reasonably tune a much wider spectrum that what's stated. If you were wanting to transmit in the VHF range, however, you might want something different, depending on the part of the spectrum you wanted to transmit on.

The mag mount in the picture looks quite small compared to the antenna. I'm guessing the mount is about 3" diameter, and the antenna is about an inch. I wouldn't expect that mount to work well if there were an adapter available. I wouldn't bother even looking for an adapter, and would just go with a different mount. I'd recommend at least a 4" mount, and if the antenna's more than three feet tall, perhaps even bigger, like a triple-magnet mount.
 
Here's a 4.5" magnet mount that claims to support antennas up to four feet long.
https://www.gigaparts.com/comet-antennas-cm-5m.html
Here's a triple-magnet mount:
https://www.gigaparts.com/mfj-336s.html
 
There are a lot of options, but I would recommend shopping around as mounts can vary greatly in price. You might want to avoid the cheapest ones, as they may have quality issues, but you could probably get by well with a middle of the road mount.

That figures! Since I use Linux for my radio stuff, I haven't had those kinds of problems. Hopefully it's not too difficult to resolve.

I haven't used the Radioddity software for this radio, but according to the Radioddity website, it's supported by Chirp. When I checked Chirp, the QB-25 is listed, but not the DB-25. Since they appear to be quite similar, they might use the same profile. Those radios are slightly different than the QYT-7900D externally, but I suspect they share many of the same components, and possibly even the same software. Anyway, have you tried Chirp? I found it to work pretty well when I started out, and I much prefer it to the manufacturer software, or at least that of the CCR variety.

By the way, I'm not sure which model of Retevis radio you're using, but Chirp supports many of them. As a bonus, Chirp is easier to use than many of the manufacturer's programming software.

If it gives you trouble, or doesn't seem to work, then change the receive code to "off" or whatever the radio calls it. That will allow you to receive the signal if the repeater isn't sending a code.

I think a lot more information is needed in order to answer your question.
First of all, there is no mention of your intended use for the antenna.
Second, there's no mention of what type of radio you're wanting to use it with.
Third, there is no useful information given about the antennas you currently have.
SWR readings are relative to the antenna and the radio you're using it with. It is not an "across the board" value. It very much depends on the frequency at which the radio is transmitting.
Please provide more information, or go back and read through the threads about antennas to see what recommendations have already been made.

If it gives you trouble, or doesn't seem to work, then change the receive code to "off" or whatever the radio calls it. That will allow you to receive the signal if the repeater isn't sending a code.

Since it looks like the antenna should be pretty well tuned to the GMRS band, I'd look at a couple of other things first.
The first thing I'd check is the SWR meter you're using. Is it intended for the frequencies you're checking? Have you used it with another antenna in the same frequency range to be sure it's providing an accurate reading? Are you using adapters to connect it? If so, they could be causing a bad connection.
The second thing I'd suggest checking is the mount. With a lip mount, you want to be sure there is metal to metal contact between the body of the vehicle and the body of the mount, so the screws on the bottom that hold the mount in place need to penetrate the paint on the vehicle for good contact. If you have access to another mount, such as a magnetic mount, try the antenna with that mount to see what your readings are.
If you have access to another similar antenna system that you know is within the desired SWR on the same frequency, you can try switching the antennas between the systems to see if the problem follows the antenna. If it doesn't, then you know to look further into the mount. If it does, then you need to look more closely at the antenna. If it was a "70cm" or "dual-band" ham antenna, then it would likely be a little longer than desired, and it could be trimmed for GMRS. An antenna designed for the 450-470 MHz range should be about right, though, and should not need trimming.

The main thing to consider is that there should be two charts, one using whole numbers (xxx) and one using fractional numbers with a decimal point and tenths value (xxx.x).
There might even be other names used for these same functions, in which case, you want to look for the chart that uses whole numbers. Those are the digital squelch codes.
The chart that uses the fractional numbers is the CTCSS chart for analog codes.