KAF6045

The radials shouldn't matter -- they form a ground plane to reflect the 1/4wave vertical (making a virtual half-wave). Being longer than the wavelength should just mean "more ground" is seen. Trimming the vertical is going to be the tricky part -- especially if it is a dual-band antenna currently as you may have to trim both top and bottom (presuming some sort of coil in the middle). Heck, you may even have to fiddle with such a coil (adjust spacing) to get it to phase properly. Probably better to just obtain a dedicated GMRS tuned antenna. Given the short wavelength, you could probably obtain a half-wave dipole and do away with the ground plane radials.

The repeater will still need its own ID circuit/system (the only repeaters that don't need an ID system are private repeaters where the ONLY users are immediate family members using the call sign of the repeater owner). 50W is the maximum output (at the antenna connector on the transmitter) permitted by regulations. The highest gain antenna you can find -- so long as it provides a signal at the desired user locations (the higher the gain, the narrower the beamwidth in elevation -- so someone at ground level may not be heard-by/hear the repeater, but someone 15 miles off may be fine [that's the ~ horizon distance for a 160 height]). Assuming 3dB loss in coax, you'd have 25W AT the antenna. A 10dB gain antenna will give the impression of a 250W signal, but as mentioned, that will be focused toward the horizon. A simple half-wave dipole will only have a peak equivalent of the 25W, but will have a beamwidth that will cover ground to sky from a short distance away from the repeater. If you've looked at cell-phone towers, you've no doubt noticed that the antennas are mounted in sets of three AND are tilted downwards to improve local ground level coverage.

Pretty much any service that is not broadcast AM or FM limits the voice band to approximately 6000Hz (Amateur AM and any remaining shortwave broadcasters run in a 6kHz bandwidth when including both sidebands, single sideband often runs less than 3kHz -- 2.4kHz is one of the settings on my rigs, or 2700Hz minus 300Hz). The services are designed for communication, and most vocal formants fall into the octave of 300-3000Hz -- they are NOT designed for musical fidelity (and definitely do not pass all the higher harmonics in the 3000-30000Hz octave [note: I'm using octave in terms of order of magnitude: 30-300, 300-3000, 3000-30000, even though the 20000-30000 is pretty much inaudible to humans... NOT musical octave where an octave is a doubling -> 440A to 880A, etc. 300-3000Hz covers about 2.5 music octaves] Broadcast FM has a 200kHz channel spacing; not certain how much is actually used for signal deviation. Broadcast AM uses 10kHz spacing (5kHz per sideband -- so just one sideband is almost the entire width of shortwave double-sideband AM).

18" and 1/4 wave? Sounds a lot more like a 2m VHF antenna rather than a UHF band.

Eaves... not so much. But END of building. https://mfjenterprises.com/collections/all/products/eve-48 (they may call it an "eave" mount, but it really fits on the end of the building with the upper bracket just under the ^ of the roof peak, and the longer bracket a foot or more below it) https://mfjenterprises.com/products/wmd-12 (if you have very narrow eaves, this one may extend enough to let a mast pass the eave, otherwise another end-of-building fit) I have two of the first -- one on end of house, other on end of garage, with a 40/20/10/6m OCFD suspended between them (the OCFD needs replacement, a few windy winters have stretched it to where the SWR is below the amateur bands). The second I have on the other end of the garage, supporting a 2m/70cm ground-plane vertical.

Tones can be useful for simplex operations if you are on a "noisy" channel, to block out the unwanted stuff... Granted, you will have to monitor the "busy" LED (or press the MONItor button to check the channel status) as someone else could be transmitting that you don't hear -- you would transmit only when the channel goes clear. As for frequency step -- that mostly applies to any operations done in VFO mode; it might be useful if you are trying to add receive-only (public service/non-GMRS) frequencies to a system for scanning purposes... presuming the radio offers slots for extra channels to be programmed.

"South Florida" is a large area, relative to /simplex/ ranges (if you are standing in a rice paddy, you might get 5 miles. From the top of a ferris wheel maybe 10 miles. In town? 2-4 miles might be reasonable). So for a simplex check, you'll need to provide much more precise location data. For a repeater... The repeater list shows an open repeater in Miami on .675 (along with a closed/permission required one on the same frequency, so getting the correct tones will be required). West Palm Beach are Members Only $$$.

Coming in late to the thread, and if I understand it you did finally manage to get a functional system. However, in general... There are something like 38 possible CTCSS tones. The odds of any particular repeater using "123Hz" is, therefore, rather low (the most common for the West MI Amateur repeaters is 94.8, while Lansing seems to prefer 100.0 -- CTCSS tones are supposed to be "subaudible", as the common voice band is filtered to be around 300-6000Hz; the higher the CTCSS tone, the higher the chance a poor filter could let it pass to the audio output). 141.3 used to be common on 462.675/467.675 back when the FCC regulations defined that as an emergency frequency (back in the days when one had to specify which two of the 8 MAIN frequencies one would be licensed to use -- this limitation went away back in 1999 when the FCC allowed any GMRS license to use all 8 main frequencies) [note: channel numbers were not used for GMRS in those days, as most radios were Part 90 LMR (business band) units and had to have whatever channels they supported programmed by a shop with the licensed frequencies] OFFSET/SHIFT is always used with repeaters -- in any service, not limited to Amateur. For GMRS repeaters, that is 5MHz + (transmit on 467.xxx, receive on 462.xxx). A 0 offset means one is working simplex (no repeater). You never stated what radio you were using [Okay, didn't notice model in subject line] (and my browser blocks embedded videos -- I try to avoid YouTube), so I can only speak in general terms. Many of the GMRS radios available are preprogrammed and only permit transmitting on (since the FCC unification of GMRS & FRS frequency assignments) channels 1-30. Channels 1-7 are GMRS interstitials, which only provide simplex (no repeater usage); 8-14 are the former FRS-only 467.xxxx interstitials, which are limited to 0.5W ERP NFM; 15-22 are GMRS main simplex frequencies; 23-30 (which may show up as 15rp-22rp, or similar notation) are GMRS main repeater frequencies. The only programming one can do for these radios is to set CTCSS/DCS tones on any channel, and possible change from FM (20kHz) to NFM (11kHz) for 1-7/15-22/23-30. Any other channels the radio supports are locked into receive-only (basically, slow public service scanning capability). Some radios may allow for up to 10 "DIY" repeater channels -- useful if you have more than one repeater using the same frequency pair but with different tones, but still limited. The Retevis RA85 [a pair came as a package with the RT97 (not RT97s) repeater] is one such, but the programming software seemed to lack the FM/NFM toggle and had everything locked to NFM. I made an inquiry about that problem and they sent me the link to the RA685 (the Amateur version of the radio) programming software -- besides allowing for the FM/NFM toggle to work, that software also enabled ALL channel slots for transmit configuration. I now have something like 30 "DIY" repeater entries in the unit. The Radioddity DB20-G, as shipped, is also quite restricted in features -- but can be unlocked (technically, no longer legal for GMRS) to open up frequency ranges and channel slots for transmit. "The bottom line is this, when I try to key up on these channels that I have tried to set to a repeater, it won’t even key up. It doesn’t show the radio is transmitting at all, the screen doesn’t turn Orange indicating I am transmitting, nothing. But if I go up or down a channel, it begins transmitting normally when I press the PTT. I have occasionally gotten traffic on the programmed channels when people have been on, which I thought was interesting since I can’t transmit." This tends to indicate, to me, that your radio is one that is preconfigured to specific simplex and repeater /channels/, and that the channels you are using are not permitted to operate with repeaters. Changing channel has put you back into an unmodified slot, and the radio operates normally there. Also, if it is a simplex channel, you would hear others transmitting simplex even if you were configured for repeater (the receive frequency from a repeater is the same as the simplex frequency).

And back before GMRS became wide-open (ie: back when a GMRS license was only good for TWO main frequencies (channel depended on radio radio programming, so the frequency could be a different channel on different radios), specified when applying for the license) the FCC DID have a designated emergency/traveller aid /frequency/... That was the xxx.675 frequency set, with recommended CTCSS 141.3. The old Maxon GMRS 210+3 HT provided two programmable channels (#9 and #10), the seven GMRS interstitials (#1-7), AND had the emergency frequency fixed in channel #8 (since anyone could use that channel for a true emergency/TA, the Maxon allowed one to select any two of the main frequencies for their license -- on the common two channel business [Part 90 LMR] HTs, the recommendation was to specify .675 as one of the two licensed frequencies to have access to it for emergency [and as it was on the license, could also be used for general purpose stuff]). .675 equates to channel #20 in the unified GMRS and FRS numbering scheme.

They are likely to (for a tailgate location) to slightly tilt the elevation pattern, and may turn the azimuth pattern from a circle to an ellipse. All the metal on one side will make it seem as if the ground is tilted.

Second image of my Tuesday 11:37 post -- though I'd really need to model the metal parts of the vehicle to be most accurate.

Universal Licensing System https://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp (strange -- I can't find an "official copy" download link; just the "reference copy"; maybe because anyone can get the reference copy if they know the call sign) Appears you have to go through the ULS License Manager route https://wireless2.fcc.gov/UlsEntry/licManager/login.jsp (which needs your FRN and password)

Note that the image references "FREE SPACE" -- which is essentially a non-existent condition in real life (even a probe moving between Jupiter and Saturn will have the radio and power source acting as some form of reflector/ground). Compare: Free Space half wave dipole (note the 2.15dBi figure -- that's where the conversion from dB Isotropic to dB dipole [dBd] comes from) "Perfect Ground", antenna 100 meters up And finally, "Real Ground" using high-accuracy model (0.005 S/m conductivity, 13 dielectric constant), same 100 meters up

The FCC stopped issuing paper licenses years ago. Sign on to the ULS, search for your call sign, and you can access a PDF copy of the license (as I recall it tends to favor "unofficial/reference copies", but there should be an option to download an "official" copy). Print & trim the paper.

There are too many variables involved to formulate a "power <-> distance" relationship. A 1W radio can reach LEO satellites, maybe a bit more power for the ISS. In totally bare regions, the same is likely limited by horizon distance (well, if just skimming the horizon, maybe 2X horizon distance -- radio to just above horizon to receive radio). Frequency -- VHF tends to work better in foliage, UHF in urban areas (the shorter wavelength can get through window and door frames which may appear as Faraday cages to longer wavelengths). The rare tropospheric ducting can pass signals for miles (Hawaii to California has been known to occur).

I'd suspect three power levels to be 100%, 50%, 25%... But then, I haven't really had much luck with getting the specified power out of mine (second sample yet!). My 15W MXT-115 actually puts out nearly a watt more than my DB-20G (~13.5 vs 12.75). I do see >20W on VHF when I tested it, and my lowest power is on the 467MHz repeater inputs (tested into a dummy load as I didn't have spare antennas for VHF... Hmm, wonder if a diplexer feeding separate VHF and UHF antennas would be viable ? )

Which means NOT GMRS; but LMR/part-90 gear.

How long a run, and how much loss at the desired frequency are you willing to live with. 100 feet of common RG-8 (Belden 9913) will lose half your power at 465MHz; LMR 400 is nearly as lossy. Cheap RG-58 loses 90%! (12W left from 100W). LMR-900 only loses 25%.

Note that those images are AZIMUTH images as specific elevation angles. My plots are elevation images. For a dipole, azimuth plots are boring. Perfect circle...

Same dipole at 3m (~11 feet) (FYI: I'm using 465MHz as that is between the 462MHz output and 467MHz input frequencies) And at 1.5m At 23deg you are down 3dB -- or half the ERP seen at 5deg.

Strange -- the manual doesn't state /how/ to change power level. The specs show that "1-7" are 5W max, and default to that.

Simple half-wave dipole, 20 meters (~66 feet) above ground. Max gain 5.57dBi. Same antenna 100 meters (~330 feet) up. Max gain 7.36dBi FYI: EZNec Pro/2+ v7.0 is now a free download (the author has stopped providing updates). https://www.eznec.com/

Strangely, I find the D74 easier to navigate than the new Icom ID-52 (the D74 also supports analog APRS). Most of the DMR stuff around me is part of the CMEN/Mi5. While one can reach Statewide 1&2 from Brandmeister, one can NOT reach Brandmeister from their repeaters. The local D-STAR repeater, OTOH, is usually linked to REF030C.

I have a similar problem with NOAA Weather broadcasts. I can stand in my driveway, near the kitchen door, and get perfect reception. Walk 5-8 feet down the driveway -- nothing. Continue walking down the driveway and it will receive well again. Basically, around my house, I have these 10ft circles of reception, with dead spots between them.

You have just set up a feed-back loop, anything repeater 1 pushes out will be /received/ by repeater 1 -- besides not having any way to protect the receive circuit from the power level of the transmitter (other than to separate the receiver from the transmitter [antennas] by a few hundred+ feet -- lots of coax to run, with lots of power losses).