Lscott

The usual rubber duck antennas, stubby antennas, have a negative gain. To get the 0.5 watt ERP the radio would have to produce more than 0.5 watts. Clearly the market for the radio is GMRS. The low power narrow band channels are an afterthought looking at what components were used. The point is anyone who is considering this radio with the idea of using it to talk to FRS radios, or have a real need too, will likely be disappointed. If the radio does what you want that's what counts. At least people know a bit more about the radio's likely performance and can make a better informed choice. That was the goal here.

One point not mentioned much are the gain figures work both ways. That is on transmission and reception. It pays to optimize the losses. A 5 watt radio likely is about as sensitive as a 40 to 50 watt one. You can run into cases where spending more money on a higher power radio to make up for the power loss but it does nothing to increase the receive signal strength. If you can’t hear the other station it doesn’t matter how much power you run. This could be the difference between using a 5 watt handheld with a roof mount antenna, or spending a lot more money on a high power mobile radio. I think enough information is here where choices can be made that fit budget and physical installation requirements. There shouldn’t be any really big surprises how the final system will perform.

I forgot to include a datasheet for regular RG-58U cable. https://catalog.belden.com/techdata/EN/9201_techdata.pdf As you can see the loss is almost double at 8.4db at 400MHz. The losses go up as the frequency increases. One table I have shows it at 10.6db per 100 feet at 450MHz. With this kind of loss one would do better sending smoke signals.

You should consider using a different antenna. The MXTA25 is listed as a 5/8 wave design. https://midlandusa.com/product/micromobile-mxta25-3db-gain-ghost-antenna/ From modeling this antenna has a net gain LOSS over a simple 1/4 wave, or 1/2 wave dipole antenna. Where you want the signal strength at the maximum is along the ground and not shooting up in the air at an angle. https://www.w8ji.com/VHF%20mobile%20vertical.htm The low loss cable you mentioned I found a datasheet for it from Belden Cable. The loss spec is 4.9db per 100 feet compared to LMR-400, 2.7db per 100 feet, at the same frequency of 450MHz which is very close to the GMRS frequencies. https://catalog.belden.com/techdata/EN/7808WB_techdata.pdf https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-400.pdf For the MXT400 radio there is an FCC test report you might find of interest. On page 7 it has the high and low power measurements. https://fccid.io/MMAMXT400/Test-Report/Test-Report-3120260.html

A small typo I made. The gain should have been 6.85db. The rest of the numbers should be correct.

I’ll leave that as an exercise for the student to figure out the system gain as they instructor used to say.

Ah no. When you see gain spec of 9dbi that’s a gain over an isotropic antenna that doesn’t exist. It’s for reference only. What you really want is a gain spec over a dipole, or a simple quarter wave, which is the smallest antenna that can be physically built. The difference in gain between the two is 2.15db. So the real practical gain is now 6.15db. But wait, we’er not done yet! Now you have to figure in your coax loss. For a typical run of 75 feet of LMR400 at 450MHz, close enough to the GMRS band at 462 to 467, the loss is another 2.03db. So your real gain is around 4.82db, which is a factor of 3.03 increase. For 5 watts in it looks like you have an effective radiated power of 15.17 watts.

Boxcar has a good suggestion. A few more points about MURS. You can use external antennas and the VHF signal seems to propagate further through trees etc. And finally you don't need a license to use MURS radios, but they must be FCC certified. GMRS radios everyone needs to have their own license unless they are a qualified family member of someone who is licensed. One thing I have noticed about operating FRS radios inside vehicles, the range is poor, around 1/2 mile is typical. If you use GMRS radios you REALLY need to use a roof mounted antenna, even with a handheld radio. Same point about MURS radios too.

You should be aware the Midland radios as far as I know are all narrow band FM. Look at page 4 "Type of Emission". https://fccid.io/MMAMXT400/Test-Report/Test-Report-3120260.html The "10K2FE3" is the FCC's technical definition for narrow band FM. For GMRS it typically should be "16K0FE3". Unless the handheld radios can be programmed for narrow band FM you might want to think about getting them. The issue with miss matched radio bandwidths has to do with the audio at least. A narrow band radio receiving a normal FM bandwidth signal will have a very loud audio, and may distort it. Going the other way a normal FM bandwidth radio receiving a narrow band FM signal will have low audio level. Trying to talk to more than one station with miss matched bandwidths everyone will be playing with the volume control and that gets old real quick. As a guide a doubling of power output may get you at most a theoretical range increase of around 40 percent. There are lots of other factors at the GMRS frequencies that will conspire to reduce this. Many have reported not seeing much of a change at all. You can use a radio from any manufacture to communicate with another manufacturer's as long as they are programed with the same frequencies, and tones if used, with the caveat above about the bandwidth.

Thanks. I missed that. I guess that's what I get for not looking a bit more carefully and just doing a quick scan through the datasheet and dashing off a post. I'm happy to see somebody is interested in the topic enough to look. 8-) So that now brings up the flip side question. Is the bandwidth now too wide? If it's 24KHz then it's way too wide for narrow band FM at 11 KHz. Now it's the reverse of what I wrote in error. Now the normal FM mode is likely OK but not the narrow band mode. Oh well. The FM deviation set for 2.5KHz and the audio gain increased, necessary in narrow band mode using the wide band filter to compensate, will work but the selectivity would suck. Since GMRS is 5KHz deviation narrow band performance likely isn't a big concern. One thing I didn't point out is the power output on the FRS only channels is 0.283 watts as shown in the grant. The FCC allows up to 0.5 watts so this radio won't even do the max allowed output power for those channels. If a potential user is looking at the radio with the idea they may need the narrow band selectivity and the max allowed power on channels 8 to 14, because of a need to communicate with FRS users, may want to consider another radio. In any case looking at the electrical design reveals an aspect of the radio's likely real world performance that isn't mentioned by the manufacture. At least for the GMRS specific version of the radio.

For the more technically inclined people you can investigate a design by looking at either the schematic, in this case it's not available on the FCC website, or the internal photos, which is better than nothing. https://fccid.io/WVTWOUXUN16/Internal-Photos/Int-Photos-4695706.pdf Looking at the PCB photos you will notice a large white rectangular part with "C50F" stamped on it. I've seen these before. They are commonly used ceramic filters. In this case doing a bit of searching you will find a data sheet for it here. http://www.quartz1.com/downloads/Tecdoc/filtr_ceramic/LTWC450F.pdf Take a look at page 4 of the datasheet figure 1. You will see the manufacture's marking looks like the one in the photos. As suspected it's a simple 455KHz IF, intermediate frequency, ceramic filter typically used in a Superheterodyne receiver designs. This would not be something expected in a typical "radio-on-a-chip" design. One thing to note in the spec sheet is the 50dB bandwidth spec of just 12KHz. Considering GMRS has a bandwidth of around 16KHz the filter is a bit narrow. However for narrow band, think FRS, the bandwidth is only 11 KHz it would be a bit too wide. I suspect the designers picked this part as a compromise where they tried to get away with using just one filter in place of the two that should have been used to save money. I think some of the commercial radio designs use two different filters for the two bandwidths. One reason why they tend to work better and cost more. And right next to it is a chip "AA32416" which appears to be the FM detector chip which would make sense. https://www.digchip.com/datasheets/parts/datasheet/849/AA32416-pdf.php Radio internal photos. https://fccid.io/WVTWOUXUN16/Internal-Photos/Int-Photos-4695706.pdf And for those who wonder what a Superheterodyne receiver is there is a nice history and write up here. https://en.wikipedia.org/wiki/Superheterodyne_receiver Looking up the numbers for the other chips, assuming they are not proprietary part numbers for the end user, one might gleam some other interesting details about the radio and it's likely performance.

You might want to try using a different HT. It’s shocking how deaf some HT radio’s receivers are. Particularly the cheap ones.

You can try plugging numbers in to the calculator at the site below. http://www.hamuniverse.com/lineofsightcalculator.html

That could be the case. You can see the FCC data on the radio at this site below: https://fccid.io/WVTWOUXUN16 The FCC certification grant is there. More of interest you can find internal photos of the radio. After looking I didn’t see the typical radio-a-chip device, which seems to be the favorite used in the cheap Chinese radios, on the circuit boards. I didn’t try to look up the chip numbers so the manufacturer could still be using a different one, or a customized version.

If you can find the detailed specifications for the radio look at the receiver section. If the type is stated as “direct conversion” the odds are very high it’s a cheap “radio on a chip” type design.

Interesting point about who owns the system and has the right to shut it down. One has to wonder where else kill switches are installed and who has their finger on the button.

I think that was the time where the government shut down cell phone service for several hours?

I think that was the time where the government shut down cell phone service for several hours?

For quickly planed events, or just a spontaneous group gathering, it's likely true. I agree with the comment for the more organized groups. The frequencies used I doubt would change that much, would have to reprogram a lot of radios which isn't practical when people need to be deployed quickly. What would be hard is figuring out their "com sec" protocols. That can be quickly changed by just handing out the radios with a sheet listing the special codes used at the last minute. With that said there are likely elements who are technically competent, various radio hobby orientated individuals, who could show up with the appropriate equipment and have no affiliation to any organized group. As pointed out the UV-5R is readily available and still very cheap. It wouldn't be a budget buster for somebody to keep a handful of these at the ready, per-programmed, show up at the event and pass them out to selected people. The positive point is those radios don't use any form of voice encryption or scrambling. So using a scanning type radio, likely easier done with an SDR dongle which can watch a wide chunk of spectrum, so when strong pips shows up zero in and see what can be heard. Might get lucky.

People are cheap. I guess if you wanted a radio for a specific use and have no interest in radio as a hobby you would buy the cheapest thing that does the job. The strange thing is these radios are cheaper than the bubble pack FRS radios, in a dollar per radio sense, in most cases.

Looks like a nice radio. What I like about it is the receiver is a true superheterodyne design. I haven't been impressed with the performance of the cheaper "radio on a chip" types that all seem to use the ubiquitous RDA1846S, or some variant of it. You get what you pay for. The D878-UV analog/DMR radio, which isn't cheap, I think uses the chip but seems to perform better than I would expect. I think the design uses a tracking filter on the receiver front end to help eliminate the nasty image responses you get with the radio on a chip design.

I got "back" into GMRS when the FCC changed the fee to something more reasonable and the extended the license term to 10 years. I was licensed before and let it expire, 5 year license term and around $100 was a bit much. Now if I ever need to keep in contact with a family member all I have to do is hand them a programed radio and some simple instructions. I also have some friends who so far have not been licensed for Ham radio, due to COVID-19 no test sessions or too busy to study for the Ham test, but filling out a form and paying the $70 was a easy. GMRS is the only way I can talk to them by radio currently.

The first point is one of the reasons why the FCC started clamping down on the cheap Chinese radios. I had a buddy that was fooling around like that with one. I got him to test for and received his Ham Tech Class license. He's having a lot of fun now, getting into the digital voice modes and hot spots. I'm only aware of a few radios older radios that have any kind of scrambler function. Many of the older FRS radios used simple voice inversion. I believe the FCC put an end to that with the rule revisions in 2017 which became effective in 2018. I know of several current higher end Chinese radios that will do digital encryption since they are both analog and digital (DMR). Several of the older Kenwood LMR analog radios have either built in simple voice inversion or the user can install a more advanced voice encryption module. I have a few of those old radios, used off of eBay of course without that option. You wouldn't believe what those boards cost. I checked in case I ever ended up with a used radio that had one installed. You never know. https://www.ameradio.com/product/512172/description.html (Just one of the several types they sell) The PDF files have some interesting info on the modules. On your last point that does bring up another question. Has anybody seen what kind of radios are being used? Apparently the link in my first post seems to show the cheap UV-5R is widely used. The article is an old one so I would guess some other make and model has taken its place.

The point is well taken. The info is just for general information and monitoring. After seeing photos of people carrying around what is obviously two-way radios I got curious if anybody happened to pick up the communications. There were a few protests by me and all I heard were comments by the mall security guards since some of the protesters had used it for parking.

I’ve noted more protesters are carrying two-way radios. Anybody have an idea what frequencies seem to be the favorite ones used? The Baofeng UV-5R looks looks it’s the go to radio recommend by many prepper and militia groups. Poor choice IMO. https://radiofreeq.wordpress.com/2016/01/19/militia-radio-frequencies/ I’m guessing most of the radios are the cheap Chinese ones since you program them for operation outside of the Hams bands with requiring modifications. They can be easily programmed for the public service frequencies which likely accounts for the reports of police radio communications being jammed in some cases.