Lscott

Just a note about that. I've had very good luck using toothpaste to polish up the plastic screen on several radios I got used. I got scratches out I thought would never clean up. It takes a lot of work to rub out the scratches, toothpaste is a VERY mild abrasive. I used it straight from the tube on a paper towel while using a fair amount of pressure. Tilting the radio so the light reflects off the surface is a very good test to see how the polishing is going. I wipe the screen down with a wet paper towel first so I can get a clear view of the surface. At the end I sometimes use an electric toothbrush to do the final polishing. I did spend about an hour or more on the more damaged screens. On several radios when I got done the screens could have passed for new if you didn't do a real detailed examination. If you can't get a replacement case or don't want to spend the money the above procedure works well. Nothing like getting a used radio at a good deal, then clean it up where it looks almost new. 8-))

1. Yes you need fuses of the proper type and amp rating. Too low in amp rating the fuse will fail during transmit, which draws the most power. Look at the radio's manual. The recommended fuse and rating is typically specified there. 2. You can try some automotive trailer power connectors. You can get something like the below cable and plug. https://www.amazon.com/807-Extension-Disconnect-Harness-Connector/dp/B07SQ1G56V (You most likely can find something like this at your local auto supply shop) Just cut the cable in half. Connect the wire end to the power supply, or battery, observing the proper colors, red is positive and black is negative. Then use the other half of the cut cable for the radio doing the same thing matching the red for red and black for black. The bonus is if you get two cables and cut them in half the second one can be wired into the automotive electrical system. Now you can freely move the radio between the vehicle and the house, for example, without having to worry about screwing up the wiring and wrecking the radio. I highly recommend you permanently attach the wires to the power supply/battery and radio then use just the plug. Sooner or later you'll screw up and connect the radio up backwards. When the "magic smoke" comes out of the radio it quits working and there is noway to put it back in either. 8-(

One other point that hasn't been mentioned before in this thread is the following. Since the original post requested recommendations for radios, and the usage will be in a farm setting, the physical construction and reliability will be very important. The radio(s) will likely get exposed to rain, fine dirt/dust in the air and likely dropped on soft and hard surfaces too. Many of the cheaper radios will fail. Just about all of the old LMR/commercial radios are designed for just this kind of environment. For example, I just got a used Kenwood TK-3170-K radio off of eBay, the seller took my offer of $15 when contacted by eBay's messaging system, with free shipping. The photos showed a nearly completely destroyed antenna on a radio with painted on ID and covered with dried up fine dirt/dust from being used outdoors most likely. When I got it I spent over an hour with a brush, q-tips, old tooth brush, safety pin, counter cleaner and alcohol cleaning it while using the safety pin to dig out the caked up dirt stuck in narrow cracks around the edge of the case. Once clean it looked OK with minor scuffs and a few scratches but programed fine. On air testing showed the radio was fully functional with a good battery pack and a new after market antenna. I very seriously doubt most of the cheap handheld GMRS radios being sold would have survived what this radio went through. eBay item number: 114446054336 While the RF performance of the radio is very important it still has to survive. A radio with great spec's is worthless if it breaks.

Yes, I’ve had that experience. It’s even worse on the Ham bands with DMR when stations don’t get their audio levels set right. Then there is the flip side too. North of my area there is a GMRS wide area coverage repeater specifically setup for narrow band operation. I contacted the owner and had him verify it was in fact narrow band. My guess is that’s all he had or just acknowledging more users are using narrow band radios. At least with my Kenwood handhelds I can program the bandwidth for normal/narrow on a per channel basis. The radios I use have 128 channels so I program one set for normal FM and the other for narrow band. At least this helps to reduce the annoying sound level mismatch with more that two stations on frequency when the other station is stuck with one or the other bandwidths. https://mygmrs.com/view?id=3768

I agree. Just because this is a GMRS forum doesn't mean it is the best solution for his requirements. This should be a healthy environment where other options can be suggested.

I did some snooping around and located some info on the Aerotron radio. Not much to see. Just had to check it out. https://fccid.io/APC9RB60ACC25B The interesting part is besides doing SSB it also had some sort of digital mode. Also the frequency tolerance is far better than the usual FM radio. Part 74 https://ecfr.io/Title-47/pt47.4.74 Part 9 https://ecfr.io/Title-47/pt47.1.9

Thanks for the info. I never heard of this radio before. The description of the method to hold the frequency centered on the channels using a pilot tone brings up a question. I'm assuming they used the pilot tone in a PLL circuit to adjust the TX/RX frequency until the tone was exactly in the filter's pass band? The pass band of that filter would need to be rather narrow too I assume.

Thanks. I was sort of expecting that kind of result. Given the usual crystal reference frequency accuracy and temperature stability makes it difficult to stay on frequency. Being off frequency by 100 Hz or so SSB signals are petty much unreadable.

My goal here was to find out if there is currently, or in the past any LMR/Part 90 radios that could in fact do SSB.

No, that shouldn't happen. On SSB the bandwidth can be rather narrow. On my old ICOM IC706MKIIG I had a optional narrow SSB filter installed. Many Hams run a 2.2 KHz to 2.4 KHz bandwidth, or a bit more. SSB is more spectrum efficient than FM, at lest for the typical bandwidths being used. https://www.dxengineering.com/parts/ico-fl-223 The above radio opens up a lot. http://www.catlog.net/_Descarregas/Manuals/01-Icom/Icom%20706MKIIG%20OBM.pdf Yes the FT991A you can only open up the HF section. http://blog.pauls.li/wp-content/uploads/2015/01/FT-991_MARS_Mod.pdf So far nobody has found a general way to open the VHF and UHF bands. There is a way to do it on a per frequency basis however using a test mode from what I've found. https://forums.qrz.com/index.php?threads/ft-991a-expanded-tx-on-vhf-uhf.623521/

Looking over the rules the FCC allows several types of emissions, modes, on GMRS: 95.1771 - GMRS emission types. 95.1787 - GMRS additional requirements. https://en.wikipedia.org/wiki/Types_of_radio_emissions https://www.law.cornell.edu/cfr/text/47/95.1771 A1D: Double-sideband amplitude modulation One channel containing digital information, no subcarrier Data transmission, telemetry or telecommand (remote control) F1D: Frequency modulation One channel containing digital information, no subcarrier Data transmission, telemetry or telecommand (remote control) H1D: Single-sideband with full carrier One channel containing digital information, no subcarrier Data transmission, telemetry or telecommand (remote control) J1D: Single-sideband with suppressed carrier One channel containing digital information, no subcarrier Data transmission, telemetry or telecommand (remote control) R1D: Single-sideband with reduced or variable carrier One channel containing digital information, no subcarrier Data transmission, telemetry or telecommand (remote control) F3E: Frequency modulation One channel containing analog information Telephony (voice intended to be listened to by a human) G3E: Phase modulation One channel containing analog information Telephony (voice intended to be listened to by a human) H3E: Single-sideband with full carrier One channel containing analog information Telephony (voice intended to be listened to by a human) J3E: Single-sideband with suppressed carrier One channel containing analog information Telephony (voice intended to be listened to by a human) R3E: Single-sideband with reduced or variable carrier One channel containing analog information Telephony (voice intended to be listened to by a human) F2D: frequency modulation One channel containing digital information, using a subcarrier Data transmission, telemetry or telecommand (remote control) G2D: Phase modulation One channel containing digital information, using a subcarrier Data transmission, telemetry or telecommand (remote control) The interesting one is running SSB. Has anybody run across a Part 90 certified radio that can do SSB on the GMRS frequencies? If the FCC seems to be "OK" with Part 90 LMR radios on GMRS would they have a problem with one doing SSB? At least the emission mode is allowed, J3E.

The following link is a test of one of those cheap Chinese “notch-plexers” you see being sold. You can buy them from the same source as the bandpass filter. They sell for around $100 depending on power requirements. Used with a couple of “clean” HT’s and a simple duplex repeater controller makes for a cheap repeater for noncritical locations. This is basically what’s in that Retivis repeater being discussed elsewhere on the forum. What I like was the temperature testing to see how “stable” they are. People forget the cavities change dimensions with temperature thus the tuning will change. http://www.repeater-builder.com/antenna/pdf/chinese-mobile-duplexer-measurements.pdf

Normally the power loss in a good quality RF connector is rather small, a few tenth's of a db. What you do have more of a problem with is with the impedance of the connector. The common PL-259/SO-239 are noway even close to 50 ohms. At UHF this impedance mismatch can cause elevated SWR, more reflected power. The general advice is to use constant impedance type RF connectors. For GMRS the typical one recommended is the "N" type. There are other common constant impedance connectors you will likely encounter, SMA and BNC. You do have to watch which impedance the connector is designed for. They are commonly available in either 50 ohm or 75 ohm versions. For GMRS and the usual 50 ohm coax you need the 50 ohm version of the connectors. You can't simply look at them to tell the difference, the physical dimensions are similar. If anybody is interested in the whole issue of coax cables, matching, RF connectors etc. the following guide has a lot of useful info. https://www.fclane.com/sites/default/files/rfguideen.pdf

That's a nice write up on preselector filters. For anybody who has an issue with too much bandwidth on the front end you can buy a cheap bandpass filter, 0.6 MHz to 8 MHz range, to put inline between the radio and the antenna. The rejection for out of band signals is petty good at 50db. I think the vendor will tune the filter for you before shipping. http://www.409shop.com/409shop_product.php?id=125434

No it's not a sarcastic comment, just an observation. I've occasionally been guilty of the same thing, blaming lack of filtering or technical short comings on "intermod". I wanted to point out there are more reasons for poor selectivity or interference. Understanding what the underlying nature of the problem may suggest a possible solution or what radio specifications are really important. You soon learn that power isn't everything, and a bad or poor RX'er design can break a radio system. If you can't hear them what's the point? Looking at the typical manufacture's spec's for many radios most never mention the above points, and with analog radios specifically the image rejection. The ARRL lab does a fairly good job of testing radios when they publish a review. You have to dig through the test results for the info. The sad part is they can't test everything out there, and it could be months or even longer before they do a test and review, if ever, on a particular model. Most Ham radios have wide open RX front ends because people want to use them as cheap scanners. I use many of my radios that way, Ham and commercial. While that maybe appealing however that means a compromise in other areas. One reason why the commercial radios mostly perform better in high noise and RF heavy environments is the RX'er design. The radios are generally single band with just enough front end bandwidth to cover the commercial section of either the VHF or UHF band they were designed for and no more. The forum is a place here to trade information. I like to includes links in many of my posts for background that saves a lot of typing. Why repeat the same information when somebody else has already done the job, and likely a better a writer. For my day job I've had to write technical documentation on occasion including for a patent application for a project I worked on in addition to regular design work. People always comment about the crappy manuals that come with most CCR's, well take a crack at writing a better one and publish it. I can tell you writing technical documentation is a tedious, boring and mind numbing work. Now I understand why most engineers hate doing it.

Looks like I cut and pasted the wrong link in the last post. It should have been this one. https://en.wikipedia.org/wiki/Intermodulation By the way the link I posted in error is a good company to use with the builtin utility in many routers to keep your dynamic address updated for remote access when you can't get a fix IP address.

It seems whenever there is a failing with a radio's performance it gets blamed on "intermod". https://account.dyn.com/ This seems to be the go to bogyman to explain the problem. I'm not so sure that's the case with the frequency it gets mentioned. There are at least two other factors to consider. The first is image response. Given the general lack of filtering on the front end, which by the way is also a problem with the name brand Japanese radios, might be a more likely cause of poor signal rejection from off channel signals. https://en.wikipedia.org/wiki/Image_response The second is based on the fact many of the CCR's use the ubiquitous RDA1846 radio-on-a-chip design. https://www.w5txr.net/upload/RDA%20%20Microelectronics%20RDA1846.pdf This chip is effectively a software define radio, a cheap one. The max clock frequency of the chip from the datasheet I have max's out at 26MHz. That's way too slow for UHF communications for a normal sampling period to be used, theory says it must be at least twice the highest frequency of interest, so something else must be going on. Normally in DSP applications aliasing is avoided, however it can be used as a type of frequency down conversion method. https://en.wikipedia.org/wiki/Aliasing https://en.wikipedia.org/wiki/Digital_down_converter http://hunteng.co.uk/pdfs/tech/ddctheory.pdf For a typical application example of the chip have a look at a schematic for the UV-5R radio from Baofeng, one of the original CCR's. http://static2.rigreference.com/manuals/baofeng/baofeng-uv5r-circuit-diagram.pdf Given the low clock frequency of the chip, relative to the frequency of interest, several signals, at different frequencies, could end up being down converted and appear to be on the same frequency. Some comments about the Anytone D578UV were made in some other posts. Additional info on that radio can be found here. http://members.optuszoo.com.au/jason.reilly1/578mods.htm About 3/4 of the way down the page is some interesting details about the internal design of the radio, specifically about the IF stage. The comment about the possibility of the third unpopulated IF strip being used in a future model for AM air band RX is nice.

The real question is are the radios being sold in the US? If so what is the FCC ID. With that in hand checking the FCC certification test report would be the definitive answer to radio’s operation. In the case above it looks like somebody did a particularly bad job writhing up the spec’s. Again mistakes in the spec’s doesn’t mean the radio doesn’t exist, or will soon. I ran across a brochure for a Kenwood commercial radio that claims an FCC certification it does not have. Even the company I work for get spec’s wrong. Our sales manager ran a full page color glossy ad on the back cover of a very well known trade magazine years ago with a glaring error that almost got her fired when the company president found out. That happened because nobody from the engineering department reviewed it for accuracy before publishing it.

Try looking here. Windows 2000 likely will work for most of the old CPS versions out there. https://winworldpc.com/library/operating-systems#

Yes I saw the MOQ number. That doesn't imply you can't buy them in single units from a vendor somewhere. The point of the exercise is there are radios available for the 900MHz ISM band. If somebody really wants one they can do the searching for a vendor. Everyone makes errors in their spec's, or the real engineering spec's changed after the original spec's were published. Some just do a better job of making far fewer errors in the published spec's or feature lists. There are other license free radio bands in the US. Some people have been experimenting on 49 MHz to 50 MHz, right below the Ham 6M band. Power is limited to 100 milliwatts. https://www.qsl.net/49mhz/ One other thing to point out is the 900 MHz ISM band is also the Ham 33cm band so you have to share it, and with old cordless phones and the other junk you find on it. https://en.wikipedia.org/wiki/33-centimeter_band https://w6aer.com/getting-started-with-900mhz-ham-band/

There is a far cheaper analog radio to look at also for the 900MHz ISM band. https://www.retevis.com/Retevis-900MHz-License-Free-Two-Way-Radio/

I think you're referring to the ISM frequencies. Motorola sells 50 channel digital radios for this unlicensed service. https://www.motorolasolutions.com/en_us/products/two-way-radios/commercial-business-two-way-radio-systems/on-site-business-radios/dtr-series/dtr700.html#tabproductinfo Here is the brochure for them. They can do 1 watt. https://www.motorolasolutions.com/content/dam/msi/docs/business/_documents/specifications/dtr700_spec_sheet.pdf If they aren't too expensive they could be fun to get a couple to play with.

Yeah, after I went back to read some other posts it made more sense it was a PL tone. My mistake.

Just an additional question was that a GMRS frequency, 462.650/467.650 with a tone of 151.4? It wasn't exactly clear to me when i read it the first time around. The frequency 151.4 looked like a typo for one of the three MURS channels in the 151 MHz range.

I wouldn't say they "squatted", but more like the FCC ignored the illegal operation to the point of no return. In fact you could say the FCC screwed up by commingling FRS and GMRS together by allowing dual service radios in the first place. It's really no different than the old CB radios days when so many people got radios and skipped getting the license. After a while the FCC gave up and made 11M effectively license free. They made their problem go away by making the unlicensed illegal operation now legal. Oh, about a restaurant employee demanding you get off "his channel", well go look for videos and stories about Walmart and MURS. Seems like some of those places think they own those frequencies too. Don't forget that MURS is open to various uses including wireless intercoms, digital data etc. You'll have that to look forward to as well when more people start using it. Oh, when you were on 151.4MHz were you using an FCC certified radio for MURS and what model was it? There aren't that many out there. If the radio was certified before the FCC created MURS, Part 90, it likely would be legal to use when programed with the correct output power and channel bandwidth. I have 5 Kenwood TK-270G-1 5/1 watt 128 channel radios for just that reason plus they work on 2M as well. I started another thread a while back on this form asking how many people use MURS.