Lscott

Yeah, I know about the software bugs with the D878UV. Hardware wise it's a nice radio. At least the front end seems better at rejecting out of band or off frequency signals compared to the other cheap Chinese radios I have. The downfall is the firmware and the customer programming software. If you look about every 1 to 3 months they come out with a new version of both ever since the radio was first released. They fix something in one version, then it's broken in the next. I don't understand why when they fix a bug it doesn't stay fixed in later releases. The last one, V1.17, that just came out a few weeks ago I just sent off another bug report about a couple of things that don't work I stumbled a cross or just plain annoying until they get fixed. Now by contrast my TH-D74A has only a few updates and when the bugs get fixed they stay that way. Yes its an expensive radio but you get what you pay for too.

The site below has some good info on the Anytone, Alinco and Btech DMR radios. http://members.optuszoo.com.au/jason.reilly1/868mods.htm Oh, mode 00014, the password is "878#" typed in without the quote marks.

Actually going to a lower loss line could make the SWR worse as seen from the radio end. The reason why is the energy reflected from the antenna back to the radio is attenuated less, more reflected power, that would otherwise be adsorbed by the feed line. The SWR can be calculated using forward and reflected power using the formula below: SWR = (1+sqr(Pref/Pfwd))/(1-sqr(Pref/Pfwd)) Where "sqr()" is the square root of the value inside of the "()". And "Pfwd" is the measured forward power going to the antenna while "Pref" is the power being reflected by the antenna miss-match back to the radio.

I would NOT recommend using PL-259 and SO-239 connectors at UHF. They are not "constant" 50 ohm impedance. Depending on how many you have and where in the system they do tend to degrade the SWR. Good connectors to use at UHF are "N" type, BNC, mini RG8, SMA are the more common ones. Many mobile and base radios use an SO-239 on the back so you can't do much about it. The better ones use the "N" type. Where you see SO-239's used look at the inside of the connector. If you see what looks like thin a web between the outside of the center pin and the inside of the outer shell, like the spokes on a wheel, cause less of a problem compared to the solid filled ones. This is done to improve the impedance of the connector to bring it closer to the desired 50 ohms. The antenna ground radials, if required, should be around 1/4 wave length long, approximately 6 inches long, and could be bent downward at a 45 degree angle from the horizontal. Some of the antennas that claim not to require a ground plain are a "J-Pole" internally. These antennas should have several turns of the coax located right at the base to decouple it from the outside of the coax shield. If this isn't done then RF current flows on the outside screwing up the antenna TX and RX pattern, RF getting into the radio resulting in TX audio distortion and in addition to causing weird SWR problems. If your SWR is 1.3 to 1.5 there may not be much to gain by improving it to the ideal 1 other than to make one feel better. Most radios are designed to tolerate SWR's up to 2 at full power anyway.

Maybe I should take another look at the 629's.

I was looking at the 628’s, not the 629’s, originally. Now I’m not sure. I just purchased a Kenwood TK-2000 package with programming cable and software new on eBay for $50. I was going to experiment using that radio and a Baofeng BF-888 with an MFJ-916 duplexer to make a simple low power VHF/UHF cross band repeater.

Which ones have you used? I've been looking at reviews on these on and off for a while and I'm not likening the comments I've read, to many negative ones. Yes I've seen the comments about the first half second being cut off. That's happen to me with radios with VOX operation or a VOX headset so seeing it mentioned with the controller isn't a concern. All it means is the electronics needs enough audio signal level to detect long enough to ensure somebody is really talking so the radio TX isn't tripped randomly. What gets me are reports about out and out failures or the audio is fine for a while then for no reason is distorted. Some reports the controller will no longer switch the TX radio on etc. One guy said power cycling his would fix the audio distortion problem on his for a short while then mess up again. Then there are people like you who say they have no issues. From those that don't report issues to the frequent ones who do I begin to question the manufactures quality control.

If you want to do an "in-band" repeater you will need two radios, a duplexer and a controller as the main components. You can buy a cheap UHF duplexer at this site. If you supply the two frequencies they will tune the filter at no extra cost. Also don't forget to get any N to whatever RF adapter you will need to connect to the radios and the antenna. www.409shop.com/409shop_shopcat.php?&usercat=4942 If you want to know how well these cheap Chinese duplexers work a guy did some testing on one here. http://www.repeater-builder.com/antenna/pdf/chinese-mobile-duplexer-measurements.pdf Then use a simple repeater controller like this one. https://radio-tone.com/product/rt-crc1-repater-controller-full-duplex/ I see ad's for the "Surecom" controllers but have read a lot of bad or poor reviews. The one above seems to be OK. Also don't forget to get the right radio interface cables with it.

Or do a "parrot" repeater. This is where you TX and the controller will record the message. When you're done it then re-transmits the message. This of course slows down the communication, and some find them annoying to use, but are simple to setup using one radio and fairly cheap. There are several YouTube videos where a guy did this putting the guts in an ammo can with a battery and charge controller connected to a used solar panel. He used the metal ammo can for the ground plane required by the antenna. Stuck it on a mountain top in a very remote area. Had it there for about a year or so running before having to service it. The repeater controller he used should be like this one. https://www.argentdata.com/catalog/product_info.php?products_id=98

Also you can't crossband between the Amateur Radio service to GMRS or MURS either.

What does the local terrain look like around the site? Another point to consider is very high gain vertical antennas have a narrow radiation pattern perpendicular to the antenna. General reciprocity antenna theory says the RX and TX patterns should be similar. Anyone close in will have a hard time getting into a repeater like this since the antenna is deaf if you're not in the RX pattern. Commercial broadcasters and some repeater installations use antennas designed so that the narrow radiation pattern is not perpendicular to the antenna but has a small "down tilt" angle of several degrees to compensate some what for this condition. A lower gain antenna has a wider RX and TX pattern perpendicular to the antenna. The gain fall off is less severe. That's why you read about people claiming that a simple 1/4 wave on UHF gave them better results in hilly terrain verses using a high gain antenna where other stations are at different elevations relative to each other.

Oh, one more point. Be careful what version of a radio model you buy used! For example the Kenwood TK-370's and TK-370G's come in several variations that cover different ranges in the UHF band. You want to pick one that covers 462 MHz to 467 MHz. There are 4 versions of the 370's and 370G's. 450 to 470 470 to 490 490 to 512 403 to 430 If you get a 370 you want the "type 1". The ID tag, on the back of the radio on the aluminum chassis under the battery, should show "TK-370-1" or "TK-370G-1" on it. The type 1 is the 450 to 470 range. The radio will also program down in to the Ham 70 cm band to around 440 MHz. The Kenwood software will complain its out of range but will let you do it anyway. The radio will work there which is convenient for those dual licensed for Ham and GMRS. 8-)

I agree. I've picked up several Kenwood TK-370's (wide band 32 channel, repeater operation, 4 watts), also have several TK-370G's (wide/narrow band 128 channel, repeater operation, 4 watts). Both have part 90 and 95 certification. If you search and wait you can get one at a fair price on eBay. The programming software is easy to find on-line. These radios use the same exact cheap "Baofeng" programming cables. Just make sure the one you get doesn't have the cloned USB to serial chip in it, the newer windows drivers don't work with them. Parts for these radios are easy to find. You can get the drop-in battery chargers, battery packs, antennas etc. The TK-370G uses the reverse SMA antennas. The TK-370 however uses a Motorola MX type but you can get a MX to BNC adapter to use an external antenna. If you buy a used radio be sure you can get the programming software and cable for it! Just about every business band radio has to be setup using the software because there is no "front panel programming" typically, at least on the hand held radios.

What is the source you got the graphs from and how were the tests done?

Military man pack radios I haven't used and don't really know much about them. I would suggest you search around the Internet for a group(s) that specialize in that kind of equipment for info.

Going for your Amateur Radio license, great! About commercial radios for GMRS use. Look carefully at the FCC certification. If you can find the FCC ID you can look up the different FCC parts the radio is certified for operation. Some have Part 95 which means they are legal to use. There are various opinions about if Part 90 radios can be legally used. That's covered elsewhere. For example I have a couple of Kenwood TK-370G-1 radios with an FCC ID of ALH29473110. I also use a Kenwood TK-370-1 with an FCC ID of ALHTK-370-1. You can look up the FCC ID's at: https://fccid.io/ The next issue with commercial radios is there could be several sub models that cover different frequency ranges. Be sure the one you are looking at will work over the 462 to 467 MHz range. The final big issue is the programming software, AND the cable. For many radios they are NOT front panel programmable. Thus the only way to set them up is with the manufacture's software. If you're really lucky the open source software "CHIRP" may work. In my experience it works great for some radios and others it's very buggy.

Yes some people do get it confused. What I'm looking for is the equivalent of a 1/2 wave antenna, thus no ground plane is normally required. The Comet CA-2x4SR does require a ground plane as I suspected from my testing. I confirmed this the other day by contacting Comet tech support. The reply I got is quoted below. "The CA-2x4SR is a 5/8 wave, so yes it must have a ground plane underneath the antenna in order to work properly. It was designed to be installed on sheet metal, like a vehicle trunk deck, hood, or even hatch back door. You need about 20” radius of metal under the antenna, but rarely is it possible to create a ground plane that provides the impedance needed at the antenna feed point. If you can use one of our lip mounts attached to the door edge, or hood edge to provide the ground plane." From my SWR scans you do need a really good ground plane. A magnet mount sort of works but a good direct electrical connection to a ground plane, or set of correctly cut to length radials, works even better from what I see.

Just and update I got an email from Diamond Antenna this afternoon. They have a new product in the works. This was the info I was sent below in quotes. "We will have the NR240A in a couple of months. This antenna, when on a mag mount is 140MHz-170MHz and 430MHz-470MHz. When it is grounded on a hatch/lip mount it is 140MHz-165MHz and 440MHz-465MHz. " Looks close to the spec's for the Comet wide band antenna. If the above is correct it seems the antenna is optimized for a wider bandwidth using a magnet mount? That is unless they got the magnet mount verses the hatch/lip mount bit swapped. Either way it looks like there will be an alternative antenna. I just wish it didn't require grounding. More new vehicles have plastic body panels so grounding gets harder to do.

I'm sure you're right. This was the point of asking. I did send an email off to Diamond Antenna a few days ago asking if they even offer anything like the comet CA-2x4SR. Never got a reply to date. I wish Comet still made the CA-2x4MB. The only failing was the spring for the fold over feature lost tension so the antenna would lift out of the socket then flip over at highway speeds. I had to wrap several layers of tape around that area to stop it. Other than that it's worked fine for years. I haven't had any issues with loose hardware, screws, or rust. If anybody has any interest I have the AA-1000 SWR scans of the CA-2x4SR on the roof of my Jeep using a 5 inch magnet mount and inside the house using a home brewed mount with 4 drooping radial elements, which gave the lowest SWR scan curves, much better that the specs in the Comet datasheet. I was rather pleased to see that. For the moment I can't seem to attach any files to upload. The message says I only have 666 bytes left. Not sure why it's still limiting me or is there a time limit that has to expire first before the upload limit is reset.

I can't seem to add any more files at the moment showing the scans for the Ham 2M and 70cm bands, which look just as good. The stated antenna gain is 4.5dbi from 145-148 and 7.7dbi from 440-450 with an SWR of less than 1.5, the graphs in the datasheet show over the above range a max SWR of 1.2. The antenna is about 59 inches in length, a big one.

I've been looking for a good dual band ground independent antenna for both the HAM 2M/70cm band and the MURS/GMRS bands. I have a new Comet CA-2x4SR antenna, which works, but requires a good ground plane. I don't want to drill any holes and the coupling with a magnet mount results in higher SWR, but still usable. I have an old Comet CA-2x4MB which is ground independent but hasn't been manufactured in years. I would like to find something like it. I recently did some SWR scans using a Rigexpert AA-1000 antenna analyzer, got similar results with spot checking using an old MFJ-269 as a sanity check, to confirm the performance. The antenna is mounted on a luggage rack using a Diamond K550KM rack mount kit on a cross rail on top of a Jeep. The scans all look very good for a large high gain antenna.

This point is interesting. Consider the following. I have a Kenwood TK-370-1 (wide band only) and a couple of Kenwood TK-370G-1 (wide and narrow band) radios. Both by the way are certified for Part 95 by the way. The TK-370-1 has an FCC ID of ALHTK-370-1 which shows a Part 95 certification. The TK-370G-1 has an FCC ID of ALH29473110 with a Part 95A certification which under the old rules was GMRS. You will also notice both radios also have a Part 90 certification too. Both radios have a stated spec of 450 to 470 MHz frequency range but will program down into the upper section of the Ham 70cm band, 440 to 450 typically for the main FM operations, and will work there. Since nether radio was physically modified, which would invalidate the certification, just programmed for both services, the FCC should not have a problem with using the same radio for both services. Hams are allowed to use radios for other services on the Ham bands so long as they meet emission requirements. So the point here is if you want to have access to both services you need to look very carefully for radios that have the Part 95 certification and can be programmed for the Ham 70cm band. With a Part 95 certification in addition to the Part 90 which should not be a disqualification.

The user programming software can be used to unlock the frequency range. At least it does on the Amateur version of the radio. Mine came locked to the Amateur Bands only out of the box. Click on the "Frequency Range" tab on the left side of the TH-8600 programming software. You should then see a small window with 3 frequency ranges on the left side, 150M 250M 450M. If you click in any of the ranges to the right you can't change the settings. Now press the "P" key on the computer keyboard. This NOT documented anywhere. Now you should get a small edit box that opens on the bottom of the frequency range window to enter a code. Type in "8600TH" without the quotes and is case sensitive. Then click "Enter". You should be able to click in any of the frequency range boxes now and change the values. Next write the code plug to the radio. Once this was done on mine I've never had to go back and change it. I can't say if this will work for the GMRS version of the radio but if somebody has one and wants to try it then let us know.

PastorGary, Thanks for the info. I wasn't sure if the radio was legal to use on MURS. There isn't a definitive clearly stated policy from the FCC I could find that states any Part 90 radio with a grant date before the creation of the radio service MURS or GMRS would be legal to use with the right programming to comply with the rules. That seems to be implied in the rules for the service in question. A bit off topic but I also have the older TK-370, not the "G" version, programed for GMRS. It has only 32 channels and wide band only. The radio has an FCC grant for Part 95, FCC ID ALHTK-370-1. I have it programed for the 22 GMRS simplex channels and 8 more for repeaters use leaving two spare. The FRS channels are programmed for RX only, 8 to 14, since they are narrow band only. The audio volume will be low but usable. The only issue with that radio is the antenna connector is the Motorola MX type. I think the newer one uses the same reverse SMA antenna connector as the TK-270G and the Chinese radios. I found an adapter that will convert from MX to female BNC for using an external antenna. FCC Grant TK-370-1.pdf

I've looked around but can't find any hard info for old Part 90 radios that are legal to use for MURS. For example I have a TK-270G HT purchased at the Dayton Hamvention. The FCC ID is ALH29463110. The grant is dated 10/25/1999 which is before the creation of the MURS service in 2000. If I read the rules and understand them it should be OK as long as the radio is programed to conform to the rules. Anybody else have a source for info on this topic? TK-270G-1 FCC - OET EAS Form 731 Grant of Equipment Authorization.pdf