Lscott
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Posts posted by Lscott
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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.
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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.
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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.
- kipandlee, berkinet and Elkhunter521
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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.
- Elkhunter521 and ChrisL
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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.
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I've had good luck with surecom controllers, but then again I only have 2,
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.
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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.
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You could just do a simple GMRS simplex repeater with two radios
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
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Also note that crossband repeat is NOT ALLOWED on GMRS (Repeaters are not allowed on MURS anyways, but crossbanding both MURS and GMRS is also not allowed)
Also you can't crossband between the Amateur Radio service to GMRS or MURS either.
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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.
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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-)
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With so many good quality used radios from Kenwood, Motorola, Vertex, Icom and others, most Part90 and many Part95 certified, and selling for more-or-less the same price, I don’t really see the point in bothering with The RT76. Also the quality brand radios usually have a huge number of branded and 3rd party accessories available as well: speaker/mics, antennas, batteries, group charging stands, etc.
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.
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I'll start the Cheap China Radio (CCR) thread by showing this picture.
That shows the sensitivity of the receiver combined with the channel rejection filtering in dB, which means, any signal value that is above the dBm curve plot will desense the receiver. You can pretty much extrapolate this curve from the last point where it is computed if no advanced filtering is used, like the SLR8000 repeater, with over 120 dB blocking for off frequency stuff, etc.. but unless you have one of those, most mobile radios don't have that kind of additional filtering. So if you live in an are with a noise floor of -50 dBm like I do, pretty much most CCRs will fall apart and desense so bad you won't hear squat. OTOH, radios like the XPR7550e, with super tight front ends, will effortlessly reach over miles when the CCR is deaf as a rock. This also shows why more sensitivity is not better, in fact, more sensitivity with a poor front end filtering means it will desense even faster.
IMO, the graph above should be pretty much definitive as to why the pricing is directly proportional to the selectivity + sensitivity on those devices: with the Motorola SLR800 repeater leading the pack at well over 2 grand, the Vertex EVX-5300, new, was around 600 bucks, the TM-V71a, is around 350 bucks new, and well, the GD77 CCR can be purchased new for 65 dollars on eBay.
And here is a very simple procedure to gauge a CCRs performance and if its even worth the expenditure.
1) First off, If no channel selectivity figures are offered, then move on. "These are not the droids you're looking for."
2) Now get the receiver sensitivity figure, usually measured in uV, but with this nice chart you can convert it to dBm at 50 Ohm, link here: http://www.repeater-builder.com/tech-info/measuring-sensitivity/dbm2uv.pdf
3) Knowing that any signal above the receiver sensitivity threshold (at any frequency) will desense the receiver you add the selectivity in dB at 25 kHz to the receiver sensitivity in dBm, pay attention to signage, the sensitivity is negative dBm.
4) Repeat the same for 12.5 kHz. Now, some brands show even narrower kHz dB figures offered. You can add it and find out, but that is usually not as important as the real selectivity for further away signals.
5) As a general rule, any signal received within the receiver frequency range (and in the CCRs even further than that) that is stronger than the 25 kHz selectivity value calculated will desense the receiver.
Have at it, and please, correct me if I made any mistakes.
G.
What is the source you got the graphs from and how were the tests done?
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Hmm you might be just the person to talk to about what to look for in a military man pack radio for ham....
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.
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Greetings! I am a recently retired Army civilian with quite a bit of military radio experience. VHF through the C-band. Mostly handheld and mobile. I plan on acquiring a GMRS license and perhaps later an amatuer technician license. Why? Why not? Well, I also have a few friends within 4 miles (rural like) that are interested in non-cellular comms.
With a military radio, let's say an AN/PRC-117G, I could program it anywhere in its frequency range (30 - 2500 MHz), obviously sticking to frequencies allowed to me. I see that in the commercial/amatuer/family radio world, the FCC frowns on that sort of thing. Meaning if I picked up a commercial radio and programmed it to do MURS, FRS, and GMRS; that is a bad thing. I get it. I also get significant rule changes in 2017 and an end to certifying certain combination radios this September.
Since I'm not likely to acquire some used AN/PRC-152A radios, I'm looking at used commercial radios. So far, I'm partial to a few of the Kenwoods that can be acquired for about $130.00. Is this a good way to go? It's my understanding if a radio was once certified for Part 90 and 95, it can still be used for part 95. Correct? Manufacturers that don't put out full specs, such as transmit power, annoy me. Bubble packs and the like.
Am I thinking along the right track?
More about me . . .
In my pre-retirement life as an Army civilian, when not managing computer software and hardware projects, I became sort of a network geek. Before widely available network broadband access, we built a dedicated wide area network, east coast to west, on leased lines. It connected federal, state, and local facilities. I had been asked to take over "communications" as we called them, meaning radios and such. I resisted, but did learn a bit to get interested.
About a decade later, I managed a project where mobile ad hoc networks (MANET) and radio voice communications were a large part. I became quite good with various military radios (SINCGARS, AN/PRC-152, PRC-148, PRC-117G, etc.) and a few commercial radios of military utility (WaveRelay, Trellisware, Motorola). When in the field doing trials, we often scanned amatuer frequencies just for grins. FM radio too. I know how to set up a retrans with two PRC-117G radios. I know waveforms (we called VHF/UHF "VULOS"). I know how to program the things using Army and commercial software.
I'm looking forward to joining as a regular member.
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:
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.
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I think there's confusion between an RF ground plane, and electrical grounding.
For UHF/GMRS frequencies, a ground plane is required for best signal propagation when you're working with a 1/4 wave antenna. A longer 1/2 wave antenna does not normally require a ground plane. The ground plane is a counterpoise to the antenna's radiating element. The counterpoise (RF ground plane) is going to reflect signals that would otherwise be radiated down by the antenna.
For plastic body vehicles - look for something like this to use as an RF ground plane: https://www.solidsignal.com/pview.asp?p=K332 - or just use a 1/2 wave antenna.
The DC ground for a vehicular antenna is provided by the coaxial shielding braid. That's going to measure continuity to vehicle ground no matter what type of plastic you're mounting the antenna to... provided the radio chassis itself is actually grounded.
I realize I'm being simplistic. That's where we need to start from when someone wants to "ground" their antenna.
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.
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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.
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I think you are going to be hard pressed to find a current production raidialess dual-band mobile antenna that will go all the way to 470 and be under 2:1 SWR. The Diamond NR73BNMO is probably the closest, but you're going to be looking at 2.5:1 at around 467. Maybe 2:1 at 462.
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.
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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.
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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.
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Why there's a prohibition of having amateur and GMRS channels together on the same Part 90-certified and 'otherwise compliant' radio, I don't know. I would expect it to be a prohibition of marketing dual-service radios, given the difference in intended use and operational procedures between the two services.
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.
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I'm quoting myself because I have experienced another data point since my post. We had a TYT TH-8600 here that was firmware locked to 2m and 70cm only. As such, I am changing my guess and say that any future part specific units based on the TYT TH-8600 will likely be locked to their appropriate frequency range if they enter the country legally. This will likely be firmware fixed so that it will require a firmware downgrade to change it.
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.
- Radioguy7268, berkinet and Hans
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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.
Anytone AT-578UV thoughts
in Equipment Reviews
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I wouldn't recommend doing this. The signals on the ribbon cable are very likely logic signals, some anyway, that have sharp rise and fall times thus a high frequency content. Extending the ribbon cable would be the equivalent of a transmission line. If the line was not terminated in the proper impedance at each end then you get reflections. Those appear as high frequency ringing on the logic level transition edges. The voltages can ring above the supply and below ground which can result in damage to the chips on the boards if they exceed the max spec values. Additionally the ringing will look like extra logic transitions further confusing the logic on the boards.
Once in my younger days I tried to use the expansion slot on the back of my then new TRS-80, it ran between 2 to 3 MHz, using a 2 to 3 foot long un-terminated ribbon cable to the solder less breadboard. I wanted to try experimenting with some computer controlled hardware. The computer wouldn't even boot to the built-in BASIC interpreter until I removed the cable. Lucky nothing was damaged. Lesson learned.