I love these radios! Expensive, but worth it, IMO. Too bad the DTR700’s are limited to 1 watt at most (830mW according to FCC filing). Even so, it’s astonishing how effective these radios are with just 1 watt of power. My Btech MURS radios would only reach past about 4 or 5 of our 6 unit condo buildings before the conversation gets annoyingly noisy. With the DLR radios, I’m able to establish connection past 24 of these 6 unit condo buildings. Using the DTRs, I had to drive another half mile away, through more condos, trees, etc., to get to their range limit! Around another part of town with densely built older homes, the range difference between the DTRs and DLRs were closer. About 16 blocks vs 14 blocks. This is with one radio in the middle of a house, and the other one roaming the neighborhood in a car. The 16 block distance was roughly 0.9 mile.
It’s funny that you say that you wish the radios had more than 1 watt, and then go on to explain how their range is better than other radios. I consistently had better range with my DTR than with my 4-watt UHF radios. The higher frequency and frequency-hopping I think give the DTR it’s incredible range. It doesn’t need any more power, and by using only 1 watt, the batteries can last a LOT longer!
Greetings Andy! Thanks for the warm welcome. I agree that it is nice to have long lasting radios, battery-wise. Nevertheless, I can’t help but fantasize any improvements towards an ideal, optimal radio. If regulations allowed, I can imagine this radio having a continuous power range between say, 1mW and 5 Watts, fully variable. The transmit power would be varied according to a set bit error rate (BER) threshold that it tracks to (realtime power control like with CDMA). So if two radios were in a direct call at close range (e.g. between adjacent cabins in a cruise ship), maybe 1mW would be all it takes to maintain clear communications. Thus, the transmit energy would always be throttled to the minimum required between the two corresponding radios in direct call mode. It would also be great if the current transmit power was displayed to show the current efficiency. Of course this wouldn’t work if a broadcast to all radios listening to the same profileID, public or private group is desired. In this case, having standard selectable preset power levels (e.g. 100mW, 1W, 5W) would offer some of this desire to save battery life when range isn’t needed.
The other half of this fantasy is to imagine how much more sensitive the receiver portion can be improved upon (while maintaining or even improving upon hopping channel selectivity, blocking immunity, spurious noise generation, increased frequency stability, etc.) using state-of-the-art RF techniques and hardware materials. I wonder if some modified form of RAKE receiver is even possible with fhss (like as used in CDMA dsss systems) to help combine the mutipath signals instead of just rejecting them. -131 effective dBm? -137dBm? I can only dream.
Back to reality. I also obtained two of the stubby antennas (PMAF4025) for the DTR700s and performed some more range testing a couple of days ago. The range seems to fall right in between the two DLRs and the two DTRs with the longer half-wave antennas on both of them. I came across an interesting result from one of the combinations. With one DTR and its half-wave antenna standing vertical in our condo’s kitchen counter on the second floor, I was able to establish a connection using a DLR 2.5 miles away at one of the discovered fringe hot spots. Repeating the same location experiment, but with two DTRs and using the stubby antennas on both of them, I was also able to establish a connection, although it was just a smidge weaker and a little more position dependent at that location. This fringe hotspot 2.5 miles away is by no means a direct line of sight (LOS). Even though the location is elevated with businesses all around, it is blocked by a series of hills starting about a quarter mile away. Lots of condo complexes and homes lie in between the other 2 miles, and lastly with our condo butted up against yet another hill… on the other side. I was able to verify the connection by taking advantage of the monitoring feature introduced to the DTRs with the latest firmware update. Without this verification, I would have found the supposed connection not to be trusted or even believed, especially in light of the arguments that VHF is way better than UHF for use around hills. Maybe it’s due to all the man-made structures, cars, sidewalk pedestrian railings, etc., that serve to act as ducting for the UHF waves.
In short, I was hoping the stubby antennas were closer performance-wise to the longer half-wave antennas. When one factors in the thinner, more flexible half-wave variant, I’m leaning towards defaulting to the half-wave and only using the stubby ones when space is an issue (like fitting them into a Nanuk 310 case). n1das has a good suggestion about wanting automatic gain control (AGC) implemented on the Tx side of the DLRs. If that did happen and they had the vibrate feature for silent alerting, I would be using them almost exclusively when absolute range or the extra features of the DTRs aren’t needed. They are just so discreet.
I have tried the PMAF4025 stubby antenna on my DTR700 radios. I have done some testing but not enough to tell if there is a significant difference in performance. The stubby antenna looks cool on the radio. What I don’t like about the stubby antenna is that it is thick and not very flexible which causes it to torque on the radio’s connector when you beat the radio around. I am leaning toward sticking with the original PMAF4024 1/2 wave antenna because it performs the best and you won’t be torquing on the radio’s connector as much. The PMAF4024 1/2 wave antenna isn’t a whole lot longer than the PMAF4025 stubby antenna which makes me think why bother with the stubby antenna at all. The PMAF4024 1/2 wave antenna also looks cool too.
I did some testing and I am back to using the PMAF4025 stubby over the PMAF4024 non-stubby antenna. I’m finding the PMAF4025 stubby antenna seems to perform a little better. It seems counterintuitive and came as a surprise given that the stock 1/2 wave antenna should be expected to perform better than the stubby antenna.
When I do range testing with a radio at home and drive around with another radio, I have a well controlled and repeatable favorite spot where I place the radio at home. I place the radio in an upstairs bedroom window that gives me the best coverage in my neighborhood. The window is a double hung i.e. sash type window and at the corner of my house. I place the radio next to the lock on the lower half (sash) of the window and with the window closed. This places the radio almost dead center in the window. When testing antennas, I use a pair of the same radio and with the same antenna on BOTH radios. I don’t test with only one antenna swapped. Any differences between antennas should be magnified when the same antenna under test is used on both radios. I live up on a hill and have a favorite hot spot on the highway as I come over a ridge about 8 miles away. When driving towards home on the highway, I can just tickle the other radio at home for a second or two while in the hot spot.
When testing with the stock PMAF4024 1/2 wave antenna on the DTR700 pair, I can consistently tickle the other radio for about a tenth of a mile stretch on the highway. With the PMAF4025 stubby antenna, I found the hot spot stretches out further on the highway to at least a quarter of a mile before it goes away. I’ve done the experiment multiple times and results are consistent. I have also tested with a pair of DTR650s with the 7" 1/2 wave antenna on both radios and I got the same results as the DTR700 pair with the PMAF4024 1/2 wave antenna. I have not tested a DTR650 pair with the 3" stubby antenna for the DTR550/650. I didn’t bother because the 7" 1/2 wave antenna is known to be the preferred antenna to use on the legacy DTR550/650 radios.
The DTR700 with the stock PMAF4024 1/2 wave antenna appears to be no worse than the 7" half wave antenna on the legacy DTR550/650 models. What was unexpected and surprising was the PMAF4025 stubby antenna on the DTR700 seemed to perform slightly better than the stock 1/2 wave PMAF4024 antenna.
Your long distance tests are very insightful. My tests are not as controlled, especially since extended line of sight is not really an option at my location. Most of my testing involves reflection of the rf waves around/through buildings, trees, metal fences, vehicles, etc. I wonder if the stubby antenna is really of 5/8 wavelength coiled up to that size? Maybe the more evenly distributed radiation pattern works well with any ground reflections to give that broader extended range?
After reading your results, I went out and did some more a/b testing, with the same antennas on both units. This time, the eventual “line of sight” is through a few 6 unit condo buildings before some rows of apartment complexes across a major street that slopes down and further out towards a canyon preserve. On the other side of the canyon are business buildings and a mini shopping mall containing a Vons supermarket that we frequent. To get there, we need to head around the canyon by way of a major freeway running through it. This route varies between 0.5 and 1.5 miles. Along this route, about 15 to 20% percent of it has dead spots. The 1/2 wave antenna seems to do just a smidge better than the stubby around just a couple of dead spots. Around other dead spots, they seem to perform the same. I couldn’t tell if the stubby antenna was any better around any of the dead spots. When I do enter the Vons supermarket, both the DTRs and DLRs would lose connection about 30 feet further inside the building, towards the rows of freezers/refrigerators. This supermarket is about 0.95 miles, as the crow flies. There are slight range differences while inside the supermarket, but we’re talking just a few feet, even between the DTRs and DLRs. My guess is that the rf noises in the building are a major source of interference.
Based on our combined testing results, I will definitely utilize the stubby antennas without reservation whenever it’s convenient to do so. They don’t seem to be so disadvantaged after all.
Lastly, I never thought I would be so fascinated with testing these low powered, highly efficient radios in settings where VHF radios are supposed to be the superior choice.
Recently, I’ve had the opportunity to perform some line-of-sight (LOS) testing. I’ve read some of the stories of these types of FHSS radios establishing contact at incredible distances for the less than 1 watt meager output that they deliver. Even n1das mentioned that one of his usual experiments involved making contact with distances around 8 miles. Knowing that, I figured I could use my DLR 1060s, which have a validated shorter reach than the DTR 700s to perform my own testing with less distance to deal with. I really didn’t want to test maximum distances for just in case I run out of space. I was at a family member’s house that’s elavated near the base of some foothills. It overlooks an expansive valley that’s heavily populated. There are patches of small foothills on the other side of the valley. The stationary radio was placed on the shelf of a window at the corner of the house that has line of sight over the valley. I started driving down into and through the valley, expecting some dead spots from time to time. That didn’t happen. Instead, I had solid signal until clear across town. It wasn’t until I hit 8 miles or so and continuing on a freeway into a depression between hills on both sides that I lost attempts to connect. Once I cleared those minor hills, I pulled off the nearest exit and headed up a nearby foothill. After an elevation gain of about 150 feet or so, I started to make connection again. Around another 50 feet higher, the connections were solid again all over. This is with a few trees, and some sparse housing in the way at my mobile location, with me in the car. Google maps showed the LOS to be 10.5 miles.
I seriously underestimated the range of these radios. Based on my observed results, I’m guessing the range to be in excess of 15 to 20 miles LOS for the DLRs. The amazing thing is that these DLRs have fixed stubby antennas that are less than 2 inches long!
It’s amazing how people keep underestimating these radios. People are always interested in getting “x” miles of range out of a pair of radios. We know that actual range may vary and is affected by a number of factors. I never got my DTR radios and DLR radios to set any range records. I got them for professional quality on-site simplex type use with family and friends. Where they blow other radios away is for reliable local on-site type coverage, particularly inside buildings. Getting several miles of range out of them under the right conditions comes as a bonus.
My DTR range record currently stands at 12 miles, from the Cocoa Beach Pier in Cocoa Beach FL to the top of the steps going down to Hightower Beach in Satellite Beach FL. There is a bit of coastline in the way so it’s not entirely line of site up and down the coast. I tested this with a friend a couple of years ago with my DTR650 radios and the 3.5 inch stubby antenna. We also tried it with a pair of DLR radios in 2015 and got the same results. We also tried it with a pair of 4W UHF analog Part 90 portables on GMRS (we are GMRS licensed) and found the DTRs and DLRs worked better. We found on GMRS that we each had to find a hot spot and stay in it in order to communicate. The received signal strength on GMRS was noisy and scratchy but usable provided we stayed in our hot spots. The DTR and DLR audio was clear the whole time. There were a few hot and dead spots with the DLRs and DTRs but they worked better overall. We also found that when the DTRs and DLRs were finally out of range, coverage was already completely gone on GMRS.
My 8 miles of range mentioned earlier is from home in Nashua NH to a ridge on the highway north of home. I can tickle a DTR or DLR radio at home from the car while southbound towards home. I can’t do the same thing while northbound due to the car body being in the way. That suggests my signal is very weak at home. I can just barely tickle the radio at home for a couple of seconds while in the hot spot and facing towards home. This makes it a good spot for testing antenna performance.
My testing of a pair of DLR1060 radios matches results from testing a pair of DTR700 radios with the PMAF4025 stubby antenna. The DLRs with their very stubby antenna does surprisingly well. My experience with the DLRs and DTRs suggests the DLRs perform just as well as the DTRs. I think any differences between radios and individual antennas are small enough that they are not worth worrying about. End users are unlikely to notice unless at the very fringe of coverage and under carefully controlled conditions.
I would like to come up with a fixture to connect to a PMAF4024 and PMAF4025 antenna to measure the return loss from each antenna on a network analyzer. I would also measure the return loss from the antennas on the legacy DTR550/650 radios. Seeing what the return loss looks like for each antenna would be insightful.
The DTR and DLR transmitter power levels from the FCC and ISED Canada certifications are listed below.
Legacy DTR410/550/650: 890 mW (+29.5 dBm)
DLR1020/1060: 880 mW (+29.4 dBm)
DTR600/700: 830 mW (+29.2 dBm)
The radios were certified at a few tenths of a dB under the 1W (+30.0 dBm) legal limit to account for measurement uncertainty and the expected amount of variation from unit to unit. The manufacturer (Motorola), not the test lab, is ultimately responsible for ensuring the transmitted power output does not exceed the 1W (+30.0 dBm) legal limit. The exact power level listed in the FCC/ISED Canada certification for each model is what was measured from the individual sample submitted to the lab for certification testing.
IMHO, the differences in transmitter power output are insignificant and shouldn’t have any effect on usable range.
Thanks n1das for heading me off before I started to make an attempt to use the argument that maybe the slight power advantage of the DLRs helps to overcome the disadvantage of their shorter stubby antennas.
My interest in range/reliability/robustness with these radios comes about due to the spread spectrum modulation method used. I guess I’m considered to be in the QRP camp, maximizing link budgets for the amount of power used. There is a company named Spektrum (a division of Horizon Hobby) that has a line of radios for the radio control (RC) community. Their radios combine wideband DSSS with the ability for that wideband to hop around (FHSS). I wonder how well such a radio implementation would do if it was adapted for the 915MHz range? Maybe we could approach Spektrum about producing some two-way radios based on their modulation technology?
I did some more testing tonight while driving through my favorite distant hot spot on the highway where I can just barely tickle a DTR radio at home. I did a total of 3 road trips and tested the following: (1) Pair of DTR650 radios with the 7 inch 1/2 wave antenna, (2) pair of DTR700 radios with the PMAF4024 1/2 wave antenna, and (3) the same pair of DTR700 radios with the PMAF4025 stubby antenna. The radio and antenna under test at home was placed in my standard spot in an upstairs bedroom window and I went for a drive with the other radio and antenna under test.
I found the pair of legacy DTR650 radios with the 1/2 wave antenna and the DTR700 pair with the PMAF4024 1/2 wave antenna performed identically. The DTR700 pair with the PMAF4025 stubby antenna did very close to the PMAF4024 antenna but not quite as good, just a hair less. The difference was so small that it’s not worth worrying about and it may be hard to repeat. I think from a practical standpoint, end users of a DTR600/700 won’t notice any difference in performance with the PMAF4024 1/2 wave or the PMAF4025 stubby antenna.
After testing the DTR650 pair with the 1/2 wave antenna and then getting identical results with the DTR700 with the PMAF4024 1/2 wave antenna, I decided to do another test with the PMAF4025 stubby antenna to complete the experiment. So for the 3 road trips tonight, all testing done in the same vehicle on the same evening, under similar traffic conditions, same weather conditions, and same snow cover and tree foliage conditions. Some of my earlier testing was done on different days and maybe in my other car so it might have affected results. The performance of the legacy DTR650 and DTR700 appears to be identical and any differences in antennas is hard to test.
The bottom line is the new DTR600/700 with the PMAF4024 1/2 wave antenna appears to perform identical to the legacy DTR550/650 with the 1/2 wave antenna. The PMAF4025 stubby antenna performed well too. So go ahead and use whichever antenna you prefer on the DTR600/700.
I agree with n1das. the differences are so small that an enviormentl chage such as the rdio not being vertical or the antenna not pointing in the correct direction would have a greater impact. Even then you would need to be at the very fringe of the coverage area to maybe possibly notice it.
Another factor that explains the better than expected range is the built in FEC (forward error correction) used in the digital modulation process. This allows the radio to ‘fix’ a bad ‘packet’.
This is some really excellent information! I see the stubby antenna is performing well in these tests. Does anyone know (or could theorize) if the same performance would be true of the 410 since it is limited to the built-in stubby antenna?
This is great information! I see most of the testing was done with 550 and 650’s. Since the stubby antennas are performing so well in the tests, does anyone know if the 410 would perform the same?
Yes the performance should be very similar. Even though the stubby antenna is shorter it is in reality a long antenna coiled into the shorter length. There will be a slight range difference. But you would have to be looking for it exactly and as mentioned earlier the differences in position , height etc could easily add up to more of a difference in the field.
The DTR410 has slightly less performance than the DTR550/650 models and DTR600/700 models due to the very stubby built in antenna. The 550 and 650 models originally had the same very stubby built in antenna but were soon upgraded to having a recessed female SMA connector to accept an external antenna which greatly improved performance. The 410 is a very old DTR model and was never upgraded to use an external antenna.