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Ham DMR Digital Kicked Up a Notch

from Stephen Reynolds, W4CNG on January 2, 2017
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Ham DMR Digital Kicked Up a Notch
(Or how to make that HT work better in the car)
By W4CNG Stephen Reynolds

The new Ham Digital Mode of DMR has taken off in the last 5+ years and lots of folks are just getting into it in recently. The repeaters are great and some of the High Site one’s can give awesome coverage. This is even better when you have multiple repeaters with overlapping coverage and is connected to the same C-Bridge or Brandmiester system. We have 6 repeaters in Atlanta connected this way thru a common C-Bridge.

The largest issue is for folks running HT’s, on UHF, where the vast majority are using a HT in the car with the rubber duck antenna. The issue is signal strength into the repeater from the portable. The HT’s have pretty good receivers with some better than others but all work well. The 4 watt transmitters with a rubber duck inside of a car is less than ideal. Yes there are 25 to 45 watt Mobiles out there that power from the 12VDC car system and feed to an outside antenna, some of which have gain at the 440Mhz frequency range. These give very good coverage for those that have them and cost 3-5 times what one of the HT’s cost, which as of this writing can be bought on EBay and other places for $100 or less.

This very attractive entry cost for a single radio with new technology is inviting to new and older hams. So you have one of the new HT’s and have used it mobile with mixed results. The most common mode is inside the car using the rubber duck that came with it, which come in small to big sizes. There are a couple of ways to improve on this without cutting holes or tapping into 12VDC power.

The first is an external antenna either mag mount, gutter clip (not many cars have the gutters on the roof anymore) or a trunk lid clamp mount from Diamond, Comet or others. The most common HT’s have a Female SMA connector on the top of the HT. This is a somewhat delicate connector used in UHF to Microwave frequencies with a near perfect impedance match for the radio. Adding this simple accessory can get your radio to an outside antenna with gain and give you something like 8-12 watts ERP with the gain antenna.

The picture below shows the basic use of the external mag mount antenna with an SMA connector and what could be simpler. Mount antenna on roof and connect to antenna port on HT.

You can take this to a next step (Picture below) by adding an external speaker/microphone to the HT. This adds ease of operation, as you do not have to hold the radio with antenna cable coming out of the top of it while you talk. Set it in the drink cup holder and talk away. This picture also shows a battery eliminator for the HT.

One thing that occurs in this process is the battery will drain over a period of time and most of the low end radios do not give you a low battery notification, they just shut down in mid transmission. There are two ways to get around this. Buy a second battery for the radio and carry it with you or get a battery eliminator. I always have bought an extra battery for every HT I have ever purchased.

One thing about external speaker mics for these low end HT’s, get the manufacturers version and not an aftermarket one for 1/3 the cost of the original or one that has the same pin spacing that fits the side of the radio if forced into the plug. You likely will get motor boating on your signal because of RF feedback into the mic from the antenna. An external antenna can sometimes mitigate this issue.

Ok these options can give you a step up into better coverage from your HT in your car. The next step can give you the external antenna and a power amplifier to boost your power to 50 watts PEP. There are some amplifiers out on the EBay market from China that can take your 4Watt HT and boost it to 50 watts PEP. The DMR mode transmits from your HT only half the time because the other half of the time is used for synchronization to the repeater and for radio’s that Roam to check for signals from adjacent repeaters that may be stronger to switch to.

Some radio’s have SMA Male connectors on the top of the HT and when using a SMA Male to SMA Male connector cable will require a SMA Female to SMA Female connector adapter (shown below on the right) to use the cable. These are available at most hamfests and can be bought on line, as Google is your friend. If you have an antenna that has a PL-259 connector you can get an SMA Male to SO-239 jumper cable (shown on the left) to make the safe connection.

NOTE: Do Not use a BNC or SO-239 to SMA Male adapter to connect to the top of the HT or to the input of the amplifier as the first bump on the adapter will tear the threads off the SMA Female connector on the radio or amplifier.

Using the combination of HT, Amplifier, External Speaker Mic gives you a very good High Powered Mobile vs. buying a 25-45 watt mobile. This way you still have the portable to take with you.

The links listed below show Amplifiers that take 4Watts DMR input and output 25 or 50 Watts PEP when connected to 12VDC. These amplifiers will work on DMR, D-Star, and regular FM. They also have a Receive preamplifier with a gain of 4db. They use Pin Diode switching and not a relay like some others use. The Pin Diode switching enables the amplifier to switch with the transmitted RF from the HT. The amplifiers have an input SMA connector and an output connector of an SO-239. You will need to get a 4-5 foot jumper cable with SMA male connectors on each end to use the amplifier. These jumpers are available from several places including HRO. The amplifiers are priced in the low $100 range with some under $100. They come from China and take 4-5 weeks to arrive when ordered. Mine took 5 weeks. You have to be patient on this. Yes it says DRM but they are DMR friendly.



These amplifiers are small and do not get hot when keyed down for a long time. They will come with a 4-5ft power cord. I installed Power Pole connectors on mine and use a cigarette lighter plug with the power plug built in. My car is the first leased car I have ever had so no drilling holes.

Enjoy these notes on how to improve mobile operation of DMR HT’s.

Author Note: I have been building Ham Repeaters in the Atlanta area since 1971. For the last 35 years I was in Land Mobile communications working for Dial Call, Nextel, Sprint and retired from Ericsson US. I have both D-Star and DMR as well as Analog FM equipment. I have partial ownership of 2 DMR Repeaters in the Atlanta area and I really like the DMR mode of operation.

Member Comments:
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Ham DMR Digital Kicked Up a Notch  
by K5LXP on January 2, 2017 Mail this to a friend!
"I really like the DMR mode of operation."

Is there something to DMR that's fun/good/better/interesting that would entice someone to buy a DMR radio? I have a DStar radio which I am terribly underwhelmed with. Clunky to use, crappy audio, limited number of repeaters. Is there something about DMR that's "better" or is it just a different way of doing the same thing?

Mark K5LXP
Albuquerque, NM
RE: Ham DMR Digital Kicked Up a Notch  
by K6AER on January 2, 2017 Mail this to a friend!
Nice well written and well thought out article.

I have used HT amplifiers for years and in the 90's I was a engineer at TPL in Los Angeles. We had a series of amplifiers going up to 250 watts out that could be driven with 2-5 watts drive in Class C.

Most HT's have a very broadband front ends and sometimes a band pass filter will help intermod problems on the receiver. The first 50 watts makes a huge difference with the out bound signal quality.
Ham DMR Digital Kicked Up a Notch  
by KB1PA on January 2, 2017 Mail this to a friend!
good article, but for the time and money you spend with all the add ons, your price is almost as much as a 45 watt mobile radio, which can be used as a base station inside also.
RE: Ham DMR Digital Kicked Up a Notch  
by N9AOP on January 2, 2017 Mail this to a friend!
Doesn't this go for any HT with a ducky operated from within a vehicle? As far as the digital modes, they are all different and incompatible. It's not like back when there was only analog VHF and everyone could talk with everyone else.
RE: Ham DMR Digital Kicked Up a Notch  
by ONAIR on January 2, 2017 Mail this to a friend!
N9AOP... Good point! They need to come out with reasonably priced rigs that cover all digital modes.
RE: Ham DMR Digital Kicked Up a Notch  
by KF4HR on January 2, 2017 Mail this to a friend!
I haven't been enticed by DMR yet. I occasionally use DStar but have always disliked its poor narrow band audio quality. I am enjoying the flexibility of Yaesu's Fusion Repeaters (Repeater Book reporting 1,536 Fusion Repeaters world wide now), along with Yaesu's Wires-X Network and Node opeation. A good comparison chart for these popular DV modes can be found here:
Ham DMR Digital Kicked Up a Notch  
by WS4E on January 3, 2017 Mail this to a friend!
Still not satisfied with any of the digital voice modes.

I find it weird that everytime any other technology went from analog to digital (movies, music, photography) the fidelity and quality went UP, but when we do it the quality of the voice audio goes DOWN.

Let me know when something sounds BETTER than full quieting Analog FM and then I will be interested.
Ham DMR Digital Kicked Up a Notch  
by KK5JY on January 3, 2017 Mail this to a friend!
Nicely done on the article. It also applies well for plain FM radios. DMR vs. FM... that's another discussion. ;-)

I'm so glad to see some manufacturers moving away from the PL-259 connector. Give me SMA or N any day, especially at VHF+. Thankfully, the flange connectors for N and PL-259 tend to use identically mounting profiles, so I happily replace PL-259 connectors with N connectors whenever I can. BNC works well for connections that tend to endure a lot of connection cycles. It's unfortunate that SMA wasn't designed for many connection cycles.

The mobile amplifier approach works well for people who really only want *one* VHF+ radio, and/or they want to take their "mobile" radio into the house or office with them when they park the car. As another comment pointed out, a true mobile radio is a better deal and a much better match for mobile operation than the best HT. Just the larger display alone is enough to make a mobile rig worth the effort, not to mention the better audio output power of a mobile. Dual-band VHF/UHF amplifiers are getting very hard to find, and they have never been cheap.

Never use a mag-mount. Ever. That goes double for VHF+. See K0BG's website if you have any doubts. Bite the bullet and install an NMO mount, even (especially?) for an HT. A good Larsen NMO kit is very cheap, and it will outlast the car. It will also cost you exactly $0 in lost trade-in value. If you sell the car, put a cheap low-profile antenna on the mount, as it will make the car look cooler. ;-) Quality hole plugs are also cheap. Any LMR shop can sell you a handful for a few dollars. NMO rocks. Just do it. :-)
Ah, For The Naughts…!  
by VE3CUI on January 4, 2017 Mail this to a friend!
Gee, things musta been just SO much simpler back in the ol' spark days, eh…?!

If any one of those original OTs from those days of yore were to miraculously be transformed to 2017, I'm sure the advanced technology would just blow him away...
RE: Ah, For The Naughts…!  
by ONAIR on January 4, 2017 Mail this to a friend!
VE3CUI... Good point! I wonder what ham radio will be like in 2117? :)
RE: Ah, For The Naughts…!  
by KK5JY on January 4, 2017 Mail this to a friend!
>> I wonder what ham radio will be like in 2117? :) <<

Whatever it is like, I'm pretty sure it will still involve CW. ;-)
RE: Ah, For The Naughts…!  
by ONAIR on January 4, 2017 Mail this to a friend!
CW? Yes, well if the world gets destroyed by a nuclear war, CW may be the only means of radio communication left in 100 years!!
2 meters yes/ 440 not so much  
by N8EKT on January 4, 2017 Mail this to a friend!
You will see significant improvemernt on 2 meters but by the time you add all the loss of rg174 like what is used in the picture or even the typical 12 to 16 ft of rg58 used on most antenna mounts, 440 performance won't be much better than a 1/4 wave duck on the ht

Ham DMR Digital Kicked Up a Notch  
by N8EMR on January 5, 2017 Mail this to a friend!
So how to make an HT better in a car is turn it into a mobile. Gotcha..
RE: Ham DMR Digital Kicked Up a Notch  
by W0FM on January 5, 2017 Mail this to a friend!
"My car is the first leased car I have ever had so no drilling holes"

If you just don't want to drill a hole in your car, fine. But please don't use the excuse that it's a leased car and not allowed.

My company has been leasing passenger cars, vans and pickup trucks since 1962. Each has at least ONE (most have several) NMO hole-mount antennas on them. Not once has this ever been an issue with the leasing company when turned back in. Not sure? Ask your leasing company.

Terry, WØFM
Ham DMR Digital Kicked Up a Notch  
by K0RGR on January 6, 2017 Mail this to a friend!
Interesting - I wonder which amplifier the OP is using, and how well it works.

DMR Tier II, which is what most ham repeaters require, uses time domain multiplexing - it splits the channel into two time slots. Your DMR HT only transmits on one of the two slots at a time - hopefully. It listens on the other slot.

I was not aware that there were inexpensive amplifiers that could switch fast enough for Tier II.

DMR vs. D-STAR - I find them similar, though DMR seems to be growing very fast. DMR HTs are much cheaper. D-STAR has a more mature network. DMR is easier to use, overall - much shorter learning curve.
RE: Ham DMR Digital Kicked Up a Notch  
by W4CNG on January 16, 2017 Mail this to a friend!
The one I have is the 25 watt version. The links will take you to a 50watt amplifier. They are labeled as DRM not DMR. They are pin diode switched and filtered on the output to keep things RF Clean. Mine has a red led that flashes with incoming RF and the Tier II radio's do listen while not transmitting. The two brands that currently Roam are Motorola and Hytera. You load the neighbor list into the radio and it checks those channels while listening and will change sites when the low signal threshold is met. Most folks do not have radio's that roam so that was not included in the article.
Ham DMR Digital Kicked Up a Notch  
by KC5JPZ on February 11, 2017 Mail this to a friend!
I do not have a digital (DMR) radio... yet. It seems that the FM repeaters in the DFW area of northeast Texas are not very busy but the digital repeaters seem to be busy. Are there technical discussions going on or is it more of the same non technical discussions that I hear on FM? I am tempted to get a two meter DMR radio, but I need a little more information. Is DMR competing with another system such as D-Star or Fusion? What digital system is most popular? Is DMR growing in numbers faster than other systems?
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