Posts Tagged ‘JMT-228’

A tiny Bluetooth TNC

One of the things I’ve been up to the last few weeks is testing a new Bluetooth TNC made by Rob WX9O who is selling them as Mobilinkd. I had to put testing on hold while my Motorola smartphone went away to be repaired (by BuzzBox whom I can recommend highly.) In the meantime word got round and Rob sold out of these gadgets before I could write about it.

The price was around $49.95 which I thought at the time was amazingly cheap and probably explains why they are all sold out at the time of writing. The module is a small PCB slightly smaller than a Baofeng UV-3R and if you remove the belt clip it can easily be fixed to the back of it. My picture shows it strapped to the back of one of the Baofeng’s predecessors, where it makes a nice inexpensive and compact APRS tracker. The board and it’s battery (which can be charged using a USB cable as shown in the photo) are shrink-wrapped in a tough translucent plastic casing.

Ready-made cables are available. Rob sent me a Kenwood-format two-pin connector which fits the later model Baofengs and the two worked together perfectly. The audio levels were just right on both transmit and receive.

Yes, receive. This is no mere tracker. It’s a full KISS TNC and decoded all the packets received by the Baofeng. The software used was the latest APRSDroid running on my Motorola Milestone (a.k.a. Droid) smartphone.  Droid and TNC paired easily and made an effective APRS mobile station.

I did try to pair up the TNC with APRSISCE on an HTC Touch Pro running Windows Mobile 6.1. The two devices paired but could not connect as the Bluetooth software did not recognize the TNC as a valid device type. I think that is a limitation of the Windows Mobile Bluetooth software rather than the TNC module.

If you are interested in APRS and would prefer to do it over the radio rather than a cellular data connection (real hams use RF, right?) then this is a nice toy to play with.

Handheld receiver blocking shootout

Ever since my outing on to Ling Fell yesterday I have been bugged by not knowing for sure whether the problems I experienced with the VX-8GR were really caused by receiver overload or blocking. I like the construction and features of the Yaesu. But a radio that makes you miss some of the contacts you have laboriously sweated up a summit to make is about as much use as a chocolate teapot. I wondered if I could devise a test to give me an idea of the relative strengths of the different 2m radios. I did, and the candidates are lined up in order of merit below, the worst on the left and the best on the right.

The test methodology was crude. I connected each radio to my dual band vertical and tuned in a weakish station: the GB3AS repeater on 145.600MHz, which is normally an S3 signal – fully readable but with some background noise on the audio. I then transmitted a carrier on 144.025MHz using another radio on a helical antenna a few metres from the vertical. I tried two power levels of the interfering signal, 3.5W (“high power”) and 0.5W (“low power”), these being the available power levels of the test radio. This 8dB difference in the interfering signal level had different effects on the ability to receive the repeater signal.

I am well aware of the limitations of the test I carried out. In real life SOTA or WOTA use a radio may be subjected to strong in-band signals from activators on other summits but they will not be as strong as the signal from a radio a few metres away from the antenna. A radio is likely to be subjected to strong signals from outside the amateur band such as pagers and other commercial signals, which the bandpass filters in modern radios due to the marketing-driven necessity of providing wideband receive coverage will do nothing to attenuate. Many strong signals may mix together to cause intermodulation effects if not blocking. However, a receiver that can handle a strong in-band interfering signal is likely also to be better at coping with many strong signals being received over a range of frequencies. So I think my test results have some validity.

Beginning with the worst receiver, the results are as follows.

  • VX-8GR. This receiver was the worst affected by blocking. Noticeable desensing of the repeater signal occurred when the in-band carrier was on low power, while a weak noisy “4 by 1” signal was killed completely. The repeater signal cut out completely when the in-band carrier was keyed on high power. Engaging the RX ATT (menu option 1) caused the repeater signal to drop below the squelch threshold so it was not much help though it did reduce the desensing effect on stronger signals.
  • JMT-228. The VX-8 was slightly worse than the Jin Ma Tong JT-228, a £30 Chinese handheld bought on eBay. In fairness, the JT-228 is slightly less sensitive than the Japanese ham radios (judging by the signal to noise ratio on weak signals) which may have helped it a bit. Desensing was noticed when the in-band carrier was on low power, and the repeater signal cut out when it was on high power.
  • TH-D72. The Kenwood TH-D72 may only be third worst (or third best) but in fact it was a whole lot better. No detectable desensing occurred when the in-band carrier was on low power. Some desensing occurred, in the form of a drop in S-meter reading and increased noise on the audio, when the carrier was on high power.
  • GP-300. Excellent performance was given by the Motorola GP-300. No desensing was noticed when the in-band carrier was on low power. There was a very slight but hardly noticeable increase in background noise level when the carrier was keyed on high power.
  • TH-205E. I bought this old boat anchor as a “spares or repair” radio for £6 on eBay for the fun of seeing if I could get it going. With the high capacity battery pack it is about the weight and bulk of an FT-817 and not something I would particularly want to haul up a summit. But no desensing of the repeater signal was observed even when the in-band carrier was keyed on high power, making this the best performing receiver of all.

Out of interest I also carried out the test on my FT-817ND and the Kenwood TM-D710 I use as my 2m base station. The FT-817ND was slightly better than the TH-D72: there was no effect with the low power carrier but the high power one brought a noticeable background hiss on the signal. The TM-D710 performed close to the TH-205E. There was barely any noticeable effect from the high power in-band carrier.

I think the results of these tests, crude though they are, are interesting. The bigger the radio, the more likely it is to have a receiver able to handle adjacent strong signals. Paying lots of money for the latest technology is no guarantee of getting a better receiver. In fact, just the opposite. An ex-commercial handheld or a ham band one from the days when wide band receive coverage was not considered important will work better than the latest marvels.

Were it not that I find the full APRS functionality of the VX-8GR and TH-D72 useful, I’d be tempted to sell both those radios and just use a dumb tracker plugged into the mic socket of one of the others tuned to 144.800. Either I use the VX-8GR for APRS only and carry another radio for making contacts or I must try harder to love the TH-D72. Decisions, decisions. But at least I now have a bit more information to base them on.

Handheld receiver blocking shootout

Ever since my outing on to Ling Fell yesterday I have been bugged by not knowing for sure whether the problems I experienced with the VX-8GR were really caused by receiver overload or blocking. I like the construction and features of the Yaesu. But a radio that makes you miss some of the contacts you have laboriously sweated up a summit to make is about as much use as a chocolate teapot. I wondered if I could devise a test to give me an idea of the relative strengths of the different 2m radios. I did, and the candidates are lined up in order of merit below, the worst on the left and the best on the right.

The test methodology was crude. I connected each radio to my dual band vertical and tuned in a weakish station: the GB3AS repeater on 145.600MHz, which is normally an S3 signal – fully readable but with some background noise on the audio. I then transmitted a carrier on 144.025MHz using another radio on a helical antenna a few metres from the vertical. I tried two power levels of the interfering signal, 3.5W (“high power”) and 0.5W (“low power”), these being the available power levels of the test radio. This 8dB difference in the interfering signal level had different effects on the ability to receive the repeater signal.

I am well aware of the limitations of the test I carried out. In real life SOTA or WOTA use a radio may be subjected to strong in-band signals from activators on other summits but they will not be as strong as the signal from a radio a few metres away from the antenna. A radio is likely to be subjected to strong signals from outside the amateur band such as pagers and other commercial signals, which the bandpass filters in modern radios due to the marketing-driven necessity of providing wideband receive coverage will do nothing to attenuate. Many strong signals may mix together to cause intermodulation effects if not blocking. However, a receiver that can handle a strong in-band interfering signal is likely also to be better at coping with many strong signals being received over a range of frequencies. So I think my test results have some validity.

Beginning with the worst receiver, the results are as follows.

  • VX-8GR. This receiver was the worst affected by blocking. Noticeable desensing of the repeater signal occurred when the in-band carrier was on low power, while a weak noisy “4 by 1” signal was killed completely. The repeater signal cut out completely when the in-band carrier was keyed on high power. Engaging the RX ATT (menu option 1) caused the repeater signal to drop below the squelch threshold so it was not much help though it did reduce the desensing effect on stronger signals.
  • JMT-228. The VX-8 was slightly worse than the Jin Ma Tong JT-228, a £30 Chinese handheld bought on eBay. In fairness, the JT-228 is slightly less sensitive than the Japanese ham radios (judging by the signal to noise ratio on weak signals) which may have helped it a bit. Desensing was noticed when the in-band carrier was on low power, and the repeater signal cut out when it was on high power.
  • TH-D72. The Kenwood TH-D72 may only be third worst (or third best) but in fact it was a whole lot better. No detectable desensing occurred when the in-band carrier was on low power. Some desensing occurred, in the form of a drop in S-meter reading and increased noise on the audio, when the carrier was on high power.
  • GP-300. Excellent performance was given by the Motorola GP-300. No desensing was noticed when the in-band carrier was on low power. There was a very slight but hardly noticeable increase in background noise level when the carrier was keyed on high power.
  • TH-205E. I bought this old boat anchor as a “spares or repair” radio for £6 on eBay for the fun of seeing if I could get it going. With the high capacity battery pack it is about the weight and bulk of an FT-817 and not something I would particularly want to haul up a summit. But no desensing of the repeater signal was observed even when the in-band carrier was keyed on high power, making this the best performing receiver of all.

Out of interest I also carried out the test on my FT-817ND and the Kenwood TM-D710 I use as my 2m base station. The FT-817ND was slightly better than the TH-D72: there was no effect with the low power carrier but the high power one brought a noticeable background hiss on the signal. The TM-D710 performed close to the TH-205E. There was barely any noticeable effect from the high power in-band carrier.

I think the results of these tests, crude though they are, are interesting. The bigger the radio, the more likely it is to have a receiver able to handle adjacent strong signals. Paying lots of money for the latest technology is no guarantee of getting a better receiver. In fact, just the opposite. An ex-commercial handheld or a ham band one from the days when wide band receive coverage was not considered important will work better than the latest marvels.

Were it not that I find the full APRS functionality of the VX-8GR and TH-D72 useful, I’d be tempted to sell both those radios and just use a dumb tracker plugged into the mic socket of one of the others tuned to 144.800. Either I use the VX-8GR for APRS only and carry another radio for making contacts or I must try harder to love the TH-D72. Decisions, decisions. But at least I now have a bit more information to base them on.

Prettiest Portable Site

We’re enjoying some wonderful weather here in the Lake District at the moment. Unfortunately I haven’t been able to get out on the hills for some radio activation. I’ve been plagued with back pain ever since I returned from Blackpool. But not only that, sometimes I have to go somewhere that is of interest to Olga.

Today we decided to take a drive down to visit Holehird Gardens, home of the Lakeland Horticultural Society. For Olga, who is if anything even more obsessed with gardening than I am with radio, this is like visiting a really big ham radio show would be for me. I have zero interest in gardening, but I do enjoy looking at a nice garden, and I enjoyed the day out as much as she did. In fact, we agreed we should visit Holehird more often.

I took along the little Jin Ma Tong JT-228 VHF radio because it is small, light and easily slips in a shirt pocket. The antenna was a short stubby helical. No sooner had we arrived than I heard Phil M0AYB/P calling CQ Wainwrights On The Air from the summit of Great Gable. Phil was rattling off the contacts, and soon heard my call. I was pleased to make a contact using 3W to such a small antenna especially as Phil was also using a stock rubber duck, though according to a panorama engraved on the slate behind me in the picture Great Gable was line of sight from where I was standing so it shouldn’t have been too difficult.

More was to come, as just after Olga had taken my picture I heard Derek 2E0MIX/P calling CQ WOTA from the summit of Hindscarth. I got in a quick call and Derek heard me first, so we had a quick chat. Hindscarth was not line of sight, I think, but Derek was using his SOTA Beam which made a big difference. I was well pleased to make two WOTA contacts using the tiny hand-held radio. I popped it back in my shirt pocket and carried it around for the rest of the afternoon but didn’t hear anyone else although several Wainwright summits were activated.

However I was too busy enjoying the wonderful warm weather and beautiful Holehird Gardens to worry too much about the contacts I missed.

What this proved to me is that you don’t need to be up on the fells to enjoy some WOTA fun. Come to the Lake District and bring a hand-held with you and you’ll be sure to make some contacts!

Jin Ma Tong’s day out

Alfred Wainwright said that he could not understand why anyone would want to walk round a Lakeland fell when they could walk over it. He never met my wife. Olga has always been a reluctant companion on my summit walks – except a few very easy ones.

In fact, the scenery in this part of the world is spectacular even from the roadside, so it certainly isn’t necessary to climb summits to have a nice walk. Of course, you can’t activate any Wainwrights for WOTA unless you are on the top. But you can still work other people who are on the summits and claim the points for your chaser score. Olga has finally agreed to my doing summit walks by myself. But we still want to do walks together so some of the time I will go for low level walks.

This afternoon there was an excuse for such a walk. Phil, G4OBK had posted that he would be activating Rannerdale Knotts, one of the lowest Wainwrights and one that is hemmed in by higher hills so that it is probably not workable from home. So we decided to go for a walk beside Crummock Water from where Rannerdale Knotts would be in line of sight. As I would be out of range of any APRS digis or gateways I decided to leave the fancy APRS radios behind and take the little Jin Ma Tong JMT-228, a Chinese VHF radio I bought on eBay. As it has mainly been used to monitor my Echolink node the antenna was just a 2 inch long stubby duck. I thought that should be able to make the half a mile path across the lake. I intended to take a better antenna “just in case” but I forgot.

We arrived at the National Trust car park at Scalehill Bridge and I had just got out of the car and switched on the radio when I heard Phil calling CQ WOTA from Whiteless Pike, LDW-106. I stood the radio on the roof of the car while I put on my boots and waited for my turn to work Phil. The audio from the tiny radio was surprisingly load and turned a few heads! Finally I got my report, 5 by 9, and we set off on our walk round the lake.

It was a pleasant walk in the warm sunshine with skylarks singing overhead. I heard Phil working Derek 2E0MIX/P and telling him he would be on the summit of Rannerdale in about 15 minutes. We found a sunny spot looking across to the bumpy ridge and waited. Eventually a couple of figures appeared silhouetted against the skyline – Phil and his walking companion Geoff – followed shortly by CQ WOTA on the radio. I called Phil for the inevitable 5 by 9 report and that was that. Rannerdale Knotts, LDW-209, was on the list. We retraced our steps, not wanting to be out too late as Olga had dinner to cook.

Half way back to the car I heard another CQ WOTA, this time from Derek 2E0MIX/P who was on the summit of Grasmoor, LDW-020. I stopped and made contact and had a quick chat with Derek while Olga took the picture on the right using my phone.

Phil had said he was going to activate Whiteside, LDW-084 if he had the time, which he did. I was back home by the time he reached it. I was listening on the JMT-228 and stubby duck antenna from inside the house and Phil’s signal was 5 by 9. (The JMT has quite a decent S meter by the way, it isn’t all or nothing like many handheld rigs.) Phil didn’t hear me until there was no-one else calling him but when he did he gave me a 5 and 5 report. Not bad for 3 watts into what many people would consider a dummy load, over a distance of 10km.

Phil did comment that the audio from the JMT-228 was a bit low compared with my other radios. I don’t think that’s surprising as the radio is probably set up for 12.5kHz or even 10kHz channel spacing, and the level is not adjustable as far as I know. Still, I’m happy with this little radio and I think it acquitted itself very well on its first outing.

Look out, Yaesu

Chinese-made VHF and UHF hand-held radios are no longer the novelty they were a few years ago when I discovered the Jingtong JT-208 and got one to try. They are no longer the shoddily made bits of junk the Jingtong was, either. Some Chinese makes like Wouxun are now directly imported into the UK and USA so unadventurous buyers don’t have to take chances on eBay. But there are better bargains and more choices to be had if you use the auction site. When I saw a smartly styled compact VHF handheld radio transceiver 136-174MHz being sold for only £40 it looked like just the job for keeping downstairs to monitor my Echolink node and acting as a backup radio for WOTA activations so I decided to order one. Shipping from Hong Kong took one week.

The radio is a model JMT-228 and is made made by Jin Ma Tong Electronics, which is not a company Google has much information about. Whilst tearing off the wrapping I experienced a heart-sinking feeling as the box was revealed together with the description “400-470MHz.” I was afraid the seller had sent the wrong model! Inspection of the manual revealed the radio comes in VHF and UHF versions, and when I looked at the back of the radio the label showed “136.000-174.000MHz.” What a relief!

Together with the radio and manual, the box contains a short helical antenna, a metal belt clip, a carrying strap, a 1500mAhH 3.7V Li-Ion battery pack similar to those used in mobile phones and digital cameras, a 100 – 240V AC charger with fold-out US-style mains plug, a USB cable (presumably used only for charging as there is no mention in the manual of programming software) and a hands-free style speaker microphone terminated in a 2.5mm stereo jack.

Here is an “unboxing” video (not made by me) from YouTube:

The JMT-228 is very light (the manual amusingly gives the weight as 200kg including the battery!) and looks rather similar to the early Yaesu VX models. It’s a bit smaller than the compact VX-8GR as you can see from the photograph below. The build quality seems very good. The radio is built on a die cast chassis as you can see when you put in the battery. It doesn’t have quite the same solid feel as a Yaesu but the light weight is a bonus. The belt clip is metal but a bit flimsy and it is fixed to the radio using one screw. There is no retaining lug (although the clip has a hole for one) so unless you tighten the screw so hard you risk stripping the threads it could rotate allowing the radio to fall off the belt.

The glass in front of the display is actually plastic which scratches rather easily – there are a couple of dings in it already that I don’t remember doing. A small thing perhaps and forgiveable at the price but something many hams won’t think about as we take the high quality of ham radio products for granted.

No claims are made that the radio is waterproof. Indeed, the manual warns: “Never expose the transceiver to rain, wet areas or any liquids, or it may be damaged. However, the speaker/mic and USB/charger sockets have stout rubber covers and another page in the manual states: “The transceiver is not fully water-resistant while using the speaker/microphone” which implies that it could be. The JMT-228 certainly doesn’t look any less waterproof than the Yaesu VX-8GR so it could probably withstand the odd rain shower, but don’t quote me on that as I haven’t tried getting it wet just to see what happens.

The manual is in Chinese and English. The English part is well written for a Chinese radio, though the most important part, describing the “Auxiliary Fuctions” (sic) is squashed into two pages and less well written so you need to do some guesswork to determine some of the functions. RC sets the CTS or DCS tones for receive, TC sets them for transmit. TOT sets a time-out timer. OFFS sets the direction of offset for repeater use, a different menu OST sets the amount of the offset.

There are 99 memories and they store the offset and tone settings in force at the time of programming. It took only a few minutes to enter in the 2m simplex channels, the three local repeaters and my Echolink node settings. Memory mode is clearly the way to use this radio on the amateur bands as it does not have automatic repeater shift as found on dedicated ham radios.

There is a scan mode, which simply scans all the memories. There is also an FM Radio mode that lets you listen to Band 2 FM radio frequencies. The sound quality isn’t the greatest for listening to Classic FM or BBC Radio 3, but it’s usable.

The antenna socket is an SMA type. Surprisingly for a Chinese made radio it is an SMA female, the same as that used on radios from Yaesu, Icom and Kenwood, so you can use the same SMA-M accessory antennas you could use on those radios. I can even use my SMA to BNC adapters! The supplied antenna is 4 inches long, presumably a helical whip, and fairly broadband with the best match, a 1.6:1 SWR, at 156 MHz. This isn’t going to be optimum (tests I have carried out in the past have showed that a noticeable benefit is gained by tuning short helical antennas to match the frequency of use) but it is no worse than the antennas supplied with Kenwood handhelds and only to be expected in a radio designed to operate over such a wide band.

The receiver sensitivity seems on a par with other handheld radios I own. Output power is claimed to be less than or equal to 5W. Frankly, I would not expect to get 5W out of a radio powered by a 3.7V battery pack. If you did, it would get very hot very quickly and the battery would soon run out. I measured the output power at 3W which I think is very good for a radio of this size. I had no trouble opening the GB3LA repeater more than 50 miles away using a 7 inch long helical (but not with the supplied antenna.)

There is no low power setting, which is a bit of a disappointment and will not help battery conservation. On receive, however, the radio seems to run forever, helped no doubt by a quite severe power saver mode. This does not appear to be user configurable nor can it be disabled so you could not use this radio to receive packet or APRS.

The modulation using the internal microphone is OK, but a bit on the low side. Using the included speaker/mic it is a bit better. Note that although this speaker/mic is similar to a hands-free mobile phone kit, the JMT-228 transceiver does not have VOX, so it is necessary to key the transmitter by pressing the button on the back of the mic. Here are some audio recordings of the JMT-228, with a couple of other hand-held radios for comparison purposes.

As you can hear, the audio level is similar to the Motorola GP300, another radio designed for use on the professional high bands. Amateur band radios tend to have a higher modulation similar to the TH-205E.

When using the speaker/mic I found that the transceiver tended to lock in transmit – presumably due to RF getting into the speaker/mic cable which is right next to the antenna. This is a bit of an annoyance, which could possibly be cured using a really small snap-on ferrite if I had one.

Despite a few niggles I think the Jin Ma Tong JMT-228 transceiver is a nice little radio and would be a good buy for anyone wanting an inexpensive and compact transceiver for use in the amateur 2m band. I think the Chinese are going to own the market for basic single or dual band handhelds very shortly and people will only buy from the specialist manufacturers if they need specialist functionality such as APRS, wide band scanning, a short wave receiver or even, dare I say it, D-Star.


Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter

 
We never share your e-mail address.

Please support our generous sponsors who make AmateurRadio.com possible:

Ham Radio Deluxe

KB3IFH QSL Cards

Hip Ham Shirts
DMMCheck Plus
R&R SpecialTEES

morseDX

Ni4L Antennas
R&L Electronics
antennas.us


Do you like to write?
Interesting project to share?
Helpful tips and ideas for other hams?

Submit an article and we will review it for publication on AmateurRadio.com!

Have a ham radio product or service?
Consider advertising on our site.

Are you a reporter covering ham radio?
Find ham radio experts for your story.

How to Set Up a Ham Radio Blog
Get started in less than 15 minutes!


  • Matt W1MST, Managing Editor




Sign up for our free
Amateur Radio Newsletter

Enter your e-mail address: