AmateurRadio.com

Do LCD displays wear out or fade with age?

The picture above shows the displays of my Elecraft K3 transceiver and my Kenwood TM-D710 VHF rig. The Elecraft display is sharp with good contrast and characters look almost black against the orange background. The Kenwood display is much less contrasty. The backlight is not as bright as the K3’s but the characters look more murky brown than black no matter how I set the brightness and contrast. It’s quite noticeable when the two radios are side by side.

I don’t think the Kenwood’s display was ever as bright as the K3’s but I don’t recall it being as murky as it is now. Whenever I look at it I keep wanting to turn the contrast up. I’ve taken to turning the backlight off altogether so it doesn’t bug me but there is no option to have it turn on automatically when a button is pressed. (AUTO BRIGHTNESS: ON appears to do nothing.)

My D710 has been running 24/7 for more than a year (with a brief hiatus when I went into hospital until I felt like running the APRS gateway again.) Could the display have faded (for want of a better way to describe it) over time? Or is my recollection that the text used to look more black than brown faulty?

According to Bob Bruninga WB4APR, Kenwood announced an update to the TM-D710 firmware at Dayton. The changes are:

– INTERRUPT ALWAYS: always displays information about every packet received on screen for a few seconds, not just packets from new stations.

– INFINITE: extends the above to retain the information about the last heard packet on screen.

– MY PACKET: now displays the actual digi path used when your own packet is digipeated so you don’t just see that it was digipeated you can see which digipeater.

– TOP button: LIST display inserts new entries at the top so no need to scroll down.

– HEADING/UP: you can toggle the compass rose to North-UP or Heading
UP.

– PREVIEW of PHRASES: When selecting phrases you can see a preview of
first 9 bytes.

– READ/REPLY keys come up when a message is flashed on the front panel

– OVERLAYS: You can now select overlay characters on any symbol

– TOTAL hops can be set as low as 0 instead of 1.

– Auto-Powerup-Time set (if GPS is connected and is locked)

The update also contains some bug fixes. It does not include support for item-in-message or any other previously unsupported APRS features. 🙁

At this time the update is not yet available for download from Kenwood’s website.

According to Bob Bruninga WB4APR, Kenwood announced an update to the TM-D710 firmware at Dayton. The changes are:

– INTERRUPT ALWAYS: always displays information about every packet received on screen for a few seconds, not just packets from new stations.

– INFINITE: extends the above to retain the information about the last heard packet on screen.

– MY PACKET: now displays the actual digi path used when your own packet is digipeated so you don’t just see that it was digipeated you can see which digipeater.

– TOP button: LIST display inserts new entries at the top so no need to scroll down.

– HEADING/UP: you can toggle the compass rose to North-UP or Heading
UP.

– PREVIEW of PHRASES: When selecting phrases you can see a preview of
first 9 bytes.

– READ/REPLY keys come up when a message is flashed on the front panel

– OVERLAYS: You can now select overlay characters on any symbol

– TOTAL hops can be set as low as 0 instead of 1.

– Auto-Powerup-Time set (if GPS is connected and is locked)

The update also contains some bug fixes. It does not include support for item-in-message or any other previously unsupported APRS features. 🙁

At this time the update is not yet available for download from Kenwood’s website.

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.

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.

What is it about ham radio that encourages boorish behaviour? Or is it just the internet? Whenever you post in any forum or specialist group suggesting that something about a particular radio is not a very good design and could be improved you will usually get several responses that amount to “I don’t think there is anything wrong, so there can’t be anything wrong.” If you attempt to defend your statement you will eventually end up on the receiving end of insults. Yahoo groups are aptly named it seems.

If you want a VHF radio that can be used simultaneously as an APRS gateway and for voice there aren’t a lot of choices. The Kenwood TM-D710 is really the only option given that Yaesu’s FTM-350 doesn’t have an accessible TNC. Like most radios capable of 50W output the TM-D710 has a fan. Unfortunately Kenwood’s fan logic is dumb. The fan comes on the instant the transmitter starts, no matter how long you transmit for or what the power level, and runs for about two minutes. This means that it runs for two minutes out of ten, triggered by my one second five watt APRS beacons. This is completely unnecessary as no significant heat is generated by such a short transmission. The noise is an annoyance – it’s significantly louder than the computer, or my K3’s fans – but more importantly this must also reduce the working life of the fan unnecessarily. One day the fan will fail when it is needed because of all the times it ran when it wasn’t.

When somebody complained in the Kenwood D710 group about the fan noise because he was using the D710 in his quiet living room, I agreed, saying it was just cheapskate engineering for Kenwood not to have incorporated a thermostatic fan controller. This upset the yahoos. I was told that it was better for the fan to run than for it not to run, that if there was a bad antenna mismatch the fan running in those first few seconds could save the PA transistors, that it was necessary for the fan to run all the time because some users install the radios in tight spaces in vehicles where the temperature reaches over 100 degrees F, that group members had equipment with other fans that were even noisier, and so on. None of which, if true, actually invalidated the argument that a thermostatically controlled fan would be an improvement over the present dumb logic. It was just “It isn’t a problem for me, therefore there is no problem.”

It was also suggested that a thermostatic control would add $10 to $40 to the cost of the radio. I’m not an electronics engineer but I doubt that it would add more than a couple of dollars to the manufacturing cost, which would not make a significant difference to the retail price given these aren’t cheap radios to begin with. Even my power supply, which cost a third the price of the Kenwood, has a thermostatically controlled fan. If Diamond could fit one without making the price of the product uncompetitive I’m sure Kenwood could have done.

Sadly, online groups have ceased to be a place where you can intelligently discuss the strengths and weaknesses of various products due to the activities of the yahoos who will brook no criticism of the thing they have purchased. I could regale you with another recent encounter, this time on the Elecraft reflector, over the stupidity of having the K3 change mode to the one last used on a band when a program sends a change frequency command, overriding the mode set by the program so you may end up in USB in the CW part of the band or vice versa. Needless to say, the Elecraft Way is The One True Way and it is the developers who won’t modify their programs that are wrong, even though by making this one change Elecraft could enable the K3 to work properly with N3FJP and several other programs whose developers won’t change them just to suit Elecraft. In fairness I should point out that Elecraft didn’t refuse to make the suggested change (they didn’t respond to the thread) it was the fanboys who defended the status quo as usual.

Frankly I’m getting tired of engaging with hams over any subject at the moment. So I have decided to unsubscribe from the majority of ham radio groups and will restrict myself to posting my thoughts here in future. I’m sure that will please many people who don’t like seeing points of view they don’t agree with. Commenters to my blog are welcome to disagree, as long as they do so intelligently and politely. Boorish comments that amount to “I don’t agree, therefore you’re wrong” without providing any supporting evidence as to why I might be wrong will be unceremoniously deleted.

One problem I have noticed with the PIC TNC I recently built is that it is less tolerant of different packet signals than any of my radios. It decodes my two Kenwood transceivers just fine but it will only decode the VX-8G at a specific audio level that is impossible to set when using the fixed output of many radios. And it won’t decode my WX-1 weather station at all.

My Kenwood TH-D72 won’t decode the weather station either. However it is the VX-8GR I am more concerned about. With the volume of the packet channel turned up, it’s braaps sound a bit thin and weedy compared to those of the Kenwoods and other radios I hear over the air. I thought that I would try to analyze the signals to see if this would give me an idea of what was causing the problem.

I used Spectran, the only free software I know that will do audio spectrum analysis. The receiver was the old Kenwood TH-205E, which being over 25 years old had IF filtering wide enough not to cause any deviation limiting. Each capture was made at the same volume level so the signal levels shown should represent the relative signal deviation.

Because packet bursts are fleeting it took a few attempts to capture the screen at just the right moment. But eventually I obtained plots for each of four radios, including the weather station. Incidentally I am puzzled that the spectrograms show a comb of frequencies. I thought 1200 baud packet was FSK using two frequencies, 1200Hz and 2200Hz. I have seen this before when using sound card decoder software for packet but I have always been puzzled by it.

The top two plots are for the two Kenwood radios. They look pretty near identical. In the absence of any test equipment to actually measure the deviation levels I have to assume that these two radios were correctly set up at the factory and represent the ideal signal to aim for. It is interesting that the highest frequency which I would have assumed to be 2200Hz actually peaks at about 2235Hz. The peak closest to the lower frequency of 1200Hz is actually 1185Hz. But there are six peaks at intervals of about 150Hz between the two and some spaced the same distance going below the lower frequency. I’m sure there’s a reason for it.

If you look at the plot for the VX-8G the top peak is at about 2230Hz and 5dB weaker than the corresponding peak of the Kenwood traces. The other peaks are lower still with the one at about 1180Hz around 8dB lower than that from the Kenwood. Some VX-8 users have complained about low packet deviation of the radio but have been told by Yaesu that it is within specification. As far as I know there is no adjustment to increase it. You would have thought from this that I would need to increase the audio level to get reliable decoding of the VX-8 compared to the Kenwoods. In fact, I have usually had to reduce it a little. As previously stated, the volume setting at which the PIC TNC will decode the VX-8G is quite critical, whereas the Kenwood signals would decode over quite a wide range of audio input levels.

When you look at the signal from my WX-1 weather station, which is modulating a Radiometrix VHF transmitter module, the peak signal levels are close to that of the Kenwoods. The lower frequency components are in fact a couple of dB stronger. However, it’s clear that the frequencies are too high. The top peak, which should be 2200Hz, is about 2290Hz. And the one closest to 1200Hz is about 1230Hz. When setting up my FoxTrak APRS tracker I had to set the frequencies using the PIC calibration routine as low as they would go before my TH-D710 would decide it, so clearly it is the frequency offset that is responsible for the packets not being decoded. The WX-1 firmware unfortunately does not have a calibration procedure. Either the PIC clock crystal needs to be slowed down a bit or I need to make a change in the source code to shift the frequencies and recompile the firmware.

But it’s the VX-8G that most bothers me most. I wish there was a way to boost the level of its packet modulation and make it more like the Kenwoods.