AmateurRadio.com

I have spent a frustrating couple of hours trying to make a PC cable to communicate with the VX-8GR. In the VX-8 Yahoo group it was stated that the cable is the same as for the Kenwood TH-D7AG a diagram of which is given in YO3HJV’s blog. It was also pointed out to me that there is a diagram in the back of the manual – the one place I never thought to look!

It is easy enough to make up. No level shifting components needed. Just a 2.5mm stereo jack for the radio end and a 9-pin D plug for the PC end. But the damn thing refuses to work.

I have tried a Prolific USB to serial adapter and an FTDI one. I’ve tried the FTBVX8G software and I’ve tried a terminal program to see if I can detect any data. Nothing. Nada. Incommunicado. I know the cable is OK because if I short between tip and ring of the jack plug I can type in the terminal program and see the text I typed echoed back over the connection.

The only thing I can think of is that the standard 2.5mm stereo plugs I have here are a bit too short. It seems to me that the  plug isn’t locking firmly into place, more that the radio is trying to push it back out again. It’s as if the tip needs to be a bit longer to get past the spring loaded contact in the socket. I measure 7/16in from the base of the plug to the tip of it. I had a similar problem trying to make a cable to send audio from my FoxTrak APRS tracker into my Motorola GP300. Then I had a plug from a speaker mic to compare it with and I could see that it needed to be longer.

Perhaps someone who has a VX-8G PC cable that works could measure the plug on theirs. Or perhaps someone will spot the stupid wiring mistake I’ve made from the photo I’ve posted.

My long awaited package from Martin Lynch was finally delivered by UPS on Saturday afternoon and as one reader correctly guessed, it was a new Kenwood TH-D72! I was lucky. The UPS tracking page had been changed to say delivery was rescheduled for Monday, so we went out on Saturday morning. You can imagine how happy I would have been to get home and find a card through the door to say UPS had tried to deliver it! I was pleased to receive the radio and although I did consider wrapping it and putting it under the tree until Christmas Day, the chance of being the first blogger to write about it was too great to resist.

This is not meant to be a review of the Kenwood, more an account of my first impressions of the radio and how it compares with the Yaesu VX-8GR which I have been using for the past few months. The first thing you notice is that the Kenwood is quite a bit bigger than the Yaesu. It’s taller, thicker and heavier. Although I think the Kenwood is nicer looking, the Yaesu feels a bit more rugged and I think its plain black finish would take knocks and scuffs better than the Kenwood’s metallic grey finish. I’ll probably need to get a protective case for it.

The additional thickness and weight can partly be attributed to the Kenwood’s battery pack which has 1800mAh capacity, compared to the Yaesu’s 1100mAh. This should translate into longer endurance in the field. Yaesu does offer an 1800mAh battery pack for the VX-8 series but it is an optional extra for quite a lot more money. Still, there is no question the slimmer, smaller VX-8GR slips more easily into a pocket for about-town use.

The TH-D72 is a dual band 2m/70cm radio so it it is more directly comparable with the Yaesu VX-8GR than with the tri-band (quad band in the USA) VX-8DR. Both radios have an integral GPS rather than the expensive optional GPS of the VX-8DR which must be fitted to an even more absurdly expensive clunky looking bracket or to a specially made Yaesu speaker mic. (Having said that, the Yaesu GPS options are good value compared to the add-ons for Icom’s D-Star radios – talk about rip-offs.)

The TH-D72 comes with the usual pathetic SMA socket for the antenna and an equally pathetic dual band dummy load, er, I mean whip antenna. The first thing I did, and I mean literally the first thing, was to fit one of my SMA to BNC adapters so I can use any of my collection of BNC whip antennas with the rig. The SMA socket sits deep in a large recess on the top face of the Kenwood, so I was able to use one of the chunky gold plated adapters rather than the slimmer black one that I use on the VX-8GR.

I checked with a piece of paper to see if the adapter tightened all the way down to the body of the radio, which is essential to avoid the risk of snapping the SMA at the first accidental knock. It didn’t, so I added a steel washer to fill the gap. I covered the knurled base of the adapter with a layer of self amalgamating tape to hide the gold finish and once an antenna is fitted you wouldn’t know that the BNC socket was not standard equipment. Why couldn’t the manufacturers fit one in the first place? By the way, neither of these radios come with a wrist strap – the ones shown in the picture were salvaged from old mobile phones in the junk box.

One of the main reasons I decided to get the Kenwood TH-D72 even though I had the VX-8GR was that I was very unhappy with the performance of the Yaesu’s GPS which is slow to acquire a fix and usually can’t manage it at all from inside the house. I found this a real nuisance as often I just could not be bothered to hang around waiting for it, while the chance of acquiring a fix once you are on the move is even worse. As you can see from the picture above, the Kenwood has got my position while sitting on the bench being photographed while the Yaesu’s GPS screen was (and remained) blank.

The Kenwood has a display to show how many GPS satellites it is receiving and as you can see from the picture above, even on the bench it does quite well. This is a nice screen to have, but with this exception I prefer the Yaesu VX-8 display which shows more information at a glance. The Kenwood display often consists of a couple of short lines of text and you have to page through several screens to get all the information. However I do like that the Kenwood position screen shows the grid locator square – the Yaesu doesn’t.

The TH-D72 has the ability to plot your track and store it in memory – not something I can see myself using though. What I do consider very useful is the ability to enter and store the co-ordinates of several locations or waypoints. You can then select one and one of the Position pages will display your distance and bearing from it. This will be very useful during WOTA operating as I will be able to enter the exact co-ordinates of the summits I intend to visit, eliminating the difficulty sometimes experienced of identifying the summit on the ground!

The TH-D72 is virtually a hand held TM-D710. It has almost the same functionality of its bigger mobile brother, in fact more: it supports the Kenwood Sky Command remote control system which my European D710 doesn’t. A pity – it would have been fun to see if I could have used it to remote control my Elecraft K3, which uses a command set similar to the TS2000.

In common with the D710 the D72 has hierarchical menus. Personally I prefer the menu system of the VX-8 series, which has just two linear menus, one for radio settings and one for APRS. I know where the ones I most often use are and can quickly zip to them using the rotary control. The Kenwood menus require a lot of clicking with the four way directional button thingy.

If you want to connect your VX-8 to a PC for memory management you need to purchase third party memory management software and an interface cable. Kenwood provides the memory management software free and the TH-D72 has a USB port which can be connected to your computer using a provided, but in any case standard, USB cable – a significant saving. Through this cable you can not only manage the memories you can also edit all the radio’s settings and access the built-in packet TNC. This appears to be completely compatible with the one in the TM-D710. I just changed the COM port number and APRSIS32 as set up for the D710 was immediately able to use the D72 instead. A menu option allows the internal GPS data to be output over the same serial connection. I haven’t experimented with this, so I don’t know if this can be done at the same time as accessing the TNC or whether APRSIS32 would be able to take advantage of it.

Hopefully the TH-D72 will, like the D710 (and unlike the Yaesu radios) be software upgradeable. I discovered, to my disappointment, that my APRS repeater objects being transmitted by my G4ILO gateway were displayed by the VX-8GR but not by the Kenwood. The packets were received but were apparently considered to be invalid. A bit of research by Kai Gunter, LA3QMA led to the conclusion that this is a bug, not just in the TH-D72 firmware but in the TM-D710 as well, as the same objects were displayed by older model Kenwoods. The problem is apparently caused by the time-stamp in the objects created by APRSIS32 which is in local time (ending in ‘h’) instead of zulu time (ending in ‘z’.) The objects are correct according to the APRS spec, so the Kenwood should display them.

The TH-D72 is full duplex. That is, it can receive on 70cm while transmitting on 2m or vice versa. There are very few current model radios that can do this, one of which (the Alinco DJ-G7) doesn’t do it very well as 70cm is severely desensed by the 2m transmission. This would make it a good choice for FM satellite operation allowing you to hear your own signal. One of these days I will try this, I just need to get round to making a suitable dual band antenna.

Another neat feature of the TH-D72  is the nine EchoLink memories. This allows the radio to store the DTMF sequence needed to connect to up to nine different conferences or nodes so you can recall them by name and transmit them to your local EchoLink repeater. If you use EchoLink it is a real boon as I can never remember node numbers – heck, I still can’t remember my mobile phone number!

The Kenwood TH-D72 is quite an amazing radio packing an incredible number of features into its small form factor. However I would not go so far as to say it is a better radio than the VX-8GR. There are things I like and things I dislike about each of them.

• Yaesu VX-8GR – Like: smaller size, lighter weight, feels more durable, more informative displays. Dislike: deaf GPS.
• Kenwood TH-D72 – Like: sensitive GPS, editable waypoints, accessible TNC, EchoLink support, full duplex. Dislike: hierarchical menus, plain displays requiring scrolling through pages to view all information, more bulky.

In the UK, the VX-8GR is being sold for quite a bit less than the TH-D72, even at the discounted price I got from Martin Lynch. If you don’t want to connect the radio to APRS software on a PC, aren’t bothered about getting your GPS position indoors and never use EchoLink then you probably won’t think the Kenwood is worth the extra money. Though it does include a higher capacity battery as standard and if you want memory management software then both this and the connecting cable will cost you extra for the Yaesu.

I’m still making my mind up which of the two of them is going to be the keeper but I suspect it’s going to be the Kenwood.

Cumbria is famous as the county of the English Lake District but it has more to offer than mountain walks. I don’t agree with Alfred Wainwright who said he could not see the point of walking round a mountain when you could climb to the top of it. There are many beautiful walks in the valleys and round the lakes which my wife (and my knees) much prefer over climbing and descending even if they don’t offer much scope for making radio contacts. Less well known, but just as spectacular, are parts of the coastline. One of our favourite outings is to park in the village of Sandwith and go for a walk along the cliffs. This is where we went last Sunday.

Map of the walk (from aprs.fi Google Maps)

The map of the walk shows the path that was tracked on Google Maps APRS, with some additions by me where my position was not tracked.

I was using my VX-8GR with the 5/8 telescopic whip in my rucksack, as shown in the picture on the right. I operate pedestrian portable like this when I don’t expect to encounter too many people who will give me strange looks or think I am a dork. The radio sits in a little mesh pocket on the side of the rucksack which was probably meant to carry a water bottle. The antenna is supported by pushing it through a string loop attached to one of the zips of the main pocket of the rucksack. It is quite stable and does not flex the spring or the mounting at all.

I don’t know what the SWR is like. Possibly it isn’t that good as the radio does not have me holding it to provide a ground plane. Perhaps I should try clipping a 19 inch “tail” to the outer ring of the BNC connector as a counterpoise? But even without it, it worked well. Most of my position beacons were received by MM1BHO across the water in Scotland so I was able to see the track after the walk. I also received some interesting APRS DX, of which more later.

But back to the walk. The weather was glorious, as you can see from the pictures. The temperature was around 20 degrees Celsius with only a slight breeze. The view from the cliffs was spectacular and always reminds me a bit of Cornwall. To think that people pay money to come on holiday to places like this!

We walked for about an hour along the cliffs, stopping now and again to watch some birds through binoculars or just take in the view. This is an important area for wildlife and the Royal Society for the Protection of Birds (RSPB) has set up several places where you can watch them with safety on the edge of the cliffs.

You can walk right along these cliffs as far as St. Bees, where there are people and cafes and ice cream kiosks. But we usually stop at Fleswick Bay, a beach backed by the high cliffs that is always quiet and secluded even in the height of the season because it isn’t possible to reach it by car, it can only be accessed by footpaths. We call it our private beach because we often have it to ourselves.

This Sunday we didn’t go down to the beach because we saw from the clifftops that the tide was in and the sea was right up to the foot of the cliffs. So we had our picnic lunch in one of the RSPB birdwatching areas instead. I made a couple of FM contacts using the VX-8GR, including one with another portable station on a 2,500ft mountain top in Wales. Then we started the walk back.

On the way back I heard the VX-8GR braaping away constantly such as I hadn’t heard since we were in Prague. On my return home I scrolled through the station list and observed that for a couple of minutes between 12:28 and 12:30 UTC I had received beacons from several DX stations including F4EQD-1 and OZ2DXE-2. These beacons had actually been digipeated by a station in south west England but that was still an amazing distance to receive signals on a VHF handheld, even if I didn’t hear them direct.

The glorious weather had also produced fantastic tropospheric propagation which was enjoyed by people in most parts of Europe. I wished I had climbed to the top of a mountain as I would certainly have heard more there than I did down on the west coast and perhaps have worked some real handheld VHF DX. But you can’t predict propagation and it was still a wonderful day’s walk.

As regular readers may recall, I have a pathological hatred of SMA connectors when used as antenna connectors for hand-held radios, which has become even more entrenched since I had the centre pin of the TH-F7E stock antenna break off in the adapter I use for testing such antennas on my antenna analyzer. I now have an SMA to BNC adapter permanently installed on my VX-8GR. The picture on the right shows my latest adapter which is anodized black and looks like an integral part of the radio. The previous one I used was gold plated with a knurled body and whilst it worked perfectly and provided a robust fitting for the BNC antennas it looked a bit ugly.

If you never change the antenna on your HT then one of these adapters isn’t necessary, but SMA connectors were never designed for multiple connections and disconnections (in one email group I saw someone state they were rated for 100 disconnections) so if you want to change between a short stubby antenna for inconspicuous local use and one with more gain the BNC adapter is the way to go.

All of my BNC whips are 2m antennas, which is fine most of the time as almost all my operating is done on 2m, but there are rare occasions when I might want to use 70cm and removing the BNC adapter in order to attach the stock antenna kind of defeats the object of it. So I ordered from eBay a Nagoya NA-701 antenna which is a short dual band whip similar in size to the ones supplied with amateur dual band handhelds but with a BNC connector.

I tried it out on my antenna analyzer and it showed a nice sharp SWR curve with the minimum around 147MHz. It could be better, but it’s closer than some stock antennas I’ve tested. I couldn’t check it on 70cm as my antenna analyzer doesn’t go up that high.

I need to devise way to make comparative tests of all these HT antennas, because asking for signal reports or seeing if you can hit a repeater is a pretty crude measure of performance that won’t reveal small differences. This little antenna doesn’t perform as well as a six inch monoband helical on 2m, nor a quarter wave telescopic, but that is only to be expected. The beauty of the BNC adapter is that if you need a gain antenna you can easily whack on something like my 5/8 wave Black Whip, which you certainly couldn’t use with a standard SMA connector.

Steve WG0AT, Rich, AC7MA and Guy, N7UN recently returned from their expedition to activate Huron Peak in the Sawatch Range in Colorado, USA, for Summits On The Air (SOTA). Together with their “sherpa” goats Rooster and Peanut, they took a GPS-equipped Yaesu VX-8R so people could track their progress.

You can see a slide show of the expedition here.

I rather like the idea of using goats to carry the heavy equipment but I think you’d get some funny looks in the hills around here. This has made me wonder what has been the highest SOTA activation to date. Has anyone activated Mount Everest yet? I bet that would create a pile-up!

As regular readers will have realized from my previous post, I have been on holiday in Prague, capital of the Czech Republic. I won’t bore you with details of where I went or what I did, though I have made a few comments about the holiday over on my other blog. So I will just describe my ham radio experiences over there.

Prague is quite a hilly city. The picture above was taken from the Botanical Gardens to the north of the city, looking towards the famous Zizkov TV Tower. This building, looking from a distance like an Atlas rocket waiting to take an Apollo mission to the Moon, is widely regarded as the ugliest building in Prague. But from a radio point of view it would be a good QTH. I quite like it. Apparently you can go up it to see the view, but that is something we have yet to do.

I took with me on my travels my Yaesu VX-8GR dual band APRS hand-held. Due to the language difficulty (I don’t speak Czech) I didn’t anticipate having many contacts with locals but I could see from aprs.fi that there was quite a lot of APRS activity in the city and I was interested to experience it first hand. I was not disappointed.

From the moment the VX-8GR was first switched on the APRS channel on 144.800MHz began receiving packets. The station list, able to hold the 50 most recently received APRS packets, filled up in about ten minutes. I was receiving position reports from fixed stations and mobiles, not only in the Czech Republic but also sometimes from Germany, Poland and Austria. I also received local weather reports, including the position of lightning strikes over a more than 300km radius and weather bulletins sent out by OK1COM. Coming from West Cumbria where you can often go a whole day without receiving anything on VHF it was quite a revelation.

I sent a greeting using APRS to Colin, 2E0XSD. By checking aprs.fi I discovered that he received it, but I didn’t receive any of the acks his client sent back, nor his reply. It appears that no-one sets up their gateways to gate messages and acks for locally heard stations from the internet to RF, so the much-vaunted APRS messaging capability is essentially useless except between stations in direct radio contact.

Later in my stay I did have a messaging QSO with OK1RQ on foot in Prague with a Kenwood hand-held. Unfortunately he was busy so I never got to meet him or any other local hams. I also received greetings via APRS from a couple of other local stations.

We needed to make some local phone calls so I purchased a pre-paid SIM card from O2 for my smartphone. This included 3G data so I was able to try the APRSISCE client from Prague. I had several messaging conversations over the internet with Lynn, KJ4ERJ, the program’s author. We also had our first voice QSO via OK0BNA, the Prague repeater, which Lynn was able to access through Echolink as it is connected to OK1OGA-L. I monitored OK0BNA on many evenings and heard only two other contacts take place on it. I did not hear any other FM contacts on either 2m or 70cm the whole time I was in Prague.

APRS works well in Prague because there is a network of several digipeaters and gateways within a radius of a few kilometres of the centre. The apartment where we were staying was just a few hundred metres from the QTH of OK1ALX who runs a digipeater and Igate, so most of the APRS signals I heard on my VX-8GR inside the apartment with the stock rubber duck were S9+.

The map on the right shows the tracks of some of our outings in the seven days before our return, tracked using the VX-8GR. Although aprs.fi reportedly stores position reports for a year, it doesn’t appear to be possible to display tracks for specific periods retrospectively, and as I didn’t have a computer with me (this was supposed to be a holiday) I couldn’t capture my tracks at the time. But you can see at the top one day’s walk in the Botanical Gardens, at the bottom a walk around Vysehrad, and in the middle a circular walk we made into the city centre and back along the river one evening.

Tracking an outing from start to finish wasn’t very convenient, or even possible, because the GPS wouldn’t pick up a fix inside the apartment and I couldn’t be bothered to stand around for 3 or 4 minutes on the street outside waiting for it to get a fix before we started. Hence the big jumps from where we were staying to where we started walking.

We were on foot or using public transport and you would lose a fix whenever you got on the metro or a tram or went inside a building, and then have to wait to regain a fix when you came out. It was too much hassle. But when we were planning to just walk, it was interesting to see where my beacons were picked up, both from higher ground and from street level within the city.

I didn’t use the Windows Mobile client for tracking much at all (apart for one short evening stroll along by the river) because using the GPS reduced the phone’s battery life to an unacceptable couple of hours. However I was impressed by the battery endurance of the VX-8GR. After reducing the beacon frequency to no more than one every two minutes and using the 2.5W power setting, it lasted all day with enough power left for a couple of hours receiving in the evening. This is particularly noteworthy considering that the power saver was disabled (as it needs to be for APRS usage) and the receiver was constantly receiving and displaying APRS data. If only the GPS was quicker at finding its position after switch-on it would be just about perfect.

Like most hams, I guess, I always keep an eye open for antennas wherever I’m travelling. Antenna-spotting in Prague is quite difficult as every building has comprehensive lightning protection consisting of tall lightning conductors looking like VHF collinears, usually connected together along the ridge of the roof. I have never seen this anywhere else.

Close to where we were staying, in a street called Vysehradska, I noticed a shop window displaying a few old radios, some vacuum tubes, what looked like a tube tester and some other electronic bits and pieces. On the roof of the building next door I spotted an MFJ multiband HF vertical antenna. I was sure that the owner of the shop must be a ham, so we decided to go in and introduce ourselves.

Inside, the place looked more like somebody’s untidy workshop than a shop. There were three elderly gentlemen, one of whom was presumably the owner. Another was leafing through a dog-eared book while the third was inspecting a vintage broadcast radio he had taken down from a shelf. They looked at us expectantly. I said “ham radio?”, anticipating that someone would understand at least that English phrase, but was met with blank stares and something we couldn’t understand in Czech.

Older people in the Czech Republic speak Russian, a legacy of the Russian occupation, so Olga then explained in Russian that I was a ham radio enthusiast and was interested in what they had in the shop. No-one introduced themselves as a licensed amateur, however. Instead, they told us that it was not a ham radio shop, but that there was one a few blocks away. Unfortunately Czech street names are confusing to non-native speakers, even to Olga. We didn’t find it. Perhaps we will on our next visit.

A week ago I received a Yaesu VX-8GR VHF/UHF APRS hand held transceiver with GPS. The transceiver performs as expected except in one extremely annoying respect – its GPS takes a very long time to get an initial fix on its position after switching on the radio. It cannot get a fix from inside the shack at all. By contrast, my HTC smartphone will get a fix in a couple of minutes whilst sitting in its charger cradle on the shack desk. Or at least, it did.

This morning I noticed on aprs.fi that the last reported position of my smartphone, G4ILO-10, was somewhere in Somerset. I started the APRSISCE application with the intent of “bringing it back home” by sending a position report with the correct location. But after ten minutes the phone had not managed to get a fix.

I switched off all my radio equipment in case one of them was an interference source, and rebooted the phone, and eventually after several more minutes it obtained an accurate fix. I am beginning to suspect that something is interfering with GPS reception in the area of my house.

If you Google “GPS interference” you will find links to numerous articles and research papers raising concerns about what is apparently an increasingly common problem. One article states that a directional television receiving antenna widely available in the consumer market contains an amplifier which can emit spurious radiation in the GPS L1 frequency band with sufficient power to interfere with GPS reception at distances of 200 meters or more. Other potential interference sources include spurious outputs from TV transmitters.

Another website states that “We are seeing increasing evidence of GPS interference and also apparent erratic behaviour (e.g. mis-reported location)” and provides a form for reporting cases of interference. This page provides links to two reports on the issue which unfortunately require registration in order to access them.

Have other amateur GPS users experienced difficulty in receiving the satellites or an increase in inaccurate position reports? For many GPS applications the effects of this could have rather greater impact than a radio ham’s inability to report his position to aprs.fi. Perhaps the US administration was rather hasty in its decision to decommission Loran.