AmateurRadio.com

I’m finding it hard to love the new Kenwood TH-D72. Despite the fact that it has a more sensitive GPS, a proper TNC that you can interface to computer APRS or packet software and is firmware upgradeable, I’m steadily coming round to the opinion that the VX-8GR is the better performing, more usable radio.

Things I don’t like about the TH-D72 is that it is bigger and heavier, has a screen that gives far less information at a glance than the corresponding screens on the Yaesu and has poorer ergonomics. I have also been harbouring a suspicion that its packet modem was less sensitive. Today I think I discovered the reason.

I recently built a Fox Delta weather station that outputs AFSK packet directly into a radio. I noticed that although my Kenwood TM-D710 and my VX-8GR decode it’s S9+ packet bursts the TH-D72 didn’t. I thought it might just be a case of adjusting the deviation but I tried the weather station on two different radios adjusting the audio level from nothing to definitely clipping and could not find a setting at which the D72 would decode anything.

Recently I set up a low power APRS repeater in the shack. It is a sound card TNC (TrueTTY) driving a low power UHF radio (the FT-817ND) running into a dummy load, which is connected to the aprsg gateway software. This gates everything that is going on in APRS within a specified radius to UHF so that I can monitor activity and reply to messages using an APRS HT anywhere I am in the house. This has been working fine with the VX-8GR but last night I forgot to switch it off and the battery was dead so I tried monitoring using the TH-D72 instead. Nothing was copied!

Again I tried an entire range of audio levels into the radio but while the VX-8GR and the TH-D710 both decoded the packets over a wide range of settings the D72 didn’t decode anything. I was using TrueTTY into my USBlink home-made VOX-based digital interface. I wanted to try different software (AGWPE) and a different sound card but Windows got confused having different USB sound devices connected to it and it is also a dog at handling serial ports. I have real serial ports occupying COM2 to COM5, a pair of virtual ports mapped between COM8 and COM9, and other USB serial devices I have used in the past have been assigned to COM1,6 and 7. AGWPE can only use COM1 to COM9 and trying to change the USB serial device to use one of the three currently unused ports in this range resulted either in Windows complaining that the port was in use even though it didn’t show in Device Manager or the application saying that the port did not exist even though it did show in Device Manager. Eventually things seemed so screwed that I restored back to this morning and gave up.

Having restored the system and checked that everything worked again one more idea occurred to me. TrueTTY allows you to specify the exact sample rate used by the sound card, to compensate for timing errors. Instead of 11025Hz I tried 11000Hz and while the D710 and the VX-8 still decoded the packets the D72 still didn’t. I then tried 11050Hz and lo and behold, the D72 started decoding!

It’s impossible to make a suggestion that there is something wrong with a radio in the owners’ groups on Yahoo as so many people can’t bear to consider the fact that something they bought is anything less than perfect and will come up with any alternative explanation they can think of. So I’m sure that the problem I have described will be blamed on the AFSK modulation being slightly off-frequency which, of course, it is.

However in the real world a radio will be used to receive transmissions from people whose modulation is off and don’t know it or may not even have any way of adjusting it. A modem that is more tolerant of these deviations from the precisely correct will decode more signals than one that expects the modulation to be spot on and in that respect the VX-8GR is by far the most easy-going and most sensitive of all the APRS radios.

It’s just frustrating to hear braaaps and not see them decoded, so I think the Yaesu is going to be the one of these two APRS hand-helds that I hang on to.

I have just added a new article, Installing APRSISCE/32, to my website G4ILO’s Shack. It is a pictorial tutorial showing how to install the APRS client written by KJ4ERJ and get it running.

Over the next couple of months I hope to add several more tutorials covering different aspects of using the program and connecting it to a radio, in the hope that they will encourage more people to get on to APRS or at least use the information that it can provide.

I started up my APRS gateway this morning and noticed an unusual symbol on the screen. I clicked on it and discovered that WE7U had posted an object to mark the epicentre of a minor earthquake measuring 3.6 on the Richter scale that occurred about 20 miles to the south of here at around 2300z last night.

It was felt in nearby Workington and even across the water in Dumfries and Galloway with some people describing it as “scary”. We were completely unaware of it. But now I know what happened, I recall that just after we had gone to bed I heard a noise from the attic like someone was up there and stood heavily on the rafters. I said to Olga “did you hear that?” and she said she thought it was a heavy vehicle passing on the A66. So that was how the earth moved for us.

Yesterday I spent a couple of hours trying out aprsg – an APRS iGate that runs on both Linux and Windows which has been developed by Tapio, OH2GVE and Antti, OH3HMI and released under the GNU GPL.

The program has no user interface. Under Windows it displays a G icon in the system tray. All configuration is done by editing an INI file, in examples of which all the documentation is contained! Despite its relative simplicity there are a few unanswered questions about how things work, so some trial and error is necessary.

The unique feature of aprsg – as far as I know – is that it lets you specify filters to control what is gated from the internet to RF. You can gate packets addressed to specific callsigns or callsign blocks (using a mask) and this can be ANDed or ORed with area based filters (either a box or a circle centered on a point.) It was wonderful in this relative APRS desert to see local stations and objects appearing on RF and being displayed on my TH-D72 and VX-8GR. It was like being back in Prague again! This is not something you would want to do in an area where there is other APRS activity but for someone who lives out of range of any digipeater or gateway aprsg could make APRS usable and fun.

The program supports multiple RF ports and can do cross-band gating using the same rules. I didn’t try this, and did not understand how to set different call-ssids to the different RF ports. It appeared to me that the gateway and everything connected to it uses the same call-ssid, though this may be my misunderstanding.

A significant limitation is that aprsg only supports KISS TNCs (and AX.25 on Linux) but does not provide any way to send a script to TNCs that need a couple of commands to get them into KISS mode. It doesn’t support AGW Packet Engine, but those who don’t have TNCs might be able to connect it to a TrueTTY virtual TNC for sound card operation.

Aprsg provides no support for digipeating – a pity, the possibility of filter-based digipeating would be most interesting. It also doesn’t provide a local APRS-IS server for users to connect graphical APRS clients like APRSISCE/32. So you would need to connect your GUI client separately to APRS-IS using a different call-ssid to your gateway.

These limitations apart, aprsg is a potentially useful program for anyone wanting to set up an APRS internet gateway. It’s quite easy to get going and has a very low resource usage.

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.

The Metropolitan Police are denying that the incident in which a car carrying Prince Charles and his wife came under attack by student demonstrators occurred through a failure in radio communications. Reports that royal protection officers were using a different frequency to those policing the protest are “untrue”, the police insist. The two teams were in communication using email or mobile phones. They what?? Perhaps they had carrier pigeons as a backup.

It seems to me that someone needs to knock on the door of Scotland Yard and suggest that they need a tactical digital communications system on the lines of APRS. If the officers escorting the royal couple could have seen on a map display where the demonstrators were and exchanged brief tactical messages with other officers in the area, this embarrassing incident would never have happened. It makes you wonder just how competent our security forces really are.

I think I may have discovered one of the best kept secrets in radio. I have been thinking, off and on, about how to make a very low power 2m FM transmitter in order to get weather data into my APRS system wirelessly. A circuit using the Motorola MC2833P chip is quite easy to build, and I even have one in my parts box, but a custom crystal to multiply up to 144.800MHz would cost about £25 to be made which just isn’t worth it.

One day I was browsing looking at various APRS articles and came across a tracker someone had built using a VHF transmitter module from Radiometrix. I had come across this site before but thought that a) these modules were only for transmitting digital data not the AFSK that we use, b) they were not manufactured for amateur frequencies and c) they were not available in one-off quantities for individual private purchasers. I submitted an enquiry, stating that I was interested in purchasing one TX1 low power (10mW) module on 144.800MHz if the price was within my amateur budget, and was amazed to be informed that they would be happy to offer the module for £13.00 plus carriage and VAT, with a lead time of five days. In total it came to not much more than £20 which is amazing considering many professional electronics suppliers specify a minimum order value greater than that.

The picture of the module is much larger than it actually is – the pins are the standard 0.1in spacing. As I am nowhere near actually needing to use it at the moment, I hooked it up on the breadboard to give it a quick test. The module does indeed accept an audio input: as described in the data sheet you should bias the input pin and then feed it with audio at a couple of volts amplitude via a blocking capacitor. I lashed it up to my FoxTrak APRS tracker and a braaap was received and decoded by my 2m APRS gateway which was enough of a test to be going on with.

There are several other products with interesting ham radio applications on the Radiometrix website. The HX1 is a high power (300mW) version of the module I bought. With the addition of a PA I could turn my FoxTrak into a standalone tracker. Even by itself it would probably have quite a decent range from the fell tops. Also of interest is the SHX1 which is described as “a small multi-channel 25kHz narrow band VHF transceiver with up to 500mW RF power output, usable for 144MHz band amateur applications.” I think you could build a little hand-held transceiver with one of these, just for fun.

Many of these products aren’t in the online shop so you can’t find out the price or buy online, which is probably just as well as I could see myself ordering some more of these toys for something to play with over Christmas. I would certainly be interested to hear from anyone who has used, plans to use or has some ideas for using any of these little radio modules from Radiometrix.