Tuesday, July 20, 2010

Misinformation

The web is a great way to get information about subjects like ham radio that you might never find if you had to rely on books. Unfortunately it's also a good way to get wrong or obsolete information. For example, people looking for advice on how to make their first contacts via amateur satellites will find many articles that explain in great detail how to work through satellites that have long been defunct - even on the Amsat website!

There are numerous websites that explain about SSIDs used for APRS. (An SSID is the numeric suffix to the call, for example G4ILO-7, which is used to distinguish an operator's APRS devices and also to give an idea of what type of device it is.) They are all wrong! Bob Bruninga, WB4APR, the inventor and ultimate authority on APRS, released an updated set of recommendations on 9 June this year to provide more flexibility for current usage.

The new recommendations are:

-0 Your primary station, usually fixed and message capable.
-1 Additional station, digi, mobile, weather station etc.
-2 Additional station, digi, mobile, weather station etc.
-3 Additional station, digi, mobile, weather station etc.
-4 Additional station, digi, mobile, weather station etc.
-5 Network sources (smartphones etc.)
-6 Special activity, e.g. satellite operations, camping, 50MHz etc.
-7 Handheld radios and other human portables.
-8 Boats, RVs or second mobile.
-9 Primary mobile.
-10 Internet gateways, Echolink, Winlink, AVRS, APRN, etc.
-11 Balloons, aircraft, spacecraft, etc.
-12 APRStt, DTMF, RFID devices, trackers etc.
-13 Weather stations.
-14 Truckers or other full time drivers.
-15 Additional station, digi, mobile, weather station etc.

These are recommendations and not set in stone, but they are intended to help people know what type of device or application is being used, particularly in situations where someone doesn't have a graphical map display and can't see an icon.

Due to these recommendations I am now using G4ILO-5 for my Windows smartphone running APRSISCE. My VX-8GR remains G4ILO-7. My main 2m station is G4ILO-0 or just plain G4ILO, and my HF station is G4ILO-1.

Of course, this page could also become out of date in the future so I am including this link back to the original document in case Bob should make any further changes.

Monday, July 19, 2010

Bill in VK

Regular readers of my blog may have detected a loss of interest in HF band operating over the last few months. I have got tired of listening to signals through the harsh noise that it is never possible completely to eliminate, I got bored with the sameness of contacts using PSK31 and I got angry at having to battle with the renegade ROS mode if I wanted to use Olivia or other digital modes. My hopes were set on Sporadic E on the VHF bands but this year's season has been disappointing with no major openings on 144MHz extending this far north as far as I am aware.

Most of my radio activity in recent weeks has been focussed on APRS, first on establishing a VHF gateway and in the last few days getting going on HF. As I haven't felt much like actually sitting at the radio making contacts this has proved to be a good way to make some use of my HF equipment, a mode of operation that doesn't constantly remind me of the limitations of using attic antennas from a poor and noisy location.

I recently set up my private Echolink node again. I now have a Kenwood TM-D710 transceiver, a dual band 2m/70cm rig with dual receivers, a built-in APRS TNC and support for Echolink. However I'm still using the FT-817 on low power into a dummy load for my Echolink node for now. Before I could run a public Echolink node I would need to buy a proper dual band antenna instead of the 2m Slim Jim I'm currently using and apply for a permit from Ofcom. I'd then lose the use of the Kenwood for local 2m contacts and WOTA chasing, while the number of stations that could actually access the node due to my poor location could be counted on the fingers of one hand. So despite its built-in support it doesn't seem worth using the Kenwood for Echolink.

The node was on yesterday afternoon and I was sitting downstairs in the conservatory with the TH-F7E having a contact with John G4LRS from near Sheffield. After I finished with John I was called by VK6FSBB (if I remember it correctly) a Foundation licensee from Australia called Bill. Bill called because he had heard that my home location was Cockermouth. He was originally from the Workington area (Maryport in fact, though he had lived in Flimby, Seaton and various other places in West Cumbria) but had moved to Australia 45 years ago. He had held a ham radio license for only eight months and I was the first contact he had ever made into this area.

Bill had played rugby for various local amateur teams and mentioned various employers he had worked for, though as an incomer to the area I didn't know any of them. When I tried to explain where exactly I lived, I realized that the town must have changed beyond recognition from the days when Bill knew it. Things like the A66 bypass simply weren't there.

I could have talked for longer, but dinner was nearly ready and Bill's hand-held was only just making it into whatever repeater he was using to access the Echolink network in Australia so sometimes he dropped out after a lot of loud hissing like an old analogue mobile phone call. It may not have been a direct contact on HF and it wouldn't count for any awards, but to be Bill's first contact back to the place of his birth after 45 years made this VK contact a special one by any standards, one to remember long after I've forgotten many humdrum HF QSOs.

Thursday, July 15, 2010

It's all down to your ears

There was a lot of excitement on the Elecraft email reflector over the fact that the majority of participants in the World Radio Team Championship 2010 (WRTC 2010) were using Elecraft K3s. There was even more glee when it was discovered that Scott Robbins W4PA, former Ten-Tec product manager, and Tim Duffy K3LR of Team Icom had taken K3s. This was like the President of Coca Cola serving Pepsi at his anniversary party!

There have not been many comments now the results are out, which show that the top two teams, from Russia and Estonia respectively, were using FT-1000MPs. The USA team of N6MJ and KL9A in third place used K3s, as did K5ZD and W2SC who came fifth, but the fourth placed S50A and S57AW again used FT-1000MPs as did the Lithuanian entry in seventh place.

So let's get this straight: the winning stations and several others in the top ten used a now obsolete radio that was introduced in 1996 which has frequently been criticized as inferior to the K3? I suspect the fact that many international competitors took K3s may have more to do with the fact that the Elecraft radio is small enough and light enough to be taken on an aircraft as hand baggage. And I suspect that the reason for the success of the stations using FT-1000MPs is that there is more to winning a contest than having a receiver with the best performance numbers.

Anyone want to swap an Elecraft K3 for an FT-1000MP? (Only joking.)

Wednesday, July 14, 2010

The End of the Internet

http://www.wwwdotcom.com/

For those who don't believe that the internet is flat.

Up the Amazon

The September issue of PC Pro (a British computer magazine) arrived today. Featured on the front cover was an article exposing the rip-off prices charged by music download sites. Madonna's Celebration (which I presume is a popular music album) would set you back £11.18 at MSN Music or £11.99 at Spotify but would cost you only £2.98 from Amazon.

Included with the magazine was a DVD which contained a free copy of Paragon System Backup 2010. As I didn't have any backup software for 64-bit Windows I thought this was fortuitous, so I decided to install it. But after handing over my email address in exchange for a free registration code it failed to install. The developers had used the ridiculously overpriced, overcomplicated and error-prone InstallShield (programmers will know what I mean) to create the setup wizard and only a few seconds into the install it threw up an error message about being unable to initialize the Javascript runtime and died.

I tried the obvious things like checking that Java was installed, running the installer in administrator mode, and even Googling the error message and trying the suggested remedy of registering the Javascript DLL, all to no avail. So I decided that I was not going to rely on backup software from a company that could not even produce an installer that would run on a brand-new computer, and consigned Paragon to the Recycle Bin (both literally and virtually.)

I spent a couple more hours downloading, being unimpressed by and then uninstalling a number of other free backup programs. I even discovered that there was a backup program included with Windows, but for some reason the version that comes with Windows 7 Home Premium has been hobbled by only being able to back up to writeable DVDs or removeable hard drives, not my network attached backup server. After being advised that the backup would take 6 or 7 DVDs I decided against it.

In the end I decided to stump up for a copy of Acronis, which most people seem to regard as hands-down the best backup software you can get. It can create disk images from which you can restore even if Windows won't run and it has a continuous backup option that backs up your files while you work so you can revert back if you mess up a file. It even has a "Try and Decide" sandbox that lets you safely try out software you aren't sure about to see if it will do anything nasty to your hard drive.

The Acronis website informed me that this paragon (small p) of backup software would cost £39.95. After checking some reviews, in my usual lazy fashion I typed "acronis trueimage" into the Google search box to find my way back to the website, and Google helpfully included three "shopping results" in its list of related sites. Included there was an offer of Acronis TrueImage Home 2010 from Amazon for £17.99.

Eh? I can buy online and pay £40 for an electronically delivered product the manufacturing and delivery costs of which are near zero, or I can have a physical product that has been mastered onto CD and put into a printed box, possibly with a manual, which has then been driven to a warehouse and stored waiting for me to buy, after which it will be put into a cardboard mailer and sent through the post to be delivered to my door, for less than half the price (with SuperSaver free delivery.) Sorry, I don't see the logic in that, but thanks very much Google and Amazon.

Tuesday, July 13, 2010

Android envy

I'm suffering from a severe case of Android envy. I was just checking the latest post in Jeff KE9V's excellent blog (glad you haven't forsaken the blogosphere in favour of podcasts, Jeff) which mentions in passing that Google has just released AppInventor, a free simple application builder for the Android platform.

What piques my interest particularly is that AppInventor includes building blocks that allow you to talk to things like the GPS, so you can write location-aware apps, perhaps even apps that are APRS related.

I own a Windows Mobile smartphone. I also own a currently uninstalled copy of Microsoft Visual Studio, which can create apps for the phone. I once wrote an app to sync the clock to an internet time server. But like everything to do with Windows it's all just too darn complicated and my ageing brain doesn't feel like getting to grips with it.

The AppInventor approach looks much easier and more fun. I see an Android in my life before too long.

Monday, July 12, 2010

Inspirational

My new work laptop came this morning. It's a Dell Inspiron 1764 with an Intel i3-350M(2.26GHz) Mobile CPU, 3GB of RAM and a 250GB SATA hard drive. It isn't the most portable laptop, having - like the Toshiba it replaces - a full-sized keyboard and a 17.3in. widescreen display. It looks and feels absolutely gorgeous, the screen is superb, the keyboard perfect for my fat fingers, and it's blisteringly fast. Click on the Firefox icon and the browser is there in a second or two.

What's more, the Dell doesn't cause any RF interference that I've noticed. The old Toshiba caused an increased level of hash that broke the squelch on my 2m FM receiver unless I cranked the knob round quite a way. Since I started receiving HF APRS I noticed that the Tosh caused a 3 S-point noise level on 30m as well, which all but prevented reception of any packets. So I am delighted with the new PC for that reason as well. I can now leave my radio station running all day as a VHF and HF APRS gateway while I work.

The old Toshiba had Linux installed on it early on in its life for security reasons plus the fact that Linux has some good web development tools. I was going to buy a PC with Linux preinstalled but I couldn't find what I wanted so I resigned myself to paying the Microsoft Tax. The Dell came with 64-bit Windows 7. I thought that I should try it under Windows for a few days just in case there was a fault and I had to send it back. But to be honest I think I may stick with Windows. It looks more polished than Linux, it's fast and I've already started to find replacements for the Linux tools I used. Firefox, which I spend most of the day using, looks and works exactly the same on both platforms, of course.

I certainly wouldn't choose Windows 7 64-bit for a shack PC as there are too many compatibility problems with popular hardware and ham radio applications. But for what I need to do to keep the business running it looks like being a good choice.

Saturday, July 10, 2010

APRS on the Wainwrights

I noticed today that Richard G1JTD had a GPS-equipped VX-8R with him on his activation of several Wainwright summits in the Fairfield round. I spoke to Richard on his VX-8R a fortnight or so ago when I was out with my VX-8GR and he mentioned that he might get the GPS option so as to do some APRS. It's good to see more APRS activity from the Lakeland fells.

You can see Richard's track captured from aprs.fi. As you can see, his position reports were only received when he was on the summits and a few other points on the highest parts of the ridge. This is inevitable given that the only digipeaters and iGates are situated around the edge of the mountains located at the homes of amateurs and not at any great height.

From my experience it's quite common to lose cellular data coverage once you get off the beaten track so smartphone based APRS isn't really much better in this situation. Running the GPS drastically shortens the phone's battery life so you are also likely to end up with a dead phone just when you might need it. I think RF based tracking is the best solution for taking APRS into the wilds.

It's a pity that the power requirement and antenna size for HF operation would make it impractical to use HF for portable APRS operation.

Thursday, July 08, 2010

On the road

The last couple of days I've been wasting way too much time tracking mobiles using the new Google Street View feature of aprs.fi, which since I wrote about it last is now live on the production server. I have been running a second instance of APRSIS32 linked to my K3 on 30m using the AGWPE soundcard modem. Surprisingly, I have found quite a few mobile stations beaconing their position on 30m and even more surprisingly they are often being picked up direct by my attic mounted MFJ magnetic loop. It's fun to follow these mobiles and see what they are seeing as they drive along, but I get a bit of a thrill when I see my station displayed as the one that gated their position report to the internet. I suppose it's a bit like reverse WSPR.

Yesterday and today I have been following Bernd DF8HL and his XYL Karin DF8HY who are touring Scandinavia an an old VW camper van festooned with antennas, as you can see from their website. It must be great to just tour in your mobile shack, going from one place to another, yet in touch with your friends by amateur radio. But Olga wouldn't agree, so instead I must content myself to do it virtually with the help of APRS and Google Maps.

Being taken for an idiot

I just received a phone call from the service department at Waters and Stanton who had just received the faulty helical antenna I returned to them.

I was asked: "What frequency did you use it on? It looks as if it as been used to transmit at high power on the wrong frequency."

Do they imagine that it would be possible to overheat an antenna in such a way as to melt the connector without having any effect on the antenna itself, leaving the connector impossible to attach to a socket? You would think perhaps the fact that the antenna was untrimmed and the top cap not placed in position would give the game away that I hadn't even used it.

In fairness, they did then agree that it must have been a manufacturing fault and they would send a replacement. But I was left feeling that I had been taken for an idiot. They didn't even have the grace to apologize to me for the inconvenience of receiving a faulty product.

Tuesday, July 06, 2010

No comment

I think something must be broken in Blogger. Two people posted comments today, one each to the two postings I made. I know this because I received an emailed copy of the comments. Neither of the comments are showing up in the blog. In the Blogger dashboard, one of the posts shows "1 comment" but when I click on that link I can't see it.

So, Paul and S.o.a.l., don't be offended. I didn't delete your comments.

I don't belieeeve it!

No, this isn't a post that was meant to go in my other blog One Foot in the Grave. But I just cannot believe the amount of bad luck I have ordering radio goods from suppliers.

A few months ago I wrote about what a difference it made to the effectiveness of helical "rubber duck" VHF antennas if they were tuned precisely to 145MHz and I described how I had tried to lower the resonant frequency of some helical antennas I already had that were too high in frequency.

A few days ago I discovered that Waters and Stanton sell a tunable VHF rubber duck with BNC socket that can be trimmed to frequency by the user. As I have decided to switch completely to BNC antennas on my hand helds I needed another so I decided to order one.

It came this morning, but when I tried to fit it to the BNC adapter on my antenna analyzer in order to start trimming it, it wouldn't go. When I examined the BNC closely I saw that the insulation had melted and deformed, presumably during the process of applying heat shrink tubing. So it is completely useless! You would have thought an "ISO 9001 Registered Firm" would have heard of quality control, wouldn't you?

I have written Waters and Stanton a snotty email containing a copy of the photograph asking if they would send me a replacement. Since I have no desire to incur additional expense sending the faulty one back I have also asked how they will reimburse me for the postage.

Save Analogue FM

Practical Wireless editor Rob Mannion G3XFD has been writing to radio clubs urging members to support a campaign to save analogue radio. However, the radio he wants to save is not ham radio but broadcast FM radio, which has been threatened with closure in the UK forcing users to switch over to the "new" Digital Audio Broadcast (DAB) system.

The much vaunted DAB was supposed to re-invigorate the UK's radio industry, provide a raft of new and interesting IP based services to audiences, permit the launch of new national, regional and local radio stations and generate new marketing revenue for radio stations. However, DAB is almost dead on its feet, as users have been reluctant to buy expensive new radios which in many cases offer poorer reception and fewer stations than they can get on FM. If this reminds you of something more amateur radio related you can probably guess where I am going with this.

D-Star was supposed to re-invigorate VHF radio usage, deliver a raft of new, interesting IP based services like text messaging, DPRS and file transfer to users, permit international, national, regional and local contacts and generate new revenue for Icom. However it is struggling to gain acceptance as people have been reluctant to buy expensive new radios that will provide access to fewer repeaters and fewer local contacts than they can get on FM and have been underwhelmed by the new features offered. Nevertheless the creeping D-Starization of the VHF and UHF bands continues, with the regulatory authorities now apparently refusing to allow new analogue repeater proposals whilst fast tracking D-Star applications through the system.

It does not seem to me to be beyond the bounds of possibility for the powers that be to decide at some point that there will be a ham radio digital switchover, that all analogue repeaters should be switched off and sections of the bands previously authorized for analogue FM use will be allocated to digital.

Perhaps we amateurs need our own campaign to Save Analogue Radio before it is too late. If you oppose the D-Starization of the amateur VHF and UHF bands, feel free to use the "No D-Star" logo on your website, your forum avatar and anywhere else that people might see it.

Monday, July 05, 2010

Threat to APRS, Echolink, D-Star in New Zealand

Steve, GW7AAV, spotted a news item on the NZART web page which states that the authorities in New Zealand have become concerned about IRLP, D-Star, Echolink, APRS and similar modes as they do not appear to fit within the New Zealand license conditions. Their concerns include the use of unattended transmitters and unlicensed digipeaters for APRS and amateurs based overseas operating a NZ amateur station via the internet.

It's easy to forget that other countries don't have such liberal licensing conditions as we do in the UK, although I would point out that operating an Echolink, D-Star, IRLP or packet radio (including APRS) node is not within the standard license conditions here either - you are supposed to apply for special permission. I know there are many who feel that is a good thing, and even that internet linking is not amateur radio and should not be allowed anywhere in the world, at all, but my opinion is that prohibiting it devalues amateur radio.

This policy is probably one of the main reasons why the APRS RF network is broken for messaging as many people (myself included) who are unwilling or unable to comply with the requirements for obtaining permission avoid the problem by operating receive-only gateways. Consequently we have the situation where smartphone-based APRS using mobile internet connections are more useful than APRS over radio.

I certainly believe that the point of our hobby is to use radio wherever possible, but where the internet makes possible something that could not practically be achieved using RF alone I think that we should be permitted to use it.

Sunday, July 04, 2010

Riding with Lynn

I've just been for a pleasant afternoon drive down to the coast with Lynn, KJ4ERJ, developer of the APRSISCE software, currently on holiday in Spain. No, I didn't nip down on EasyJet for the day. Actually I was following him on APRS using the Google Street View feature in the beta version of aprs.fi.

With the new software, when you click on a station you get the option to Track in Street View. If you do then the browser window splits in two, with the top half showing the view the person you are tracking sees, facing the direction he is going, and the bottom half showing the track on the map. It works pretty well. You just have to remind yourself that you are viewing images previously taken by Google, not live images!

This is beta software, so you won't find it on the regular aprs.fi just yet. But it's a pretty cool application, I think you'll agree!

VHF NFD washout

Conditions could hardly have been worse for the RSGB's VHF Field Day contest this weekend. Yesterday I worked a few southern Scottish portables on 2m and 6m, plus the Lincoln Radio Club station G5FZ/P on 2m, and that was that. There did not appear to be a shred of Sporadic-E on either 2m or 6m, according to DX Sherlock. 6m was so quiet my K3 S-meter wasn't even moving.

Today when I turned on the radio I tuned both 2m and 6m without hearing a single signal. The map on the right probably shows why. We awoke to heavy rain and gale force winds, and I immediately thought of those poor guys on hilltop sites with their guyed poles supporting their beam antennas. If the wind didn't force them to take the antennas down I dare say the rain and the poor propagation made them decide they might just as well give up.

This has been a really disappointing year for me too, VHF-wise. After working Spain and Portugal on 2m on two separate occasions last year - the last being exactly one year ago - I improved my antenna by 3dB and my output power by 6dB in the hope of doing better during this year's season. But I have worked nothing and as far as I know the sporadic-E this year has hardly been heard this far north. DX Sherlock showed that a couple of well-sited northerly stations managed to make a few contacts a few weeks ago and I fleetingly heard a station from Romania complete a contact and call CQ at that time, but that was that.

Something is becoming clear to me that I never realized when I lived in the south, which is that just a couple of degrees of latitude can make a huge difference to the amount of Sporadic-E you get. The season isn't over now but it must be on the wane and I'm soon going to be away from the radio for a couple of weeks, so it's looking as if 2010 is going to pass for me without any 2m Sporadic-E DX.

Saturday, July 03, 2010

D-Star's hidden blacklist

The QRZ.com thread resulting from the news about the French petition to have D-Star made legal has not degenerated into the usual flame war. This afternoon it produced this interesting post by Gavin, G0LGB whe makes some observations that are quite jaw-dropping.

Gavin claims that "Repeater groups are being persuaded by financial incentives, free or drastically reduced equipment, fast-track applications via RSGB/Ofcom, to convert their under used repeaters to D-Star." The logic of how converting an under used repeater to use a little-used digital mode will increase traffic escapes me. More likely it has to do with starting to establish a network by the back door in the hope of encouraging more users, after which the busy repeaters will come under pressure to change too. We are having D-Star forced upon us whether we want it or not!

The other worrying claim Gavin makes is that the repeater keeper has the ability to ban users, not just from the repeater but from the D-Star network as a whole. This would be fine if it was simply used to ban miscreants - though why someone would pay £500 for a radio just to swear or play music is also a mystery - but apparently people have been banned just for voicing opinions unpopular with the repeater owners (somewhat reminiscent of my own experience with the ROS digital mode!) This is possible because the system is digital - all packets of audio or data originating from you are stamped with your call so the network knows who you are and where you are (or at least which repeater you are in range of.)

I think that, regardless of the merits or otherwise of using digital voice on the VHF bands, D-Star is not the way to go. It vests too much power in the hands of one manufacturer, Icom, and in individual repeater owners. It's just unacceptable to have a situation that could result in you being barred from your hobby just because a repeater owner disagrees with your views. I suspect that the people who find APRS too much like Big Brother won't like this either.

Friday, July 02, 2010

SMA Failure

I'd heard about the famous fragility of the SMA connectors used on modern hand-helds but today I got bitten by it. I was using my RigExpert antenna analyzer to check the resonance of the stock antenna supplied with the VX-8GR (which I found to be rather broad) and thought I would check the antenna supplied with the Kenwood TH-F7E for comparison. That was sharper, but the SWR was high - the best match was at 160MHz. As I was unscrewing the antenna from the SMA to BNC adapter I heard a snap. When the antenna came off I saw that the centre pin was still in the socket of the adapter. Damn!

These SMA sockets are not meant for constant swapping of antennas. The centre pin is thin and fragile, and to make things worse the pin rotates with the antenna as you screw or unscrew it, subjecting it to a twisting action that must eventually cause metal failure. All it takes is for the female to be a bit tight, if you'll pardon the expression, and the result could be castration of the antenna.

So I've had it with SMA connectors. I bought two BNC to SMA adapters several months ago and the only reason I was still using the SMA antennas is that I don't have any short BNC antennas suitable for using with the radio on my belt. But now one of those adapters will go on the VX-8GR permanently.

What's most upsetting about this is that I've spoilt my TH-F7E which I was planning to sell, as the original antenna is now useless. So now I'll have to buy a new Kenwood antenna before I can sell the radio (£24 from W&S, eek!)

Is APRS Broken?

As I wrote yesterday, I have been experimenting with APRS on the HF bands (30 metres.) This morning I spotted a couple of mobile stations beaconing position reports, or more likely I was receiving the digipeated copies of them. I can see that position reporting on HF could be useful if you want to be tracked and are out of range of any VHF digipeaters or gateways, but HF stations with their much larger capture area and four times slower data rate really couldn't sustain many fast-moving mobiles sending position updates every minute or so.

APRS is meant to be more than just a system for capturing position reports using radio and I find the facility to exchange messages with ham friends and know that they received them (even if they aren't immediately able to respond) to be very useful. It isn't a substitute for conventional digital contacts, it's an additional way of communicating. However, unlike on VHF where you probably know the people whose calls you see on your screen, on HF there is no way of knowing whether someone wants to chat, or even if a particular station is attended. Unless the intention is to chat direct by radio, using HF seems to me to be an inefficient way of reaching the APRS-IS internet backbone. So apart from giving someone in the middle of nowhere an extra chance that their packets will be received - which would be a rather boring use of an expensive HF radio - I'm still unsure of the value to me personally of running an HF APRS station. The technology is interesting but the practical use eludes me.

Despite this I was still keen to try APRS over HF. As I didn't know whom to contact I decided to send a greeting to Lynn, KJ4ERJ, currently holidaying in Spain, who I knew (from checking aprs.fi) was online at that moment. I disconnected my APRSIS32 client from the internet so I would know that if my message was received, it would have been picked up on the radio.

The message went out on 30m, and was repeated several times as no acknowledgements were received by my station. In the meantime I decided to send a second greeting message to Colin, 2E0XSD. No acks were received for that message either. Eventually I checked aprs.fi and sure enough my messages had made it to APRS-IS through various gateways in Switzerland and France. They had even made it to their destinations and Lynn and Colin had both sent replies. But I never received their replies over the radio, either.

The screengrab shows a section of the raw messages list from aprs.fi which includes the paths of my messages as they were received on the internet. It appears that nearly all were received and digipeated by HB9MM-4. I'm not sure if that station also gated my messages to the internet.

The way I understand APRS to work, any messages sent to me (and any acknowledgements of messages sent by me) should be relayed back to me over RF by any stations that have heard me on RF. The acknowledgements and replies from Lynn and Colin were on APRS-IS and could be received by the HF stations that were hearing me. But they were not transmitted. I was receiving a strong signal from HB9MM-4 so it is very unlikely that the packets were sent and none of them were decoded.

What's the use of a system for messaging if it can't be relied on to work as intended? It seems to me that APRS is broken and is really only useful for collecting position reports where the traffic is all one way - to the internet.

Thursday, July 01, 2010

APRS on HF

A post about the French ban on D-Star on QRZ.com has predictably become a platform for everyone who dislikes D-Star to reiterate their views on why it should be banned altogether, not just in France. These reasons boil down either to its use of a proprietary codec or the fact that it involves linking radios using the internet.

I admit to toying with the idea of making a post on the lines of "what if internet linking of radios was banned worldwide? Wouldn't that be a real catalyst for innovation, to try to replicate internet facilities using entirely amateur radio RF based methods.?" But further thought as to what would be the effect on APRS if it were denied the use of the APRS-IS internet backbone made me realize that the effect would be catastrophic. The amount of traffic would be far too great to be carried over any HF network, while the number of hops needed using a VHF network to achieve worldwide coverage would also be far too many and far too slow. You might be able to do something using a sophisticated network of amateur satellites, but that would be far too expensive. While some uses of the internet do devalue the use of radio itself, in my opinion, many of them make possible things that could not otherwise be achieved. The internet is an integral part of APRS just as it is probably an integral part of whatever D-Star is meant to achieve.

Which led me to the question of what exactly is the point of APRS over HF radio? I understand the purpose of the VHF APRS infrastructure, which is to capture the messages from local APRS stations and pass them to APRS-IS. But given that it would be impractical for messages from one side of the world to be conveyed reliably to the other using RF, what is the point of APRS networks on HF?

I started off the day trying the latest version of Cross Country Wireless's APRS Messenger software. This is an interesting product in itself, in that it enables APRS traffic to use various PSK data modes, which are arguably more reliable on HF than the 300baud packet most people use. Unfortunately there are not many users. I switched to using 300baud packet and my screen quickly filled up with callsigns from all over Europe. But when I looked at aprs.fi to see its map of stations received by my station I saw only one.

The reason, I surmised (since I am far from being an expert on this) is that my client software, APRSIS32, is doing "the right thing" and not forwarding most of the messages I received as they had already propagated by the maximum number of hops. The one station whose messages I did pass on, F6KPH-4, had against it the note "Seriously bad path." Following this was the explanation: "This station is transmitting packets with a configured path of over 3 digipeaters. This causes serious congestion in the APRS network and errors when plotting the station's route on a map. Please consider using a path of WIDE1-1,WIDE2-1 or WIDE2-2, or even WIDE1-1,WIDE2-2 if you are moving very far away from an iGATE."

I don't really understand this WIDEx-x business, I just do what I am told. But I think I get the gist, which is that APRS messages sent over HF should be configured to take no more than three hops. If they don't reach a gateway by then, they will be lost, which is just tough luck, because the HF channels can't handle the congestion that would be caused by messages being rebroadcast more than three times.

Which brings me back to the question of what exactly is the point of APRS over HF for the average amateur? It is certainly interesting to see what you can hear using your own equipment. But if it is impractical for an RF based network to ensure that a message could get from Sydney, Australia to New York, New York without touching the internet, what useful purpose is achieved by transmitting and receiving APRS on the HF bands?