Bicycle Mobile

VK4MSL/BM: The mystery of the bad antenna

Well, for a few weeks now I’ve been (metaphorically) tearing my hair out, trying to figure out why I had such bad antenna problems on VHF. HF, I still have work to do as right now, the RF just induces currents where it pleases, including in my microphone cabling, but that’s a different matter. VHF until recently had been rock solid.

I tried replacing coax, re-terminating leads, checking solder joints, replacing antennas. Yesterday, I re-wired the entire antenna system, doing away with the BNC connectors in the top box and hard-wiring the antenna mounts to the coax inside. Rode up to Ashgrove today thinking I had fixed the problem.

Nope.

Each bump in the road, I watched the S-meter graph move from S9 to S4 and back again.

What could it be? Why is it that it only occurs when I’m mobile, and not stationary? There’s a bad link somewhere, but where? No amount of jiggling cables was locating the problem. Finally today, I decided to take a peek inside the FT-857D.

Ohh, well that would do it!

I looked closely at the point where the N connector solders to the PCB. I noticed a small line around the wire where it met the solder blob. So I picked at it with pliers, and pulled it away from the blob: it was a dry joint!

Tomorrow, I shall know if this was the final problem. At least I don’t run full power on FM, my license only affords me 30W continuous, so the only time I do 50W is when I’m doing SSB at which point it’s only on voice peaks.

Update: It’s been a few days, the difference is like the difference between chalk and cheese. Prior to the fix my set was deaf as a post, and it’s not hard to see why!

VK4MSL/BM: Heard in Albany WA

This last week the local repeaters here in Brisbane have been rather quiet.

One repeater I used to use a lot has been acting up, and so rather than potentially try to exacerbate a possibly worsening issue, I figured I’d leave it well alone until it was fixed.

Another I lurk on, has been working fine, but many of the people I’d talk to, are away on holidays.

So, I figured I’d dust off my trusty HF whip and give the lower frequencies another crack. This time last week I was getting nowhere on 15m. Maybe wrong place at the wrong time (Aside: is there ever a right time to be in the wrong place?) and so didn’t get anywhere.

40m I knew worked on this particular antenna, so I’ve been lurking there… calling in on the Coral Coast net on 7060kHz in the mornings, and tuning up and down the band on the way home. I make note of my listening frequency via APRS-IS, see my tracker or look for VK4MSL-10 on aprs.fi.

I knew the antenna worked there, not perfect, but it did work. It works particularly well when the other station is equipped to pick up weak stations. Earlier this evening, I set out from my workplace listening on 7060kHz where I was this morning. I noticed it was chock-a-bloc full of stations north of us. Indonesia and surrounds by the sounds of things.

Couldn’t make a head or tail of what they were saying, so I moved up the band, stumbled across a couple of “local” stations chatting around 7175kHz. Turns out one was portable in Barcaldine, didn’t catch the name, but the callsign was VK2DQC, I think. (I didn’t write it down.) We chatted for a short while, but apparently my signal was up and down like a yo-yo.

No surprise, I started the QSO walking up Greer Street, Bardon, continued my next over riding down The Drive, Cecil Road and Bowman Parade then up through Sunset Park. Anyone who knows that stretch knows it goes up then down then up again then down. I finished the chat as I came down Monoplane Street, Ashgrove.

Tuning around, I found another pair talking on 7158kHz. Bob VK6KJ and Bruce VK2??. As they were talking a third station, Joe, W5?? called in from Florida USA. To say I was impressed would be an understatement, all three were coming in Q5, and signal strengths in excess of S6 in most cases. Bob was peaking S9.

Joe mentioned is misfortune of having some equipment destroyed in a storm, and this necessitating the replacement of a computer along with its OS. Apparently he’s not a fan of “Window 8” (as we call it at work). I did try to call Joe but must’ve doubled and wasn’t heard.

I did though, manage to make contact with Bob. He was located in Albany, about 400km south-southeast of Perth, and running 400W into a two-element beam pointed at the US. With my measly 100W and stubby home-made antenna, I apparently was registering a Q5S5 signal with the odd drop-out.

Clearly Bob’s end was doing all the work, but impressive nonetheless. Seeing as the evenings can be particularly quiet, I think I’ve found a new past-time to while away the hour-long trip home, stirring up HF on the deadly-treadly-mobile!

2013/08/05 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Public Syndication 0

VK4MSL/BM Mk3

Over the last year or so, I’ve done a number of improvements to the bicycle mobile station. I’ve kept meaning to document what’s happened, as a number of people have asked about the station, and not everyone gets to see it up close.

A big move was when the FT-290RII 25W PA died, I was using the FT-897D a lot, and that thing is a heavy lump of a radio to lug around. So I bought its smaller sister, the FT-857D with its remote head kit.

A second move was from the heavy 40Ah battery pack to a much lighter 10Ah pack. Then, in July last year, I bought myself a new pair of wheels. The ’09 model Boulder pictured earlier still gets regular use and is good on the road, but longer trips and on hills, it’s a drag, and the tyres are not good on dirt.

Thus I bought a Talon 29 ER 0… in contrast to the Boulder, this bike is designed with mountain-biking sports in mind, so a little heavier duty, better gearing and suspension. Sadly not dual-suspension … they don’t seem to make one that will take a pannier rack on the back like I require. Nonetheless, this one has been going well.

VK4MSL/BM Mk3: New and improved

Rather than buying an open basket like I did on the other, I went one step further, I bought a motorcycle hard top-box and mounted that on the back. Thus the FT-857D could live in there, sheltered from the weather. I later also bought pannier bags: my battery, some tools, spare tubes, visors for the helmet, etc, live in one bag, my clothes live in the other.

The station is otherwise, not much different to how it was in concept. The antennas now mount on opposite sides of the top box with right-angle aluminium. I still have to work on grounding for the HF side but even then, the station still delivers respectable performance on 40m.

On my way to BARCfest this year, I was being heard S9+40dB in Newcastle with 60W PEP. I’d have ran 100W, but due to the earthing problems, I found I was getting a bit too much RF feedback.

The 2m antenna is similar to previous ventures, just a 51cm length of RG-213 with the jacket and braid stripped off and a PL-259 plug soldered onto one end. It’s a simple design that’s easy to make, easy to fix, cheap and can be constructed from readily available parts. If you can make your own patch leads, you can make one of these.

VK4MSL/BM: 2m antenna. Just some RG-213 and a PL-259 connector is all you need

70cm remains a work in progress. In theory, a ¼λ antenna resonant at 144MHz should also resonate at 432MHz, as this is the ¾λ frequency. In practice, this has been a pain to tune. I basically just stick to 2m and leave it at that.

As for coupling the radio to the head unit… I could use the leads that Yaesu supplied. One distinct disadvantage with this is that it ties me into using only compatible equipment. The other is that the connectors are just not designed for constant plugging/unplugging, and the 6P6C and 8P8C connectors become unreliable very quickly if you do this. A solution was to make up a patch lead to go onto each end, and to use some standard cable in the middle.

Initially I did this with a 25-pin printer cable, but found the RF problems were terrible! Three lengths of CAT5e however, did the job nicely. Yes, I sacrifice one pin, right in the middle. 24 pins is more than enough. I allocate six pins on one end for the head unit cable; choosing the wires so that the connections are consistent at each end.

The other end, I have a standard convention for microphone/control cabling. The balanced nature of the CAT5e works well for microphone cabling on a radio like the FT-857D which was designed with dynamic microphones in mind.

The only other connectors I need then are for power, and for lights. Power I just use Anderson PowerPole type connectors, the 30A variety… and for lighting, I use ruggedised 6-pin automotive connectors.

VK4MSL/BM Mk3: Rear connections onto top box

At the handlebars, things have been refined a little… the switches and push buttons are in plastic boxes now. Here I still have to work on the front basket mount, this compromise of a former broomstick handle hose-clamped to the handlebars is a workaround for the basket bracket’s inability to clamp around the rather thick handlebars. This arrangement is fine until one of the hose clamps slips (which happens from time to time).

For now I put up with it. The controls from the radio are now mostly on the left side… Since the rear gear shift and front brake are on the right-hand side, I do far more with my right hand than with my left. Thus doing this, I free up my right hand to actually operate the bike and use my less-busy left hand to operate the radio.

VK4MSL/BM: Front handlebar controls

I mentioned earlier about HF… the HF antenna should look familiar. It’s actually the same one I’ve been using for a while now. Most distant contact so far has been into the Cook Islands on 20m. I’ve had successful contacts on 80m, 40m, 20m and 15m with this antenna. 10m and 6m are the two that elude me just now.

VK4MSL/BM Mk3: With the HF antenna

It is a little difficult to see the entire antenna. I did try to pick the angle to show it best… but if you look above the tree, you’ll see the tip of it immediately above the top box. Below is a close-up shot to give you an idea where to look.

VK4MSL/BM Mk3: Base of HF antenna

One big advantage of the new set up, is that night-time visibility is much better than before. On the front I have a LED strip which lights up the path maybe 2m ahead of the front wheel. Not a strong light, but ticks a box… my main headlight is on the helmet — people frequently assume they’re being filmed by it. On the rear however, is a different story:

VK4MSL/BM Mk3: All lit up

It doesn’t look like much in the day time, but it is quite bright at night. The back uses two LED strips mounted in behind the red plastic on the top box, and one can easily read a book in the light produced. Looking in the rear vision mirrors at night, the red glow can be seen reflecting off objects for a good 100m or so.

On my TO-DO list, is to mount switches to operate the brake light (just above the callsign). Options include reed switches, hydraulic switches in the brake lines, or strategic placement of micro-switches. I’ll have to experiment. The other electronics is in place.

As to the other bike? It’s still around, in fact if you look at the photo of the VHF antenna, you can see it in the background… along side the trailer I use when I do my grocery shopping.

I’ve done away with the basket on it, and gotten a second mounting plate, so the same top box fits on the back of the other bike, along with the same pannier bags, and same front basket. It has done about 2800km since I bought the Talon (mid July, 2012), the Talon itself has done 2617km.

Thus I’d estimate the Boulder is well and truly past the 10000km mark, probably closer to 11000km now. It’s still the primary means of getting around, averaging close to 100km a week and with a heavy load. Not bad for a bike that’s designed for a little recreational riding.

2013/06/09 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Public Syndication 0

VK4MSL/BM: Stationary test on 15m

Well, this afternoon I decided to fix a couple of problems with the bicycle mobile… firstly, the mounting of one noisy headlamp. I’ve re-done the mount using a more solid piece of plastic this time, so we shall see how it goes. No noise on HF so things are looking up there. I also fixed the headset connection which was causing speakers to drop out… the problem turned out to be in the headset connection on the bike, rather than in the helmet.

It was approaching 2PM and thus nearly time for the daily Travellers net on 21.185MHz USB. I’ve never made a contact on 15m before, but knew the antenna did tune up there, so I gave it a shot. Ross VK5KMH popped up with a 58 signal out of Adelaide listening… after a prolonged silence, I decided to throw a call out. Ross responded, reporting my signal into his station was also a 58 signal.

This was from the driveway at my home location, using 100W transmit power (not far from where I reached VK100WIA on 20m with a CB whip). So evidently this home brew whip works quite well on 15m. I have since brought the FT-897D inside and plugged it into my G5RV-like antenna, and after moving off frequency to tune, I notice Ross is still a 58 signal, so evidently my HF antenna doesn’t do much better than the whip does.

2011/05/01 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Homebrew Public Syndication 1

VK4MSL/BM: HF contact on 80m

Well, the antenna I tuned up in my last post, I can say, while it doesn’t work that great on 80m, it did get a contact into Victoria this evening on the AWNOI net. Terry VK2TEZ near Coffs Harbour gave me a 4-3 signal report, so still lots of room for improvement… part of that was due to static crashes from storms in NSW, but I think with a better tuned antenna, we should be able to get towards having a workable antenna. At the moment the autotransformer I use has ~95 turns, with output taps at 0, 25, 50 and 75 turns. I think one somewhere between 0 and 25, and/or some extra turns might help… so I might wind a new one and see where that gets us.

The headlight still continues to give me grief. An interesting discovery though this evening. Since the battery is no good, I’ve permanently mounted it to the bicycle frame. This was achieved by removing the plastic bracket which is used to mount the headlight on the handlebars or on the helmet mount (using a rubber O-ring), and replacing this with a bracket bent out of a short piece of aluminium. It fastens to the bicycle frame at the front right above the front wheel, using a bolt hole normally used for mounting rim brakes (my bike has disc brakes).

The upshot is that the headlight’s casing has a pretty good electrical connection to the bicycle frame. Turns out this is a big no no with these lights. Kiss goodbye HF if you do… you’ll get crap everywhere from 400kHz right up into the VHF. I’ll have to do some further investigation, but I found that if I insulated the case from the frame, it helped on the 400kHz and HF emissions. I think something parasitic is causing the 2m grief as this continues (that, or it’s less critical on the case being earthed).

For a while I thought it might’ve been something lurking around 415kHz… the standard IF frequency of most superhetrodyne receivers, but alas, can’t see anything there. Otherwise it’d explain why it appears to be everywhere. I definitely suspect it’s not supposed to be oscillating there though, so I think parasitic oscillations are the cause here. I’m slowly researching my own power supply for the LED in this headlamp, so its days are numbered.

The insulation was achieved by breaking a cheap plastic picnic knife, drilling a couple of mounting holes, and mounting the headlight on that. That quelled the HF interference quite a bit, and I was able to listen to the HF bands on my way into Brisbane. At least it was nice to listen to something other than that sodding wedding in the UK. (C’mon fellas, yes, great and all but can’t we just confine it to one station?)

I was concerned about the longevity of this arrangement however. And as it turned out, I was right to be concerned. It broke as I approached the Normanby Fiveways. I went over a bump, heard a crack, and noticed the headlight dangling by the power lead. I pulled over, threw it in the basket and grabbed the backup headlight. At least there was one on the helmet, a 1W LED, so I still complied with local laws for night riding. I didn’t have a mounting for the backup light, I just pointed it forward sitting in the bottom of the front basket, with it on flash as a warning to drivers.

Once at the destination, I reverted the headlight back to being directly mounted on the bicycle frame. Interference was intermittent, but when it was acting up, it did wipe out 80m with S6 noise. Not good when most stations are barely making S6 as it is. I wound up turning off the main headlamp as for the most part I could see where I was going, and I knew the route. As I got out of town this was less of an issue due to the lack of traffic, and of course I was on bicycle paths or the footpath for 90% of it. That at least allowed me to hear what was going on with the net.

The other flaw I had was that the helmet’s speaker connections were acting up… wound up unplugging the earpiece side of the headset adaptor and using the internal speaker. Thankfully I could still use the helmet’s microphone and the rest of the wiring harness… just not the speakers in the helmet. I noticed this as I pulled out of my street, in fact I was aware there was a problem, but now I know where the problem is now. I’ll get onto it tomorrow. And I’ll look at a better way to mount this headlamp in an insulated fashion as an interim solution to a power supply replacement.

2011/04/29 by Redhatter (VK4MSL) Amateur Radio AWNOI Net Bicycle Mobile Homebrew Public Syndication Thinktank 0

A headlight to avoid

If you ever decide to put any kind of sensitive receiver on a bicycle, you’ll want to avoid this ugly duckling of the bicycle lighting world:

Nitelights Illuminator 900

These lights are great from the illumination point of view, and they’re not badly priced either. However, from an EMC viewpoint, they stink. I was given one as a present some time ago. The first night I got it, I mounted it on the helmet, charged up its battery, then went to work the next day. That evening, tried using the radio on the bicycle as I rode home. The interference rendered the radio totally useless.

At first I couldn’t figure out why the signals sounded so bad on receive. I was stuggling to hear repeaters that were normally quite strong. The only thing that was new was the headlight. I got home, switched on the set in my room and tuned to 2m sideband, then put the headlight on flash. The tell-tale static from the radio gave away the headlight as being the culprit. Worst of all, the emissions weren’t conducted, they were radiated.

Since then I’ve spent the last few months trying to figure out ways to make this headlight less noisy. The following page serves as a notepad, and I’ll keep adding to this as time goes on.

Initially when I used it I kept the battery in my shirt pocket. This proved to be a fatal mistake, since the roughly ¼? power cable proved to be a very effective radiator of this interference. I found winding the power lead up into a tight coil and moving the battery to the top of the helmet right behind the headlight helped things a bit. Adding a 2.2mF capacitor in parallel to the headlight further reduced emissions to make it barely tollerable.

Then the battery pack died. After a few weeks of non-usage, the cells collapsed. So for a while the problem solved itself, I could no longer use the headlight. The headlight’s battery pack runs at a nominal 7.2V (typical 8V). Since I run a 12V supply on the bicycle, I set about making a step-down power supply that could drop my 12V supply down to 8V approximate to run the headlight.

Initially I tried using a LM7808 linear reg. This worked, with one major drawback: the linear reg got bloody hot. Turns out this headlight draws about 1A of current when at full brightness. That means in order to drop 4V, the reg was dissipating 4W of power. Ooops! Poor thing.

I designed a crude switchmode power supply to do the work. Using a voltage divider to provide a voltage reference, I used a LM311 comparator to detect when we were under voltage. The output signal from this would pull down on the gate of a IRF9540N MOSFET which acted as the main switch. Hysteresis was used to fine-tune the switching behaviour. Capacitors at both sides would smooth the waveform. 470µF was used on the input side, 330µF on the output (we still have that 2.2mF capacitor not far away). I also made liberal use of 100nF decoupling capacitors to try and control the rate of switching.

On the breadboard with a dummy load, my circuit performed pretty well. A fairly smooth output with a bit of ripple at high load. I mounted it in a box and tested it with the headlight, and presto, the headlight was back in service. I mounted both on the bicycle directly, so as to minimise cable length and therefore radiation.

Since now the radio shared a power rail with the light, I knew there was potential for conducted emissions to cause problems as well as radiated. The next evening I tried it out… 2m was lousy with the headlight turned on. The good news is that it wasn’t much worse than before, but it still rendered the radio useless at times, particularly if the signal was weak from the repeater.

Recently, I added some 470µH inductors in series with the headlight and my switchmode power supply. I also tried common-mode chokes to no avail. A 1mF capacitor has been added in parallel to the 470µF capacitor in my power supply to further try and reduce the noise.

Low-pass filtering on headlight: 2.2mF capacitor in parallel, 470µH inductor in series

Part of the problem was that I was shooting blind to try and find the interference. Today, whilst tuning up the HF antenna, I decided to experiment and see what bands this headlight had an influence on. To my (unpleasant) surprise, interference was severe right down to 80m. I used the spectrum analyser built into the FT-897D to hunt for the culprit, and found it lurking at around 400kHz. When the power supply initially starts up, it’ll be up around there, then it sinks down to 392kHz as the case warms up:

Noise from the headlamp detected around 400kHz

This appears to be the fundamental frequency for the switchmode power supply built into the headlamp. It would appear to have a fairly sharp square-wave type pulse, as it contains very strong odd-order harmonics. The same interference can be observed at around 1260kHz (3rd harmonic).

The fact that this frequency is so low, probably suggests it is being intermodulated with a parasitic oscillation at some higher frequency. This I have not yet found, the CRO showed some other hash over the signal, but I will need to do some further investigation, probably with a more sophisticated spectrum analyser than the primitive one found in my transceiver.

I’d be interested to hear from others who have had issues with these headlamps. In particular, interference to AM/FM radio reception or transceiver operation would be quite useful if the need to persue this with the ACMA ever comes up. The manufacturer of the headlights has so far been unresponsive to my queries, so in the meantime I can only recommend that people avoid using these headlights if they intend to use any kind of radio receiver whilst riding at night.

In the meantime, I’ll be chucking further notes here as I find more on this issue.

2011/04/17 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Public Syndication Rants 1

VK4MSL/BM: New HF antenna

Well, I figured I better post up pics and notes on the improved antenna design for my HF bicycle mobile station. I spent some time tuning it up today, and without resorting to the autotuner, I’ve successfully managed to tune up all bands available to me from 40m through to 6m. 80m still remains ellusive however.

The new design incorporates a version of the autotransformer used in the earlier attempt, using more turns of wire on the same size former, and multiple output tap points. This allows me to accomodate a very wide turns ratio to match the antenna to various bands.

VK4MSL/BM HF: The autotransformer

Band	Test Frequency	Primary turns	Secondary turns	Approximate SWR	Comments
80m	3.590MHz	1	90	Too high to measure	This seems to get the strongest signals. Autotuner is able to tune from here.
40m	7.120MHz	26	48	~2:1	+/- a turn on the secondary to cover the entire 40m band.
20m	14.210MHz	26	1	~1.2:1
15m	21.200MHz	26	27	~1.4:1	Slightly out, there is probably a better one.
10m	29.200MHz	26	27	~1.1:1
6m	53.000MHz	26	52	~1.2:1	+/- a turn on the secondary, able to hit VK4RBX with 10W from the driveway

On the top of the autotransformer are for selecting the secondary tap; one of 0 turns, 25 turns, 50 turns or 75 turns (caveat; I might be slightly out with my counts here). Having done this I think in hindsight I’d have been better off moving the 0t one down to maybe 10t instead, as there aren’t too many bands that seem to work on the 0t setting. The primary side is selected by means of a wire soldered on to a thumbtac. The wire wraps around the tube with a piece of balsa wood for the pin to stick into. You select the turn by piercing the insulation as you push the thumbtac through the wire and into the balsa wood behind. Crude, but it works.

VK4MSL/BM HF: Primary tap

In place of the CB whip, I have taken a fibreglass whip and cut it down, stripped the winding, and used it as a support with a base-load spring to take any shock loads. In place of the original antenna winding, is two sections of brass tubing which telescope out. This allows for an antenna that can be partially dismantled and reassembled on the run, unlike the other antenna which was permanently fixed at 6′ length.

VK4MSL/BM HF: Mark II

I have a third solid section I can insert in there too, which would further extend the antenna to 2.5m, but it becomes very top heavy when I do this. The antenna can extend to 1.6m length, or for portable use I can throw a wire up into a tree, or support it using a squid pole and connect that wire to the autotransformer output taps.

I didn’t make any contacts while tuning the thing up, although I was hearing New Zealand on 20m quite strongly, and on 10m I could hear the VK8 (Northern Territory) beacon going quite well. I tried a few calls on 28.390MHz, but had no contacts.

I’ve also re-inforced the antenna bracket. Prior to doing this the antenna would sway wildly from side to side. Yes, it meant the cars gave me a wide birth (something I greatly appreciate) but I fear had adverse affects on the signal, and probably was asking for trouble in the long run. Putting a brace between the two brackets seems to steady things up just a little bit, and now I can rock the bike side-to-side quite violently without the antenna swinging too far.

I’m yet to go mobile with the new improved station. Weather permitting, I shall give it a try Monday evening. I have a meeting with Brisbane area WICEN. Due to headlight QRM I may or may not be active while mobile, we’ll give it a shot, but I should be able to work portable once I get there.

2011/04/17 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Homebrew Public Syndication 1

New antenna

For a little bit I’ve been struggling with poor performance on my bicycle mobile station. It was an intermittent fault. Sometimes it’d work great, other days the FT-290R II would complain bitterly about a SWR issue, and receive performance would be abysmal. But then I’d set off anyway, get a block away, and the problems just disappeared. Or the thing would be working perfect, and I’d get down the road and it’d stop working.

Damn frustrating. Intermittent faults such as these are the worst kind to try and locate. I thought of all kinds of possibilities, but the one thing I hadn’t considered was the antenna.

Performance had been pretty patchy ever since the weekend before LCA. It was on the Saturday that somewhere between Annerley and Milton, I lost the ¼ wavelength stainless-steel whip that I had been using. So I spent that evening rigging up a SO-239 socket so that I could use the commercial antenna I had; a Nagoya NL-77BH that I bought at BARCfest in 2008.

I rigged that up, and on the Monday I did successfully make a contact from the bicycle on my way to LCA, but it was patchy. I did find a few glitches, so fixed those, and Friday I made a contact in the afternoon, but it was still pretty hit-and-miss. Not the consistent behaviour I got out of my ¼ wave at all. Okay, maybe the coax is damaged. Tried different leads, no dice. Recently I bought a front basket for the bicycle, and so I could put the FT-290RII in there. Ran coax back to the antenna, last Wednesday afternoon and Thursday morning it worked beautiful. However Monday it gave me no end of grief.

Suspecting that the weight of the radio pressing down on the BNC terminations may have damaged that section of coax, I grabbed a length of RG195 and terminated it with BNC connectors. Still no good. Using the SWR meter in the FT-897D, the impedance match was out by miles.

Today I had another look. I took the antenna off the bicycle and placed it on a mag-mount antenna base, and placed the base in the centre of an open garage door. So big ground plane, not much different to most cars. Checked SWR, still through the roof. Tuned to the Mt. Cotton repeater on the FT-897D, no signal. Pulled out a hand-held, perfectly clear 5/8 signal on its original rubber-ducky antenna. As I was unplugging the antenna base, I watched the signal strength suddenly shoot up and the radio crackle to life when the shield was disconnected (leaving just the centre pin). I had noticed a dead short before, but thought it was the antenna mount on the bike… something was up.

So, I grabbed a bit of solid copper wire, a PL-259 plug, and some offcut insulation. I made a new ¼ wavelength antenna, cutting it initially at 60cm. Swapped it for the NL-77BH and the performance was beautiful. Check SWR, and yes, it’s high, but then again, 60cm is waay too long. I estimated about 51cm and folded the wire over at that point, twisting the excess around the body of the antenna. Signal strength immediately went up two S points, and on checking SWR, it was significantly reduced. I moved it back to the bicycle where I tweaked it further.

Once happy, I cut off the excess, used pliers to fold the end sharply and soldered the folded end to the body of the antenna to prevent it hooking anything. Then used some heat-shrink tubing to finish it off so there were no sharp ends to poke eyes out with. The antenna provides a good match from 144 right through until 148 MHz at 30W using FM.

I haven’t tried a contact on the bike yet, nor have I got any pics to share, but the radios seem happy with it, and it appears to be hitting repeaters in the area once again, including Ipswich. Given it’s a good 30km between The Gap and Marburg (as the crow flies) with some decent hills to boot, that’s not bad going.

It would appear the additional complexity of these high-gain commercial antennas comes at a significant cost, they don’t like getting shaken to bits on the back of a bicycle. I’m not sure how repairable the commercial antenna I have is, it may be a case of throw the thing out, at which case I think any love affair I had with commercial mobile whips might be over. At least my ¼ wave antennas can be made for <$20 in about 10 minutes from parts I can buy in town, versus spending >$50 and having to wait for it to arrive in the post.

2011/03/09 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Homebrew Public Syndication 0

New toy

I picked up a few new toys recently. I’ve been looking around for a small microcontroller based device to act as a combined remote face / DTMF generator for my FT897D. The idea is that this device could interface with the FT897D via its CAT port, and allow me to adjust the frequency and mode, recalling the information from internal flash or an SD card.

The remote face would then be mounted on the front of the bicycle, and connect to the radio at the rear to allow easy bicycle mobile operation. An extension of this would be control of a separate 2m radio, and a GPS to allow APRS from the bicycle.

The idea was to have the memory work like a relational database. Rather than just recalling memory channels, and having a big long list, I could scroll through the repeaters by callsign, location (service area), or combined with GPS, proximity. Modern flash technology would make this easily doable.

Likewise, for DTMF, rather than having to carry around a cheat sheet or remember IRLP node numbers, wouldn’t it be nice to just be able to scroll through a node list by country/region/callsign, select one, hit the “Call” button, put your callsign across and have it automatically dial the moment you raised the PTT?

I don’t have the ability to manufacture PCBs of the standard required for ICs such as most 32-bit microcontrollers. SOIC is about as fine as I can muster, and prototyping services are expensive. Thus I was looking for a stamp module or premade board.

Luminary Micro (now TI) make a few nice ones, and during my work at Laidley, I got to use the LM3S8962 Ethernet/CAN evaluation board. One nice feature was that it had the JTAG built-in via a FTDI USB-serial chip. However, the licensing for the board support package irks me — despite their code being useless on anything other than one of their chips, they still see it necessary to modify the BSD license adding a clause that prohibits its use on non-TI microcontrollers. I had a crack at writing my own “free-software” Stellaris library, but haven’t gotten that far with it.

I happened to stumble on this board based around the STM32F103VET. They were being sold on eBay for about $60 at the time, so I decided at that price I’d buy three. ST’s driver library appears to be very liberal in its licensing (in fact they claim there is “no license”, I don’t know if this means “public domain”, or whether I treat it like BSD).

The LCD panel uses the Ilitek ILI9320 display controller with internal graphics RAM, and is capable of 18-bit colour. The board also features a RTC backup battery, Texas Instruments TSC2046 touchscreen controller and on-board RS232 level converter. The STM32 also functions as a USB peripheral, and can be programmed using the stm32loader bootloader script via RS232.

Interestingly, the LCD controller documentation states that no part of that documentation may be reproduced without written permission. I’m not sure if writing an open-source driver classes as “reproducing” the documentation (as I’d be making documented #define statements in C).

The devices come with example source and have a pre-loaded µC-GUI demonstration on them. So far I’ve managed to distill enough out of these sources to get working touchscreen, LCD and UART. I’ll probably start looking at FreeRTOS next and seeing if I can get a workable device going.

STM32F103 board running a simple "Hello World" app

Hello world application for STM32

Guess now I had better start planning my application. 🙂

2010/12/12 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Homebrew Public Syndication Thinktank 0

VK4MSL/BM: First true bicycle-mobile contact: ZL3SV

Well… it seems my tinkering has paid off. This weekend was the weekend of the International Lighthouse Lightship Weekend… and also a federal election.

On Tuesday, I bought a trailer for the bicycle … this is primarily so that I can transport groceries, etc… to home since I’ve got the place to myself for a few weeks and need to be independent. Being so low to the ground, the trailer is hard to see, so I made the decision to move the CB whip over to the trailer, not only does it now radiate a signal, but it also alerts drivers to the trailer’s presence.

I was up to 3AM figuring out how to mount this antenna on the trailer… but eventually I cobbled together a mounting, moved the homebrew autotransformer over, and hey presto… I had nailed the propagation and visibility problems all at once. SWR is still horrid with the CB whip on the trailer, but the autotransformer brings it down to a manageable <15:1 SWR, which the AT-897 can deal with easily.

On the way to the event, I had the station on 14.200MHz… I heard a Chinese station… a BT call, and also later, a New Zealand station. Didn’t make any contacts until I got to the Bulwer Island lighthouse (AU0003) where I made contact with VK5SR, Cape Jaffer Lighthouse (AU0007), registering a weak 53 signal.

On the way home this evening, I first started hunting for a 40m tap on the autotransformer… found one that gave me a 10:1 SWR on 7.080MHz… Okay, not great, but better than the >25 I’d get otherwise.

Around Bardon, I was hearing some VK7 stations, tried to make contact, but I was in amongst their noise floor. As I got to Ashgrove, I tuned around and heard VK3ARK, Cape Liptrap Lighthouse (AU0037). Managed to make contact, and initially registered a 56 signal, but quickly dropped off as I rolled down the hill towards St. John’s Wood… by the time I hit Royal Parade I had dropped off completely. They got that I was mobile, not sure about the bicycle bit… but never mind. 🙂

I travel to the end of the road, trying to put out a few calls, then when I join the bike path I pause, and have a tune around… a very loud signal on 7.145MHz just about blew me away. I listened for a bit as I cycled… it was Gary ZL3SV, in the South Island of New Zealand.

He was in contact with a US station in New Jersey at the time. I could just make out the US station, however Gary just about blew me off the bike… so I waited for a break and called in. 2 others also jumped in… VK4FMVC and VK3BOT. I was barely able to hear VK3BOT, couldn’t hear VK4FMVC (40m can be like that). Gary could hear me though… he was getting me a strong 58 signal. When I checked the S meter briefly, he was registering 59+. This was around 7:00PM (UTC+10).

I was doing 100W at the time… running off a 9Ah SLA battery. I suspect I’d be lucky if even half of that was being radiated by the CB whip… Gary mentioned he was using 200W into a 1500′ centre-fed sloper… undoubtedly an excellent system. I’ll have to see about sending a QSL card over to NZ. As I continued home, there was also a VK6 station that joined us on the frequency, however I didn’t get to make a contact there… and I was nearly home.

I don’t think I’ll make HF a regular habit on the bike, but I’ll consider doing it again sometime. I’ll also see if I can document the setup a bit more… as it’s showing a good deal of promise. This was one contact I really didn’t think I’d be able to make.

2010/08/22 by Redhatter (VK4MSL) Amateur Radio Bicycle Mobile Public Syndication 0

Bicycle Mobile

VK4MSL/BM: The mystery of the bad antenna

VK4MSL/BM: Heard in Albany WA

VK4MSL/BM Mk3

VK4MSL/BM: Stationary test on 15m

VK4MSL/BM: HF contact on 80m

A headlight to avoid

VK4MSL/BM: New HF antenna

New antenna

New toy

VK4MSL/BM: First true bicycle-mobile contact: ZL3SV

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