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- Written by: Alex M0TOT
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Please find attached some information on the buggy, ROVer, I built during the various 'lockdowns'. No radio licence required !! There is also a video clip of a slightly earlier version of the vehicle undergoing some kitchen-based testing.
Regards
Alex M0TOT
In the video below, you can also see some early operational testing taking place. The ROVer also has an FPV front-facing camera and 'headlight' LEDs installed. The video clip is in .avi format and is approximately 94Mb in size.
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- Written by: Maintenance Guy
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Refusing to pay good money for something I can build myself
It's been too hot of late to be grafting unnecessarily, and I'd rather spend time planning than throwing failed prototypes in the bin (though I do my fair share of that too) so I've been thinking deeply about what already exists that I could re-use for a simple low-cost tilt-over mast project. Hours of trawling through both eBay and my many spare parts bins as well as closely scrutinising the endless commercially available offerings followed. I came up with a few fancy but overly complicated designs and then was struck by my epiphany moment.
Don't ask me why, but I've always mused over what cool projects could be constructed with scaffolding and/or the modular Key Clamp fittings range. Yeah, sure - I know I'm weird, but there is just about every conceivable Key Clamp fitting imaginable. If I'm honest this is all born out of my frustrating inexperience with welding stuff. I've got all the welding gear and no idea, but that's for another time.
So I scanned the Key Clamp catalogue and came up with what looked like some suitable parts. I have to retrofit this system to a 1m tall ground post concreted into the middle of my lawn. With the camo tape that's applied it runs to about 44m OD. The fibreglass telescopic mast that I'm using is 48mm OD (very slightly tapered bottom to top, but only by around 1mm). That's about standard scaffold pole dimensions (48.4mm or 1 29/32" apparently). Lucky for me.
There are other ranges of Key Clamp fittings to suit 27mm, 34mm and 42mm tubing if that's what you need, but scaffold size is the most popular.
Before we go any further, when I mentioned the concept of this project on the 70cms repeater net last week, Russell asked me why I was building a tilt-over system for a telescopic pole. Good point.
Well, it's because it's going to be semi-permanent and I'm going to weatherproof all the joints, so de-telescoping it will be a major headache and I want to be able to drop it to the ground quickly and easily when Tomasz Schafernaker tells me it's going to get a bit sketchy out there.
Shopping List
Key Clamp handrail fittings type 173 female x2 (sourced from eBay - item number 263969449130 from seller pegasusindustrial)
Key Clamp handrail fittings type 173 male x2 (sourced from the same listing above)
M10 x 40mm bolts with nuts and washers of your choosing
Paint: Hammerite Dark Green Hammered finish (your choice of course, if required)
Shims if required. I purchased eBay item number 351775109744 from seller everyexhaustpart) and introduced it to my angle grinder. The seller offers to make three free cuts for you, but they completely ignored my cutting request. Annoying.
The Plan
So, here's the plan: A simple bottom swivel, and an equally simple latching mechanism at the top of my (existing) 1m ground pole which will employ a quick release wingnut and bolt.
I'm going to need some split shims to take the existing 44mm OD pole up to the 48mm required for the fittings, so a couple of those were constructed out of stainless steel (48mm OD is a common size for car exhaust tubing). This tube has a 1.5mm wall thickness and therefore an ID of approximately 45mm - near enough for my application.
Some Fettling Required
I ordered the Key Clamp fittings a little bit blind. I didn't know if they would swivel through a full 90 degrees, but it looked close so I took a punt. Turns out I didn't receive the fittings as per the eBay listing photos anyway, but no matter. The reality is that they achieve about 88 degrees, and so I took a little at a time off with the bench grinder until I had the full movement I needed.
I ground away just that part of the male fittings that was coming into contact with the corner of the female part. You can see from the photo that it amounted to around three millimetres - down level with the edge of the protruding tab. While I was about it, I smoothed out the bores to remove the high spots of zinc, just to stop them chewing up the surface of the pole/mast unnecessarily. It was an easy job with some coarse Emery paper.
Never let it be said that I'm anything if not a stainless steel fixings freak and I've built up quite the collection, so M10 x 40mm Allen head bolts and washers were liberated, an M10 nyloc nut and a stainless wingnut too.
A test-fit of everything looked promising, and everything worked as expected without any fouling, which was a relief. Let's face it, you can never guarantee that some unforeseen obstacle won't arise that you just hadn't considered.
Fortunately, this good news meant that the next step was to give everything a coat of dark green Hammerite paint (rust protection where the grinding took place, and to help tone down the visual impact).
I applied one coat in two stages over 48 hours. This stuff is very forgiving, but it's not a quick-drying paint and you'll need some spirit-based brush cleaner. The male parts I painted internally too, as I knew I had enough clearance.
Finishing off, the bottom of the mast was wrapped in a few turns of back electrical tape (just to protect the finish and tighten the fit very slightly) and then the bottom grub screw was just done up finger tight. All the grub screws got a smear of Teflon grease before assembly. The female fitting that sits at the bottom of the fibreglass pole comes manufactured with a large hole in the casting, so water drainage won't be an issue. Shims were fitted to the ground pole and the clamps were tightened down firmly. The stainless shims allowed a really good clamping force to be applied. No chance of them coming loose accidentally. I would have complete confidence mounting a 10m alloy mast in this way as long as the concrete base was up to the job.
The final fitting which clamps to the fibreglass pole a metre up from the bottom was originally just going to be left finger tight too, but at the last minute I decided to engineer a little slipper shim to spread the load of the grub screw and stop it cutting into the pole over time. Just enough to apply some grip and to stop the whole thing rattling in the wind. There's also a photo of this part once it's fitted.
The 49:1 transformer will clamp around the fibreglass mast just above this point. I'll cover that in a future article on the actual antenna build itself.
The Jubilee clip (or 'hose clamp') on the fibreglass pole is to prevent the pole from lifting up out of the base fitting. Not sure how that could happen, but better to be safe than sorry. This obviously won't have any function while the pole is being lowered from its vertical position, but the weight of the pole and the close control of the mast-master means that's not a problem that I've encountered thus far.
Here's the completed bottom swivel. Take care not to overtighten the nyloc nut if that's what you choose to use. I overcooked it and had to cut the whole thing off with the angle grinder as the nylon insert can form a perfect wedge between the threads and no amount of force will free it. This is therefore Take #2.
The 'old' radial wires seen in the last picture will soon be combined with two 4 foot copper earth rods and will be connected to the counterpoise of the matching transformer and will also provide an anti-static ground.
There you have it. If you're not worried about using stainless steel parts or painting the end result, you can get yourself an extremely robust tilt-over mast base for less than £25
Berni M0XYF
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A few weeks ago, I posted an article on an RF choke I had built. I was very happy with the results when using it in the shack on my Cushcraft trapped vertical antenna. Much reduced noise levels, and also slightly improved reception reports when using WSPR and FT8. Not sure exactly why that was, but less RF in the shack allowed better manual ATU tuning I suppose, and also less noise being transmitted with the data signals, I'm going to surmise. So all good and I was ready to run some more objective tests. Then came the antenna change to an End-Fed Half-Wave. Apples should be compared only to apples, so I cleared the partial observation fluff from my head and decided to start any comparative tests from scratch using alternate fruit.
The antenna is not properly installed yet - it's awaiting installation of a second supporting mast, but I couldn't resist seeing if it was useable and it absolutely is. Much better results than the vertical it has replaced. But there was a new problem which I didn't really expect. A heap of RF in the shack. Just what my RF choke was built to avoid. Disappointing. All my USB peripherals began playing up - a sure sign of unwanted RF. I'm not too concerned at this point, as the antenna is going to be raised much higher, and I'm only getting problems when using more than around 60W on bands where the SWR is less than ideal. Still, the plan was always to mount this choke outdoors, and then to potentially install a second one at the transceiver end of the coax as well. This is what my guide and mentor Ian GM3SEK recommends anyway, so I'm just going to push on with my plans at this point.
So step one is to mount this enclosure outside. I had a Male-Female-Female-Male PL259/SO239 join in my feedline anyway, where some idiot cut through the coax with a pair of edging shears earlier this summer, and I didn't want the choke too close to the antenna so this seemed the perfect place to insert it.
Off to the workshop to find, cut and fold a suitable 2mm sheet of aluminium and form it into the above bracket. M5 x 16mm stainless button-head Allen bolts screw straight into to mounting holes on the rear of these excellent Fibox enclosures. The holes are untapped, but M5 bolts self-tap a perfectly adequate thread in the housing and would tighten up way more than the (approx. 3Nm) torque that I used to solidly secure the mounting plate to the back.
One other modification I made to the enclosure before relocating it outdoors was to add a really neat little pressure compensation valve to the underside of the unit. It only requires an 8mm hole.
I tried hard to find these two-way pressure valves in the UK, but to no avail. I had to source them from HF Kits in the Netherlands which is fair enough, but the £13 UPS shipping cost was tough to swallow. They did arrive within a couple of days however, and as I felt bad about the postage being more than the parts, I ordered loads of other HF goodies to make myself feel better...
The valves (part number RND 455-01100 if you want to try and source them elsewhere yourself) are there to solve the potential problem of the pressure differential between the inside and outside of the IP66/67 enclosure as the internal coax and toroids heat up and cool down with normal use. If you just punched a hole in the enclosure, it'll just fill up with spiders and moisture over time, so I've been told.
Another little job completed, and on to the next one.
Berni M0XYF
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- Written by: Alan G8YKV
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The idea is to locate the hidden transmitter by means of radio direction finding. The person with the hidden transmitter transmits a signal on a set timetable on a previously announced frequency; be aware of last minute frequency changes due to interference. The trackers then have to locate the hidden transmitter by measuring the strength of the received signal from various locations that they decide to travel to between transmissions.
What do you need to go Radio Direction Finding?
- A means of transport
- Small beam antenna
- Mobile (or preferably handheld) radio for the frequency being used
- Map, normally OS Landranger Series, for MSARS we tend to use map#198
- Pencil, ruler and compass
- Variable attenuator is nice to be able to reduce the received signal when you get close.
What do you have to do?
The trackers normally start from one location, for MSARS, Cyprus Road Car Park is usual.
Make sure your radio is tuned to the correct frequency, and on the first transmission swing the beam to get the maximum signal level.
Mark the direction of the signal on the map with the aid of a compass if your sense of direction is not good. From here proceed to another point where you can park up safely, preferably 90 degrees from the direction of the signal and take another reading when the hidden transmitter transmits for the second time.
Repeat this a third time and you should have a triangle at the crossing points of the pencil lines. The transmitter should be in that area, but beware, 'it ain't necessarily so' - signal reflections can cause havoc!
Repeat the measurements until you find your target. The stronger the signal the more attenuation you can use. If you do not have access to an attenuator you use your beam horizontally, or remove the antenna all together, just using the handheld if you are very close but cannot find the transmitter.
You may need to abandon your vehicle in the latter stages if the target is very well hidden.
The person with the transmitter should be located in a publicly accessible area, but not necessarily in plain sight.
This is not an exhaustive guide but an insight into how to go about it for the first time.
Good Luck
Alan G8YKV
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Construction time again
Wheels, sliced bread, gravity. No point in trying to re-invent them. I'm not creative enough or committed enough to publish ground-breaking new research, discover fundamental truths about the human condition or reassemble a disassembled clothes peg. I do like to build and own nice things though, so my philosophy in this regard comes down to seeking out the very best of other peoples' work, and then copying it. I'm very happy to give all the credit that's due, as long as I get to keep the shiny thing that I produce.
Thankfully, in the amateur radio world, I'm discovering that this approach works out pretty well due to the unselfish and benevolent nature of the people that wear the mantle.
I came across a chap called Ian White GM3SEK giving a lecture on good RF housekeeping at an RSGB convention. It was very inspiring, and I built one of the mains filters he championed. I'll write that up another time, but his website led me to rediscover the work of another guru, Steve Hunt G3TXQ, who also had an impressive website. I remember it well, because Steve is sadly no longer with us, and he rather emotionally wrote about his deteriorating health on his blog. You can view the whole site at www.karinya.net
It's great that the site has been kept operational by those he left behind, as it's a really positive legacy. Highlighted there is one of the best technical papers I've read during my training, which I'll link to at the end of this article. It's on getting the most out of an RF choke across the amateur HF bands - hence this project. Why wouldn't you build one? Give yourself the best chance, I say.
I'll let you read the paper in your own good time - it's almost compulsory I would suggest - but here's the spoiler.
Just take a moment to suck all that up. What a great reference image. Unless you have specific requirements below 7MHz, just build the best. Nine turns of 50Ω coax on three FT240 52-mix ferrite toroids. So I did.
Parts list
Ferrite Toroids: Fair-Rite 52 mix 12.7mm x 60mm - available from Mouser
Coax Cable: TWO metres of RG142 High Power 50R Coaxial Cable - available from Enigma-Shop
Enclosure: Fibox PC 95/75 HG 100mm x 100mm x 75mm in UV Stable Polycarbonate - available from Farnell
Coaxial Sockets: Amphenol 83-1R (SO239) - available from Farnell
Stainless Steel M3 nuts (nyloc) & bolts: eBay, Amazon, wherever.
Get on with it
I'm not going to drag this out.
Apply a few drops of super-glue between each of the toroids and stick them together. Let it dry for a few minutes. You can tape them with something like PTFE tape instead if you think you might want to re-use them individually for something else later, otherwise this becomes a permanent marriage.
Why did I choose RG142? I don't intend to run a lot of power through this, but it would nice to have the option in the future. I also don't want to ever have to worry about how hot it's getting, so I went with the high-power capable option given my limited knowledge about these things. Now, to make life a little bit easier for myself further down the line, I decided to solder the 3mm shield tag (which bolts to the SO239 chassis-mounting point) before I started. I'm not sure this made any difference to be honest. I was worried that soldering the relatively small diameter RG142 core into a big 'ole SO239 socket was going to be tricky, mechanically speaking. Turned out not to be the case at all. Other factors would make this seem like a walk in the park. More on this later.
Wind 9 turns of the coax around the tri-toroid creation. You can wind it quite tightly without risk of 'collapsing' the dielectric and causing a pinch-point. I used a 'crossover' mid-wind to allow the two 'tails' to stick out on opposing sides of the resulting choke.
Don't forget, each time the coax passes through the centre equals one 'turn' - whichever orientation or winding pattern you use.
You may want to avail yourselves of the extra hand offered by numerous cable ties. Whilst winding as tightly as you need isn't an issue, having the whole lot unravel in an instant if you let any part of it go is a distinct possibility. Employ the first cable ties early, liberally, and as soon as you get the ninth turn completed. You can always snip off those you don't need later.
Size matters
So, I know you counted the turns, right? Because you're reading an article about winding an RF choke? Sure, I get it. I can count too, and my choke only has eight turns. I could have left it - I'm sure it would probably have done a reasonable job, but I'm just not made like that. One metre of RG142 isn't quite enough for nine turns on three toroids. Unfortunately, at my chosen supplier, it's only sold by the metre, so make sure you order TWO metres like I did at the second time of asking.
OK, now let's put that lot aside and turn to the enclosure work.
I should say that I chose this box because I liked the construction quality, the sturdy lid-clamping bolts (they may look flimsy, but they are actually really substantial, and are semi-retained in the lid to avoid misplacement) and the IP67 rating. I also spent the additional money on the polycarbonate version as I want the option of leaving it outside for an extended period of time.
Mark and drill the enclosure to take the SO239's. I chose to fit mine in the middle of the lower half of the Fibox enclosure. With hindsight, it may have been better to fit them higher up to make it easier to solder the SO239 connections - I'll never know now. I used the trusty step drill to punch the two 16mm holes (I didn't quite drill the full depth - just enough to properly seat the sockets) and a 3mm drill for the mounting bolt holes. The polycarbonate machines well - it's fairly hard material. If you don't have step drills, then you should consider getting a set. They are just so useful for all manner of things.
Ah, and it was all going so well...
Bringing the whole lot together was a bit of a nightmare. I'm not really sure why it was so hard. Maybe the box wasn't quite big enough, or that RG142 wasn't the right choice of coax. It's certainly a handful to work with once coiled. I also found that the most frustrating part was soldering the centre core of the second socket connection. Not enough room to work, the soldering iron kept touching the box (burning polycarbonate - aromatic...) my fingers (past caring at this point) and the plastic dielectric and outer protective coax sleeve.
I gave up when the centre core snapped off at the end of the exposed dielectric for the third time. It's really brittle - you only get to bend it twice before it breaks off. My solution was to cut two additional sections of the inner core out of the spare coax I had, and pre-soldered these to the SO239 and the second shield tag. I then installed the second SO239, and finally made the two connections where I could get to them (and see them, more to the point!)
It looks a mess, but there is sufficient clearance between the signal core and the braid at all points, and the joints are electrically sound. Basic continuity and isolation tests checked out OK.
Couldn't wait to get the lid on, so that no-one will ever see what's inside. I'm naturally self-critical, but maybe I'm being a little bit hard on myself having seen the inside of similar offerings from the likes of MFJ etc. Some of that stuff is properly embarrassing. Nonetheless, I'm going to re-make this entire thing at some point. I may try an alternative coax type, but the first thing I'll try is just to mount the toroids at 90° so that the coax 'tails' are naturally pointing straight towards the SO239 sockets. Physically there is just enough room vertically to do this, and the lid would then hold the guts firmly in place too.
Well, at least it works - that's the main thing
I've only performed some perfunctory testing to date. I'll do some objective testing over the next few weeks, but already I can notice a significant reduction in noise at the receiver. The choke is currently installed at the radio end of the feedline, but I may insert it in the middle (outdoors) and then also try it at the base of the antenna itself to see what difference it makes. I might even put one at either end eventually. Other immediate effects I've noticed, are seemingly much improved hit-rates to the Americas, Australasia and the Gulf states (although this could be improvements in the band conditions themselves on both 20m and 40m) using high duty cycle modes like FT8, JS8 and WSPR - with no discernible heating of the choke coils even at 100W input power. I'm sure I could hear more people on the 80m net this morning too, so I'm hopeful of some real-world improvements. Manually tuning my MFJ-949E was a lot simpler too. Touching the tuning knobs and chassis whilst making adjustments no longer causes a noticeable fluctuation in the reflected power levels, so I'm thinking that's down to less RF floating around the shack. I'll have to experiment with switching the choke in and out of line on various frequencies and report back, but it's looking good so far.
Here is a link to Steve Hunt's excellent paper: High Performance Common-mode Chokes - first published in Radcom Plus May 2015
Berni M0XYF
