Portable Operations #1 – Field mast

The objective for 2016 is to get out of the shack and into the wild with a radio. This has been on the agenda since day one, but like every idea there are teething problems, interuptions and cost implications!

That said we took one step closer today when I finalised my antenna mounting platform for use at field day events. This is a two pronged attack, giving me a mast I can mount an HF antenna on along with my BBHN node, which will give me Mesh access for WX, Cluster reporting and logging. While I mention WX have a look at this – blitzortung.org. It’s always useful to know how far away the serious trouble is!

So, on a bright and cheery Sunday morning I took a little trip to Fort Purbrook to see if my latest creation actually worked as it was based on a sketch and dimensions I was gifted and unfortunately I wasn’t able to actually get a hands on, prebuild examination of the trig point to get things straight in my head before I started hacking up my very limited supply of free plywood. Added to that, I have the woodworking finesse of dry rot, so the margin for error was slimmer than the shrinking exchange rate value of the pound!

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In the words of Shrek, “That’ll do Donkey, that’ll do!”

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When it drys out from the soaking with drizzle this morning I’ll give it a quick once over with yacht varnish to stop mould and the like setting in while in storage. The whole kit breaks down very nicely to a light weight bundle for transporting.

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An alternative 2m antenna

After busting a gut to get my Diamond X30 up in the sky I was slightly disappointed with the absence of 2m activity. Admittedly I had a cracking WBFM reception for commercial radio and the POGSAC pager things I have been playing with utilising an RTL-SDR dongle were much improved, but I seemed to be missing a trick.

From consulting with the mine of information who is Mike (G0JMI) of Alton Antenna Arrays it transpires that as good as the Diamond X30 is, like everything it has its limitations.

Basically, the X30 is very similar to other verticals and its radiating section is about 3/4 wavelength on 2m (or there-abouts).

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Above is the predicted vertical-plane radiation pattern for this form of antenna when used on 2m (145MHz) and you can see a bit of a gap at the lower bottom end where we would like energy to be if we are going to work stations at ground level.

When used on 70cm (434MHz), the vertical works as a 9 1/4 wavelength antenna and throws more radiations laterally making it better for working stations at ground level.  The predicted vertical-plane pattern for 70cm is below.

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The alternative 2m antenna to overcome this gap is a 2m half wave dipole.

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As can be seen from the predicted vertical-plane radiation pattern for a 2m (145MHz) dipole and you can see that lots of useful power goes horizontally to allow us to work stations at ground level.  This antenna on 70cm has a similar radiation pattern to the 9 1/4 wavelength type outlined above, so is good for that too.

The X30 as a 2m 3/4 wave vertical is good for working stations through satellites because of the amount RF thrown upwards.

As such, making a simple half wave dipole for 2m work, especially joining in the local club nets seemed like the ideal solution.

The components to build one were very few and far between – a dipole centre, two lengths of aluminium tube, some RG58 coax and half an hour.

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And there you have it! The hardest part was winding the 6 turns into the coax to make the choke-balun and getting it to stay there. If you’ve ever tried wresting an uncooperative snake you’ll know what I’m talking about!

Tuning the dipole down to centre frequency involved nibbling off 3mm lengths from the dipole arms until the SWR was down to 1.2:1. That proved a little problematical as I was relying on the FTL meter attached to my rig and when I got down to the predicted length all of a sudden the SWR which had been coming down nicely started to increase!

With a bit of assistance in the form of someone more knowledgeable, an antenna analyser and a trusty Oskerblock SWR200 dating from the 1970’s, all was eventually overcome. If anything it demonstrates that reliance on cutting edge tech to make things isn’t necessarily the way to go. The MFJ-269C antenna analyser wasn’t as accurate or reliable as we’d hoped and by relying on gut instinct and the two analogue meters of the Oskerblock we got there.

I’ve now got a very nice homebrew antenna that is great on both 2m and 70cm’s and can be used for both the local club net and satellite work!

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Another antenna joins the party

So as storm Abigail gave Scotland a good shoeing this weekend, the south of England decided to join the general weather trend to a slightly lesser degree. With this in mind it would have been the ideal opportunity to build one of the growing pile of constructional projects I’ve got sat on the work bench but no, this genius thought it’d be a good idea to stick another antenna on the side of the house.

The radio club were in the process of resurrecting the 2m FM net which is run on 145.250 +- using the Club Call M0GZN/A and it seemed silly to be missing out on the action simply due to lack of antenna. So I duely parted with some of my hard earned in exchange for a Diamond X30 from the nice people at ML&S. A trip to Nevada resulted in a mounting bracket, 5ft pole, a lot of RG58 and Type N connectors.

Now I’ve got no problem with heights but the absence of a suitable surface to plant the ladder and the growing gusts of rain and drizzle meant the gable end of the house wasn’t a fun place to be on a Sunday morning! I can safely say the Health and Safety Risk Assesment for this one went “Chances of coming out of this one unscathed – Rizla cigarette paper thin!”

That said it was slightly reassuring that, as the coach bolts tightened on the bracket at least it would take my weight if everything went south in a hurry! The idea of a prolonged stay in A&E wasn’t on the agenda that’s for sure. This time I borrowed/nicked a tool belt from a friend and I can safely say, despite looking like a complete berk and Super Mario’s taller cousin, it made life one hell of a lot easier at the top of the ladder.

The whole lot was firmly planted, feeder tacked to the brick work and through the wall into the shack just as the weather really turned nasty. I even managed to tidy the garden and deadhead the numerous tubs on the patio while I was at it.

To avoid any domestic or neighbourly issues, I intentionally sited the X30 on the far gable end which is away from the rest of the world, at a height equal to the TV antenna which is on the other side of the house. The row of trees close by aren’t ideal but they’re not mine and I can’t do anything with them. Any antenna is better than no antenna and when sat back in the garden all that can be seen is the top 6″. Anyway, who looks at the roof of the house when you’re laying out in the sun? Exactly!

M0XXF ‘Wasp Loop’ Antenna

The ultimate aim at the moment is to liberate all things radio from the confines of the man cave to the arena of fresh air. This needs a different radio (we’re aiming at an Elecraft KX3 but until the Elecraft fairies leave one at the foot of the bed . . .) and a portable antenna.

In the grand schemes of things I’m planning a budget for this project and that needs to include the antenna. The original thought was towards a Buddiepole.

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http://www.buddipole.com/ but with a price tag just shy of £400 for the basic kit, before you add all the little extras that you either want or need, that’s a big chunk of cash! So you’re left with the situation of owning a radio but still being confined to the indoors.

This set me thinking. I’d seen a demonstration of a magnetic loop by Graham (M0CYX) and was impressed with what a 2 foot diameter loop of copper wire could do.

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You can see the loop on the back of this rig and the reduction in size to a Buddipole is obvious.

For those of you (you know who you are) who may be scratching your head already at this one, here’s the science part.

A radio wave is composed of both a magnetic (H)  and electrical (E) field. These fields are at 90 degrees to each other and are in phase.

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The relationship between the magnitudes of the E and H fields is constant and one cannot exist without the other.

https://en.wikipedia.org/wiki/Radio_wave is worth a read if you want some background.

http://adam.curry.com/enc/20150119092647_article-antenna-mag-loop-2.pdf is another invaluable read on this topic.

The upshot of this is that you can receive the magnetic field as easily as the electrical field with the correct antenna.

Now I was trying to remember what a Wonder Wand Wonder Loop was called and was trawling the internet trying to find the cost (considerably less than a Buddipole by a factor of 4) when I stumbled across a few snaps of homebrew loops which got me thinking. Could I make one of these for cheaper than I could buy one?

My initial though was no, as a lot of the antennas people had made were quite serious engineering jobs utilising copper tubes or aluminium sections. Also, they didn’t seem very portable. You’d either needed a Transit van to move them around or you’d spend a month of Sunday’s bolting the required pieces together. Admittedly each to their own and part of my brief is quick deployment to maximise time on the ground or air as the case may be.

As much as I like building things, spending a fortune on the tools to make something or the raw materials, when you can buy something that does the same thing seems a bit defeatist.

Also in the absence of Elecraft fairies, I’m not spending anything on anything if it can be avoided! And then I stumbled across this.

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This is the G4ILO Wonder Loop from http://www.g4ilo.com/wonder-loop.html. Julian’s site is truly inspirational and if I could spend a month just sat reading it from front to back I would.

Now the list of build materials was incredibly short on the electrical front and the fixtures and fittings similar, which meant this could be a runner!

Why am I doing this when I haven’t got a portable rig yet? In the immortal words of Ferris Bueller “Life moves pretty fast” and there’s no point contemplating your navel when other sides of a project can be progressed.

The biggest problem for this build would be finding a suitable capacitor as my eBay and Google search crashed and burned in an instant. It transpires that variable air spaced capacitors are very much a thing of the past. The necessary component can be seen here to the right of the photo.

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Annoyingly I had a few of these as a kid when I made a crystal radio, but I can’t for the life think where they went as most of my junk has travelled with me over the years and I’ve still got components I bought with pocket money as a kid in my storage trays and racks.

That wasn’t very encouraging in the slightest and I was just about to consign the idea to the “forget it pile” when I decided to consult the mighty knowledge base of the FPARC Forum.

Light blue touch paper and retire! Talk about champions! In less than 12 hours I had offers of capacitors, reduction drives and lots of advice. All I can say is the inventor/engineer streak must be in most men as I’ve got piles of stuff in cases for the “I’ll need that one day” moment and it looks like the rest of FPARC are the same. Except they’ve actually got useful things. My radio scrap is nil and I need to start bin diving.

To anyone out there reading this, if you’re about to bin anything with a knob or dial on it, especially if it’s old and TV, Hi-Fi or radio related please, please, please can I have first refusal?

A rummage around the back of the garage resulted in a project box, fittings and the like which had been gathering dust. All this within 18 hours of my post on the forum!

OK, 24 hours on and we’re doing even better than yesterday! Courtesy of Mick (M0GWD) we have one reduction drive

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Rod (G4SPS) dug out a Johnson 167-152-9 single gang, air dielectric capacitor with a ceramic base, silver contacts and two  solder lugs. The part number reveals that it’s 11.6 to 202pf. As the man said in his email “Close enough for government work!”

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The only snag with arousing the interest of the assembled mass of FPARC is that it spurns a real ground swell of interest. Not a bad thing BUT next thing you know, there was a suggestion that we ought to hold a magnetic loop contest, so no pressure what so ever to get this thing right!

The all round nice guy Mike Parkin (G0JMI) of Alton Antenna Arrays had offered up another option from an old ATU he had laying around, which appears to be in the 200-300pf range and gave me other options.

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Another rummage around the garage had yielded even more bounty in the form of a nut which fits the thread on my camera tripod so I can build a suitable mount, number plate fixing bolt covers, M spec nuts and bolts in assorted sizes, Velcro, uPVC electrical conduit and a few more odds and sods.

At this rate purchases for this were going to be limited to the N7VE SWR Indicator Kit http://www.qrpkits.com/swrindicator.html , screw terminals, spade connectors and a few off cuts of coax which I hoped to be able to get from Nevada. Annoyingly I would have to buy the indicator kit as I’d no toroids or power resistors lurking in my stash and by the time I’d sourced them and paid postage it would have cost as much as a nice little kit that someone’s already put together.

That said I was thinking about dubbing this project the “Skinflint Loop” or “Scrounger Loop”. Not very catchy though!

That little conundrum was resolved the other weekend when I shot up to Mike’s on my bike to collect the capacitor. It was one of the hottest weekends so far and foolishly I cracked open the visor on my helmet to let some air in only to be rewarded by a wasp ducking in at 30mph plus and peppering my face with wasp venom in disgust at the Man v Wasp encounter. When I took my lid off when I got home my face resembled a chipmunk that had been given a free reign in the peanut factory! Just what was needed. That said the naming problem was overcome. The M0XXF ‘Wasp Loop’ was born.

Two weeks on and things hadn’t progressed very far due to a combination of things going bang elsewhere that needed fixing, the inconvenience of having to go to work and people on eBay listing item locations as “within the UK” only to find they were actually shipping from Guangdong Province, China. Not sure how that sits in the grand scheme of things but it generally inconveniences project progression!

The first stage was to mount the 350pF capacitor. Now this thing is a big old beast and is considerably heavier than the other bits and bobs I had accrued. The solution was to fashion a bracket from aluminium to support the mass robustly rather than hanging it on a few M3 screws and small angle brackets. As the case is inverted on completion, the whole weight would be hanging on very small screws with the real possibility that it could pull them through the drilled holes in the case and causing the tuning knob to catch on the case. The way to avoid this was to use anything larger than the small M3 screws I had in abundance.

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The larger size of the capacitor meant I needed a taller box than the one I had to hand. When the central spindle is rotated the air separated plates stand proud of the chassis making this thing bigger than anticipated.

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With a bit of work the mounting brackets started to take shape

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With some gentle filing the existing holes in the chassis of the capacitor will take an M4 machine bolt. This thing hails from the days of imperial measurements so nothing I’ve got fits and I’m not chasing down half a dozen imperial sized bolts.

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You get the general idea of how this will work. Top tip for this project is protect the bottom of the project box. This is going to be your sunny side up when done and with it sat on a workbench in amongst metal swarf will ruin the finish. Masking tape was used to cover it up at an early stage.

The idea of using the larger fixing got me thinking. The G4ILO article warns of the need to insulate the capacitor mounting screws where they protrude through the case and uses number plate fixing covers. Why not avoid the possibility of giving yourself an unexpected surprise with a stray kilovolt of electricity by using plastic bolts to mount the capacitor to the case? eBay came up trumps with nylon machine bolts.

The next snag to overcome was some form of dial or indicator. The problem with a reduction drive is the gearing ratio means that rotations of the knob don’t reflect the degree of movement on the device the other side of the gear box. With a sealed unit there’s a need for a pointer so you know where the capacitor actually is otherwise it could all become a bit frustrating despite the more intricate movement which results.

An unfortunate cock up with eBay (reliance on technology to do your bidding, literally can be fraught with mishap!) meant I waited longer than necessary to get my hands on one of these

It’s another type of reduction drive but has a nice metal pointer on it which means you can track what you’re doing and can mark the necessary frequencies for the antenna.

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A few stages on and we’ve got the capacitor sitting nicely on it’s mounting bracket, the reduction drive hooked up and a few case holes drilled. There’s a temptation to do a blow by blow photo log of this build but that would get a bit boring, so we’ll move on a bit. The thing is this has taken a good six weeks plus to achieve what, if you’ve got the time, can be completed in an afternoon! That said, the time scale has made this even more rewarding.

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This is the completed unit minus a few stickers, but you get the idea.

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A real fiddly bit was making a mount so that the whole antenna could be tripod mounted to reduce ground effect. Two snapped needle files later I’d got a suitable hole in the case to fix the correct sized bolt to attach to the shoe of my tripod.

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And there we have it, one unit at beta stage ready for testing. I used the same mini trunking support idea as the G4LIO project and found that where my box was slightly tapered in profile the mast leant forward making things unstable. A uPVC window packer was used to space the trunking at the top of case to restore the vertical orientation.

The best bit of this project was being able to let antenna expert Mike G0JMI give it the once over for me, only to find that without any modification whatsoever it worked. Not just worked, but was an absolute killer on 20 and 17 meters. Operation requires the unit to run through an ATU, but the antenna analyser images below show the great SWR readings.

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Successful QSO’s were made using 10W with LY3X in Lithuania on 17M USB reporting 57 and E7SE in Yugoslavia reporting 58; using 20W R90IARU in the Ural Mountains on 40M and on 20M OM3TWM reporting 57.

Points to note are that when tuning the unit hand capacitance really does effect the results, but by tuning slightly under, when your hand is removed the ATU can fine tune quite nicely. Also the feeder really does effect the unit. The capacitance of the cable noticeably effects the unit so I’ve made a dedicated cable to use with the antenna.

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I’m really pleased with the results of this project as it hasn’t been the smoothest of builds simply due to interruption but I’ve now got the means for portable work. All I need as a radio to plug it into!

I’ve got a mast!

To be honest I’ve been so busy chasing QSO’s all over Europe and Eastern Europe the past few months I’ve been neglecting my pile of projects and housekeeping, so now that the weather is good it seemed like a good time to do something about getting my 30 meter 1/4 wave counterpoise antenna off of the top of the rotten fence post in the middle of my back garden and up onto something more becoming!

Back in March I started hatching a plan based on the advice of Mike (G0JMI) from Alton Antenna Arrays. Mike suggested trying http://www.aluminiumwarehouse.co.uk/ as a source of cheap aluminium tubes to build a sectional mast. The original plan was to use a 2.5m length of 40mm diameter 16swg tube and a 2.5m length of 44mm diameter 16swg slotted inside each other to give the overall 5m height. The 44mm section is fixed in position by driving a circular stake into the ground and slotting the aluminium over the stake.

It’s a very neat and cheap solution compared to the prices you pay for bespoke masts from radio suppliers! The only snag I had was the absence of any decent lawn or earth at the point I wanted to site the mast to anchor it. The joys of concrete! I looked at trying all sorts of anchoring solutions until I had the inevitable Gru “Lightbulb!” moment. (If that just passed over your head, watch Despicable Me and all will become clear). I’d got a perfectly good fence post set in a Metpost socket anchored in God knows how much concrete at the far corner of the garden behind the shed. There was potentially enough of the wood available to attach a square section tube to it.

I decided on a 5m 1.5″ x 1.5″ x 16swg tube costing a whole £16. The pisser was then having to pay the same again for delivery but you can’t have everything! A quick rummage around eBay provided a nice end cap to keep things dry inside, a few dog bone insulators and 100ft of Paracord. The local builders merchant came up with a cleat hook, eye bolt and some M6 coach screws.

Yesterday I nearly wet myself at the sight of a courier carrying the largest loo roll innard known to man up the drive. I was expecting a strip of aluminium not this thing!

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Ironically it took more effort chopping the cardboard tube up to get it in the bin than putting the mast up.

Now naively, 5 meters doesn’t sound much inside my head, but when I held the tube up against the house it all came into perspective. Perhaps a shorter one would have done?

Now the whole idea of having a hobby is not to hack your neighbours off with it. Never has that been more true with amateur radio! There are huge great sections in the exam syllabus for the radio exams about EMC and interference and alongside that there’s the professionalism of the sport, which says wherever possible don’t go sticking a thing that looks like a 5 meter light sabre in your garden for fear of causing a bit of neighbourly angst! To coin a phrase “With great erections, comes comes great responsibility”. (I’m sure someone can correct that misquote for me!)

Liberal application of a hacksaw reduced the height to an item akin to a high level washing line, which is not an uncommon sight in the back gardens of the numerous back to back terrace runs in the local area.

Now the next hurdle to overcome was anchoring this thing down in a safe and secure manner. I genuinely didn’t want it to come crashing down in a storm on my neighbours let alone anyone else’s property!

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The weapon of choice to overcome this hurdle was a coach screw, more than one to be honest. Anchoring it in both horizontal planes meant it was going nowhere! Seriously, this thing is solid which is very reassuring.

Strangely, when I did my exam one thing that stuck in my head working through the Advance! course material was the paragraph about rusty bolt rectification. I don’t know why it stuck in my noodle, but it did because I then got a question on it in my exam, which was a banker! Then, last month RadCom had an in depth article on metallurgy including corrosion, rusty bolt rectification again! Now with all that in mind, preventing galvanic corrosion between the aluminium mast, steel fixings and so forth was top of my list. A top tip from my man at CP Fastenings was to heat shrink everything and place either nylon washers or insulating tape between surface unions. Worth the 5 minutes to do it, as in the salty atmosphere of the south coast of England, things corrode quite nicely with little encouragement!

So with all that in place and a few holes drilled we were off. Now typically, none of the other bits I had ordered had arrived so overnight a temporary lashup was made which could be easily undone when all the final pieces were to hand. Despite the 16mph gusts of yesterday the temporary fitting hadn’t budged! Again, reassuring.

Today, everything else was waiting for me on the door mat when I got home. So in no less than 15 minutes, everything was in place and the 30 meter counterpoise antenna was fixed to it’s new home, looking no more imposing than a washing line. I’m more than happy as I now have the ability to experiment further. My trusty 728HFA limited space antenna is hidden beneath the eaves of the house and works a treat, but admittedly being able to swing it through 90 degrees and run it away from the house and all the electrical noise it contains would be an interesting experiment. That’s for another day.

In the meantime, I can enjoy the rest of the summer sunshine / pouring rain beneath my new washing line.

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Stealth antenna install

Yesterday saw the arrival of a package from Alton Antenna Arrays! Today’s project was to get my Alton Antenna Arrays 728HFA 40m to 10m ‘special’  out of it’s box and out into the big wide world where it could do its thing.

So at about 0900hr I ventured outside to be greeted with an air temperature hovering just above 4 C and light drizzle/sleet! Not ideal antenna installing weather that’s for sure, but unless I wanted to wait until the spring it was time to “Man Up”.

Any author of guides or books  which talks about installing things at height would have had kittens but to be honest if you take things slowly and minimise the chance for calamity a solo install can be done. Don’t get me wrong I don’t have a problem with heights, but I do have a good understanding of the Law of Gravity and the idea of being the next case study in advanced stupidity on 24 hours in A&E was not top of the agenda! You know exactly what I mean don’t you?

“Barry, aged 56 years from Ilford was admitted to A&E after falling from his 20th floor balcony after over reaching while trying to abstract the electricity from his neighbours external power socket. He was putting up his 11 kilovolt Christmas light display dressed only in flip flops and a pair of boxer shorts at the time. Barry was discovered 4 hours later by his recently “purchased” wife Ting Tong, laying on the pavement in a pile of McDonald’s food cartons which miraculously broke his fall and saved him from any lasting damage.”

We digress! The plan for the antenna was to conceal it beneath the facia board on the rear south facing aspect of the house, so as to keep the domestic and social peace. I’ve got exposed roof joists beneath the weather boards and these made ideal attachment points.

I used 75mm vine eyes screwed into the joists and attached the antenna using cable ties.

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I piloted the thread holes with a bradawl and gently wound them into the woodwork to the depth of the thread which gives a 50mm clearance from the structural woodwork.

Cable ties were used to attach the antenna to these anchor points

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I was anticipating the length of the antenna to be much longer and was pleasantly surprised when the overlap at the other end was 4-6 inches. The dog bone insulator attached nicely with another cable tie to the plastic downpipe of the guttering to stop it slapping around in the wind more than anything else.

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I was hoping that 3 attachment points would be sufficient, but looking at the bird droppings beneath the eaves it was apparent that the local avian crowd used this as a hang out and the weight of a bird on the wire wouldn’t do it much good. As such I dotted a few more vine eyes along the eaves and made supporting loops from more cable ties.

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The only need for power tools came when the matching box needed to be anchored to the brick work

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I make no apologies for the quality of the photos, it was cold, grey and miserable out there, but hopefully you get the idea. All that was left was to neatly cable grip the feeder wire down the building so it joined the bundle of other TV and satellite aerial  cables running along the back of the house and all was done.

At the minute the cable is simply looping through my room window which is on a vent setting and can happily accommodate the 6mm cable without issue. Once I’m happy I’ll make a hole through the wall and feed the cable into the shack permanently. 3.5 hours work and no injuries! It’s hardly visible except for the small matching unit. Plugging the antenna into the SoftRock gave a nice wide spectrum and lots of extra signals which had been alluding me up until now. Happy days!

 

 

 

 

 

 

40m LPF built

Now seemed as good a time as any to get the final few bits and pieces sorted for the SoftRock ready for transmitting.

The 40m LPF was easy enough to build on a scrap of Veroboard before entombing it in its tiny aluminium sarcophagus.

Total build time one hour and I’m really pleased with the finished product.