Construction Archives - Page 4 of 4

Custom coax connector exterior wall mount box

I decided for home I wanted a box just outside where my radio sits that I could plug different antennas into easily, so I looked for a tidy way to run antenna feed lines through the exterior walls. Most were running to a large waterproof box that the antenna feeders plugged into but were a lot larger than I wanted. The box would offer a socket and be cabled through the wall and into the back of the radio. I also wanted it to be basically waterproof and compact.
There are many waterproof boxes on the market of course, but none I felt would be ideal. Then a good friend then got his hands on a 3D printer so we decided to print me a box to my design.

First step is to draw it up. I planned for 2 connector positions (one for each output from the FT-897D) and made it suitable for both single hole bulkhead type connectors and 5 hole panel mount connectors. It will take SO-239 and N-type (my preference) connectors. Both will be cable mount and crimped, which I use in my day job at L Band and above and much prefer to pretty much all other cable fitments for flexible coax.

The coaxes will be fed through a hole straight through both skins of the house through a vertical mortar joint at an upwards angle and the wall plate part of the box fixed to the wall with two fixings into the horizontal mortar line. (My bricks require an SDS drill to drill holes in, plus this is easier to repair if removed later).

A simple slide on cover open only at the bottom extending down past the connectors will shield it from even the most horizontal rain.

Now to send the files over to my very generous friend Paul for 3D printing. He did an initial print of my design exactly as drawn, which took some time for the cover as we didn’t print it the most efficient way up. We got it done, but before I had chance to fit it discovered it was printed in PLA rather than the ABS we thought it was. So Paul decided to redesign it with printing in mind in smaller parts that would be cemented together, having already proven on my Cobweb antenna that this approach was a better plan.

Paul’s design was four pieces rather than my two:

Here is some of the 3D printing and assembly:

The two parts of the weather cover:

For the feeder from the coax box outside to the radio I wanted to add a hi band and mid band ferrite choke as described by GM3SEK here. I wound one with RG223 which was a springy slippery nightmare and one on RG58 which was much easier. There was no way to get the coils of either sitting tidily with just cable ties so I used masking tape to keep things tidy. As where they will come through the wall is very hard to get to I need to wind them on first and will have to pass the shorter tails out through the wall and fit the connectors outside.
hi and mid band chokes

Holes all drilled from outside, and short tails pulled through from inside using the smaller drill and some wire:

Connectors fitted. As well as remembering to fit the crimp ferrules make sure you feed the coaxes through the hole in the coax box BEFORE fitting the first N-type type connector beautifully. Otherwise it needs to be cut off and wasted. Grrrrr. The final SO239 and N-type socket fitments are not as tidy but electrically good:

Antenna cable and rain cover fitted. I have also smeared the cables and backs of the connectors with a good layer of vaseline in case any water does manage to run down the wall and down the cables:

From concept to reality. Cool.

If anyone with their own 3D printer is interested is making use of this design my friend Paul has made it available on Thingiverse and Youmagine.

Last updated 4th March, 2017

Base station mount for fishing pole mast

My current circumstances preclude my having a permanent mast up for antennas so I am having to stick up a portable style telescopic fishing pole with an inverted vee dipole when it gets dark, and take it down again before I go to bed. Quite tiresome but better than nothing.

I started by strapping my 8 metre fishing pole to the rotary washing line that is installed in the garden but it’s a bit of a faff in the dark and I get covered in cobwebs, and it’s a bit wobbly. Also its location means I don’t have room for a 40m inverted vee, and the locations I have for the ends of the dipoles are not in line with the pole so that means it is always stressed and bent over quite a lot. So I needed another solution.

Using the very useful Link Dipole Calculator on the SOTA Mapping pages I was able to calculate that there is room for a 20/40m inverted vee if I use a 10m fishing pole and mount to to the corner of a 6 foot brick wall in the back garden and I can arrange the ends of the dipoles to be in a straight line with the mast to relieve stress on it. Both solutions have one end of the dipole coming close to building which is not ideal but the higher pole will help and at least it’s a bungalow so most if not all the actual radiating elements should be above the roofline.

Next challenge is to come up with a quick and simple arrangement to erect it. After looking around and some thinking I decided I needed some sort of cup to sit the bottom of the mast in and a sleeve higher up to extend the mast into giving it secure support. Scouring the DIYs the closest I could find for the upper sleeve was some black 50mm downpipe. This also had suitable wall fixings that keep it fairly close to the wall. However it turned out to be a beautiful fit for the top of the bottom section (no use to me), but sloppy on the next section up.

I was trying to think of ways to line the pipe to get a better fit and how I might secure it in the pipe and in talking to a friend who is very good at engineering solutions he suggested heating the pipe and bending it inwards in several places. Perfect!

As there is quite a bit of play I used strips of cereal bar box and masking tape to build up the pole to a nice fit on the tube to keep it centred around the pole.

Then a bit of masking tape over the outside to keep it still.

Once set up I used a heat shrink gun to heat up small areas of the pipe and used a teaspoon to press the soft pipe against the pole and hold it there until the plastic cooled a little. I kept the teaspoon in a cup of ice water between uses to keep it cool and cool the pipe quicker. I did three sets of four indentations. Set one at 0° 90° 180° and 270°, 2nd set at 45° 135° 225° and 315°, 3rd set as the first. Then I took off the top card and masking tape and pushed the top edge in as well for a bit more support. I left the bottom entry oversize for easy entry.

This worked better than I expected! The fit is very close. If I had known how good the pipe would keep the new shapes, I would have wrapped a sheet of printer paper around the pole to have a little freedom on the fit. However, it works and here is the pole standing upside down with the pipe fitted showing it gripping the pole.

The cup for the base of the pole took a bit more searching for. Nothing was quite the right size, or if it was it was flimsy plastic. It doesn’t need to be industrial but will need to stand the leverage the top 8 metres or so of pole exerts when the wind blows. After much looking and considerably over budget at £10, I got a metal camping mug from Mountain Warehouse. Of all the metal cups I found it was the only one that was close to the right size and also was parallel sided, which would be useful.

First the handle had to come off. I wasn’t sure how it fixed on so I started sawing it off. First cut through just plastic, then the 2nd hit metal as I cut closer. I decided to just try and break it off. Came off easily and I was able to see it was only a tab spot welded on. So the other was off in seconds.

I had also though of how to attach it to the wall as screws through the side wouldn’t work as the heads would be in the way of the pole and the wall thickness of the double skinned cup are very thin anyway meaning it would deform. So it had to be fixed at the base. A simple metal shelf bracket was chosen, cheap and plenty strong enough. In order to line up correctly with the black pipe, the centre of the cup needed to be 55mm from the wall. To make it easy to do I drew a circle a little smaller than the cup base, and positioned the centre of it 55mm from a base line, printed and cut it out, and taped it to the base. It was then easy to line the shelf bracket up with my centreline and the upright part with the base line (left in the photo) so I could mark where the new holes in the shelf bracket needed to be (it goes without saying the ones already in it were no use).

I was then able to drill the bracket and the cup with new holes for fixing the cup to bracket, and a couple extra for rain drainage. As the metal is very thin I also cut a disk of 1.5mm aluminium sheet to spread the load of the screws. I just printed a circle the right size, cut it out, taped it to the aluminium and cut round it with tin snips. A quick file of the corners and it was sorted.

Now just needs bolting up together. I used nyloc nuts so I can do it up tight enough to be sure but not need to crush the cup getting the nuts to stay tight. The disk and bracket spread the load well anyway, but I know they should never come undone. All the fittings are A2 stainless steel so should last a while outside.

So the pole can sit in the cup but not rest on the heads of the screws I cut a sheet of rubber matting to raise the pole base off the heads. May help absorb some (tiny fraction of) shock if the mast happens to collapse down one day. Ready to go on the wall now.

All set and just need to screw these to the wall. And a rubbish picture taken in the dark with my phone with the mast in situ.

Last updated 4th March, 2017

First portable lightweight link dipole

Following my first wire dipole which is too heavy for portable and I am using it at home, I am making a multi band link dipole for portable use for SOTA activations on the hills and mountains.
Instead of traps it will have links where we can make or disconnect sections of wire in to be resonant on different bands. It will be cut for 20m, 30m, and 40m. The 30m dipole should work as 5 half waves on 6m, and the 40m dipole should work as 3 half waves on 15m.

Via the SOTA reflector I found this very useful link dipole designer:
http://www.sotamaps.org/extras.php
and used it to design the dipole like so:

The 4 foot support at the ends will be my trekking poles, which enable me to keep the end elevated with a lesser ground footprint, which needs 61feet as it is.

I decided to adopt a very similar design as my first dipole (here) with a flat plate centre and cable ties. The plastic I used before I found to be a little brittle so I don’t expect it to last repeated portable batterings on hills. So I found some bare FR4 board and used that.

Coax stripped back and wires attached. I decided to not go for the loop of coax at the top many go for to stop water ingress, but go for a simpler style and will waterproof it with some liquid electrical tape. I have gone for RG58 as it’s less lossy and mechanically good and not that heavy really. It can always be lightened up if really necessary later.

Showing the soon to be 20m antenna wire.

To mount the dipole on the fishing pole mast I have made this piece of uPVC which is very light and pretty strong which slips down over the thinner section and sits on top of the thicker section below like so:

And attached to the dipole itself:

I have to put a word in for the Barenco crimp PL-259 connectors I got for RG58.
I prefer crimp to any other style due to the reliable retention on the braid (if you have good braid-the Barenco supplied RG58 has a good braid).
This connector also has a reduced diameter tip which lets you use the iron on the outside to transfer heat and keep the main contact section clean of solder.
It also comes with a stiff plastic strain relief that is such a good fit I didn’t think it would fit, but can be fitted and looks like it will give some support.
Product link

Next job is tuning it up and adding sections.

Off to a local hilltop common to set up the mast and antenna and tune the dipole sections.

I’m using an 8m fishing pole and will mostly use it guyed. I decided the middle size guy ring from SOTAbeams was the best option as it sits nicely on a joint and is a nice height but also not too steep an angle to collapse the pole, hopefully. I have a ground stake to strap the pole to for assisting in erecting it and holding the base steady. I tied four guys, but may use just 3 depending on location.

Antenna attached, will be at 23 feet above ground.

As I prefer to take the weight hit and reduce coax losses, I am using RG58. To save it bending the thinner top of the pole with the weight hanging away from the pole, I am using velcro cable ties to keep the coax against the pole to below the guy ring.

Raising the mast. This is SO much easier than hoisting a 20 foot aluminium scaffold pole on your own!

I used the MFJ269C for tuning the 20m section of the dipole. What an amazingly useful bit of kit!

Once the wire was trimmed to nearly be resonant in band I tied on the string I am using to make the link supports. This shortened the dipole making it closer to resonance, then a final trim to tune. It actually read and SWR of 1.2:1 at both band edges, with 1:1 to 1.1:1 in the SSB portion, where I will be operating. Then trim off the ends the same amount as the length of the 2mm bullet connectors I am using for the links. I used the sockets on the ‘uphill’ side of the links.
Soldering the link on, literally ‘in the field’.

I’d pre-cut the next sections and already fitted the plug of the bullet connectors, so the link was soon made. I don’t think you’ll get much lighter link supports than these!

We soon had the 30m dipole tuned up nicely, and ends prepared for soldering. Except the brand new gas iron G1YFC had bought failed to work again. Managed literally two solder joints! That’s going back. So I will need yet another dipole building session tonight, as I plan to be using this tomorrow for SOTA activations.

We took the opportunity to work some stations on 20m and test the battery supply. We started on 50W, then 75W, and in the end went for 100W. Why not…
We used about 1.1Ah in about just over an hour. We’d use more contesting or calling CQ more often, but we were scanning the band and calling into other stations.

Final round of antenna making.

Bullet connectors now soldered on at home I headed back out to add the 40m sections of the dipole. First I checked the match of the 30m dipole to check it wasn’t different from the previous install as this time I set the pole and antenna up on some grass near my home and wanted to see if there was much difference. All seemed fine. At least the dog walkers and cars driving by were amused. Or was it bemused…

Anyway, tip of the day if you are using string for your links is to make sure you tie the knots with enough slack. I made one link string a little too short so it was same length as the link, which meant with stretch the connector may pull out.

One problem of a double fisherman’s knot tied in wire and thin nylon cord is it’s pretty much impossible to untie them. I couldn’t cut either as I’d have to start over, so I had to tie a couple of knots in the link string to make it shorter.

Once done I could trim the 40m wires to resonance. I thought I was near so I tied the final knot to join in the bottom guy string, leaving (I thought) plenty of trailing wire to trim.
Wrong. I trimmed as much of the wire as I dared but was resonant pretty much at 7.000MHz, and I will be using SSB. My only option now (as I was getting tired of it now anyway) was to shorten the wire by adding knots. That did do the trick.

Next stop, some summits.

Last updated 10th February, 2016

Super useful home brew tool

As I have recently been beavering away making wire dipoles (something new to me – much more used to making long yagis) I thought I would share this well known, but amazingly useful multi-tool.
Best of all it is usually free as long as the XYL doesn’t find out:

The humble wooden clothes peg (clothes pin).

The beauty of this marvel is it can hold contacts for you while you solder them without sinking the heat away or melting. Here I am using the weight of my wire strippers to keep it from moving around.

Not only that, if you are making a wire dipole as I am here, the humble peg helps out once more by holding one end for you to measure off the amount of wire needed.

This is nothing new, but worth sharing for those who may not have seen this tool in action.
Another good reason to stick with traditional pegs not those plastic ones!

Last updated 10th August, 2015

Ultralight 144Mhz portable yagi

As part of my plans for SOTA (Summits On The Air) operation I want to operate on 144Mhz SSB with a small lightweight yagi.

After much research and a lot of reading up on lightweight yagis (I’m more used to building long high gain yagis for contesting) I have decided to go for a DK7ZB design. A 5 or 6 element yagi with max boom length of 2 metres.

So I headed off to Wickes to see what they have, only choosing Wickes as it was less across town to battle through the traffic coming back. I was looking for PVC pipe and pipe fittings.

Most of the smaller bore pipes less than 38mm seemed just too floppy. The 38mm waste pipe was nice and rigid, but probably was heavier than a suitable aluminium boom would have been. I kept looking and discovered there were two types of 22mm pipe and one was floppy, but one seemed rigid enough. It was a 2m length and although I was thinking of two 1m lengths for portability, I am leaning towards the single piece boom for now.

Next element clips in the form of pipe clips. The design of the pipe clips varied, I needed ones with flat sides to drill for the elements. Some have a central rib about as wide as the 3mm elements would be and it was clear it was unlikely I could drill spot on through it. So I managed to find some that didn’t have the rib. A big bag for 59 pence.

I also got a pair of T pieces. My thoughts here are to mount the boom through the T piece permanently and drill a hole in the T part to drop over my fishing pole mast.

to be continued……

Last updated 10th August, 2015

FT-857D & FT-897D portable battery power

I have decided that I want to start up activation of SOTA (Summit On The Air) summits, and where applicable WAB (Worked All Britain) Trig points. So this is going to require battery powered radio equipment.
I decided against (for now at least) the very popular Yaesu FT-817ND all band lightweight rig as I have no other HF transmitting equipment, and 5 watts only from my disadvantaged home location and antenna opportunities I felt will be too limiting.
So I have bought the Yaesu FT-897D for it’s versatility in being able to have fitted internally an AC PSU or battery power. I also prefer it overall as a base unit to the other potential option the Yaesu FT-857D. I will have to live with nearly four times the weight of the FT-817ND and twice the weight of the FT-857D.
Edit: I have since bought an FT-857D to use for SOTA activations.

Batteries.
Seeking a lot of advice from many members on the SOTA reflector I have bought 2x 8400mAh LiFePo4 Zippy batteries. Lithium based batteries are a lot lighter for same capacity than SLAB (sealed lead acid batteries) and are what everyone is using, including the model aircraft enthusiasts. These are 4 cell batteries that have the right voltage range required for the FT-897D (and FT-857D). If I was powering an FT-817ND I could have gone for a 3 cell LiPo battery as the FT-817ND doesn’t need as much voltage and just wastes the rest in heat. Not an issue for me. This particular battery can discharge at 30C (30x capacity) so more than enough for a 100watt rig. One SOTA activator with an FT-897D gets about 1½ hours use on SSB at about 75watts output power still keeping it in safe discharge zone.

Zippy 8400mAh LiFePo4 battery

I bought these batteries from Hobbyking, and they came very quickly, free delivery too.
Link to product

Charger.
These batteries need a specialised charger to ensure safe charging and care of the battery.
I initially wanted an AC powered charger (against recommendations from experienced SOTA operatives) but at Hobbyking UK warehouse they had none in stock. So I ended up with a DC input charger.
This will ultimately be much more versatile meaning I can use it in the car or at home on a PSU.
The model I got is the Turnigy Accucel-6 50w 6a balancer/charger lihv capable.

Turnigy Accucel-6 50W 6A Balancer/Charger

This I also got from Hobbyking.
Link to product

Edit: Since buying the above charger I decided it was too slow so I have bought a 150W charger. I still use the 50W so I can charge both batteries at the same time now.

Turnigy Accucel-8 150W 7A Balancer/Charger

This also came from Hobbyking.
Link to product

Connectors.
The general concensus among the portable operators was to use Anderson Powerpoles as the DC interconnection connectors. These are rated at 45A and mate together to make pos and neg pairs. They are hermaphroditic which is quite useful and makes connection in the field simple and error free.

Anderson Powerpole pair

You can get these from many places, I looked for alleged genuine ones from eBay, and bought from a vendor with 99.9% positive feedback.
Link to product

However, the batteries come with a 5.5mm bullet connector pairing and heavy duty leads. Too big to fit easily into the Anderson Powerpoles. So I was recommended some small leads with 5.5mm bullets one end, and a connector that can be replaced with the powerpoles on the other much easier due to more suitable cable size.

5.5mm bullet leads

These come two in a packet very cheaply from Hobbyking.
Link to product

Battery safety.
In order to extend the longevity of the batteries they need to be looked after. Over discharging them can lead to capacity loss or complete failure. The recommendation made to me was to monitor the battery use with an inline meter capable of measuring the Ah used. For this I found a Turnigy 130A Watt Meter and Power Analyzer.

Turnigy 130A Watt Meter

I couldn’t find one like it in stock at Hobbyking, so I did take a punt on one from eBay. The vendor has 100% positive feedback so I risked it. It does work OK.
Link to product

Power lead.
Finally, to save myself having to mess about removing the rig power lead from the base station PSU all the time, and making up another Anderson Powerpole pair for the back of the PSU (when it has perfectly usable 30A binding posts), I bought a new DC cable to use exclusively for portable operation.

Yaesu DC power lead

Ebay for this one. More expensive than I expected too. But looks like the original one.
Link to product

First stage of assembly.

This didn’t go as well as planned!
First I fitted a pair of 45A Anderson Powerpoles to the Yaesu DC power cable. This went OK, though was not easy. I needed a small jeweller’s screwdriver to push the contacts in to get that all essential final click. But I did manage it.

Next I tried to fit a pair of the Anderson Powerpoles to the the mAh meter. This was a failure. The wire size of the meter leads is just too big. No way on this earth could I get the contacts in. I think with the correct crimp tool it may be possible but even then I think it will be a game.
I abandoned that for a rethink.

So I decided to fit an Anderson Powerpole pair to the bullet connectors. I at least then have the option of powering the rig from the batteries with no meter.

As the adapter leads with the bullets are so short, I decided to cut back the connector housing with side cutters to retain as much wire as possible.

I was then able to grab the brass contact just in front of the soldered wire end with the side cutters and twist to pull it out and then break it off.

It was then easy to de-solder the brass contact from the wire.
Note: I did this to a second lead from another bag of two, the the wire was kind of spot welded on rather than soldered. I had to cut that one.

I then fitted these bullet connector leads to a pair of Anderson Powerpole connectors. One went in with just a lot of difficulty, the other one wasn’t that easy! I still have the mark in my hand 12 hours later from pushing it in with the jeweller’s screwdriver (the only thing thin enough to get in the tiny space). After thinking I would never do it, I did finally get it in.

It’s clear to me the only way to use these 45A contacts without needing the crimp tool is with relatively small gauge wire.

Though while writing this page I have just this second had an idea for a possible work around for me.
The contacts look like this:

I was forming the ‘flaps’ of the cable entry around the wire with pliers and a Yellow/Red/Blue simple electrical crimp tool. I might try cutting some ‘flap’ off which will reduce the overall resultant diameter and may give me a chance to fit it in. I am soldering the joint anyway, so should be secure.

Second try at fitting plugs to the meter.

Another try this time cutting just a little off the connectors. I only cut about 1mm off, but that’s a lot in the scale of these fitting them in.
As supplied at the top, cut down slightly below:

This enabled me to push the pre-tinned wires (as supplied to me) into the remaining contact area, and squeeze them up to grip, and sweat it in securely with solder:

I got the first one quite easily with my jeweller’s screwdriver. Yes! Second one (in the photo) I actually pushed in by hand! Which is not bad as the wire is very flexible and has next to no rigidity.
Got the second pair on with the screwdriver and all is done, phew!

Finished portable DC feed system:

All ready for the hill tops!

Last updated 26th April, 2016

First ever HF inverted vee wire dipole for 20m

As a recently re-active Radio Amateur that has not been active for nearly 20 years, access to HF is a new thing to me. I was very keen and active on VHF and some UHF, but never active on the “DC” bands.

Roll on nearly two decades and here I am with a “shack in a box” Yaesu FT-897D. SO I decided to start with a simple mono band dipole for 20m. Nice and simple to make with things I have lying around. Some RG223 feeder and some heavyish DC black and red wire. A sheet of perspex called into play and some cable ties and we are in business.

Here is the feed point of the dipole. I must remember to solder to the centre core before bending it next time. The top hole is for nylon cord to tie it to a mast.

Finished (apart from tuning) dipole. Both halves of the driven are wound onto the small spool.

Next it was load up the car with my youngest daughter, the radio and some bits and pieces including a mast, and head off to a nearby drive on small hill to test it.

Once on the hill I remembered how awkward it is to erect a 20 foot scaffold pole on your own on hard ground. An old big screwdriver was deployed into the ground to slip the end of the pole against to push it up and after some convincing my wheelchair bound daughter was pressed into holding onto a guy rope while I adjusted the other two. I hadn’t spaced them very well, there was an angle of about 160° between two, so I leant the mast over away from them to be safe. The wire elements were unrolled from the spool and using some nylon cord tied to the wire ends (leaving some adjusting tail) and pegged out. Tuning was done by bending back and keeping neat with two clothes pegs on each element. Didn’t take long to get a decent tune that didn’t register any movement on transmit.

Now to test it!
By now time was getting on so we didn’t have long, but we settled in with myself in the back and my daughter draining her phone battery and mine as I was using it as a wifi hotspot for her.

Didn’t work a lot of stations but got a few nice contacts and people could hear me pretty well considering.

Last updated 10th February, 2016