Category: Portable operation

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.

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……

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!