Sotabeams Linked Dipole 20m SWR

I had need to throw up the sotabeams 20m dipole here at home while I am operating as VI4LWF a special event call sign for the Armistice Day celebrations. I wondered why the autotuner went bonkers when i keyed up for the first time and so i thought i should take a look at it on the VNA, well it looks little on the long side to me, especially when operating up around 14.310 where most VKFF activators congregate. Its not bad, it just could be better.


Antenna is Done

So i got the dipole up now in its final position. The coax is now clamped to the mast so there is no flapping about in the breeze. The ends are up at their finished height. All up we have 7.6m apex and about 3m at the ends. Seems to be working ok, rx is certainly up.


SWR is as good as it is going to get and much broader banded than the old shortened dipole.

Photo bombed by Buster the Boxer. This is some fancy engenerding going on here. There is a 6ft star dropper 2ft in the ground right up the masts clacker providing the main support, the 2nd star dropper is screwed to the retaining wall and some big automotive clamps tying the 2 together. No idea what the safe working limit on all these things are LOL, but it did not move much during the big storm we had go thought last night. So i think it should be ok.


New Dipole and Mast

Today i pulled down the old antenna and mast and put up a new and improved version of each. The old shortened 40m dipole was only ever meant to be a temporary solution that stayed in place for 3 years. So it was time to bring her down and put it to rest.

I bought a flag pole cause it seemed like a quick and simple way of putting up a new dipole and a balun because i want to be one of those balun guys who has to tell you what kind of balun he is using even though its kind of not important to the conversation but the word balun gives the air of technical know how and ability especially when you say its a 9 to 1 balun which is really an unun or as I call them 9:1 onions, because endfails will make you cry, but I digress. <– this is called sarcasm to anyone who is going to get hurt feelings over their antenna of choice, don’t email me call your local politician and complain to them.

Erected the flagpole and hoisted up the balun and new dipole cut for 40m on the flag raising rope, saluting while humming the national anthem and got the ends up in a temporary fashion to check the long or short of it with the analyzer, when the wife gets home from work. She comes out the back, looks at the new flag pole and remarks, Oh great, its storm season and you go and erect a dirty great big lightning attracter. Chuckles to herself and leaves me to antennaring like i know what i am doing. And if my Pythagoras is correct, when i put the ends up about 4m in the air, i should have 50mm to spare. The joy of living on a postage stamp block in the city.


L Match With SWR Bridge Cont:

Putting the finishing touches to the antenna tuner project, I just need to cut the shafts down a little and put the knobs on. I have given it a test into 2 dummy loads, a dummy load and my 40m antenna LOL, and the led comes on super bright with 5w going in. All in all I am pleased with the outcome, though i would have preferred it in a smaller case, but the inductors use kind of determined the case it when in.



QRP L Match With SWR Bridge

So with the new year comes new projects, I am not going to set out what my overall plans and goals are as I have started way to many things and never bothered to see them through or to complete them. So with that in mind, I am building a L match

Its hard to make out, but you can just see the LED glowing, the signal is 10v p-p from the signal generator, the load is a decade resistance box. At infinite swr there is 1/2 the p-p voltage at the junction of the rectifier and capacitor. As swr approaches 1:1 the voltage drops to a point where the LED turns off. Its simple and its a winner.

It will get paired up with the sotabeams switched inductor and a 8-370pf air capacitor. as an L match. Should be good enough for the kinds of girls i go out with. Below is the schematic I am following for this project and a link to the authors site is at the bottom of the page. In the final build I will use 3w 50ohm resistors and the diode i used was a Schottky, i don’t recall the numbers it was just something i had in the parts box, I used the Schottky for its lower voltage drop, though that is probably not all that critical seeing that LED’s are current limited, not voltage.

Link to authors blog post: HERE



Sotabeams Linked Dipole

After 2 years and 100 odd activations, I somehow managed to break the sotabeams linked dipole. Its been used, abused and not treated very nicely and its never let me down. Even once i noticed it was broken it was fixed with some electrical tape and we kept on trucking. Sotabeams, value for money thats for sure. Now to work out how I am going to fix it.


Antenna Trap for 15m

With all the sporatic E around lately, I decided that I needed an antenna for 15 and 10m that I can deploy quickly at home and make some contacts with. I know there are better options, but I do not have space to errect other antennas and I need approval from my land lord to have anything permanent. So for ever i have been using a 40m dipole on 40,15 and 10, to some success mind you, especially on 15m.

So i figure that a trapped vertical for 10 and 15m should be a large improvement over the 40m dipole. My initial tests using a 15m vertical and 2 elevated radials seemed to do quite well, a 9db SNR improvement via Reverse Beacon Network over the dipole, making stations workable that the dipole could not even hear.

So on the CNC machine i routed up some Trap Boards, using a pair of 2000v 100pf caps in series for 50pf capacitance paralleled with whatever inductance was required to make resonance at 15m.

With silicon wire for the radator, and some zip ties for mechanical strength, its not a set and forget depoloyment, this thing will die quickly in weather, but, for something i put up on weekends, it should be fine.


Checking the resonance of the circuit. Looks about right to me.

And this is the completed trap, i should have added some more wire to the toriod rather than bunching the turns up, but i was lazy. Will see how it goes and pull it apart and make changed if needed.


A Vertical Dipole for 15m

Sometimes a simple construction project can be fun, I mean you cannot always be knee deep in solder, resistors and capacitors. Sometimes you find a need that needs fulfilling even if its just a boring antenna.

Next weekend (At time of this post) I am partaking in a WWFF VKFF mass activation weekend and working dx is going to be a big part of my strategy for the 8 parks i will be activating over 3 days. So i thought lets go vertical and lets make it a dipole so there are no stupid radials and counterpoises to contend with.

I wont boor you with formulas and measurements, i am pretty sure you all know how to google a frequency length calculator to make a dipole, but rather just to show you how i went about making this and the results i achieved.


I constructed a T out of some old conduit i had laying about, this is to get the feedline coming off at 90 deg to the antenna for 500mm.


The feedline should come off the T at a 45deg angle to the antenna, i do not have the room to do that at home, this results in a narrower bandwidth for the band in use.


The antenna was a little long 5cm in fact. it has since been trimmed and is now swr of 1.5 or less across all of 15m


The ultimate test is what it does on the air. A quick test on Reverse Beacon network showed that i was being heard in places on this antenna up to 10db snr higher than the 40m dipole i use at home. And for those China stations, it meant being heard rather than not being heard. All in all i am happy with how things have turned out and i look forward to getting this baby in the air next friday and working some DX.