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.
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.