I’ve discussed this before. 40m band quarter-wave does resonate on 15m.
But is it worth it?
You bet.
Tag Archives: 15m
What is the report for the IOTA contest
All contests have some sort of report, mostly the signal report then additional pieces of information, from your age to your shoe size (seriously).
Here’s me on 15m during IOTA 2017:
(100 Watts, recorded straight out the TS590SG into Audacity)
Antenna: DX Commander Vertical 80m-10m
Working 15m band on a 40m vertical antenna
Note: This article discusses the merits of a 3/4 (three quarter wave) vertical -vs- a 1/4 (quarter wave) antenna.
You can build a 40m vertical quarter wave antenna and ground mount it with 16 x 4m radials and operate it at the third harmonic; 21MHz.
Actually, all my experimentation has shown that if you multiply the quarter wave resonance by 3.03, you’ll have the next available usable band. In this case, if you tune a 40m vertical to 7.00Mhz, you’ll have the whole of the 15m band to play with with a centre-point of 21.300Mhz. Oh, and you’ll still have the whole of 40m band under 1.3:1.
Now here’s the controversy:
Most people who read antenna publications or the ARRL handbook believe that if you actually make this antenna, you’re creating a cloud-burner on 15m.
Technically correct (sort of) – but for DX, wrong.
On the surface, the 10m long 40m vertical that’s used on 21.225MHz does indeed look like a cloud burner. Here it is. 15m band in green -vs- a pure quarter-wave in red).
(click to expand quarter-wave in red, three-quarter wavelength in green)
Multi-banding 10m long 1/4 wave 40m vertical antenna for 15m band
I’m always curious to discover if a mono-band antenna will work efficiently (or otherwise) on another band. I recall that when I first studied antennas, it was explained that a dipole antenna will be resonant on every third harmonic. That means a dipole for 7.1 MHz should also work on the frequency three times bigger, in other words 21.3 Mhz. Actually, experience tells me that the real resonant frequency will be a little higher.
1/4 wave vertical for 40m band can also be a 5/8th for 15m band