Will 40m Antenna Work on 2m?
Some time back, I was told by a VU friend that 40m antenna will work on 6m also, presumably as 7th harmonic. We know very well that half wave dipole antennas work well on odd harmonics and it is common practice to work 15m (21 MHz) band with 40m (7 MHz) dipole antennas. I have also had a few contacts in that fashion. I have checked the VSWR of my 40/10m combination half wave dipole on 6m and found it around 2:1, well within the tunable range of the automatic antenna tuner in my FT-F10. Thought of checking how 40m antennas fare on 2m as 147 MHz will be 21st harmonic of 7 MHz.
I have a quarter century old TM 261 VHF base station which works only on low power. Connected it to my end fed half wave antenna for 40-10m. It is supposed to resonate at all multiples of the fundamental frequency of 7 MHz. I found an SWR around 2.5:1. If it was a radio with built-in automatic antenna tuner for VHF, which I am not sure if there are any around, I could have tried it for 2m as the automatic antenna tuner would tune this SWR well!
Next I connected my 40/10m combination half wave dipole. For the 40m component, 2m will be the 21st harmonic. For the 10m component 5th harmonic will be 140 MHz. VSWR was seen as around 2.3:1. In both cases, I was checking at 145.025 MHz, the transmit frequency for accessing Calicut VHF repeater located at around 4 km from here. After that, when I was having a 40m QSO with VU3IXV located about 10 km from here, I asked him to transmit on Calicut Repeater frequency with his VHF radio and antenna which would be heard here on 145.625 MHz. As the 40/10m combination half wave dipole was connected to FT-710, I listened using my end fed half wave antenna.
I could hear Calicut Repeater feebly only after opening the sqeulch in my TM 261 as the repeater signal was not strong enough to open the squelch. May be those with radios having antenna tuners covering VHF/UHF bands could try these experiments and find out how well 40m antennas will work on 2m, the 21st harmonic or even on UHF, where 434 MHz will be 62nd harmonic! Of course, there is a potential risk of mismatched SWR while testing causing damage to your radio! I was not much worried because it was a very old radio, already on the shelf.
As a tailpiece, you might wonder why I tried these experiments as I already have a limited VHF/UHF antenna setup which I use for LEO satellite operations. Few days back, I was trying to motivate a senior ham with a high end HF/VHF/UHF radio to try listening to a high elevation pass of International Space Station. I told him that his VHF antenna might work on UHF as third harmonic, as my CP22E VHF antenna was my workhorse for my initial LEO satellite contacts. Then he told me that his VHF antenna came down in the monsoon storm. So I wondered whether he will be able to listen to the Amateur
Radio on International Space Station using his 40m antenna.
I do want to try out myself by listening using my 40/10m combination half wave dipole. But as I am busy trying to get some satellite contacts during ARISS passes, I am hesistant to try it out. Moreover, my IC 2730 radio and power supply are kept at first floor to reduce cable length for LEO satellite contacts. I have to transfer the rather heavy linear power supply and the radio downstairs to test with my HF antenna. Still do intend to try listening to a high elevation pass one of these days with 40m antennas.