On Using 30m Antenna for 10m!
Many of us routinely use 40m antenna for 15m which works as third harmonic. But how many of us have used 30m antenna for 10m? I have not used it personally. Yet I have been able to compile the experience of four hams who have successfully used it. When VU3CDK mentioned to me that he is planning to reduce the length of his 40m antenna to length corresponding to that for 30m and try that for 10m, I wondered why he should try that. It is quite easy to make a 10m antenna and I am using a combination 40-10m antenna to work on 40, 15 and 10m bands. Anyway, his report of using it was really an eye opener for me. He calculated the wire length for 28.4 MHz and worked backwards for the third harmonic in 30m band and arrived at a length of around 7.9m. He adjusted the 40m dipole antenna to get this length by folding the wire. He could get SWR of around 1.5 and power output of 4.5 W with his uBITX QRP radio.
With that setup, he could have a QSO with VU3JXF from Kolkata, which was around 1600 km from his QTH in Mumbai and got 5,4 report. That was an excellent performance of a QRP radio on SSB, working on third harmonic of 30m antenna! He could hear VU3JXF with 5,9 report. He could also hear HS0ZPX very strong on that antenna. On another day he could hear YC2DBW, VU2DSI and 9K2GR also well. Looking at his success, I thought of posting it on QRZ forum and getting the opinion of the larger ham radio fraternity out there.
Though I had presumed that nobody would have tried that earlier as getting a 10m antenna up is quite simple, there were a few who have used 30m antenna for 10m for quite some time! WB2WIK responded thus: “Resonates best when the 30m antenna is tuned a bit below 10 MHz…but it still works even if it isn’t.” KB9GHN had another option: “I use a 44 foot vertical doublet antenna. 22 feet each side. Almost a quarter wave each side for 30 meters and about a 5/8ths wave on 10 meters. Works well.”
The latest response by M0AGP was even more interesting: “I have a fan dipole that includes both 30 and 10m. The result is that I have an SWR dip on the lower part of the 10m band from the 10m dipole and also an SWR dip in the higher part of the band from the 30m dipole – the result is I can operate across the entire band without a tuner. I also use the 30m dipole on 6m, where I worked DXCC in three years including Japan, China and Australia – I never expected that to happen – I have no other 6m antenna.” These wonderful observations from our ham radio fraternity should help us work more bands, even with lesser number of antennas. In many locations, there are a lot of restrictions for the number of antennas which you can have. Even I have that problem with very limited space for multiple antennas and tuner is a costly option in this region.