Will our homebrew antennas run into problems if we try to use the 70cm band? I had thought that the 2m and 70cm bands were harmonic frequencies so it would be okay, but the question was brought up so I thought I'd better check.
Cramming. Heck yes. My brain (well, at least the backs of my eyes) actually hurts.Matt,
I too was wondering this. My thought was no because of that formula used to determine antenna lengths for various frequencies and wavelengths (which I can't remember at the moment)...
But, I bet Nathaniel or Dave with chime in. I think Nathaniel may be a tad busy with a possible new addition to the family and Dave is probably cramming for that Yoda test
But remember, you guys did not use 1/4λ whips, but 5/8λ. This length is really a special case, since it's not technically a resonant length. It's acts like a 1/2λ antenna in terms of resonance, but why is really not important. Anyway, a 1/2λ or 5/8λ would by itself maybe work at different frequencies if it wasn't for the impedance. You have to use that pesky matching network and that makes the whip specific to one frequency.
Maybe yes would be the correct answer, but with a stipulation.Ok, if I am understanding correctly our home brew antennas will not work for both 2m and 70cm as built. However, they could be use for both frequencies with the addition of an antenna tuner?
If there is very little action on 70cm, isn't this a moot point?
The MFJ-1724B. Looks similar to the antenna I use for around town and on trails with low trees, a Larsen NMO2/70SH. It's 1/4λ on 2m, coil a few inches up and center-loaded 3/4λ on 70cm, overall about 19" tall. I would have guessed that was the same. But if it's 1/4λ on 70cm, remember that's about 7" and so the coil is probably spaced about that far up.It's a 1/4 wave on 2-meters with a simple inductive trap at the 70cm 1/4 distance from the base. I'm afraid I don't know the properties of an effective trap, but a few spirals seems to do the trick!