Peaking SOTABeam HF antenna traps
I am building a trapped dipole antenna for 20-30-40m and decided to try SOTAbeam traps for 100W.
I made 14MHz and 10.1MHz traps according to the helpful instructions, but found one of the traps hard/impossible to tune to 10.1MHz. I was at beat getting 10.04Mhz, which is 60KHz below the edge of the 30m band.
Knowing it resonated at 10.04MHz, and assuming 100pF 5% value for the supplied cap (it was already installed so didn’t test it directly), one works out the implied inductor value in nH. Then, asking what capacitance C would be needed to resonate at 10.1MHz, I calculated the net change is to add 3.4nF in series with the 100pF.
Doing this creates a slightly lower C in the LC parallel circuit, hence higher capacitive reactance, and this forces the resonance slightly higher - as desired.