Can I use regular air variables from an old transmatch for tuning?
Most loop literature would say that the wiper connections on commonly found air variables are too lossy. Also voltage capacity is an issue. Any capacitor used should be able to withstand high voltages in the 3-4KV range if you are running 50-100 watts. If you are using welded stator or butterfly capacitors with a high enough voltage rating there should be no problem or significant losses. However, high voltage stator or butterfly capacitors with a large capacitive range usually cost about the same as a nice used Jennings Vacuum Variable. I personally use the vacuum variables. A cheap alternative to expensive high voltage variables is the use of coax for monoband utility. Take a good piece of coax, separate the braid from the conductor for a couple of inches and attach each side to each open end of the loop. Use varying lengths of coax to create different capacitance values for tuning. Trim the coax till you reach your desired resonance. This works very well if you don’t mind being stuc
