23-07-2024, 05:28 PM
AN HF loop needs tune at the loop if in attic or on roof.
RX can use varicaps via DC on coax (via balun)
TX needs a motorised vacuum cap.
Typically 1 turn at 1m to 3m dia.
To reduce local electrical interference you need a screen earthed at the loop drive point and open circuit at the top. It need greater spacing from the loop as frequency increases as it look like a capacitance in parallel. At MW & LW you can use multiple turns of cat 5 / cat 6 (10 to 20), using each twisted pair as one wire. Thus a 10 turns coil has 40 turns when the wires are in series (x8 inductance) and 10 turns but higher Q when all four shorted twisted pairs are in parallel. Then it needs screened with two pieces of Alu. foil earthed at drive and open at top. You can use screened cat5, but the screen is only earthed at one end and only on LW as it is too much capacitance. The screen could double as an HF unscreened loop and one French LW/MW/SW VHF set had a large drum with two vertical coils at right angles instead of a ferrite rod. A knob on the set rotatated it. The finer more turns coil for LW. A third wire was an open helix around the drum, earthed on LW and MW, and optionally a SW aerial.
https://www.radiomuseum.org/r/schneider_..._1961.html
A Vidor valve portable with the beading is actually a tuned VHF loop. Only one of two UK AM/FM valve portables, the other was the Ever Ready.
https://www.radiomuseum.org/r/vidor_cn436cn_43.html
I forget how the LW & MW aerial works.
RX can use varicaps via DC on coax (via balun)
TX needs a motorised vacuum cap.
Typically 1 turn at 1m to 3m dia.
To reduce local electrical interference you need a screen earthed at the loop drive point and open circuit at the top. It need greater spacing from the loop as frequency increases as it look like a capacitance in parallel. At MW & LW you can use multiple turns of cat 5 / cat 6 (10 to 20), using each twisted pair as one wire. Thus a 10 turns coil has 40 turns when the wires are in series (x8 inductance) and 10 turns but higher Q when all four shorted twisted pairs are in parallel. Then it needs screened with two pieces of Alu. foil earthed at drive and open at top. You can use screened cat5, but the screen is only earthed at one end and only on LW as it is too much capacitance. The screen could double as an HF unscreened loop and one French LW/MW/SW VHF set had a large drum with two vertical coils at right angles instead of a ferrite rod. A knob on the set rotatated it. The finer more turns coil for LW. A third wire was an open helix around the drum, earthed on LW and MW, and optionally a SW aerial.
https://www.radiomuseum.org/r/schneider_..._1961.html
A Vidor valve portable with the beading is actually a tuned VHF loop. Only one of two UK AM/FM valve portables, the other was the Ever Ready.
https://www.radiomuseum.org/r/vidor_cn436cn_43.html
I forget how the LW & MW aerial works.
