Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
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Hi Martin, ? We are talking about the small excitation loop that is ?interfaced to CH0 port of VNA. Yes, you are correct the current limiting resistor will be 50-56 Ohms for the specified upper frequency 30 MHz. I constructed a similar small loop from 3 mm copper wire and soldered SMD type two small in parallel 100 Ohms resistors using SMA connector as well. I am still not giving up the idea – avoidance off coupled loops but using a dummy circuitry that represents impedance response of a receive loop antenna for frequency range 1-32 MHz. If you remember in old days for measurement the sensitivity and tuning shortwave receivers were used dummy circuitry between the signal generator and input port of receiver. The dummy circuitry represented impedance of open-wire type antenna in MW and SW bands. ? Regards, Raphael ?
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From: [email protected] < [email protected]> On Behalf Of Martin - Southwest UK via groups.io Sent: Monday, July 15, 2024 3:51 PM To: [email protected]Subject: Re: [loopantennas] Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos ? On Mon, Jul 15, 2024 at 06:24 PM, Raphael Wasserman wrote: within 3 dB the current in excitation loop will be maintained the same from 0 to fc frequency.
OK, so this applies to the excitation of the reception loop, by means of a smaller source loop. Are we talking about the inductance of the reception loop, or the excitation loop, I assume it is the latter. The small excitation loop I used, had an inductance of approximately 300nH, and if we take 30MHz as the upper limit, then I calculate the required resistor value to be around 50 Ohms. During my tests, I placed a 10dB resistive attenuator between the excitation loop and 1:1 balun, and the coax to the generator. This can be seen in the photo of my test setup. The small black box with the white label is the 1:1 balun transformer. The black thing below it, is a clip-on ferrite, to provide a bit more choking impedance around 50MHz. I fitted the attenuator as a precaution, so that the generator wouldn't attempt to level the output during a sweep, when presented with a non 50 ohm reactive load. However, I believe it would also have performed the function you are suggesting.
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