There is a better known and internationally recognized method for coupling to a magnetic antenna in IEC315-1. Like Swinyard, the IEC method is also intended for broadcast receivers. Again, the measurement is in the near field, but I suspect the given equations do account for it. The setup is shown in the following diagram:
/g/loopantennas/photo/296366/3805879
IEC315-1 is located behind a paywall, but the Indian government has made available a free version at:?
https://ia601904.us.archive.org/33/items/gov.in.is.12193.1.1989/is.12193.1.1989.pdf
> I have been considering to construct a different jig/ dummy antenna?
> circuit consisting of pi-type attenuator with unequal shunt arms - towards?
> generating source 50 ohm resistor and towards antenna amplifier 2 ohm?
> resistor or 0.5 ohm.?
?
One problem that I can foresee is - the dummy antenna's attenuation will impede the use of hobby-grade VNAs (e.g. nanoVna) because of their limited dynamic range.?
?
> Between the attenuator and input of amplifier under test to be included?
> additional circuit that represents dummy loop antenna - series arms of?
> fixed inductances, say 700 uH or more
?
Do you mean 700 nH (0.7 uH) instead of 700 uH? The 700 nH x 2 series arm inductances means the loop must have been made from a very fat tube because according to LZ1AQ, 1.7 uH represents a loop with a 40mm diameter conductor! For "normal" 3.4 mm dia. wire, LZ1AQ specified 3.6 uH. ?
> I am not sure if the LPF in LZ1AQ's design serves as an equalizer?
> for the frequency response of the amplifier from 15 to 25 MHz.
> I crossed another paperwork, where was presented S21 of this LPF.?
> At frequency 20.05 MHz -5dB drop,
?
Simulation shows the gain reaches a peak at 28 MHz (blue trace in the graph linked below). At 30 MHz, there is a ~ 1 decrease from the peak. The response without the LPF is also shown for comparision (red trace). Without the LPF, the gain is significantly reduced over 15 ~ 30 MHz.?
/g/loopantennas/photo/296366/3805459
However, my experimental prototypes exhibit peak gain at ~23 MHz; i.e. ~23% lower than simulated. At 30 MHz, the experimental gain decreases 5 dB from the peak. I have not determined the cause of the discrepancy between simulation and experimental. ?
/g/loopantennas/photo/296366/3805017
I suspect the experimental peak frequency can be shifted back to 30 MHz by either reducing L1-2 or the 100 pF cap (C5 & C10).?
/g/loopantennas/photo/296366/3805458
?
> My circuit is intended to simulate a loop with a loosely?
> coupled 50 Ohm port. All the following plots are taken?
> from the "loop" side of the simulator, with the 50 ohm?
> port terminated in 50 ohms.
?
Hi Martin,
My simulation agrees with yours that your prototype dummy has a coupling factor k ~ 0.7. To better approximate your loop aerial's impedance, k = 0.2 is required.?
/g/loopantennas/photo/296366/3806328
Incidentally, the 60s era's frequency discriminator coils achieved k = ~0.3 at 10.7 MHz by using an open magnetic path (solenoid) and separate cores. Photo of the aforesaid in fig. 1 of the following article: www.researchgate.net/publication/353832328_What_simulation_of_the_Foster-Seeley_discriminator_can_reveal
73,
Chin-Leong Lim, 9W2LC.
