That antenna looks like a 100k reactance capacitor at 1 MHz. (about 1.5 pF)
The coax probably is something like 50 pF, so even without the radio in the mix, you're looking at a 1:30 voltage divider.
Thankfully, AM radio signals are strong. At 1 km from a 1kW station at 1 MHz with a 75 meter 1/4 wave monopole, the field is about 300 mV/m. At 10 km, 30 mV/m, etc.
A typical AM MW receiver has a sensitivity of say, 30-40 microvolts/meter. So even with a 30 fold hit you've still got plenty of signal.
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-----Original Message-----
From: <
[email protected]>
Sent: Apr 8, 2025 9:15 AM
To: <
[email protected]>
Subject: Re: [nanovna-users] Dummy Antenna and FM Alignment
Thanks for answering my post guys.
Some additional information: here's a photograph of the whole antenna network. The antenna is about 43cm in length from the central stud of the base to the tip of the antenna. The base is grounded (interior side) to the car body directly. The cable is 327cm (10.7ft) and is ended by a ISO male plug, possibily ISO 10559 but not sure.
The radio is totally unbalanced.
It seems some of you guys think the impedance mismatch won't be much of an issue, while others suggest taking measurements of different cars, average, and build a matched network to emulate the antenna to the radio and a 50ohm load to the generator. I suppose the network although more work would yield better results? And also perhaps allow me to tune the radio regardless of its impedance?
Thanks a lot.
