Headphone Antenna for 170 - 240MHz

[stephen168]

Is anybody know the impedance or characteristic on the headphone antenna at 170 - 240Mhz?
When I measure the sensitivity of the receiver, can I just connect it to the sig. gen directly (50OHM input). Or I need to add a impedance transformer from 50 OHM to close to the impedance of headphone antenna.

 

[VEBill]

That frequency range is about a 30% bandwidth. Over such a relatively wide range, the impedance would very widely.

It's likely that the receiver circuit card contains at least one reactive component (L or C) to make a first approximation match from the antenna to the rest of the receiver.

You can help the measurement by inserting an attenuator pad (maybe 10dB) between the signal generator and the receiver. This will help to damp down any reflections from any mismatch. You obviously need to adjust the measurement for the value of the pad. Some signal generators have built-in adjustable attenuators on their output, but it's better to have the pad at the other end of the cable (right next to the receiver).

Also, depending on your purposes, just do it the simple way and see what you get. Might be accurate enough if you just need an approximate value.

Are these headphones the sort used by musicians on stage?

 

[VEBill]

typo: "...would VARY widely."