Antenna tuning, resonant, Z-match, or something else

1

It occurs to me that due to the rapid phase changes around resonance, I should ask this question:

Considering ONLY the impedance presented to the ports of the SDR, should I tune for 50 ohms, or resonance, or some other point, and if the third option, then where?

For example, a simple whip for 146 MHz will be resonant with a particular length of whip, but very unlikely to be 50 ohms. A different length will present 50 ohms with some reactive component.

Another question comes to mind: How (is?) the kraken protected from ESD on the antenna ports? A rolling vehicle can accumulate 6 to 10kV easily relative to ground, and brushing low foliage will present that charge to the antenna(s) that make contact.

2

According to our DFing expert, it’s fine to tune the antennas to resonance as long as they are all identical.

The Kraken has a fast ESD diode, a gas discharge tube and a BAV99 on each of the inputs.

3

“Identical” is a strong word. :slight_smile: I understand, but no two real antennas are “Identical”.

I learned the ESD issue when I was working with Joe Agrelo on his doppler DF design. He didn’t protect the inputs, and a lot of preamps got popped. Unfortunate.

4

Yeah he mentioned that the minor differences between antennas are relatively insignificant at the wavelengths we deal with on the Kraken.