HF Loop antenna with differential amplifier

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Joined: Mon Jun 18, 2018 1:49 pm

HF Loop antenna with differential amplifier

Post by Tony_m » Thu Jun 21, 2018 1:19 pm

Recently I've ordered differential HF loop antenna amplifier kit from RHelectronics

This amplifier has very similar design as this one:

Antenna tuning is done by MVAM115 varactor diode or varicap (instead of variable capacitor), by using multi-turn potentiometer (100K on the right side of this schematics).

My question - can I make a circuit o bypass this varactor diode in order to get un-tuned, but wide bandwidth active antenna? Or make a switch to choose tuned and un-tuned antenna option?

Why I need this? Because having narrow bandwidth antenna is great to listen one specific signal (it rejects other signals), but it's pretty useless if you want to see whole band at same time. I don't mind if in "bypass mode" this antenna would be less efficient (no resonant frequency).

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Joined: Sat Jan 14, 2017 11:07 pm

Re: HF Loop antenna with differential amplifier

Post by hotpaw2 » Tue Aug 07, 2018 4:36 pm

Small HF loop antennas are by nature narrow-band. If you remove the tuning capacitor, then that will just let whatever stray capacitances tune the antenna to some random frequency, but the antenna will still have a narrow-band selectivity, not be un-tuned or wide-band.

For a wide-band HF antenna, you need something more like a huge (building-sized) discone.

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