Re: Variable gain preamp anyone?


Tom Crosbie G6PZZ
 

I’m doing that already Chris with my current amp. Not one of yours, just some cheap Chinese lump hooked up to a longwire.

My attenuator is quite a lump and I was hoping to replace it with something that takes up less shelf space.

Hopefully I’ll be ordering a CCW unit quite soon and start experimenting with loops.

I’ve also got some material that’s just slightly weirder than a bicycle wheel to use as a loop that I don’t think that has been used before.

Three decades ago, after solving an engineering problem, a G4 told me I was a first class bodger and it pleases me to be still living up to that reputation after all this time!

 

 

From: CrossCountryWireless@groups.io <CrossCountryWireless@groups.io> On Behalf Of Chris Moulding
Sent: 26 September 2020 17:11
To: CrossCountryWireless@groups.io
Subject: Re: [CrossCountryWireless] Variable gain preamp anyone?

 

I just want to raise a point about using the Loop Antenna Amplifier + with a variable supply.

It will be possible to reduce the gain by reducing the voltage applied to the amplifier.

The reduction in gain below 5 V is caused by the bias voltage dropping to a barely workable level.

The amplifier would be prone to generating cross-modulation and intermodulation at that point and I wouldn't recommend it.

For the best RFperformance run the amplifier with a bias-tee at 12 V and add an external attenuator between the amplifier and the receiver if you want to reduce the overall gain.

Regards,

Chris

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