Hi Leong,
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I'm not sure if I agree with your comments.
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The PA0FRI may have significantly higher gain over 6-18 MHz, but this just demonstrates the poor frequency response of the circuit, when used with a typical loop. Do you actually need this additional gain to overcome coax loss ? I don't think so. A 30-story apartment block is likely to be in the region of 30 x 3m tall, approximately 90m or 300ft. This shouldn't be a problem. If you were to use RG-58, the loss at 30MHz for a 90m length is around 6dB. The LZ1AQ or Wellbrook, will have more than enough gain in hand to overcome such losses.
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The PA0FRI, and the G8CQX, have a moderately high value of input impedance, so the overall common mode impedance when used with a loop is likely to be higher than that achieved with an amplifier with a much lower input impedance. In practice, I don't think the PA0FRI / G8CQX, is particularly good in terms of CMRR.
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The LZ1AQ can be made quite small if SMD parts are used.
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However, the main issue with the PA0FRI / G8CQX design, apart from the very poor frequency response, and lack of loop impedance tracking, is that the third order Intermodulation performance is quite poor. Even the modified versions with additional output buffer stages are not much better.
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Without saying it out loud, I think you can tell what my opinion of the design is :-)
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Regards,
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Martin
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On Wed, Jan 29, 2025 at 06:12 AM, <biastee@...> wrote:
I can think of 3 situations where the PA0FRI may be preferable to the LZ1AQ.
