On Tue, Jan 21, 2025 at 06:30 PM, Joe Tomasone wrote:
The lowest power HT I have is the Yaesu FT-2D, which outputs 100mw on the lowest power setting.?
When figuring power levels, assume that something will go wrong and it will transmit at full power.? To do otherwise is to court disaster.? You can tweak levels once you have a working, stable setup.
Learning to think in dBm for power levels (100mW=+20dBm) will help you do the calculations more readily.? Power is in dBm, gain or attenuation are in dB; watts just don't work well.??
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There are also different power limitations on your analyzer.?
The damage level is the highest one.?
There is a power limitation to the input attenuator.
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Then there is the power going into the input mixer, which determines the level of internally generated distortion products.?
Many commercial analyzers specify their attributes (internal IM, harmonics, etc.)at -30dBm or -40dBm into the mixer.?
So you need to understand how much power is going into the input connector and what attenuation you have dialed in between it and the mixer.
This working level will be much lower than the damage or mixer overload level, and you may need to adjust your levels via external and/or internal attenuation to optimize performance.? If you can remove a step of attenuation without changing the distortion levels you are still in a linear range and are not overdriving the mixer.? If the distortion gets worse, add attenuation back.? Some commercial units have 1dB or even smaller attenuation steps to more finely adjust the attenuation for finding the sweet spot between noise and distortion.
It is good practice to use at least 10dB of front end attenuation to present a good VSWR at the analyzer input.? Many analyzers default to this value and make you type the number in (no up-down keys or knob) to select 0dB.?
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You should only engage the LNA when your other efforts to pull a signal out of the noise have failed.? Try lowering attenuation, narrowing the IF bandwidth or use/increase averaging first.? An LNA will always reduce your dynamic range and will be more prone to distortion than the mixer.??
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These are powerful instruments but it takes some work and study to make the most of them.? ?
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Here's a good intro to spectrum analyzers from Keysight: ?
Of course Alan Wolke, W2AEW, always has great videos: ?
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73, Don N2VGU
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Donald S Brant Jr