Quote:
Originally Posted by theredhouseinn
Now, the crunch, the output of bands 4, 5, & 6 is about 18 dB down on the bands 1, 2, & 3.
This is again pointing me towards the coil former material causing low Q.
John.
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I'm sure this has everybody wondering what is going on.
I have been pondering how an electrical insulator might degrade and fail and become lossy in a frequency dependent manner. I'm assuming it still looks like clear plastic and is not crumbling away.
Assuming it has not become electrically conductive (and you could check with the meter) then it would have to be acting like a very lossy dielectric.
If this was the case, then both the amplitude and the rate of change of the applied electric field would increase the losses, so in theory it would be worse at the high frequency end and worse with higher signal levels as the volts/sec would be higher in both cases.
Still, in the signal stages vs the oscillator, the signal levels are very low in level, relatively, so that its very surprising a plastic former could have such an effect to give an 18dB drop. But it is possible.
So just playing the devil's advocate, is there any possibility at all that your test equipment, or test setup is giving misleading readings due to some sort of problem there or signal loading of the circuits you are testing ?
One quick test to avoid any frequency dependent loading effects on the RF/IF is just to look at the DC voltage out of the detector, with a properly matched RF signal into the antenna (resistor padder network-dummy antenna) and substitute in another L/O signal from a generator with a low Z output and a stable level into the mixer.