On Sun, Sep 25, 2022 at 03:29 AM, Alan wrote:
Impact of 100M ohm
With a receive frequency of 1MHz and a Q=1000 that would? produce a -3dB audio bandwidth of 500Hz with an AM broadcast. A Q=100 would give a much better sounding bandwidth in a receiving application.
?? The 100M¦¸? as you say adds a very small reduction in Q, but the tube also adds losses especially at high frequencies as shown in this graph from the 260A manual.
? Note: the input impedance is down to 4M¦¸ at 4MHz. So, even if it was possible to bootstrap the tube, it would not eliminate the loading of the tube.
? But, the OP wants to build a Q meter for the frequency range 1.5 MHz to 150 MHz, that will take need a high input impedance voltmeter that will hold up it's high impedance up to 150MHz. Although Qs at 150MHz are generally lower that what is possible at 1MHz, so the input impedance can be somewhat relaxed without causing as much reduction in Q.
The only quibble re the 1000Q coil and BW, after you add the losses of the other components and load the coil enough to extract an audio signal you can hear, the loaded Q will be lower.
If audio BW is ever a problem it is easy to spoil the Q, not so easy to improve it after the Q coil is finished.
?I'll remain a bit skeptical on the litz in AM radios, what I have seen is not a large litz, using only about 7 strands. But, I will need to check and to be sure the strands are actually insulated from each other.
??????????????????????????????????????????????????????????????????????????????????? Thanks,? Mikek
