I setup my existing amplifier with my Boonton 260 Q meter to measure the input capacitance of the amp. The lead wires are about 1" long. The Boonton has a fine trim capacitor marked it 1/10 pf divisions. I peaked the Q reading, then added the amplifier. I had to decrease the value of the fine trim capacitor by just slightly over 1pf (1.025pf). After adding the amp and readjusting for peak Q the Q was reduced from approximately 1300 to 1276. The capacitance was lower than I expected and the loss of Q is more than desirable. Here's a picture of the amp on the Boonton with leads.
Mikek
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Ok, please go back to the section above and consider what you are saying here. The purpose of the input cap is to isolate the entire amplifier from the circuit being measured. Because this cap reduces the current to very low values there won't be much impact to the Q. Yes, there will always be some and this can be minimized.
If you don't like 2 pF from the connector, you are going to hate the capacitance from the coax. Driving it from the output of the first stage amp will help minimize it, but even better is to isolate it with the input cap at the probe end of the coax. Get the benefit of both effects. Not to mention the losses in the coax.
Actually, I think it is the test fixture where the capacitance is not so important. The variable cap is part of the test fixture, no? So the capacitance added by the coax is just part of the capacitance of the test fixture adding to the base capacitance of the variable cap. With such a large range a couple of added pF won't impact the range significantly will it? Since it is part of the test fixture the added capacitance will be the same for all measurements and is adjusted out when you tune.
Try searching on "bakelite electronic soldering strips" or "bakelite soldering lug strips". Actually I like your 3D soldering. Can't get any lower capacitance.
Joerg, you seem not understand the innermost sense of the crystal- radio people. They are closely related to audiophools, and it is quite impossible to use sensible technical argumentation here.
The question of best MF band coils has been solved already in the
1930's: A honeycomb coil wound with Litz wire (gloves on). The canonical fixing / insulating material is beeswax.
I don't get that at all, can you back that up with any facts?
I don't know have you tried a 6" polystyrene tube with 0.0625 wall thickness, wound with 660/46 litz wire with 12 turns per inch?
If anyone has an interest, here's a pdf of multiple honeycomb coils and data. I think it is from the 30's or 40's. I can't seem to get it to download properly. But what I could see doesn't give Q directly, so needs to be calculated.
Mikek
Mikek
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The Q is over 500. It was claimed in this thread that PVC is not suitable as coil winding material and this proves that it is quite suitable. Which I already knew because I've used it in RF power amps decades ago.
The energy present in the environment, for example energy from the local radio transmitters. You can then use that to demodulate the signals of others.
However, AFAIK Rick is a guy working in digital electronics.
Only when mounted on a polished mohagony slab of wood, with the user wearing Sundays's best and a bow tie :-)
BTW, I have a Loewe radio with the 3NF type. That is probably the first true integrated circuit from 90 years ago because it contained multiple tube sections, capacitors and resistors.
Again, context. You are living in a different world. PVC is *not* suitable in the crystal radio world because there are *much* better materials. If PVC was the only material available it would be a *great* coil support. If mud was the only material available it would be a
*great* coil support.
I understand the concept, I'm asking specifically. Have you built anything like this?
If you are talking about the graph on page 10, that isn't loading correctly for me either. But it appears to be the same graph on page
Likewise the bad image on page 14 is the same as the image on page
16, etc. Even in a PDF viewer not in the browser the pages render
*very* slowly. Even just scrolling back a couple of pages makes it start all over again. Very hard to view. I think this document needs to be recovered by re-imaging it and turning it into a new PDF file.
That's what I was wondering all the time. In the ranges tested there are largely just AM stations, no CW or morse code. Even at 10kHz BW the audio experience will not be very pleasing, it'll sound more like on a telephone.
Then there is the tempco. Someone opens a window and whoops the resonant frequency goes somewhere else.
However, the crystal radio guys I've met were more down-to-earth and unlike audiophools did not spend $199.98 for a few feet of gold-plated cable with individual electron spin control and all that.
Your numbers are meaningless because a coil is not a radio. Why don't you learn about the actual topic rather than just trying to rain on other's parade?
How much bandwidth is available on an AM radio station??? Do you actually know much about crystal radios?
Again, you are not speaking from knowledge. There are ham radio antennas with exactly this sort of high Q and they manage to maintain tuning during 100 watt transmissions.
Why are you guys trying to discuss a topic you actually know little about.
Q is a measure of the losses. Having a high Q in the coil means the coil has lower losses. Having a higher Q in the tuning capacitor means it has lower losses. The lower the losses the more power that ends up in the headphones.
The Q of the radio won't be the same as the Q of the components because you are sucking off power to drive the headphones. Besides, the number you came up with (10 kHz) would be perfect for AM radio if you can get that, that is the channel spacing. Great selectivity.
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