Antenna ferrite loopsticks verses air core?

Yes, needs a Q spoiler! Mikek

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Certainly! For example,

+0.35v @ 150pA -+- | +-------+---------+------. | | | | 2.2G 22G 22G 2.2G | | | | | 10pF | | 10pF| +---||--+--. .--+--||--+------+---> 3.2Hz | \ / | | | / | 10pF Cload \| / \ |/ | Q1 |--------' '-------| Q2 === .. GND | | === Q1-2 = 2n5089 === GND GND

A very silly oscillator

Dissipation: 55pW

Au contraire! This basic astable forms the foundation for a 3.2Hz micro^H^H^H^Hacrocontroller, with applications for personal space travel, over-unity energy devices, and reversing global warming. :-)

Cheers, James Arthur

(Who once designed a modestly hi-Z amplifier for some crystal radio buffs. :-) (A work still in progress.)

You're making slightly more sense than Rickman, who hasn't responded to *any* of the numbers I suggested, but one thing still puzzles me.

Why worry about increasing Q above 500, when you can get more than the extra 0.2% (lost energy at Q=500) by adding 3 inches more antenna wire?

Doubling the Q doubles the voltage and halves the current, four times the impedance. It creates NO EXTRA POWER, except the tiny

1/Q resistive losses that are eliminated.

For a Q of 500 the power loss (hence the maximum possible saving) is only 0.2%. If you have a 40 foot long wire antenna, you can gain 0.2% by lengthening it by ONE INCH.

Furthermore, raising Q to 1500 (say) merely restricts the amount of side-band energy you gather in the first place. The amount of loss depends on how much energy exists in the high-audio part of the program material - but the point is that you're discarding that power in the hope of getting *more* power, but all you're doing is destroying your audio fidelity. Ben Tongue understands all this, but it seems that you don't understand him.

If you needed a high impedance to match your phones, and if you can tolerate the loss of high frequencies in the audio, you could use a higher Q. But you'd be better to limit the RF so you get the full audio bandwidth, then use an audio transformer to match your phones instead.

Does that make my points clearer?

Clifford Heath.

I know that. I said that. It creates NO EXTRA POWER, and only (from starting Q of 500) makes a TINY reduction in the net power after losses - because the losses were so small to start with.

Now go back and read what I wrote, before you respond again, because this response wasn't even relevant to what I actually wrote.

Clifford Heath.

If you aren't going to read the thread for context, then just stick with your taxes.

We're talking about increasing Q above where it starts to exclude some of the signal frequencies. Of course there is also noise excluded in that process, but that's unlikely to improve SNR.

Because we don't have any convenient audiophools to ridicule, but we can enjoy ridiculing radiophools.

It *is* a hobby. No one builds a crystal radio set because he wants to listen to talk radio.

You comments indicate you neither understand the hobby nor do you really understand the technology, but I believe the latter is a choice on your part. You seem to be deliberately refusing to try to understand what is being said.

Your comment above about not being able to hear a few dB is a good example of your mindset. Rather than trying to understand why anyone would care if tweaking the core material for a coil adds a few dB, you make a comment showing your disdain. Open your mind. Look at the bigger picture. You tell me why anyone cares about the few dB from optimizing this one feature? Someone could just as easily point to the many things you are involved in an nitpick any one action. But that would in no way diminish the activity as a whole.

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Rick C

You have eyes, yet you can not see.

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Rick C

Somewhere in the process of being in this discussion I cam across a web site (perhaps Kleijer's) that deeply analyzed the losses in the detector diode. I we pretty impressed.

Save a few dB in the coil, a few dB in the tuning capacitor, a few dB in the diode and use a very sensitive pair of headphones and you have a

*much* improved radio!

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Rick C

Probably Ben Tongue's site, he has multiple writings about diodes, The diode you pick is very dependent on the signal strength.

Mikek

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This seems to be a US specific thing. In Europe, there are not much local MF broadcasts any more. The situation was different 50 years ago, but now it is hard to find a local LF/MF/HF transmitter within

1000 km, thus a simple crystal radio is more or less useless.

That is US country specific.

Why should I deliberately bang my head against the wall ?

1-2 dB of extra loss is significant in UHF EME (moonbounce) communication, in which the amplifier itself has a noise figure in the order of 1 dB (i.e. 100 K noise temperature). For any MF communication circuits, the band noise is huge from location to location, from day to day or from hour to hour, so a 1-2 dB variation doesn't really cause problems.

I really do not understand why you make such fuss about LF, MF and lower HF. However, those few decibels are of great concern in UHF/SHF bands.

Why do you want to keep the receiver completely passive ?

A small solar cell o the headphone will charge a small battery, that can be used to drive a small RF/IF/AF amplifier over the night.

How about a two circuit MF AM receiver, with one resonant circuit tuned to your local strong MF (AM) station and the rectified DC power is used to run the "DX" receiver ?

I don't know the math but logically I don't see that adding 3 inches to a 50ft antenna is going to have the same effect as doubling Q. Here's a video, this guy built a very nice set, it's worth watching.

Mikek

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People have built them as you have suggested.

Mikek

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Are you suggesting the converse is true? Where external noise sources and interference are substantially above the thermally generated noise floor and first amplifier noise, the SNR will magically improve if you use a bigger aerial?

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Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

Because the added 3 inches will add equal amounts of signal and noise, resulting in no net improvement. It's always fun to drag things to their logical extreme. Instead of 3 inches, add 3 miles of wire. The recovered energy will be huge and possibly sufficient to draw an arc. But, so will the received atmospheric noise be huge by the same amount. Besides less loss, a higher Q also means more selectivity, so the receiver won't act the like the first crystal set I built in middle skool, which received and demodulated most of the AM broadcast band simultaneously. There's an upper limit to Q as set by the modulation bandwidth. The AM broadcast band runs about 10KHz per channel, so the maximum usable loaded Q would be: Q = 1,000 KHz / 10 KHz = 100 Any Q more than 100 at BCB frequencies will begin dropping the higher audio frequencies from the modulation. Too narrow band, and all you can hear will be CW (Morse Code). There's also the problem of tuning stability, where anything that causes the high Q coil to drift in frequency, will produce even harmonic distortion of the audio. Copper wire is not particularly temperature stable and will require some form of frequency or tuning stabilization.

Ok, back to taxes...

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Jeff Liebermann     jeffl@cruzio.com 
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Nearly everything you wrote is not relevant to the conversation I have been having. Why did you choose me to reply to? I was not addressing you.

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Rick C

** In another post on the same date, I pointed out the obvious truism that there is no such limit to the s/n of an AM broadcast.

In the primary reception area of an transmitter, the SIGNAL can be hugely bigger than the ambient and natural noise.

Only when DXing is the signal seriously compromised by noise. Even then, a directional antenna will favour the broadcast over noise arriving from all directions.

FYI:

the opposite of a false statement is not usually a true statement.

..... Phil

.... Phil