15 votes
Accepted

Why would you need a signal generator to receive early satellite transmissions?

The earliest Soviet satellites, like Sputnik 1, transmitted what amounted to a CW stream -- just pulsed RF at pretty low power (later Sputniks transmitted data by pulse width modulation, still ...
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  • 3,891
12 votes
Accepted

Can SDR receivers be detected remotely?

You might be able to detect a regenerative receiver. This is because this receiver topology uses positive feedback to increase the Q of the tuned circuit. If the feedback is too much it becomes an ...
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7 votes
Accepted

Is there a best ratio of L to C in a resonant circuit?

There is no hard and fast rule. Consider that in some LC circuit applications, a lower Q may be desirable in order to achieve a wider bandwidth. In other cases, a very high Q may be desirable for ...
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  • 18.2k
6 votes
Accepted

How does this Pixie circuit produce a beat frequency?

Q1 forms a Colpitts crystal oscillator. It uses the reverse biased D2 as a varicap (variable capacitor) to pull the crystal frequency by 700 to 800 Hz, This frequency beats with the received frequency ...
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  • 18.2k
6 votes

Shaving Quartz Crystal for New Frequency

It is the thickness of the crystal that primarily determines its operating frequency. When crystals are manufactured, they are gradually ground down in a special fixture. The operator monitors the ...
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6 votes

Design of oscillator

I would like to applaud your interest not only for homemade transmitters but also a theory! I started to build my own receivers and transmitters not a long time ago and completely understand how ...
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5 votes
Accepted

Toroid Coupling Issue in Common-base Amplifier

The problem is most likely the type 43 core material. It is quite lossy at 21 MHz and is a poor choice for the auto-transformer. Unlike a transmission line transformer, the auto-transformer relies on ...
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  • 18.2k
5 votes
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Shaving Quartz Crystal for New Frequency

didn't do it, but back in the day stumbled across this, and thought it might be on-topic. EDIT: inserted original text below. To: Multiple recipients of list From: carreiro@netcom.com (Paul ...
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4 votes
Accepted

SSB demodulation

To understand better, I'd suggest you follow this: 1) If you have an AM transmitter at 10.000 MHz (let's use simple numbers). If someone whistles in the microphone, at, say, 1kHz, two sidebands will ...
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  • 699
4 votes

"Local oscillator generates a frequency twice lower than received signals". Why and how does it work?

The oscillator may really be running at half of the received frequency. Search for Poliakov mixer on the web for an example of this.
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  • 51
3 votes

How can I tell the frequency without an oscilloscope, or frequency counter?

You can use a radio receiver that has appropriate coverage, but the catch is that you have to sweep across the entire frequency range the oscillator might be oscillating at — you're limited to the ...
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  • 23.1k
2 votes

"Local oscillator generates a frequency twice lower than received signals". Why and how does it work?

Mixing products from the oscillator. Best way is to use the oscillator on a higher frequency. Example: receiving 10 MHz, mf is say 9 MHz, so the oscillator is on 19 MHz. Demodulation does it´s work ...
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  • 21
2 votes

Shaving Quartz Crystal for New Frequency

I can second the comments about bon-ami. Way back 2/3 of the way through the last century, we also used some of the super fine abrasives used for the later stages of grinding amateur telescope ...
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2 votes

Shaving Quartz Crystal for New Frequency

I only scanned that whole quote. I have my father's W9EHS SK, FT crystal grinding equipment. It has two special grinding compounds and the two plates. One of the plates has a rosette-like shaped ...
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2 votes

SSB demodulation

I would suggest looking at a couple of sites: http://www.radio-electronics.com/info/rf-technology-design/superheterodyne-radio-receiver/basics-tutorial.php http://users.tpg.com.au/users/ldbutler/...
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2 votes

Doppler Shift Compensation in Inter Satellite Communication

I am jumping in late, and I hope that the OP received an out-of-band answer, or found their own answer. I have a problem with the question, given the statement that the OP is using a Kostas Loop for ...
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  • 266
2 votes

Does the waveform of the VFO necessarily have to be sinusoidal?

A small extra bit of information... Even though many VFO circuit descriptions, as you say, make it a point mentioning the 'cleanliness', by far most mixer circuits then proceed to convert the sine ...
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  • 699
2 votes
Accepted

Does the waveform of the VFO necessarily have to be sinusoidal?

Does the VFO signal necessarily have to be a sinusoid? Absolutely not. For each frequency component on a mixer's inputs, it produces at the output the sum and difference of those frequency components....
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2 votes

Frequency divider in premix oscillator (PMO)

Not really a problem – just a technological challenge. The challenge, in almost any case, lies in the fact that per definition, the input is a harmonic of the output of the frequency divider, and ...
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2 votes

"Local oscillator generates a frequency twice lower than received signals". Why and how does it work?

This appears to be a design that uses a harmonic mixer (or a subharmonic mixer, both names are used on the Wikipedia page). While these are more commonly used at microwave or millimeter wave ...
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2 votes

78.5MHz AM receiver self-oscillation

When designing circuits for the VHF region, careful design and construction practices must be utilized in order to obtain stable and repeatable gain. Here are a few thoughts that may improve the ...
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  • 18.2k
2 votes

How to use FE-5650A rubidium frequency standard?

See http://www.leapsecond.com/museum/fei5650a/FE5650A-pin-out.gif for the pin out of option 58. http://www.leapsecond.com/museum/fei5650a/ supplies more detail.
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2 votes

Can SDR receivers be detected remotely?

A direct sampling SDR does not need a LO anywhere within the frequency range or tracking the signal of interest. A processor running off of a fixed clock frequency well above twice the RF signal ...
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  • 12.5k
2 votes

How can an RF coil emit at 3 different frequencies at the same time during Amplitude Modulation?

First off, an RF coil does not oscillate. It can have an oscillating current in it, but it is just one part of an oscillator circuit. In an AM transmitter, the sidebands are not generated in the ...
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  • 252
1 vote

How can an RF coil emit at 3 different frequencies at the same time during Amplitude Modulation?

It's a mathematical equivalence. One of the trigonometric identities. If you amplitude modulate a sine wave, or sum 3 pure sinewaves of certain frequencies and amplitudes together, you get exactly ...
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  • 12.5k
1 vote

Design of oscillator

The good news is you must know that engineers must learn to read and write specifications before they can learn how to design. So don't even try. You must start with good specs !!! (lots of ...
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1 vote

Design of oscillator

I find these Electronics Tutorials on Oscillators to be very instructive. LTSpice, the free electronic simulator from Analog Devices, includes example circuits for Clapp, Colpitts and Hartley ...
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  • 7,693
1 vote

Toroid Coupling Issue in Common-base Amplifier

I thought I'd come back to this having discovered the real reason why I wasn't developing the expected voltage across the 50 ohm load. Glenn's answer was good and is still very relevant, but I made a ...
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  • 937
1 vote

Is there a best ratio of L to C in a resonant circuit?

There is definitely a best L to C ratio. You write: For 7030 kHz for example L=2.33 μH and C=220 pF, or L=23.3 μH and C=22 pF, or L=513 nH and C=1 nF, etc. If we increase the inductance, we can use a ...
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  • 899
1 vote

78.5MHz AM receiver self-oscillation

I see two coils in close proximity in the "as built" photo. One coil is connected to the detector; the other to the antenna -- and their axes are colinear. Whether this was the intent or not, your ...
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