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Zero Beat


What is central to that....is the concept of "heterodyning".

When two signals are mixed in a circuit you get "extra frequencies" from the process. Most popular are sums and differences.

When two signals are "mixed" that are "close enough" together....the difference frequency will be audible. If they are 1 KHz apart, you will acutally hear a 1 KHz squeal.

The way you use that to your advantage... is to tune...with the presence of another oscillator as reference. When they are close enough to be audible, a high frequency audio tone will be heard. As they get closer together that high pitch will come down because the "difference" frequencies are coming down. When they finally approach each other the "difference" will eventually come to 0 and you will no longer hear an audio tone.
 
An SSB signal has no carrier so the receiver has to inject a carrier onto the signal in order to "decode" it A CW signal needs a separate carrier to "beat" with to produce that "beep" sound. The receiver injects that carrier which is tunable. The difference in frequency between the incoming signal and the carrier that the receiver injects appears as a tone on CW and as a different pitch on SSB. When both the incoming signal and the receiver's injected frequency are identical it is called zero beat. You can see this on AM when two signals very close in frequency mix as the signal strength wavers up and down as the two signals add and subtract in strength as they mix in and out of phase.
 
If you play guitar think of it like how you tune it.

You play one of the tuning harmonics or open string and compare it to the same note or harmonic tone on the next string. It's tuned when you hear no warble between the 2.

If it's off, typically you lower the pitch of the string being tuned to make it warble then increase tension to bring it up to pitch with no warble.

Now you just zero beat two strings together.
 
I'm stretching my knowledge here.....
I think some radios have an additional oscillator...called a BFO for "Beat frequency Oscillator".... if a radio doesn't have one..... I'm out of steam at this point....
 
Correct me if I'm wrong on my signalgenerator I have 2 bnc connections one connection is for modulation in/out other is for rf/out. Now does the modulation input from generator goes into antenna jack of radio then antenna gets connected to rf/out of signalgenerator?
 
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Er, no...

You send an AUDIO signal to Modulation In - like a Line In from a Stereo system. You may have more options but I'd have to see your BACK Panel to help more...


RF out goes to Radios Antenna Jack - THRU a buffer resistor (Use 50 ohm ACROSS the Center to Shield)
 
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kaos513,
Feel free to correct me if I am wrong. I have a similar RF generator (Mine is an HP 8657D. Very similar to yours)
There is a BNC jack on the front panel labeled "AM/FM 1 V Peak In/Out". I believe you can use this jack to directly inject an audio tone (1KHz or 400 Hz in my case) into the microphone jack to "peak" the transmit of your radio (though I have never used mine this way) or you can supply an audio tone from an external audio tone generator (of any audio tone you wish) into this jack that will be mixed with the RF output to peak the receiver section of your radio. (using the "Ext" button on the front panel of the RF Signal Generator)

Most alignment instructions state to "inject a 27.185Mhz, 1000Hz (or 1Khz) @ 30% modulation" (or something very similar) to peak the receiver section. Using the RF OUTPUT jack on the Signal Generator and pressing the "Int" button on the left side of the front panel that is connected to the antenna connector of your transceiver.

Using the supplied BNC jack on the front of your RF signal generator, you could use an external Audio Signal Generator and inject an 800Hz or 300Hz or 199Hz or whatever tone you wish into the RF Signal Generator that will then be mixed with the RF signal output to align the receiver section.

Personally, I use the standard 1Khz tone the signal generator supplies for receiver alignment as it provides a "comfortable tone" for my ears to focus on while peaking the various coils. I also have a separate audio signal generator that will inject a single tone or a two tone input into the microphone for transmitter alignment.

I hope this helps.

73
David
 
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Er, no...

You send an AUDIO signal to Modulation In - like a Line In from a Stereo system. You may have more options but I'd have to see your BACK Panel to help more...


RF out goes to Radios Antenna Jack - THRU a buffer resistor (Use 50 ohm ACROSS the Center to Shield)
 

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Thanks - here's some help for you...
upload_2020-4-14_18-38-47.png
And GOOD NEWS
Did not see this before!
YOU DO HAVE TEST TONES!
AWESOME!
Self contained...
upload_2020-4-14_18-43-40.png

The rest should be pretty self explanatory for you....
upload_2020-4-14_18-46-17.png
Just remember this thin g generates a CARRIER SIGNAL
YOU can Modulate it or not - AM or FM modes
Use Rear panel for 50 ohm out...​
 

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