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Author Topic: Does anybody zero beat a QSO anymore?  (Read 36543 times)
AA4PB
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« Reply #30 on: January 24, 2014, 09:21:25 AM »

In this case, "zero beating" means tuning your transceiver until your transmit frequency is exactly the same (i.e. zero beat) as the other station's transmit frequency. That's done by tuning the signal until the beat note is equal to the transceiver's frequency offset (800Hz in your case). The exact frequency is different for different transceivers.

The "beat detector" that was mentioned is a tuning aid with an LED that lights when the received audio note is equal to whatever frequency the detector is set to. In most cases these use a phase locked loop (PLL) that is adjusted to the same frequency as your transceiver's offset. Then you get a visual indication when the tuning is correct in lieu of requiring you to have a perfect pitch ear.

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K8AXW
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« Reply #31 on: January 24, 2014, 09:51:46 AM »

PB: I understand your explanation to mean that I've been doing it properly and the whole discussion here has been over 100-200Hz because of differences in hearing?

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AA4PB
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« Reply #32 on: January 24, 2014, 10:00:05 AM »

PB: I understand your explanation to mean that I've been doing it properly and the whole discussion here has been over 100-200Hz because of differences in hearing?

You are doing it correctly. The only time it should become a problem is if the other station is using a very narrow filter and your tuning error results in you being outside the bandwidth of his receiver so that he doesn't hear you.
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PA0KDW
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« Reply #33 on: January 24, 2014, 12:28:14 PM »

There is another point here, may be it is already mentioned, Most of the text I let pronounce due to visually impaired.

I am used to homebrew my own equipment.

For CW a direct conversion receiver and transmitter is OK.  However you have your sharp CW filtering in the audio, say at 800 Hz center frequency.
That means that you get two points of reception on your frequency scale with 800 Hz beatnote left and right of the transmitting frequency of the received station. So when you transmit you need an offset that is the same (800 Hz), however it must be on the same side of the transmitting station. So in one of your two receiving points you have a severe tx offset of the received station.

Frans
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K8AXW
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« Reply #34 on: January 24, 2014, 05:45:19 PM »

Frans:  You are 100% correct.  I built a direct conversion 40m CW transceiver many years ago (I still have it) and one of the first things I had to focus on was using the correct side-band.

I haven't used this rig for many years but as I recall there was a protocol on which side-band to use for the various bands, exactly like the existing SSB protocol.

You've made a good point.  I have been having a very difficult time understanding what has been discussed here.

Al - K8AXW
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KE7TMA
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« Reply #35 on: January 28, 2014, 05:32:23 PM »

If the other guy isn't within my 500Hz passband he isn't answering my CQ.
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KI6LZ
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« Reply #36 on: January 28, 2014, 06:10:49 PM »

Gave up zero beating years ago. Would suggest the same to all. After a CQ everyone zero beat to me and I could not copy anyone. Now I offset my xmit freq abt 30-100 Hz and seem to get through to CQers easily.
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KE7TMA
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« Reply #37 on: January 31, 2014, 03:03:26 PM »

Gave up zero beating years ago. Would suggest the same to all. After a CQ everyone zero beat to me and I could not copy anyone. Now I offset my xmit freq abt 30-100 Hz and seem to get through to CQers easily.


Isn't this more of a sign that your transceiver's indicated and actual frequencies are out of calibration than anything else?
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WA9CFK
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« Reply #38 on: February 03, 2014, 10:53:44 AM »

If two stations were at true zero beat they would not hear each other. Most modern transceivers offset the transmitted signal a small amount.

When using a separate transmitter and receiver I set my transmitted frequency a tad above true zero beat. This is particularly true with direct conversion receivers which tune both sides of zero beat.

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AA4PB
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« Reply #39 on: February 03, 2014, 11:03:11 AM »

If your transmit frequencies are zero beat (i.e. identical) then you will hear each other. You won't hear him if you set your receiver zero beat to his transmitter.
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WA9CFK
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« Reply #40 on: February 06, 2014, 02:37:06 PM »

With a modern transceiver you tune in the signal in until it sounds good, transmit, and the rig has taken care of the frequency offset etc.

When I play with my 1960's vintage receiver, I can tune above and below the zero beat note and listen; so where do I set my transmitter?
 
My experience is to tune the receiver through zero beat on the received signal, to a pleasant sounding note on the low frequency side of zero beat.

Then I listen to my transmitter signal as it passes through the low side frequency zero beat to the same note on the high frequency side.
 
This offsets the transmitter frequency up the same amount as the lower offset I selected for the receiver or the same as the received frequency.

Try not to think too hard on this or like me you will be mumbling to yourself.   Shocked    It was a lot easier as a rock-bound novice when you transmitted then scanned the band or a reply.  Wink
   
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W1JKA
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« Reply #41 on: February 07, 2014, 03:45:36 AM »

Re: WA9CFK  reply #40

You nailed it, it's called the KISS principle.

Your two answers concerning modern vs. vintage gear should be added to the multiple guess question pool for the Extra Class learners permit issued by the FCC.
« Last Edit: February 07, 2014, 04:05:22 AM by W1JKA » Logged
KF4ZGZ
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« Reply #42 on: February 08, 2014, 10:37:36 AM »

Not many.
And I ,for one, am glad. It allows me to take a few seconds, zero beat, and bust a cw pile-up with one call on 100 watts and a crappy antenna.
SHHHHHH!

It can be out little secret!

Matt
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AA4PB
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« Reply #43 on: February 08, 2014, 11:05:58 AM »

With a modern transceiver you tune in the signal in until it sounds good, transmit, and the rig has taken care of the frequency offset etc.

If you want to be exactly on the other station's frequency (zero beat) then you have to tune the transceiver until the tone of the CW signal exactly matches your Rx/Tx offset. That is normally equal to your sidetone frequency if the transceiver is properly aligned. If you are using a wide filter and you just tune to some tone frequency that sounds good to you, you may be off frequency by several hundred Hz. If the other station is using a narrow filter he may not hear you at all if you are that far off.

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KI6LZ
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« Reply #44 on: February 08, 2014, 11:17:10 AM »

Here's one instance where you don't want to zero beat. During a contest, think it was sweepstakes, after calling CQ I had at least 5 stations calling me. For some reason 4 were zero beat, nearly same signal strength. The 1 that was off by 80 HZ I could copy, those zero beat I could not make out any letters of their call sign. As mentioned earlier I always have a shift somewhere between 30 and 100 HZ to avoid those that zero beat. I always seem to get through. Tip of the day.
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