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Author Topic: Zero beat for CW using seperate trans and rec  (Read 949 times)
KE1MB
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Posts: 65




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« on: August 25, 2002, 02:56:40 PM »

I have a Heathkit HR 1680 and 1681 transmiter and receiver. This is a CW rig. There is a "spot" switch. When I turn on the spot switch I will hear a tone in the receiver. At what point do I have the transmitter and receiver on the same frequency? Do I tune the receiver untill I reach the lowest possable tone untill there is only a reading on the s meter, is this a zero beat? or do I adjust the receiver untill I hear a tone on the speaker. I am new to this and am not really sure how to use a seperate transmitter and receiver for CW.

thanks
Joe
KE1MB
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AC5E
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Posts: 3585




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« Reply #1 on: August 25, 2002, 05:26:14 PM »

Hi Joe: Well, that question brings back memories!

The usual drill back in the 1950's and 60's for those of us with an automatic TR switch was to find a station calling CQ, turn on the VFO (only), tune (spot) the VFO until the VFO was at the same pitch as the desired station, release the tune/spot/vfo switch and turn on the transmitter switch, wait for the other station's K, and then hit the key.

If you did not have either a TR relay or one of EF Johnson's neat tube type TR boxes you usually had to manually switch the antenna from the reciever to the transmitter before you hit the key, otherwise you would fry the RF circuits in the reciever.

And some of the real dyed in the wool CW set would actually unplug the antenna and change it to the transmitter before they could make a call.

Hope this helps you sort it all out.

73  Pete Allen  AC5E
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W4TYU
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Posts: 518




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« Reply #2 on: August 26, 2002, 02:29:03 AM »

Likewise a lot of memories.  
My method  using SEPARATE transmitting and receiving antennas was:
1. Tune the receiver until the lowest possible tone was heard. This is "zero beat"

2. Key the transmitter and tune the vfo until you again hear the lowest possible tone in the receiver. The transmitter and receiver are now on the same frequency.
To operate, retune the receiver until you have the pitch of the sidetone that you like.

It is quicker done than said.

Ole man JEAN   W4TYU
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W8MW
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Posts: 314




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« Reply #3 on: August 26, 2002, 05:27:41 AM »

Yup that sure does bring back memories.  Joe the spot switch lets you determine the frequency of the transmitter VFO without actually transmitting a signal over the air.  That's a handy feature which was lacking in some gear.  

A great thing about separate rx/tx is the ability to achieve Dead Zero Beat.  This was once a point of pride among CW ops, knowing that all stations in a QSO were operating on the exact same frequency. That kind of precision became pretty much a lost art as transceivers took over.  

GL with the FB boat anchors!

73, Mike W8MW  
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AC5E
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« Reply #4 on: August 26, 2002, 05:54:13 AM »

Chuckle: my problem was always that the VFO was so strong it completely blanked the station I wanted to call. So I had to tune for the same tone instead of true zero beat. But I usually made the contact anyhow.

73  Pete AC5E
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W5HTW
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« Reply #5 on: August 26, 2002, 06:17:20 PM »

Likewise a lot of memories.
                My method using SEPARATE transmitting and receiving antennas was:
                1. Tune the receiver until the lowest possible tone was heard. This is "zero beat"

                2. Key the transmitter and tune the vfo until you again hear the lowest possible tone
                in the receiver. The transmitter and receiver are now on the same frequency.
                To operate, retune the receiver until you have the pitch of the sidetone that you like.

                It is quicker done than said.

                Ole man JEAN W4TYU

That is zero beat, but means moving the transmitter VFO with the transmitter on the air.   I use the Drake twins, and the Collins S-Line 75S3B which has a tuneable BFO.  The Drake does not, but does have passband tuning.  

Almost all separates (and yours is included) has the spotting capability.   You are tuning around on the receiver and hear someone calling CQ.  

1.  If you have an adjustable BFO, set it to zero-center first.  If you do not have an adjustable BFO, just go on to step 2, below.

2.  Tune your receiver to zero beat the incoming signal - so that the pitch goes so low you no longer hear any tone at all.

3.  Press the spotting switch on your TX and move it so that you hear your own spot signal also at zero pitch.

4.  Release the spotting switch and rotate your adjustable BFO to a pleasant pitch to your ears, OR, if your receiver does not have an adjustable BFO, move your receiver VFO dial off frequency by about 600 Hertz - to whatever pitch suits you.  (If the other guy has already ended his transmission, just press your spot switch again and don't move your transmitter, but instead move the receiver VFO or BFO to get the pitch you want.)

All this can be done in under ten seconds, and more like four or five seconds if your transmitter isn't far off freq and needing retuning.

73
Ed
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