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Author Topic: Zero Beat  (Read 1057 times)
KF5YU
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Posts: 18




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« on: October 01, 2002, 10:21:05 AM »

I have an ICOM 751A that uses a 700hz sidetone for cw monitoring. I assume that if I audibly match the cw sidetone to the incoming cw signal that I'm zero beat. Am I correct? As a side note, I would be curious if anyone has had good results with optional filters in the 751A for cw use. I tried the 250hz 455if filter and the audio quality is awful.
Thanks...
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WB2WIK
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Posts: 20611




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« Reply #1 on: October 01, 2002, 04:43:53 PM »

Yes, if you tune the received signal to match the sidetone frequency, you will be zero beat with the IC-751(A).

The narrow CW filter for the '751A, as for most rigs, sounds lousy, especially with a speaker.  Using good communications headphones, it will sound a bit better.  But it is annoying to most people (including me) to listen to audio that is so restricted in frequency response -- it sounds hollow and muffled, and that's normal.

I prefer to use much wider filters for CW, and rely on QRM fighting tools such as notch filters, passband tuning or IF shift, and, in more modern rigs, DSP, to minimize interference.  Personally, I have probably $1000 worth of narrow CW filters in various rigs, and rarely use any of them.

WB2WIK/6
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DJ1YFK
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« Reply #2 on: October 09, 2002, 07:53:52 AM »

Unfortunetely this is not the case with all RIGs. My FT-890 has a sidetone of about 830 Hz while the BFO-Shift is 700 Hz ;(
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K6SDW
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« Reply #3 on: December 04, 2002, 07:24:44 PM »

I struggled with which CW filter to add to my 751A and decided on the 500hz, low-IF CW filter and use the other QRM-fighting tools, PBT shift and the notch filter, to eliminate QRM... So far, I'm happy with this setup, although the quality of audio does indeed suffer when the filter is in the circuit. The 751A does an excellent job of getting rid of close-channel QRM when the 500hz filter is in so I guess less than stellar audio is the price to be paid for little or no interference, eh?

And, I do a agree that when running CW and a crowded band a good-quality headphones is the only way to go!

73....ed
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VE3WBE
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Posts: 8




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« Reply #4 on: January 05, 2003, 06:24:52 PM »

Ihave a Yaesu 890 and I gather from a previous post that the sidetone is around 830 and BFO is 700 Hz. If I  tune an incoming signal to a null what frequency is it transmitting on? Is it what I see on display or that value + [or-] 700 hz?  Thanks in advance for your help.   Ron VE3WBE
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