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BFO, CW, sideband question



 
 
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  #11  
Old October 29th 05, 07:53 AM
Wor
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Default BFO, CW, sideband question

Hi!
Just to make things more complex (or simple). When you tune from LSB to USB
you also change the frequency of BFO, putting it on one side or another of
the IF filter. If you listen to LSB on USB position you can put the
simulated carrier frequency on the right place, but signal is out of IF
passband.
Sorry for my bad English. Hope you understand.
Damir 9A3IV


  #12  
Old October 29th 05, 12:42 PM
Scott
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Default BFO, CW, sideband question

Actually, I think the convention is LSB below 9 MHz and USB above 9 MHz.
That comes from the fact that most old rigs used 9 MHz as the I.F.
Doesn't really matter though since our voice bands are 40M and 20M (CW
only on 30M), so by convention, we use LSB on 40M and below and USB on
20M and above. However, one can reverse this if one desires. It will
just confuse new people when they try to tune you in and wonder why they
can't get you tuned in...

Scott
N0EDV

Doug Smith W9WI wrote:
Jaggy Taggy wrote:



It is traditional for amateurs to transmit the lower sideband below
10MHz and the upper sideband above 10MHz. Hence, you need to use LSB to
receive SSB signals on the low bands -- the upper sideband simply
doesn't exist on these signals. And vice-versa on the higher bands.

  #13  
Old October 29th 05, 01:43 PM
William E. Sabin
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Default BFO, CW, sideband question

Modern radios such as the FT1000MP Mk V automatically change the internal
local oscillator frequencies so that USB, LSB and CW appear on the same
indicated signal frequency, which is what we want. In CW we get a certain
pitch frequency such as 500 Hz (not zero beat) at the signal frequency. The
value of this pitch frequency can be changed from the front panel by the
operator to suit his preference.

In my homebrew rcvr I use the CW USB setting only. As I tune up the band I
hear the high pitch of a signal first and it then decreases pitch as I
continue to tune up the band (my preference). I use a single xtal filter
frequency for USB/LSB and a single xtal filter frequency for CW. The BFO
xtal frequency and the VFO frequency counter digital readout (not the actual
VFO frequency itself) are automatically changed to their correct values in
LSB, CW or USB mode. In CW mode I then have a 500 Hz beat note, which is
what I want, not zero beat, and the CW BFO xtal is then the correct value
for CW USB.

For a brief description of my homebrew rcvr see QRZ.COM, W0IYH.

Bill W0IYH

"Wor" wrote in message
...
Hi!
Just to make things more complex (or simple). When you tune from LSB to
USB
you also change the frequency of BFO, putting it on one side or another of
the IF filter. If you listen to LSB on USB position you can put the
simulated carrier frequency on the right place, but signal is out of IF
passband.
Sorry for my bad English. Hope you understand.
Damir 9A3IV




  #14  
Old October 29th 05, 02:35 PM
Doug Smith W9WI
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Posts: n/a
Default BFO, CW, sideband question

Scott wrote:
Actually, I think the convention is LSB below 9 MHz and USB above 9 MHz.
That comes from the fact that most old rigs used 9 MHz as the I.F.
Doesn't really matter though since our voice bands are 40M and 20M (CW
only on 30M), so by convention, we use LSB on 40M and below and USB on
20M and above. However, one can reverse this if one desires. It will
just confuse new people when they try to tune you in and wonder why they
can't get you tuned in...


Yeah, and more than once I've scratched my head about what type of voice
encryption someone was using in the middle of 20 meters before it dawned
on me to try listening on LSBgrin!

The 10MHz figure is somewhat arbitrary since indeed there are no amateur
voice frequencies between 7.3 and 14.1MHz - and commercial services
don't follow our LSB/USB convention.

As I understood it, the decision to use different sidebands in the two
spectrum areas came from the design of some early SSB equipment. If you
used a 9MHz IF and a 5.0-5.5MHz VFO, you could cover both 80 and 20
meters without having to mess with heterodyne oscillators. But since
you'd be using addition on 20 vs. subtraction on 80, the sidebands would
flip.

(there's GOT to be a better way to say that but it's too darned early in
the morning!)

At the time either there wasn't a phone band yet on 40 or phone
privileges there were very new & SSBers didn't care that much about it.
15 was also very new or non-existant, and I suspect most SSBers didn't
believe anyone had a receiver stable enough to receive SSB on 28MHz!
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

  #15  
Old October 30th 05, 12:44 PM
Scott
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Posts: n/a
Default BFO, CW, sideband question

Yup, you've got it!

Now for the $64,000 question (which will only buy about 21,000 gallons
of gas these days!)...With these modern rigs, if I want to answer
someone calling CQ on CW, how do I adjust my radio to be on exactly the
same frequency as they are calling on (to conserve spectrum for other
operators)??? My "old" TS-520 has a "Tune" position, which sets the bfo
frequency exactly to the I.F. frequency (I don't have the service manual
in front of me, but follow the logic here). As I tune the radio (with
the VFO) in this TUNE position, when I have the VFO set to provide zero
beat, I will be right on his frequency since my BFO is running at the
I.F. frequency (9 MHz) and the combination of the far end transmitter
frequency and MY VFO frequency gives an I.F. output at 9 Mhz, so the
difference in frequency is zero. Whent I then return my switch from the
"Tune" position to the CW position, it shifts the BFO 800 Hz in SOME
direction (up or down, I can't remember and I don't really care!). Now
his signal mixed with my VFO and my now shifted BFO (which is now
running at 9.0008 MHz, for example) provides a tone of 800 Hz. Easy!

My "new" TS-690S doesn't have a TUNE position. The manual says to tune
for a tone frequency of 800 Hz (or whatever you have the "CW Tone"
frequency programmed into the radio). My question is how the $#@% do I
know when I have an 800 Hz tone coming out of my radio? Do they really
expect me to have a freq. counter hooked up to the speaker? I have
overcome this by setting the RIT to display either 800 Hz up or down
(can't remember which right now), turn on the RIT, zero beat they guy,
turn off the RIT and then I will be on his frequency. I find it's
easier to CALL CQ and let the other guy worry about getting on MY
frequency

Scott
N0EDV


Doug Smith W9WI wrote:



As I understood it, the decision to use different sidebands in the two
spectrum areas came from the design of some early SSB equipment. If you
used a 9MHz IF and a 5.0-5.5MHz VFO, you could cover both 80 and 20
meters without having to mess with heterodyne oscillators. But since
you'd be using addition on 20 vs. subtraction on 80, the sidebands would
flip.

(there's GOT to be a better way to say that but it's too darned early in
the morning!)

  #16  
Old October 30th 05, 03:29 PM
Doug Smith W9WI
Guest
 
Posts: n/a
Default BFO, CW, sideband question

Scott wrote:
Now for the $64,000 question (which will only buy about 21,000 gallons
of gas these days!)...With these modern rigs, if I want to answer
someone calling CQ on CW, how do I adjust my radio to be on exactly the
same frequency as they are calling on (to conserve spectrum for other
operators)???


Newer rigs tie the sidetone to the offset, so that if you zero-beat the
sidetone with received signals you're transmitting on the same frequency
as the other guy. In most rigs if you close the key without putting the
rig in transmit (i.e., break-in is off) you'll get a sidetone without
muting the receiver, allowing you to zero-beat the sidetone.

Older rigs often had a "SPOT" button which keyed up low-power
transmitter stages to allow you to zero-beat the transmitter against
received signals. My FT1000MP also has such a button - I'm sure the
electronics behind it are very different but its purpose and function
are the same as in the old rigs.

To be honest I don't worry about it. After 30 years of CW operating I'm
pretty good at getting it right!
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

  #17  
Old October 30th 05, 06:02 PM
Tim Shoppa
Guest
 
Posts: n/a
Default BFO, CW, sideband question


Scott wrote:
My "new" TS-690S doesn't have a TUNE position. The manual says to tune
for a tone frequency of 800 Hz (or whatever you have the "CW Tone"
frequency programmed into the radio). My question is how the $#@% do I
know when I have an 800 Hz tone coming out of my radio?


The sidetone you hear when you key down is going to be pretty close
to the 800Hz offset you need. So just tune the other guy until he
sounds roughly the same note.

Do they really
expect me to have a freq. counter hooked up to the speaker?


Gees, give guys a 8-digit frequency counter and they think they
have to be tuned to 1Hz to work somebody else. Most of my rigs
had more than 800Hz of chirp when I bought them :-).

Tim.

 




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