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Author Topic: USB on 7.230 40 meters?  (Read 13046 times)
WB2EOD
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Posts: 219




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« Reply #15 on: July 11, 2013, 04:46:19 PM »


The convention of using LSB on 160, 80 and 40 and USB on everything else goes back to the early days of SSB.
Within the transmitter, the signal was generated as upper sideband in the 8-9 MHz range.
One or more mixers then brought the signal to the correct frequency.
On 20 meters, for example, the 8.3 MHz USB signal might be mixed with a 6MHz signal, the output would be the SUM of the 2 signals or 14.3 MHz upper sideband.
On the other hand for 80 meters, the same 8.3MHz USB signal would be mixed with with a 12 MHz signal and the DIFFERENCE would be 3.7MHz.  Since we are 'subtracting', the original USB signal would be inverted to LOWER sideband. 
I have heard this explanation more than once and it does seem technically (if not historically) sound.

73
WB2EOD
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G3RZP
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Posts: 4589




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« Reply #16 on: July 12, 2013, 03:23:38 AM »

I've found references in the late 1940's/early 1950's to using a 5 MHz USB generator with a 9 MHz VFO: this gave LSB on 80 and USB on 20.
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W9GB
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Posts: 2623




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« Reply #17 on: July 12, 2013, 06:50:02 AM »

Quote from: KB9WQJ
For 2 nights in a row now I have heard a group at 7.230 USB (rather than LSB)
Correct.  I sometimes listen to this frequency of surplus military radio collectors, when they have technical discussions of various surplus, military/gov't radios (many that only operate USB or ISB).  Most of these surplus US military/state department/government radios (TransWorld, Collins/Rockwell, etc.) only have USB (no LSB mode).

BTW, THE 60 meter (5 MHz band) is also, USB -- just like the NTIA stations (who use commercial/military radio equip.), we share those 5 channels with.

When I was a Novice in early 1970s,
I use to listen to an AM group based in Ohio at 7240 kHz, they were entertaining.
« Last Edit: July 12, 2013, 06:59:09 AM by W9GB » Logged
N2EY
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Posts: 3879




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« Reply #18 on: July 12, 2013, 10:24:19 AM »

The convention of using LSB on 160, 80 and 40 and USB on everything else goes back to the early days of SSB.

That part is true.

Within the transmitter, the signal was generated as upper sideband in the 8-9 MHz range.
One or more mixers then brought the signal to the correct frequency.
On 20 meters, for example, the 8.3 MHz USB signal might be mixed with a 6MHz signal, the output would be the SUM of the 2 signals or 14.3 MHz upper sideband.

That was a common arrangement.


On the other hand for 80 meters, the same 8.3MHz USB signal would be mixed with with a 12 MHz signal and the DIFFERENCE would be 3.7MHz.  Since we are 'subtracting', the original USB signal would be inverted to LOWER sideband. 

I don't know any transmitter that did it that way. Not one.

I have heard this explanation more than once and it does seem technically (if not historically) sound.

But it's not what happened at all.

First off, it should be remembered the late 1940s the bands, subbands and licenses in the USA were somewhat different than today. In those days, the US ham bands were 80/75, 40, 20, 11 and 10 meters. 160 had been a popular ham band before WW2 but had been taken over by LORAN and we got it back in bits and pieces over several decades. 11 was given to hams as a sort of compensation but was shared with industrial, scientific and medical machines. 30, 17, 15, and 12 meters were years in the future.

On top of all that, 40 meters was all-CW, no phone operation allowed. So US 'phone hams focused on 75 and 20 - which were narrower back then.

The origin of the LSB/USB convention is what G3RZP posted: the use of an SSB generator in the 5 MHz range and a VFO or crystal oscillator in the 9 MHz range. This was done in the late 1940s. With such a system, the sideband inverts on 75 but not on 20. Both bands covered.

The original filter method used an LC filter down around 20 kHz, and needed two conversions to get to 5 MHz, followed by a third to get to the ham band. Lots of complexity but it worked. Crystal filters of the necessary characteristics did not exist yet, and mechanical filters were only good up to 500 kHz or so.

The phasing method came to the rescue, with the development of the Dome audio phase shift network. For some reason, it became popular to generate the SSB at 9 MHz and use a 5-6 MHz VFO to convert to 75 or 20. This scheme worked on other bands too - mix 9 MHz SSB with the third harmonic of the VFO and get on 40 or 10, mix with the second harmonic and get on 15. Commercial exciters such as the Central Electronics 10A, 10B and 20A appeared as early as 1952 using this method.

With the use of a 9 MHz SSB generator and 5 MHz VFO, the sideband DOES NOT invert when switching bands! But with a phasing-type generator, this is no problem because a simple phase reversal in one audio channel does the trick. A DPDT switch is all it takes.

There is a persistent urban legend that the USB/LSB convention came from the use of a 9 MHz SSB generator and 5 MHz VFO to get 75 and 20. This is a myth, because sideband inversion doesn't work that way. You only get inversion if the local oscillator is higher in frequency than both the input and output signals.

73 de Jim, N2EY

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G3RZP
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Posts: 4589




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« Reply #19 on: July 13, 2013, 04:20:40 AM »

Always puzzled me why third method wasn't more popular - I suspect because the complexity was more expensive than a crystal filter.
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W4OP
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Posts: 422


WWW

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« Reply #20 on: July 13, 2013, 02:14:46 PM »

With the use of a 9 MHz SSB generator and 5 MHz VFO, the sideband DOES NOT invert when switching bands! But with a phasing-type generator, this is no problem because a simple phase reversal in one audio channel does the trick. A DPDT switch is all it takes.

There is a persistent urban legend that the USB/LSB convention came from the use of a 9 MHz SSB generator and 5 MHz VFO to get 75 and 20. This is a myth, because sideband inversion doesn't work that way. You only get inversion if the local oscillator is higher in frequency than both the input and output signals.

73 de Jim, N2EY


Thanks Jim- I  have gotten tired of dispelling this myth over the years.

Dale W4OP
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G3RZP
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Posts: 4589




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« Reply #21 on: July 13, 2013, 03:17:31 PM »

One problem to watch with 9 MHz SSB  minus 5 MHz VFO is the spur of 4 times VFO minus two times SSB. i.e.,  20 to 22 MHz minus 18 MHz gives a spur covering 2 to 4 MHz, and falls in band. This really needs a balanced mixer to get rid of this 6th order spur.
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K9MHZ
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Posts: 406




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« Reply #22 on: July 27, 2013, 09:37:57 AM »

...All aviation radios only operate on upper side band...

Aircraft Band is AM.  


KE3WD....Maybe an example of doing your homework before correcting someone.  The voice portion of the VHF aircraft band is AM.  That's ATC, AIRINC, CTAF, company freqs, etc.  HF aircraft freqs are USB.  In the civilian world, it's used primarily over water for ATC, and in the military it's the same as well as some dedicated command and control freqs.  All USB.  When you check in with San Francisco or Gander Radio for example, you'll be assigned a primary and secondary HF USB freq, and then receive a SELCAL check with your aircraft's unique SELCAL address.  The freq that you dial into the control head is the freq of that sideband....NOT the 1.5 KHz offset deal that we have to do on 60 meters.  That's because everyone's on USB, so it would be a pointless step to compute an offset.

Today however, SATCOM and especially CPDLC are taking over in a big way.  CPDLC is near-real time ATC via data linking with the controlling agency.  The communication of that data linking goes through a hierarchy of onboard radio gear....VHF comm, then HF comm, then satellites....and will burst data when it has success, since using satellites is expensive.  This all relegates voice HF USB and SELCAL to a backup status, so listening to an HF USB ATC freq today would sound pretty dead....mostly HF SELCAL checks.  Those who still do get ATC via HF USB  are operating older gear, or are not otherwise equipped with modern gear.

 
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K9MHZ
Member

Posts: 406




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« Reply #23 on: July 27, 2013, 09:40:30 AM »

...All aviation radios only operate on upper side band...

Aircraft Band is AM.  


KE3WD....Maybe an example of doing your homework before correcting someone.  The voice portion of the VHF aircraft band is AM.  That's ATC, AIRINC, CTAF, company freqs, etc.  HF aircraft freqs are USB.  In the civilian world, it's used primarily over water for ATC, and in the military it's the same as well as some dedicated command and control freqs.  All USB.  When you check in with San Francisco or Gander Radio for example, you'll be assigned a primary and secondary HF USB freq, and then receive a SELCAL check with your aircraft's unique SELCAL address.  The freq that you dial into the control head is the freq of that sideband....NOT the 1.5 KHz offset deal that we have to do on 60 meters.  That's because everyone's on USB, so it would be a pointless step to compute an offset.

Today however, SATCOM and especially CPDLC are taking over in a big way.  CPDLC is near-real time ATC via data linking with the controlling agency.  The communication of that data linking goes through a hierarchy of onboard radio gear....VHF comm, then HF comm, then satellites....and will burst data when it has success, since using satellites is expensive.  This all relegates voice HF USB and SELCAL to a backup status, so listening to an HF USB ATC freq today would sound pretty dead....mostly HF SELCAL checks.  Those who still do get ATC via HF USB  are operating older aircraft, or are not otherwise equipped with modern gear.
 
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G3RZP
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Posts: 4589




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« Reply #24 on: July 27, 2013, 10:57:19 AM »

While the older Non Directional Beacons (NDB) in the 200 to 1600 kHz or so band (mostly below about 600kHz) are disappearing fast and many airline pilots will tell you that it is so long since they had to do a 'hold' pattern using NDBs that they have forgotten how!
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