[Elecraft] Sideband reversal

[N2EY@aol.com]

In a message dated 1/28/02 11:32:14 AM Eastern Standard Time, 
rondec@easystreet.com writes:

> > The Swan-350 (and possibly other swan rigs) reversed sidebands
>  > between upper
>  > and lower bands.  It was an analog rig, so there were backward
>  > scales on the
>  > dial for the reversed bands.

The Swans used a single-conversion design with an IF in the 5 MHz range. The 
VFO
is above the signal frequency on 80 and 40 and below it on 20, 15 and 10. End 
result
is the sideband convention observed. 

However, that convention long predates Swan. It began much earlier.

>  > In fact I think this is how the convention of
>  > using LSB below 20m, and USB for 20m and up got started.

By the time Swan appeared it was long established.
>  
>  The early "low cost" commercial SSB filters used an i-f of 9 MHz. 

True.

>  With
>  simple, single conversion designs that resulted on the output sideband 
being
>  the lower one on bands below that frequency and on the upper side for those
>  above.
>  
Actually, it doesn't work out that way.

It is true that if you have a 9 Mhz IF and use a 5-5.5 MHz VFO, you can cover 
both
80 and 20 in a single conversion design. Many rigs used this scheme. Some 
added
40 by heterodyning or tripling the VFO to 16-16.5 MHz. 

One of the bands "tunes backwards" with this scheme, but it does NOT invert 
sideband on one band and not the other. The same sideband comes out as went 
into
the mixer. 

To invert sidebands, the heterodyne oscillator must be above the input and 
output
frequencies of the mixer. Otherwise no inversion occurs.

>  The 'convention' has gotten so ingrained that I was "reading the mail" on 
40
>  SSB one day and heard some ops telling two others who were on USB that they
>  were transmitting "illegally" since the FCC required lower sideband on 40
>  and below and upper on 20 and up. Not true at all, of course. 

Yup - but good operating practice in most situations.

> The choice of
>  sidebands is just a long-standing convention based on what was 'convenient'
>  for the manufacturers.
> 
See above!

The K2 has the LO below the signal frequency on some bands and above it on 
others. This minimizes the range needed to cover 160 thru 10 with the VCO. The
firmware figures it all out automatically.

73 de Jim, N2EY