IF Shifting vs. Sync Detection
 

Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

Liberals for Guns wrote:

Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

Depends on what one is listening to. IF shift (or passband tuning as it
may be called) will work with both AM and SSB signals.

As far as I know, the 'sync' function only works to 'even out' AM signals.
It would be best to get a receiver that includes both functions.

I'm using various Drake products here, and I don't really know if the R8
and R8B actually use a true IF shift, though they do have a 'passband
shift' function. They both have an audio notch filter.

The R8B has a 'selectable sideband sync', whereas the R8 does not.

The R7 has a 'true IF shift', that is there is no seperate upper and
lower sideband switch, one merely shifts the passband tuning or 'IF shift'
control to upper or lower , or anyplace one wishes to put it. The R7 also
has an 'IF notch filter' versus an audio notch filter which is much
better.

The R7 is overall a better receiver as far as 'flexibility' is concerned,
but it does suffer slightly as far as audio issues are concerned, and it
does not have a 'sync' function.

dxAce

Liberals for Guns wrote:
Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

"DX Ace" is right: a sync detector only works on AM signals. Really, it
doesn't by itself allow you to select one sideband or the other either;
that's a function of filter bandwidth options. A sync detector that
receives *both* sidebands is very much possible and worth doing, as it
would reduce selective fading problems.

(that said, any receiver I'm aware of with a sync detector does allow
selecting which sideband you use, and as you noted, that's worth doing too)

IF shift allows continuous adjustment of the passband, rather than just
selecting upper or lower. You could knock down interference 2KHz below
the desired station without deleting the entire lower sideband. Or,
while monitoring a SSB station.

That said, in practice I rarely use the IF shift in my receiver...
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:

Liberals for Guns wrote:
Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

"DX Ace" is right: a sync detector only works on AM signals. Really, it
doesn't by itself allow you to select one sideband or the other either;
that's a function of filter bandwidth options. A sync detector that
receives *both* sidebands is very much possible and worth doing, as it
would reduce selective fading problems.

(that said, any receiver I'm aware of with a sync detector does allow
selecting which sideband you use, and as you noted, that's worth doing too)

IF shift allows continuous adjustment of the passband, rather than just
selecting upper or lower. You could knock down interference 2KHz below
the desired station without deleting the entire lower sideband. Or,
while monitoring a SSB station.

That said, in practice I rarely use the IF shift in my receiver...

As I rarely use that in the R8 and R8B... though at times I might use the
selectable sideband 'sync' in the R8B, and merely the 'sync' in the R8.

Normally, the 'passband offset' control in the R8 and R8B is hardly ever moved,
at least here.

dxAce

On Wed, 18 Aug 2004 13:28:20 GMT, Doug Smith W9WI
wrote:

IF shift allows continuous adjustment of the passband, rather than just
selecting upper or lower. You could knock down interference 2KHz below
the desired station without deleting the entire lower sideband. Or,
while monitoring a SSB station.

Could you knock out the 2KHz interference with a notch filter as well?

Liberals for Guns schrieb:

Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

Synch detectors aren't all created equal. The one in the AR7030, for
example, is not sideband selective and therefore needs to be used in
conjunction with IF shift and a sufficiently narrow IF filter in order
to isolate one sideband. On the other hand, this is also the most
flexible solution overall, only beaten by something like Icom's Twin PBT
(of which I don't know the effectiveness). Do keep in mind that a good
SSB filter will allow for far greater sideband selection than an
ordinary (sideband selective) synch detector - while the latter may
allow for something in the order of 30 dB, the SSB filter in the AOR is
already at 48 dB in 3 kHz distance from the carrier freq, which includes
the filter bandwidth of about 2.1 kHz @-6 dB (i.e. with one -6 dB border
on the carrier frequency, a 1 kHz tone on the other sideband will
already be suppressed in the order of 50 dB). Additionally, IF shift can
also be used for SSB and may prove useful in adapting the CW offset to
the listening habits when used in conjunction with a narrow crystal
filter (or imagine you want to use a 1.6 kHz filter for SSB DX).
Interestingly, sideband selective synch detectors are the exception
rather than the rule - Sony can do this thanks to its CXA1376 IC (and in
the older 2010/2001D, with AM Stereo ICs like it's also done in the
Grundig Satellit 500 and 700), sideband selectivity is also claimed for
the SE-3, I don't know what Drake uses in the R8B and later SW8s, but
all the rest seem to use both sidebands (AR3030, AR7030, IC-R75, R8/R8A)
with only part of the receivers being able to compensate for this via IF
shift (like the AR7030).

Stephan
--
Meine Andere Seite: http://stephan.win31.de/
PC#6: i440BX, 1xP3-500E, 512 MiB, 18+80 GB, R9k AGP 64 MiB, 110W
This is a SCSI-inside, Legacy-plus, TCPA-free computer :)

PS: I forgot the JRC NRD-535DG with its sideband-selective ECSS
function. I don't know whether DSP rigs like the NRD-545 or HF-1000
really count, they don't have conventional analog detectors anyway.

Stephan
--
Meine Andere Seite: http://stephan.win31.de/
PC#6: i440BX, 1xP3-500E, 512 MiB, 18+80 GB, R9k AGP 64 MiB, 110W
This is a SCSI-inside, Legacy-plus, TCPA-free computer :)

the latest drake designed sync detector also does opposite sideband
phase cancellation. this is a significant technological advancement
and makes all other features usually a waste of time. no need to shift
the IF or other old technology stuff.

one button and almost all interfence on the opposite sideband is
destroyed.






Liberals for Guns wrote in message . ..
Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?

The sync' detector needs a carrier from an AM signal to work . The IF
shift works for SSB (no carrier) as well.

Liberals for Guns wrote:

Can someone help me understand something about IF vs synch. I've read
that IF shifting can get rid of an interference that is occurring
slightly lower or higher than the desired frequency. So, if you've
got noise within the filter range and it's on the lower side of the
frequency than you simply shift everything up so the noise is out of
the "window". My question is that I'm not sure why you just couldn't
use sync in to get rid of the interference. By just listening to the
upper sideband the noise wouldn't be there. Right? Do I need to pay
for an advanced feature like IF shift when I could get away with
simply using a sync detector function?


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B i l l E v e r h a r t wrote:

IF shift allows continuous adjustment of the passband, rather than just
selecting upper or lower. You could knock down interference 2KHz below
the desired station without deleting the entire lower sideband. Or,
while monitoring a SSB station.

Could you knock out the 2KHz interference with a notch filter as well?

You can knock out a tone with a notch filter (but it won't escape triggering
the AGC; a notch filter is taken as audio processing).

You can knock out 2 kHz offset SSB with a brick-wall audio filter, if it's
offset in the direction of the sideband (2 kHz higher for USB); though in the
case of 2 kHz you'll be left with fairly muddy audio in the remaining 0-2kHz.
Nothing much you can do in audio for AM, or SSB offset in the other direction.

I use the passband tuning on the R8B to pick up the full audio of broadcast
stations if there's nothing in the adjacent channel and it's worth the trouble,
using (say) upper sideband synch detection and offset the IF to the upper side.

The synch detection keeps the audio from distorting even though the carrier
is nearly out of the passband, and so you can reach to the high audio frequencies
with the wide 6kHz filter leaning way to one side. Ordinary AM mode would distort
as the carrier amplitude fell.
--
Ron Hardin


On the internet, nobody knows you're a jerk.