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.

On Wed, 18 Aug 2004 12:18:36 GMT, 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?

One of the values of synchronous detection is that it can be effective
even on signals within the passband. Shifting the passband can result
in 'blocking'. In effect the intefereing signal may be outside the
passband, but is still seen, and drives the AGC, effectively reducing
the level of the desired signal.

It is also rare in most receivers for the skirts on the passband to be
sharp enough for this to work well. Usually a Q multiplier set on null
is a better approach, you just put a black hole in the passband at the
desired spot.

Synch other attraction, and perhaps the most attractive features is
something that passband tuning cannot help with. Selective fading of
the carrier. Sometimes it isn't really interference it is selective
fading causing the sidebands to have more energy than the carrier,
causing severe distortion. Synch detection insures adequate carrier
energy.

yes, interestingly, there was an article in 73 magazine IIRC some years
back which described how to retroactively add IF shift to some older radio
receiver(s) using only a handful of parts, basically just add ability to
tune or shift the IF oscillator up or down in frequency so as to move it
w.r.t. the IF chain etc. I had envisioned a far more complex circuit,
based on its relative rarity, but it turned out to be a lot easier circuit
than I expected...

fyi - bob monaghan
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

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

Only if it's a single-frequency carrier. (like a Morse Code signal, or
a spurious carrier from a computer or something like that) A notch
filter removes a particular frequency very well but doesn't do much
against signals on other frequencies. Another SSB signal 2KHz below the
one you're wanting to monitor cannot be "notched".
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Here in Sactown, Radio Australia's 9.590 mhz signal has an annoying hetrodyne
which can't be eliminated in either upper or lower sync sideband on a Sony
2010. On ICOM's R-75 hower, in regular am mode, that het whistle can be
eliminated with passband tuning.

yes, interestingly, there was an article in 73 magazine IIRC some years
back which described how to retroactively add IF shift to some older radio
receiver(s) using only a handful of parts,

Sounds like a worthy article, and a VERY worthy project. Is there somewhere I
could find this article online (or a similar project for retro-fitting IF
shifting to older receivers)?
Linus

GrtPmpkin32 ) writes:
yes, interestingly, there was an article in 73 magazine IIRC some years
back which described how to retroactively add IF shift to some older radio
receiver(s) using only a handful of parts,

Sounds like a worthy article, and a VERY worthy project. Is there somewhere I
could find this article online (or a similar project for retro-fitting IF
shifting to older receivers)?
Linus

Assuming the same issue had an article about adding an FM detector to
old shortwave receivers, I don't think the "IF shift" article is
worth tracking down.

Unless the description was horrible, the thing made no sense. My recollection
is that he put a varicap across an IF transformer, and called that IF shift.
Tha author showed no understanding of what IF shift was.

Michael

I'll try to find the cite to the 73 article, it is in my articles files
IIRC ;-) Can't be that complicated*, but whether it will work well with
all older radio receiver designs? Should be available via interlibrary
loan, or I can mail you a photocopy if you can't find or get it locally?

from google,
http://www.universal-radio.com/catal...hf/3450if.html
another reference to the 73 article,
http://lists.contesting.com/archives.../msg00290.html

grins bobm

*Since my Drake R4B has IF shift, in a tube/transistor hybrid, it can't be
that complicated to have IF shift in your radios ;-) ;-)
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

but whether it will work well with
all older radio receiver designs?

I guess I should have been a little less vague. I wouldn't want to add an IF
shift function to a tube model, I just thought it would be neat to try to
install such a function on a more modern radio which didn't have that feature.

Should be available via interlibrary
loan, or I can mail you a photocopy if you can't find or get it locally?


I will look around, starting from the leads you provided. If you do find a
copy, let me know. I'll pay for the trouble! :-)
Linus

yes, I found the brief article and the cite is 73 Amateur Radio Magazine,
August 1989, p.53, "IF Shift, Cheap - Easy IF Shift Add-on to your Older
Rig" by Terry F. Staudt, LPE, W0WUZ (LPE is licensed professional
engineer, IIRC?). He reviewed a number of 1970s upgraded receivers (A, S,
or Mk II versions ;-), and discovered how they did IF shift or passband
tuning in those updated models. The modification uses a varicap Motorola
MV 1872 and a pot and trimmer capacitor to vary the first IF transformer
frequency. He added it to a Galaxy V mk II transceiver, noting "the
circuit works wonders". You do have to make two adjustments to the
modified IF transformer to preserve selectivity etc., which he describes
briefly ;-)

If you can't find the article locally, let me know, email me directly with
your address to and I'll mail you a photocopy.

Drake IF tuning, IIRC, the R4C had an odd "feature" (aka bug ;-) in
that it didn't provide IF or passband tuning in all modes, as the earlier
Drake R4B did, although you could modify the R4C to do so (and other
mods too).

I probably shouldn't note that I found another 73 article in my search
that discusses how crystal filters could be built to provide any desired
CW or SSB bandwidth (though you might have to grind a crystal or two to
get precisely the bandwidth you want ;-) ;-)

grins ;-) bobm

--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

Hi Michael,

you may well be right, though there weren't any followup complaints or
correction IIRC on the article. With 73 magazine in bankruptcy court now,
it is too late for you to publish a correction ;-)

I don't think the idea was to replace or supplant the crystal filter skirt
selectivity with IF shift, or to change or shift the crystal passband.

Since some radio receivers only have one IF stage and one IF transformer,
as an example, shifting its frequency would be shifting the entire IF ;-)

Then again, some of the 455 Khz IFs use murata style resonators which are
at least as good and selective as some quartz crystal filters (so I'm
told, anyway ;-) In such a case, it would seem possible that detuning the
first IF transformer so an interfering signal is above or below the main
IF passband and out on those many dB down skirts, while leaving the
desired signal within the IF passband, with resonator skirts or subsequent
crystal filtering etc. providing the selectivity, as usual, could work?

Again, I can't reject the idea out of hand, for all radios or setups. When
an LPE (licensed professional engineer) tells me he has reviewed many
example cases and studied how IF shifting works, it carries more weight
than some of the stuff I see on and off-line ;-) ;-) At least the cost of
the experiment is low (~$5?), so it may be worth testing for some
experimenters?

regards bobm


--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************