But I get audio even when
they are summed together!!! i.e There is no sideband suppression.

There is no sideband suppression with I/Q demodulation until you get
your carrier synchronized to the transmitter's carrier. If there's no
mechanism for doing this, you don't get sideband suppresion through I/Q
demodulation. (Well, you may experience rapid fading if you're within
a few Hz, but I don't think you want that!)

There are some homebrewers who do not-completely-suppressed carrier
with synchronous detection. It's sort of SSB but not traditional ham
radio SSB. In traditional ham radio SSB you try to suppress as much of
the carrier as you can, and this won't help you synchronously
demodulate it.

Without that synchronization, just use a bandpass (IF+300 Hz to IF+3000
Hz for example for USB).

Tim.

"Tim Shoppa" ) writes:
But I get audio even when
they are summed together!!! i.e There is no sideband suppression.

There is no sideband suppression with I/Q demodulation until you get
your carrier synchronized to the transmitter's carrier. If there's no
mechanism for doing this, you don't get sideband suppresion through I/Q
demodulation. (Well, you may experience rapid fading if you're within
a few Hz, but I don't think you want that!)

There are some homebrewers who do not-completely-suppressed carrier
with synchronous detection. It's sort of SSB but not traditional ham
radio SSB. In traditional ham radio SSB you try to suppress as much of
the carrier as you can, and this won't help you synchronously
demodulate it.

Without that synchronization, just use a bandpass (IF+300 Hz to IF+3000
Hz for example for USB).

Tim.


But he's not talking about synchronized demodulation, he's talking about
SSB demodulation.

Phasing demodulation was around before "synchronous detection" was described
in CQ in the late fifties. Where the carrier comes from is irrelevant, it's
about the proper combination of phase shifts to select which sideband
is being received. Add the outputs, and you get one sideband, subtract
them and you get the other.

Synchronous detection merely adds a means of locking the locally generated
"carrier" to the incoming signal. And of course, one can have sync
detection without selectable sideband.

But he's talking about SSB, and there's neither a carrier, nor two
sidebands to sync to.

But if he is doing this right, he should not receive the incoming sideband
if he has the combinations set up for receiving the other sideband.

I have no idea what's wrong, but this has nothing to do with synchronous
detection.

Michael VE2BVW

On 23 Feb 2005 07:37:41 -0800, "Tim Shoppa"
wrote:

There are some homebrewers who do not-completely-suppressed carrier
with synchronous detection. It's sort of SSB but not traditional ham
radio SSB. In traditional ham radio SSB you try to suppress as much of
the carrier as you can, and this won't help you synchronously
demodulate it.

I got the impression he was using an I-Q system to implment a hilbert
transform. The result is an image suppressing system that can
demodulate SSB with a baseband IF.

Essentually what a KK7B R2/miniR2/R2pro(RX) and the companion T2
(transmit) using aboth a 90degree I-Q RF path and an +45 and -45
degree audio processing path.


Allison