direct conversion receiver Question
 

Hello Mike,

If you Google on "Synchronous AM Detector" and "Exalted Carrier Reception"
you'll find lots of info

This is good place to start....
http://www.radio-electronics.com/inf...t/sync_det.php


Regards ............ Zim

direct conversion receiver Question
 

Hey OM:

In the ole NTSC days gone bye, that's how they detected the video
signal in the last of the ole NTSC TV's, took the SAW filtered IF and
squeezed the video out by converting the RF right to video baseband,
with the carrier as an LO OSC all inside one little tiny IC

I just never new what happened to the frequencies that were below ZERO
from the mixer.

73 OM
de n8zu


On Jul 11, 11:50 am, "amdx" wrote:
In a direct conversion receiver, does the osc. run at
exactly the same frequency as the received signal?

Assuming the answer is yes;
Is it possible to have a high Q LC front end at the output from the
antenna,
split the signal and feed one output to the rf input of the mixer and feed
the other splitter output to an amplifier and use the amplified signal to
drive the osc input of the mixer?

Simple block diagram of proposed idea;http://i395.photobucket.com/albums/p...conversion.jpg

--
MikeK

direct conversion receiver Question
 

--
MikeK
"Graeme Zimmer" wrote in message
...
Hello Mike,

If you Google on "Synchronous AM Detector" and "Exalted Carrier Reception"
you'll find lots of info

This is good place to start....
http://www.radio-electronics.com/inf...t/sync_det.php


Regards ............ Zim
Thanks Graeme,
I'm thinking about building the mixer that was in QST Feb., 1993, an
article by
Jacob Makhinson. Titled, "A High-Dynamic-Range MF/HF Receiver Front End"
The mixer uses a quad FET IC, (Si8901 from Calolgic corp.)
The only online reference that I can find is here; See pdf pages 26 (text)
27 (schematic)
http://files.bluecrow.net/Amateur%20...ok_2007/11.pdf
The front end is designed in three modules, preamp, mixer, and post amp.
Anyway I'm thinking about building the mixer and playing with it in the
AMBCB.
Even thoughts about building an I/Q receiver.
Mike
(Note; I do more thinking than building ;-)

direct conversion receiver Question
 

In article ,
amdx wrote:

Thanks Graeme,
I'm thinking about building the mixer that was in QST Feb., 1993, an
article by
Jacob Makhinson. Titled, "A High-Dynamic-Range MF/HF Receiver Front End"
The mixer uses a quad FET IC, (Si8901 from Calolgic corp.)
The only online reference that I can find is here; See pdf pages 26 (text)
27 (schematic)
http://files.bluecrow.net/Amateur%20...ok_2007/11.pdf

Google around for "H-mode mixer" and "Tayloe mixer" if you want more
information. http://www.webalice.it/romano.cartoc...mode_links.htm
will get you started with *many* links to investigate.

There has been a lot of interest in this sort of switching mixer
topology in recent years... quite a few articles in QEX for example.
Many designs have come out, some of which are based on general-
purpose multi-FET parts such as you suggest, and others which are
based on CMOS "fast bus switching" ICs, such as the FST3125 and
similar. This seems to be a very good topology for handing signals
having a very wide dynamic range... I believe that Elecraft uses a
design of this sort in their K3 transceiver.

The front end is designed in three modules, preamp, mixer, and post amp.
Anyway I'm thinking about building the mixer and playing with it in the
AMBCB.
Even thoughts about building an I/Q receiver.

Yeah, I've been toying with that sort of idea too... making a
"binaural" direct-conversion receiver. There was a binaural design
published in QST a year or so ago, which uses the NE602 or similar
Gilbert-cell mixers... building one which uses H-mode switching mixers
and a couple of low-noise audio amplifying chains could be fun.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

direct conversion receiver Question
 

In article ,
"amdx" wrote:

--
MikeK
"Graeme Zimmer" wrote in message
...
Hello Mike,

If you Google on "Synchronous AM Detector" and "Exalted Carrier Reception"
you'll find lots of info

This is good place to start....
http://www.radio-electronics.com/inf...t/sync_det.php


Regards ............ Zim
Thanks Graeme,
I'm thinking about building the mixer that was in QST Feb., 1993, an
article by
Jacob Makhinson. Titled, "A High-Dynamic-Range MF/HF Receiver Front End"
The mixer uses a quad FET IC, (Si8901 from Calolgic corp.)
The only online reference that I can find is here; See pdf pages 26 (text)
27 (schematic)
http://files.bluecrow.net/Amateur%20...ok_2007/11.pdf
The front end is designed in three modules, preamp, mixer, and post amp.
Anyway I'm thinking about building the mixer and playing with it in the
AMBCB.
Even thoughts about building an I/Q receiver.
Mike
(Note; I do more thinking than building ;-)

You should look at the Northern Radio Model N570/571 Marine SSB Radios,
that were designed and built back in the Early 70's. They used at rather
unique design with a Double Balanced Mixer at the Receive Antenna Port,
that moved the IF up to a low VHF biDirectional Amp and Filter, and then
back down to a 10.7 Mhz IF with another Double Balanced Mixer, and on to
the Crystal SSB Filter, and Demodulator. The Double Balanced Mixers were
driven by an LO System that canceled out any Frequency Drift, by using
opposite Mixing Images.

direct conversion receiver Question
 

Hi again Mike,

I'm thinking about building the mixer that was in QST Feb., 1993

You might have a look at my old DSP receiver at:
http://members.wideband.net.au/gzimmer/


Regards ............. Zim

direct conversion receiver Question
 

Graeme Zimmer wrote:

You might have a look at my old DSP receiver at:
http://members.wideband.net.au/gzimmer/

I have built several Softrock kits and have no inclination to use any
other receiver as a result. It's a receiver from heaven.

Looking at yours and the simple block diagram I am curious about how
this differs from quadrature processing.

Can you provide a few words of explanation.

Jack K9act

direct conversion receiver Question
 

Hi Jack,

Looking at yours and the simple block diagram I am curious about how this
differs from quadrature processing.

I'm not sure I understand your question.

As the diagrams show, the VFO is divided by four to produce 90deg quadrature
LO signals which drive two mixers.The two audio channels pass through two
BPF filters, one of which has a Gilbert transform to give 90 deg delay. It's
the standard Phasing Method..

If you're asking about Binaural reception, it's the same as above, but less
the Hilbert transform so there's no sideband suppression..

Admittedly that page is somewhat condensed (simplified) over the original.

Regards .......... Zim ........ VK3GJZ

direct conversion receiver Question
 

What about SSB and CW? Would syncro conversion detect just the upper
sideband?

No. You can select either sideband.
Just change the sign when you combine the I and Q signals.

this is a fairly simple intro.
http://www.nxp.com/acrobat_download2...tes/AN1981.pdf


................ Zim

direct conversion receiver Question
 

raypsi wrote:
Hey OM

This thread begs the questions:
What about SSB and CW? Would syncro conversion detect just the upper
sideband?

It is not possible to use synchronous detection with SSB or CW because
there is no carrier in the signal. So the circuit that recovers the
carrier will work on the modulation and the result is unusable.
(i.e. no audible modulation with SSB, and at best a 0Hz tone with CW)

Because the lower sideband would be below ZERO hertz?
If you use a BFO how do you get below ZERO hertz?
Doesn't the Fourier transformation of the mixers' LO and rf input in
a syncro conversion produce frequencies below ZERO?

There are no frequencies below zero. When you are using only a single
mixer, both sidebands will produce frequencies above zero. And there
will be no suppression of the "unwanted" sideband.
(the synchronous AM detector is a dual-sideband detector)