Bill,
I use a 'constant impedance termination' that provides a 50 ohm
termination at the IF frequency, as well as shunting unwanted
frequencies to ground. I also use 3 dB pads on the RF input and IF
output ports. So all ports are happy with the termination that I've
provided.
I am using a Level 7 device and providing it with 7 dBm of LO power.
The preamp/mixer combination is working quite well.
Bob WA6UFQ
--- In softrock40@..., Bill Dumke <billd@n...> wrote:
Bob,
That is the BIG problem of using a diode mixer. They are lossy. They
are cheap and dirty, but for IM, intermodulation, performance they are
not as good as a well designed active transistor mixer, which also
has a
better noise figure and some gain besides to help overcome the IF noise
figure. JFETs have long been the mainstay of RF front end mixers at
HF,
VHF, and UHF, but they need to be biased and driven correctly with the
LO power, and matched correctly on the output for best IM.
Matching on the output is also important for a double balanced diode
mixer to get best IM, but nobody ever does it. And I am not talking
about a straight 50 Ohm load at all frequencies. You want a short
circuit everywhere else except at your IF frequency for best IM
performance. This holds for all mixers, inculding direct conversion
mixers.
Bill
Bob Hillard wrote:
Bill,
The preamp is needed to overcome the 6 dB loss of the double balanced
mixer.
Bob WA6UFQ
--- In softrock40@..., Bill Dumke <billd@n...> wrote:
It looks like a good idea. It would solve a lot of direct
conversion
and DDS problems we have been talking about.
But I would recommend avoiding putting a preamp in ahead of the
SoftRock
30 Tayloe IF receiver. Even if the preamp was perfectly
linear, which
it won't be, it will still degrade the 3rd order intermodulation
performance of the Tayloe detector by 2/3 of the preamp's gain
in dB.
For most HF operation, at least on the lower bands, I doubt you will
need it anyway.
Bill, WB5TCO
softrock40@... wrote:
Hello,
This email message is a notification to let you know that
a file has been uploaded to the Files area of the softrock40
group.
File : /SDSTransceiver Block Diagram.bmp
Uploaded by : cat100bob <rhillard@a...>
Description : Software Defined Superhet Block Diagram
You can access this file at the URL:
To learn more about file sharing for your group, please visit:
Regards,
cat100bob <rhillard@a...>
------------------------------------------------------------------------
YAHOO! GROUPS LINKS
* Visit your group "softrock40
<>" on the web.
* To unsubscribe from this group, send an email to:
softrock40-unsubscribe@...
<mailto:softrock40-unsubscribe@...?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service <>.
------------------------------------------------------------------------
------------------------------------------------------------------------
YAHOO! GROUPS LINKS
* Visit your group "softrock40
<>" on the web.
* To unsubscribe from this group, send an email to:
softrock40-unsubscribe@...
<mailto:softrock40-unsubscribe@...?subject=Unsubscribe>
* Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service <>.
------------------------------------------------------------------------
