These Data were submitted on: Monday, July, 28, 2003 at 12:17:36
URL: Fred www.qsl.net/oe8fnk
Address: OE8FNK
E-mail: mycall@qsl.net
CPU:: Celeron
CPU Speed:: 600 Mhz
RAM:: 288 MB
SOUND CARD:: M Audio Delta 44
SOUND DRIVER:: Oss397L
ADDITIONAL CARD1:: Creative ViBRA16C PnP (ISA)
ADDITIONAL CARD2:: CMedia CM8738 (on MB, unused)
VIDEO CARD:: Matrox G450, dualhead, one in use
VIDEO DRIVER:: from Matrox web (for X11) with openGL
LINUX DISTRIBUTION:: Redhat
LINUX VERSION:: Red Hat Linux 8.0 3.2-7
KERNEL VERSION:: 2.4.18-14
GCC VERSION:: gcc version 3.2 20020903
SVGALIB VERSION:: svgalib-1.4.3 (?)
TEXT: Linrad works, with 25 khz BW from homemade RX: I use the VXO of the IC-202s. RX is
2x Ext.
Preamp, SA602AN Mixer to 10.7 MHz, one more stage with Crystal filter (30 Khz) (this has to
optimized) and then convert to baseband with 2xSA602 for I+Q. I know that the SA602 is not
the best, and I have absolutely no idea about the performance. But it will improve...
I plan using 2 RX and 2 Antenna inputs with 60Khz BW. Currently have only 35db from Preamp
+ 45db in the Receiver, this raises the noisefloor only 5db. Received sucessfully CW, SSB
(!) signals, 2m beacons, and meteor echos.
*INSTALL PROCESS*
All the Linux and Linrad install process was easy, earn my money with Linux. The
/etc/vga/libvga.config needs the "chipset VESA" line. No problems with compilation.
Took several hours to find out how to configure the soundcards. Tried ALSA first, without
any success. After switching to OSS the soundcards are recognized by Linrad, and osstest
gives the needed information about the devices.
Q&A: Q1: What is the total amplification needed for a 2m Receiver into a Delta 44?
Q2: Anybody knows how to modify the IC-202s VXO for better phase noise?
tnx
Leif's answer:
Hi All,
I found this question from OE8FNK:
> Q1: What is the total amplification needed for a
> 2m Receiver into a Delta 44?
The Delta44 saturates for 10V peak to peak when set to minimum gain.
This is 3.5V rms.
When talking about gain at RF we usually mean power gain.
At audio frequencies we talk about voltage gain.
This can be confusing because the input impedance of the Delta44
is very high so it does not consume much power.
To avoid any confusion, assume a 50 ohm resistor is connected
across the Delta44 audio input. 3.5V rms is then 0.25W = +24dBm.
(nearly all the power goes into the resistor)
The Delta44 noise floor is at about -146dBc which becomes -122dBm
across the 50 ohm resistor. The noise figure is thus 174-122 = 52dB.
For a noise figure of 0.4 dB at the antenna input you will need 65dB
gain if the noise figure of the preamplifier is 0.2dB. There will
probably be some noise from various other sources than the preamplifier
and the Delta44 so you will need some additional gain to overcome
that. You might also want to come closer to the ultimate 0.2dB
noise figure limit given by the preamplifier in this example.
I would guess you arrive at 70 to 75 dB gain in total.
The NF of the Delta44 itself is actually much lower than 52 dB.
If the soundcard were properly matched (transformer) to 100
kiloohms or whatever the input impedance is, it would se perhaps
25 times more voltage and have a NF in the order of 25 dB.
73
Leif / SM5BSZ
More answers from Leif
Hi All,
I found this question from OE8FNK:
> Q2: Anybody knows how to modify the IC-202s VXO for better
> phase noise?
There are two problems. There are some comments in QEX Jan/Feb 2003
page 44. There is a pdf on the Linrad home page.
The relevant text is:
--------------------------------------------------------------
At 144MHz, even an IC202-- the purest commercial transmitter
I know of-- is not good enough. It is possible to lower the
noise floor of an IC202 by about 10dB: First, replace the 470
ohm emitter resistor of the LO with a 150 ohm resistor in
series with an RF choke. Then decouple the base of the first
frequency multiplier stage for low frequencies by installing
a 1 ?F capacitor in series with an RF choke.
Modified like this, it is just about good enough to be used
as the LO in a direct-conversion 144-MHz receiver, but only
if a low-level Schottky-diode mixer were used. A high-level
mixer needs about 15 dB more LO power and would therefore give
much higher susceptibility to LO sideband noise.
--------------------------------------------------------------
If you want to use the 144 MHz signal for a direct conversion radio
you should also reduce the gain at 144 and increase the level
on the low frequency side of the crystal filter. I do not remember
the details. Performance is at:
http://antennspecialisten.se/~sm5bsz/dynrange/rig_compare.htm
73
Leif / SM5BSZ
Hello Leif, and Hello all.
Thank you very much, Leif, for taking the time to answer all my questions.
you wrote:
>Then decouple the base of the first frequency multiplier
>stage for low frequencies by installing a 1 ?F capacitor
>in series with an RF choke.
This means 1 microFarad?
thank you for the dyn. range link. After 6 month of continuous reading and learning
from your website I still didnīt find all links :-)
73 es gd dx
Fred
Hi again Fred,
> you wrote:
> >Then decouple the base of the first frequency multiplier
> >stage for low frequencies by installing a 1 ?F capacitor
> >in series with an RF choke.
>
> This means 1 microFarad?
Yes.
> And thank you for the dyn. range link. After 6 month of
> continuous reading and learning from your website I still didnīt
> find all links :-)
It is a new link;)
There is "Update information and complete list of files for this site"
at the top of SM5BSZ Home page. Not always updated, but it is valid most
of thre time.
73
Leif