Check out the analysis Conrad posted.
{^_-}
On 20220709 14:57:45, Siegfried
Jackstien wrote:
toggle quoted messageShow quoted text
antenna ...lna .....cable to shack.....splitter ... (and a
handfull of receivers)
the noise figure comes from the front lna ... not?!?
other things to consider is overload of the lna if you have
strong signals close to your station (even if outside of the fm
band)
whatever it may be ... a radio station, cell tower, airport,
ham operator?? in that case a filter between antenna and lna
does do wonders :-) and if that setup is only used for fm dxing
a bandpass 88 to 108 is a good thing to add
dg9bfc
Am 09.07.2022 um 23:49 schrieb
Conrad, PA5Y:
If you do add a splitter it is best to do a system
noise analysis; there would be very little point in having
a 4 way resistive splitter with a 9dB RX NF connected to
it using the LNA example I gave. Its not difficult to
calculate and AppCAD is free. The idea of the attenuator
is to set the optimum gain for the conditions/ required
sensitivity.
It is not totally optimal in terms of SFDR, but it is
flexible, and you won’t be far off.
Regards
Conrad PA5Y
that 18 db gain may make a bit deaf receive shine :-)
or dig out that rare dx signal
or give you enough oumph on the cable to use passive
splitters for a handful of receivers without worry about
losses (last would be my thinking)
if you only want to do fm dxing then an added filter may
help to clean up the receive a bit (and also such a filter
plus cabling adds loss)
just thinking ;-)
dg9bfc sigi
Am 09.07.2022 um 20:42 schrieb jdow:
The cheapest one would probably be good enough. The next
one up might be slightly better because you get a nice
noisy power supply and (possibly redundant) Bias-T tap for
it. The most expensive one would only be needed if you
have some exceptionally strong signals nearby.
18 dB gain may be a little high with only 2.5 dB of cable
loss. Something like one of the old HP 1 dB step variable
attenuators might be good on the receiver input. Adjust it
for a suitable compromise for dynamic range and signal
strength. I suspect you do not need this 10V version of
the amplifier.
(Did I just save you a bunch of money?)
{^_^}
On 20220709 11:12:30, Simon Brown
wrote:
I'll start saving and buy a
masthead preamp (below). My income is way down now due
to COVID and other cost of living issues. Not a great
time to be relying on donations.
They have a bit of input filtering
already, don't know if it's enough.
According to the user manual
with the preamp and noise reduction on the MDS at
91.1MHz is -138dBm in 500Hz, which equates to
-165dBm/Hz. This is a 9dB noise figure and is
probably 3-6dB worse because the NR makes things
appear better than they are. If you add 2.5dB to
that noise figure you can see that an LNA will be of
great benefit.
I suggest that a system noise
figure of around 2-3dB is optimum for Band II DXing.
Regards
Conrad PA5Y
What's the S3 noise figure on
Band II ? I have maybe 2dB loss in the 25m RG6, so
am wondering what the total NF is.
BTW I put the BPF before
the LNA to help protect it from 144MHz EME high
power. I am not suggesting that a PGA103+ will
saturate from normal Band II situations.
However, it has a little bit too much gain, so a
good filter and an attenuator does no harm. The
S3 really is excellent. Just like you said 😊
73
Conrad PA5Y
Hello Simon, I have done a
noise analysis and you WILL benefit from an LNA.
I have a PGA103+ preceded by a band pass filter
and it seems to work very well. However, I am
still waiting for a bigger antenna. I ordered an
OPTDES which never arrived. So, I will ask a few
of the local Band II DXers for an alternative.
73
Conrad PA5Y
The ELAD S3 is the best
Band II receiver I have. Am thinking about a
preamp on the mast for those very weak
stations - if I get close to receiving weak
signals from across the pond (USA, Canada).
I have attached 3
pictures all with Console running.
The RSPdx is the
only on of these three that has a decent
signal. Running uno is fine also.
It is the other two
that are causing problems. The native
software yields the same lousy signals.
There is a lot of noise on these two
receivers for the station in question. I
have fiddles with the R2 slide controls
in both Sharp and Console. The Elad
appears not to have any RF gain
capability.
The frequency I am
using for this exercise is 98.9, 92
watts, 25 km away. I am using the same
antenna for all three radios. The
antenna is pictured in an attachment.
Same feed line to all three radios. My
HF+ Discovery works fine also.
As I said in a
previous message, the Elad S2 is the one
that really puzzles me. I would have
expected it to come out the best (based
only on price, that is).
Anyway, please let
me know if more information is needed.
Thanks for looking
into this.
On Friday, July 8,
2022 at 11:38:57 PM PDT, jdow <jdow@...>
wrote:
Frequency?
{o.o}
On 20220708
14:47:30, George Stein - NJ3H via
groups.io wrote:
92 watts not
25.
On Fri,
Jul 8, 2022 at 2:24 PM, George
Stein - NJ3H via groups.io
Further
to my last message. The
station in question is 25 km
away and running a mere 25
watts.
Using SDR Console:
With the Elad S2 and and the
Airspy R2, the reception was
very noisy.
With the Airspy HF+
Discovery and the RSPdx, the
signal was full quieting.
With the edge going to the
HF+ Discovery.
This was not a scientific
test, just a casual
observation. The only thing
I am surprised about was the
Elad S2 performance.
I then used the native
software for each device and
had the same results.
Regards and YMMV,
George
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