There is also a converse on preamp use that needs to be stated IMHO -
and mostly pertains to bands below 15 meters.
If there is a significant (3 to 6 dB) increase in noise heard in the
receiver when the antenna is connected (tuned where there are no signals
present) then the receiver gain is sufficient and the addition of a
preamp (or turning the internal preamp on) will only reduce the dynamic
range of the receiver.
For those who are not familiar with dynamic range, it is the difference
between the weakest signal that can be heard and the strongest signal
that will not cause overload.
What this means to normal operating is that when the band consists of
very strong signals as well as the weak ones you would like to copy, you
will be better off turning the preamp off and perhaps even inserting
some attenuation or turning down the RF Gain.
Now, if all stations within the bandpass of the receiver front end are
weak, adding preamplification will not create receiver front end
overload, and can be safely added.
So whether or not a preamp will help depends on the band, the antenna,
propagation conditions and many other factors. No blanket statements
can be made, particularly on the lower HF bands.
For 10 meters and above, band noise drops drastically with frequency and
what Ed has stated is certainly true.
73,
Don W3FPR
On 9/6/2014 4:36 PM, Edward R Cole wrote:
Maybe most of you already know this, but...
It has been accepted that the K3 receiver needs a little help of a
preamp on 10m and 6m (especially 6m). That is why Elecraft came out
with the PR6 and later the PR6-10 preamps.
At lower frequencies the level of sky noise is much higher which
overwhelms any noise generated internally by the receiver, thus a
preamp would only contribute gain making both noise and signal
louder. But around 30-MHz sky noise starts dropping so that it is
necessary for the first stage of a receiver to be "quieter"
(technically that is called a low noise figure). If the noise
generated in the receiver is significantly equal to sky noise the
receiver sensitivity is not optimum (meaning you can't copy weak
signals). This trend continues downward with increase of frequency up
to 1.2 GHz where sky noise is minimum (on earth). One cannot receive
"weaker" signals without a low-noise preamp close to the antenna at mw.
So, use of the internal preamp is generally not needed below 20m as
all it will do is increase noise volume and not improve receiver
sensitivity. But at 15m it often helps. At 10m the internal preamp
is inadequate to obtain maximum sensitivity and an external low-noise
(figure) preamp can really help.
Like I said at the beginning, maybe you already knew this...
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
