Joe and others:
This is the power spectrum of the noise of the INA's when they have 0 dB
gain. I really do
dislike these amplifiers immensely and I am guessing that Gerald will
not use them in
future products! In addition, some of this noise can be coming from the
power supplies
that are quite poor switchers (NMA1215S) which provide the rail voltages
for the
INA's. BLECH! My quietest nicest receiver is the SDR with a well
designed external
supply giving me +/- 12V (15 V is massive overkill), and a different
front end that has
lower gain and higher IP3. I find the "Low" and "Off" settings not to my
liking and
never use them.
I will write up all of my radio modifications and get Gerald to put them
on his web site
or on the friends site. This will take me about two weeks to do since I
need to take
digital photographs, etc. I have W3IWI's and W2GPS's radios. I will use
them as the
photograph radios.
Bob
Joe - AB1DO wrote:
Hi all,
I am noticing a “strange” phenomenon, visible in all of the console
versions I have, i.e. from 1.3.4 on. On the far left hand side of the
panadapter display, and _only when preamp is off_ I see the noise
floor rise to a peak. To focus in on this more, I used SPEC to center
what turned out to be an approx 3kHz wide central peak with many
harmonic spikes:
In the above, the rig is connected to a dummy load. When the preamp
setting is increased, this peak gets smaller, to virtually disappear
at a preamp setting of med or higher. The preamp is the ONLY
adjustment I can make that seems to influence it at all. If I turn the
power to the SDR box off (after having turned the console on with it
powered on), the central peak remains visible, but the harmonic spikes
reduce greatly in value. When tuning up or down, the peak remains on
frequency until it reaches about + or – 1.5kHz, at which point it
flips to the other side, that is from –1.5kHz to +1.5kHz and v.v. It
is also visible on every single band, at every single frequency. Also
the peak value of –110dBm is absolute, that is if I calibrate the
console to show a noise level of say –90dBm, it is not visible.
Before I go tearing the whole shack apart here in search of the
interfering source, I’d like to know if anyone else has experienced
this, if it is something inherent in the S/W or hardware, or if it has
something to do with my settings (I recalibrated everything using
Elecraft’s XG1 signal generator, but to no avail). If none of these,
I’d appreciate a clue as to what I should be looking for.
My setup uses the Delta 44 and USB adapter.
Thanks,
Joe
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