On Fri, 01 Aug 2014 15:22:10 -0500, Lostgallifreyan
wrote:
Jeff Liebermann wrote in
:
For FM tuners, it's dBf (dB over 1 femtowatt) usually into 300 ohms
but sometimes into 75 ohms:
The Tecsun PL-390 uses dBµ (micro).
Yep. The Tecsun PL-390 uses a Silicon Labs SI4734 DSP chip. I've
done some work with similar chips and think they are wonderful.
http://www.kaitousa.com/PL390.htm
https://www.silabs.com/Support%20Documents/TechnicalDocs/Si4730-31-34-35-D60.pdf
One of the chief benefits to all an all digital receiver is the nearly
"brick wall" IF filter, which works nicely at keeping HD Radio crap
out of the receiver. I'm not sure if you have that problem in UK:
http://www.telegraph.co.uk/technology/8071209/BBC-launches-HD-radio.html
but if you do, the SI4734 should remove the junk from the adjacent
channel. Note that the HD Radio occupied bandwidth is about 400 KHz,
while conventional FM is a bit less than 200 KHz.
http://802.11junk.com/jeffl/crud/KCSM.jpg
Too bad the PL-390 won't do synchronous AM or SSB. The chip can do
it, but it's only available in the later PL-880 receiver.
http://www.kaitousa.com/PL880.htm
I'm not sure where the dBf stuff came from, but my guess(tm) is that
it was used to simplify the sensitivity specs so that the numbers came
out positive integers.
Most of this is new to me, but I read
that Tecsun's dB referencing makes them useful to EMI and RFI engineers,
We call it EMC (electromagnetic compatibility) in the US.
http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/ElectromagneticCompatibilityEMC/default.htm
I don't think using dBµ will make much difference as I'm constantly
converting from various field strength units to voltages and powers.
If you're into this, you might want to save this page:
http://802.11junk.com/jeffl/coverage/VZW-water-plant/Field%20Intensity%20and%20Power%20Density.pdf
I forgot which book I stole it from.
and
one related radio beign especially useful for tracing noise, having a plug-in
rotatable magnetic loop antenna as well as a long(ish) whip.
Direction finding is fine for finding the general area. However, for
close up, one needs a "sniffer". For that, I use an Alinco DJ-X2 AM
receiver with the stock 17 cm antenna. It's not very sensitive but
good enough for finding unwanted emitters. Your Tecsun PL-390 would
probably work equally well.
At this point pouring scorn or praise on Tecsun radios is interesting to me
either way, because for the first time in a while I have found a radio I care
enough not to be indifferent to it.
I guess that means you like it.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558