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Re: [Discuss-gnuradio] USRP need antenna?
Re: [Discuss-gnuradio] USRP need antenna?
Wed, 20 Apr 2005 22:17:41 -0400
Mozilla Thunderbird 1.0.2 (Macintosh/20050317)
Suvda Myagmar wrote:
Eric Blossom wrote:
As far as I know nobody has said anything about not needing an
antenna. You need something. Try a 3 foot long piece of wire.
For the broadcast AM band, longer is better.
A cheap "FM dipole" works great for the FM broadcast band. By "FM
dipole" I mean those really cheap T-shaped wire antennas that came with
your stereo. They're typically available at the local drugstore for
about $3. Don't bother trying RadioShack, they don't carry them, only
the $20 amplified antennas that you don't need.
I tried 2 different antennas. First, tried with FM/UHF tv antenna that
has 2 extendable wires and one loop. Had to cut off the input
connector of the antenna and just stick the bare coaxial wires in one
of the RX A/RX B jacks on the USRP receiver board. I could tune and
hear only one FM station among several; and even that one with a lot
Next, tried FM dipole that looks like T shaped tape, the one you hang
on wall. This one had 2 parallel inputs, each flat U shaped, I guess
they're supposed to be secured between nut and bolt. I cut them off,
stuck bare wires in the receiver jacks. Nothing, can't tune to a
single AM/FM station.
These antennas I assume don't have any gain control. I read on Ettus
website the following:
Can I do interesting things with just a USRP and BasicTX/BasicRX, but
no RF frontend? Do I need a separate RF front end to capture, say, CW
or phone transmissions in the amateur bands? Or can the BasicRX fill
For reception you would need to add gain and filtering in front of the
BasicRX daughterboard. This can be done pretty easily with
MiniCircuits parts, or you can use the 10.7 MHz IF output of common
scanners and receivers. The BasicRX board will handle signals up to
around 100MHz directly. For higher frequencies you'll need to
It seems like I need an antenna with gain and filtering... Where do I
get those? I'm totally illiterate in harware, electronics areas.
Well out of the options there are, you should go with the scanner with
Here is one example:
*AOR's **AR8600MKII New Wide Band All-Mode 100KHz to 3GHz Scanner
In general you would look for something like this:
"The 10.7 MHz IF output can be used with ..."
This thing would cost $900-$1000 and you may get away cheaper if you
spend some time on the web.
What I wonder about now is what the output level is, there is a good
chance though that it is what you need.
If you have an order of magnitude more money (or a university lab) you
can go with a spectrum analyzer IF output at 21.4MHz, cool but expensive.
I wonder though, whether there is not a cheaper way like the antenna
with an amplifier you mentioned. There is a chance that there are FM
antennas with amplifier and filter since amplifier bandwidth can be
"costly" (designwise) too.
Oh here is one (the first I found with google):
* signal amplification variable from -10dB thru +30dB (30 times to
gain) to bring weak stations to full quieting *** and tame strong,
harsh, local signals
* full tunability with a "hi Q," 400 KHz bandwidth. This adds some
70dB+ in Spurious Response selectivity
* an electronic antenna switching system to bypass the SLEUTH's
amplifier when not needed. Also with the SLEUTH's direct "in/out"
Antenna Signal switching system, instant A/B comparison is always
* a low profile, cabinet in satin black. 17 3/4", 19" or 19"
This seems to have a preselector and even though not electronically
controllable should do the trick for you. Still, it seems expensive at
$350. This should at most cost $50.
The problem is that the cheap stuff never talks about bandwidths.
To get a more accurate view of things let me find out what I get from my
scanner antenna (SA7000). In the FM range I have a bunch of signals at
around -80dBV(rms) my
scope tells me. This would mean 282uV P-P over the 50Ohm input. If we
assume the AD converter supports a -1V-+1V input range (somebody correct
me) the lowest value would be triggered by 488uV(or 488uV/2 ?) this is
not enough. Fortunately we have an integrated amplifier (PGA) which
gives us +20dB so that the signal at the AD converter will get 2.8mV P-P
now at its input (I can hear something now). The additional +30dB will
amplify this to 89mV. This will give me a much larger number of stations
Notice that there is also noise contributed by system internal sources,
so my estimate may be optimistic.
Maybe you can ask some EE people at your university for help, they may
even part with an SMA connector. If not, Froogle is a good source at
least for the connector:
*SMA* Jack 3PC *Crimp* Style RG-58
*$1.29* - Marlin P. Jones & Assoc.: Reviews
3 pc. *Crimp* type Female *Connector* for RG-58A, Teflon Insulator, Gold
Plated Center Pin. WT: 02
The cheapest I found so far. Notice that cheap is not always good
enough, but in this case it may just do.
For completeness lets play with Minicircuits:
ZFL-500LN f=[0.1-500MHz] Gain=+24db Price=$79.95
PLP-100 f3dB=108MHz Price=$11.45
PHP-100 f3dB=82MHz Price=$14.95
Around $100. Well, expensive but fun to play with :) (overkill is
involved though). Any order you hook them up is fine but I would put
the filters first. The amplifier probably needs 15DCV power supply, make
sure you don't mix polarities. You also need an SMA cable (from the usrp
to the contraption) and adapter for your antenna to SMA. Your local HAM
radio store may have a cheap antenna with a BNC connector, so you will
need a BNC female to SMA male adapter (around $6-$11).
Don't take any price information for granted and wait for peer review
before you waste money. In short, I guarantee nothing.