Re: [Discuss-gnuradio] USRP need antenna?

[kt1023]

Hi,


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 
> of noise.
>
> 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 
> that role?
>
> 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 
> downconvert.
> --------------------------------
>
> It seems like I need an antenna with gain and filtering... Where do I 
> get those? I'm totally illiterate in harware, electronics areas.
>
> Many thanks
>
> -suvda

Well out of the options there are, you should go with the scanner with 
IF output.

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):

http://www.magnumdynalab.com/x_sleuth.htm

It says:

   * 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
     available

   * a low profile, cabinet in satin black. 17 3/4", 19" or 19"
     rackmount available.

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 
too.

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 
<http://froogle.google.com/froogle_url?q=http://www.mpja.com/productview.asp%3Fproduct%3D11835%2BRC&fr=APWDXX8x5yh7J6FGn6A4KAZne78gkoFLLfyc0_WkNgRcAAAAAAAAAAA>
*$1.29* - Marlin P. Jones & Assoc.: Reviews 
<http://froogle.google.com/froogle/merchratings?store=mpja&q=SMA+Crimp+connector>  
Add to list <javascript:document.t11143567655000865506.submit();>
3 pc. *Crimp* type Female *Connector* for RG-58A, Teflon Insulator, Gold 
Plated Center Pin. WT: 02
 ** 
<http://froogle.google.com/froogle_url?q=http://www.mpja.com/productview.asp%3Fproduct%3D11835%2BRC&fr=APWDXX8x5yh7J6FGn6A4KAZne78gkoFLLfyc0_WkNgRcAAAAAAAAAAA>
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.

Have fun,

Kilian