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Re: [Discuss-gnuradio] USRP need antenna?

From: kt1023
Subject: Re: [Discuss-gnuradio] USRP need antenna?
Date: Wed, 20 Apr 2005 22:17:41 -0400
User-agent: 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 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


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):


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

   * 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,


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