What impedance are the wires and antenna?

Well, maybe that’s the wrong way to phrase it. I need to make or buy an
FM
antenna (I realized I accidentally grabbed the VERT900 from my lab, and
they
don’t have an FM antenna).

Some sites seem to imply that coax is usually 70 ohm, but it looks like
here
http://wireandcable.thermaxcdt.com/item/high-performance-coaxial-cables/mil-c-17-coaxial-and-twinaxial-cables/m17-113-rg316-id-72-?&seo=110
That the Thermax RGS-316 may be 50 ohm? I just need to know so I don’t
ruin
it…

I checked ettus labs and couldn’t see an answer.

On Tue, Jul 28, 2009 at 03:37:02PM -0400, Jonathan C. wrote:

Well, maybe that’s the wrong way to phrase it. I need to make or buy an FM
antenna (I realized I accidentally grabbed the VERT900 from my lab, and they
don’t have an FM antenna).

Some sites seem to imply that coax is usually 70 ohm, but it looks like here
http://wireandcable.thermaxcdt.com/item/high-performance-coaxial-cables/mil-c-17-coaxial-and-twinaxial-cables/m17-113-rg316-id-72-?&seo=110
That the Thermax RGS-316 may be 50 ohm? I just need to know so I don’t ruin
it…

I checked ettus labs and couldn’t see an answer.

Antenna:

http://www.radioshack.com/product/index.jsp?productId=2062691

75 ohm Matching transformer (close enough):

http://www.radioshack.com/product/index.jsp?productId=2062054

Then you need an F-to-BNC and BNC-to-SMA or something similar, unless
you’re plugging it into a TVRX (which has an F-connector).

Coax is commonly either 50 ohm or 75 ohm. Cable TV uses 75 ohm.
For this application, either will work fine.

Eric

Thanks Eric!

2009/7/28 Eric B. [email protected]

On Tue, Jul 28, 2009 at 03:55:26PM -0400, Jonathan C. wrote:

And I am using the Basic RX, if that makes a difference.

It will work more-or-less, but it’s not really the daughterboard to
use to receive broadcast FM. The TVRX is a much better choice.

The USRP1 samples at 64MHz, which means that when using the Basic Rx
to attempt to receive the broadcast FM band, you’ll be “bandpass
sampling” and there’ll be a fold at 96MHz (3/2 fs), right in the
middle of the broadcast FM band. You won’t be able to separate out
96M-f from 96M+f for any frequency offset f.

Eric

I will try and get a hold of the TVRX board, but in the meantime, are
there
any workarounds? Is this because the BasicRX doesn’t have a filter and
whatnot in it to specifically target the radio frequencies?

2009/7/28 Eric B. [email protected]

On Tue, Jul 28, 2009 at 05:02:42PM -0400, Jonathan C. wrote:

I will try and get a hold of the TVRX board, but in the meantime, are there
any workarounds?

Use an FM dipole antenna, or for that matter, just plug a 75cm
(1/4 * 3e8/100e6) wire (not coax) into the center of the SMA connector
and tape it to the wall.

Is this because the BasicRX doesn’t have a filter and
whatnot in it to specifically target the radio frequencies?

Yes. Read up on “bandpass sampling” for the details.

Eric

And I am using the Basic RX, if that makes a difference.

2009/7/28 Jonathan C. [email protected]

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