Re: [softrock40] Re: WWV 30M Antenna?
A 6 or 10 dB pad will force the input to 50 ohms. gfz
--- On Thu, 9/25/08, drmail377 <drmail377@...> wrote:
From: drmail377 <drmail377@...>
Subject: [softrock40] Re: WWV 30M Antenna?
Date: Thursday, September 25, 2008, 10:21 PMHi Robin,
If you're in the continental U.S. and your local power-line noise
isn't too bad, I'll venture to guess that with a Softrock receiver you
should be able to receive at least one WWV frequency at any time of
the day with something like ten feet feet of wire hanging out a window.
The design of the Softrock receiver requires a 50 Ohm antenna for
optimal operation. The receiver gain and bandwidth are roughly
inversely proportional to antenna impedance. This is explained in
Youngblood's four-part 2002/2003 QEX article "A Software-Defined Radio
for the Masses" which may be freely downloaded here:
http://www.arrl. org/tis/info/ sdr.html
In addition to or instead of an antenna tuner as mentioned by Tom, a
pre-amplifier may isolate some of the antenna mismatch affects. In
your case where you mention a short antenna for WWV reception, you
might want to try an "active antenna". Here's a page with some links
to active antenna circuits:
http://www.discover circuits. com/A/active. htm
A google search for active antennas will yield a lot of links, some to
pre-built off the shelf units. Do tell us about your results should
you decide to move forward.
Best 73's, David WB4ONA
--- In softrock40@yahoogro ups.com, k5nwa <k5nwa@...> wrote:
> At 05:39 PM 9/25/2008, you wrote:
> >I'm wondering if any of you use your 30M Lite kit to receive WWV, and
> >if so, how little of an antenna can you get away with?
> >Robin Midgett K4IDC
> >615-322-5836 office - rolls to pager
> >615-835-7699 pager
> >615-301-1642 home
> >Radio Gear For Sale:
> >http://www.people. vanderbilt. edu/~robin. midgett/index. htm
> The input filter of the SoftRock requires a 50 Ohm resistive antenna
> otherwise it's frequency response is shifted and the receiver is
> pretty deaf. But if you have a tuner to make the wire look like 50
> Ohms resistive source then a short wire will work just fine.
> The shortest I used was 8' with a tuner to make it purely resistive
> and it worked fine. The length you can get away with depends on your
> www.softrockradio. org www.qrpradio. com
> "Blessed are the cracked, for they shall let in the light."