From: Ken Javor [mailto:[email protected]]
Sent: Monday, November 13, 2006 4:20 PM
To: [email protected]
Subject: balun info
Experts,
I need to build/buy a 1.9 GHz PCS band dipole receive antenna. Haven't found
anything to buy. What is a suitable material and balun design to go from 72
Ohm balanced to 50 Ohm coax? Could I use an old T3 balun (400 -
1000 MHz tunable dipole) and just modify the elements? I will need to
build two so I can calibrate an antenna factor. I will transmit 0 dBm or less.
Thanks in advance!
Ken Javor
Ken:
A dirty little secret about the old Empire T3 Dipole was that it's balun
didn't work all the way to 1000 MHz. Everything was sweet until about 950 MHz,
and by 975 MHz, the balun could be causing about 5 dB more loss than expected.
At 1000 MHz, you would be down about 8 or 9 dB.
The competing Stoddart / Singer 90330-2 dipole used a sliding short in
addition to adjusting the arm lengths (was that a J-match?). This worked well
up to about 1300 MHz.
One of the nicest and most flat matches was achieved by Schwarzbeck. They put
a little film resistor network at the junction of the dipole arms, creating a
purely resistive match. The only drawback was that you sacrificed some
sensitivity, and you had to be careful to not use that antenna with a signal
source above a few milliwatts.
At 1 GHz, you are high enough that horns are not too huge, so why not consider
building / buying a rugged little horn like an EMCO 3115 or even an ancient
Polarad CA-L?
Ed Price
<mailto:[email protected]> [email protected]
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (FAX)
Military & Avionics EMC Is Our Specialty
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