Hey /g/ I want to listen to 850mhz trunking with my rtl-sdr.

Colinears are pretty easy to make.
http://jeroen.steeman.org/Antenna/collinear-coax

So cool but useless without a good range.
For range, you need, you guessed it.

>>56201112
Start with a 1/4 wavelength vertical and go from there. When it comes to UHF range is going to come mainly from antenna height. The repeater is going to have a tower so most of the work is done for you. You just have to get something good enough to pick up the repeater which is designed for use by shitty mobile stations anyway.

>>56202680
Why 1/4, if I do full shouldn't that be better?

>>56202989
>>56202989
1/4 wavelength is the smallest resonant length. for a vertical. if you're going to do 1/2 wavelength you should do a vertical dipole. 1/2 vertical is resonant but it is the near infinite impedance resonance so you get a poor match. 3/4 vertical and 3/2 vertical dipole has more gain. If you're going through the trouble of adding more than that you might as well go colinear.

>>56203531
Where does one learn this kind of knowledge in life? Self-driven curiosity and the internet or formal education?

>>56203728
Little from Col A, little from Col B

>>56203728
When I was 14 I came across a bunch of old ARRL books. Various license manuals, the arrl handbook, and antenna book. I read everything I could get my hands and tinkered. Went to school for EE out of high school and became better at knowing where to look. It just snowballs.

You can get very knowledgeable about radios with the ARRL handbook and antenna book.

You would be better off just buying a co-linear or dipole antenna unless you have equipment to tune your own. If you have a spectrum analyzer with tracking generator and a directional coupler, then you could measure return loss and tune your home brew antenna. Otherwise, just buy one.

>>56206210
You're over thinking this. He's trying to pick up a repeater in line of sight with a $20 usb sdr. If he can read a ruler with an accuracy of .5 cm he's ahead of where he needs to be. Police scanners with untuned rubber duck antennas have been doing this for more than a decade. That's the purpose of a repeater. One good setup on a tower so your other stations can be shit.