My setup is up and running

g4jvf · 2017-02-19T12:08:29.982Z

YAY!
Downloading data…
Used my own CHIP and burned the image.
RTLSDR V.3 with NOOELEC pre amp.
Made a helical antenna, put it on a chair outside and it connected and is downloading data.

SNR is averaging about 3.5…
Temporarily running on a USB battery…

Great stuff, now to improve the signal by messing with various antennas…

Thanks for all the helpfull information on here folks

Phil

outernet.png993×790 1.44 MB

g4jvf · 2017-02-19T13:53:58.962Z

Bit of tweaking with the antenna direction and I’m now getting an average of SNR 4.7…
Nice little antenna

Phil

Mudflap · 2017-02-19T15:43:28.235Z

Be careful someone does not sit down!! (Grin)

Interesting set up!

g4jvf · 2017-02-19T18:05:00.445Z

Been running over 7 hours now…
Surprised how well the battery has held up…

neil · 2017-02-19T18:42:42.166Z

good onya. Well done…

K4RKR · 2017-02-19T20:37:56.948Z

I like your antenna. How about a HOW-TO post?

g4jvf · 2017-02-20T12:19:59.912Z

I used the construction dimensions from this web site…
http://www.uhf-satcom.com/lband/

Mine is wound the opposite way for RHCP.
I used some sheet steel of 0.5mm thickness for the reflector and 14SWG tinned copper wire for
the helix.
An SMA female socket on the reflector connects to the end of the helix and some epoxy holds
the bottom turn in place.
Will be building another with maybe a couple more turns and some plastic support rods to keep the turns solid.

Phil

pe1chl · 2017-02-20T18:05:59.406Z

For good matching of a helix you would need a stripline parallel to the reflector before the first turn.
If I remember correctly the helix is 140 ohms so to match that to 50 ohms you need a 84 ohms stripline.

g4jvf · 2017-02-20T18:52:15.012Z

Yes, I’ve been reading about that…
This one has the first quarter turn bent parallel to and 1mm from the reflector to help with matching…

Phil

pe1chl · 2017-02-20T18:58:43.748Z

In the past we made 23cm helixes for the packet radio links in the local club and we used a section of
copper strip (cut from a large variable coil as used in an antenna tuner…) soldered to the first turn and kept
parallel to the reflector. It should be 1/4 wavelength long. Of course those antennas were used for
transmitting and it is more critical in that case. Receive tolerates such a mismatch when you don’t mind
the signal loss.

g4jvf · 2017-02-20T20:02:23.569Z

Thanks for the info… something to experiment with…

Phil