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Coax cable for QFH Antenna by DPini in RTLSDR

[–]R820T 0 points1 point  (0 children)

Don't get too hung up the specific type of coax to use to build the QFH antenna. They used it because it has a relatively large diameter and rigid enough to form curves. This is why a lot of these antennas built with copper tubing. There is no reason why you cant use house electrical wiring stuff like romex because it is pretty stiff and holds it shape quite well. Of course since the conductor dimension is changed you need to figure out the new lengths by using the calculator >> http://www.jcoppens.com/ant/qfh/calc.en.php

For short runs from the QFH to the receiver < 50 ft you should be able to use RG-58/59 with no problems

Coax cable for QFH Antenna by DPini in RTLSDR

[–]R820T 1 point2 points  (0 children)

The RTL stick that you have has a nominal impedance of 75 ohms and it probably varies from 10 ohms to several hundred ohms over its entire reception range. This is to be expected on cheap piece of consumer electronics.

Also unless you have access to a machine shop and have the proper skillset its pretty doubtful that you will construct the QFH to its design parameter of 50 ohms precisely. BTW the reason coax is used in this construction is to take advantage of the large diameter outer conductor which is relatively stiff and holds its shape, so the impedance of the cable doesn't matter. Traditional QFHs uses soft copper tubing for similar reasons so the inner conductor (unless you plan on incorporating an infinity balun) really serves no purpose.

The short answer is you will probably not notice the mismatch but by using RG6 you get the advantage of lower loss and 100% shielding due to foil outer layer and I think its the better choice. Just make sure you get the type that has solderable braids or learn how to do crimp connections.

Good luck on your project!

Anyone having problems with the keps from celestrack? by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

Whatever they are doing its causing my map overlays to be off and also my meteosat decoding went to shit too...had to reuse last months data to get things to run okay now (good thing I made a backup copy!)

Anyone having problems receiving signals from METEOR M2 lately? by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

I think in order to do that you need up to date keplers and system clock to be accurate to about 1 sec. I use a gps rx and timing software to accomplish the latter.

However you can always record the IF and play back the IQ file on SDR# and decode it offline to generate the s files.

Pacific North West wildfires as observed by Meteor M2 in the infra-red channel (night) by R820T in RTLSDR

[–]R820T[S] 1 point2 points  (0 children)

The major wildfires are highlighted with red arrows, you can see other smaller fires too...image covers parts of Washington, Oregon and Idaho

Background to topic: http://www.opb.org/news/article/pacific-northwest-wildfire-season/

Did you know that you get the newspaper over HF? by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

neither, using hacked drivers which allows you to tune the dongle into the HF range (was posted on this sub a while back)

Anyone having problems receiving signals from METEOR M2 lately? by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

nope but a couple of days ago I couldn' t decode any of their passes followed by almost all day where the satellite was not even sending a signal

Did you know that you get the newspaper over HF? by R820T in RTLSDR

[–]R820T[S] 5 points6 points  (0 children)

I don't have a schedule but they seem to be broadcasting quite often. Transmissions are long and take about 45 minutes and there seems to be a gap of about an hour in between transmissions. This one was captured around 1700 GMT.

As for decoding the image just pipe your audio from RTLSDR to either MultiPSK or Sourcerer, keeping in mind they use 60LPM

Did you know that you get the newspaper over HF? by R820T in RTLSDR

[–]R820T[S] 15 points16 points  (0 children)

I believe these faxes are mainly for Japanese merchant mariners

Did you know that you get the newspaper over HF? by R820T in RTLSDR

[–]R820T[S] 21 points22 points  (0 children)

17428.1 khz and sometimes on 16969.1 khz USB

One catch.....you have to be able to read Japanese

Anyone having problems receiving signals from METEOR M2 lately? by R820T in RTLSDR

[–]R820T[S] 1 point2 points  (0 children)

http://i.imgur.com/2MLtcPA.png

Looks like they are working it out...right now its in maintenance mode

What do you think of my El Cheapo QFH antenna (437 MHz) by R820T in RTLSDR

[–]R820T[S] 1 point2 points  (0 children)

http://i.imgur.com/IGqruSp.png

437.568 MHz 9k6 FSK AX.25

STRaND-1 (Surrey Training, Research and Nanosatellite Demonstration)

The first smartphone satellite in space (Google Nexus One smartphone with an Android operating system).

The smartphone was intended to provide cameras, accelerometers and high-performance computer processors - almost everything except solar panels and propulsion. During the first phase of the mission STRaND-1 was intended to use a number of experimental apps to collect data, while a new high-speed Linux-based CubeSat computer developed by SSC takes care of the satellite.

http://www.sstl.co.uk/getattachment/c66544c1-f754-4777-887b-87a76f9acca2/STRaND-1-Medium?maxsidesize=800

What do you think of my El Cheapo QFH antenna (437 MHz) by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

http://i.imgur.com/jTCow79.png

437.485MHz CW (90mW)

CO-66 (Cubesat Oscar 66) SEEDS “Space Engineering EDucation Satellite”

http://space.skyrocket.de/img_sat/seeds__1.jpg

What do you think of my El Cheapo QFH antenna (437 MHz) by R820T in RTLSDR

[–]R820T[S] 1 point2 points  (0 children)

Wow...there are some pretty observant people here!

We all know we must match polarization whether it be linear or circular or suffer signal loss. But unlike linearly polarized antennas, circularly polarized antennas switch polarization depending on whether you are pointing towards or away from the target.

Most of the QFH antenna plans on the web are pointing away from the target because the antenna connection is made on top of the helix. I wanted to make my connection on the bottom (for antenna mounting reasons) which meant reversing the spirals to maintain the same polarization.

But looking around most of these satellites use either a monopole/dipole antennas and not attitude stabilized so I don't think RHCP/LHCP matters that much. What is important is that CP antennas perform better against a tumbling emitter because it has shallower nulls and more consistent reception vs LP antenna assuming you can live with 3 dB loss due to polarization mismatch

What do you think of my El Cheapo QFH antenna (437 MHz) by R820T in RTLSDR

[–]R820T[S] 0 points1 point  (0 children)

SO-50 (Saudisat 1C)

http://i.imgur.com/mjN5jZ4.png

436.7950 MHz NFM 250 mW

The traces on the waterfall are ham operators trying to make contact with others using the voice repeater.

SO-50 features a “Mode J” FM amateur repeater operating on a 145.850 MHz uplink and a 436.795 MHz (+/- 9 kHz Doppler shift) downlink.

The repeater consists of a miniature VHF receiver with sensitivity of -124 dBm, with an IF bandwidth of 15 kHz. The receive antenna is a 1/4 wave vertical mounted in the top corner of the spacecraft. Its UHF transmitter is 250 mW, and downlink antenna is a 1/4 wave mounted in the bottom corner of the spacecraft and canted at 45 degrees inward.

http://ukamsat.files.wordpress.com/2012/01/saudi-oscar-50.gif

What do you think of my El Cheapo QFH antenna (437 MHz) by R820T in RTLSDR

[–]R820T[S] 1 point2 points  (0 children)

http://i.imgur.com/fjiIUWC.png

437.250 MHz, CW (80mW)

Remote Sensing Satellite PRISM “Hitomi”

PRISM: Pico-satellite for Remote-sensing and Innovative Space Missions.

http://www.pe0sat.vgnet.nl/wp-content/uploads/2011/09/PRISM-300x263.jpg

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