Архив за 26.09.2017

Emulating a receiver

Hi all,

I'm pretty new to the world of RTL-SDR devices and I just recently got a cheap one off Amazon in addition to a Yard Stick One. My goal is to essentially replace my ceiling fan's receiver and transmitter.

It runs on a frequency of 304.186 MHz. I was able to capture the signals with gqrx, visually convert them to binary, and then send them with rfcat on the Yard Stick One. This works and I'm successfully able to control all functions of the fan. Now I'm trying to build the receiver (my reasoning for doing this is that I want to be able to keep track of the current state of the fan based on input from the remote).

I'm not really sure how to approach this. I tried using rfcat to listen on the correct frequency but it does not return consistent data. For example, if I press the light button on the remote, rfcat spits out codes that don't look anything alike for each press. Shouldn't they be the same each time? I've also noticed that there are multiple codes that will successfully turn the light on and off. Maybe I just need to listen for "similar" codes being sent if that's even possible.

If anyone could give me a nudge in the right direction, I'd greatly appreciate it!

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Comment on Using our new Dipole Antenna Kit by Max

Firefox does not display the images and if i save them IrfanView tells me why

Is this capture at 40 degree elevation expected?

V-dipole is installed. At 2 degree elevation, the new setup can see NOAA signal now. THis was from 7am this morning. However, wxtoimg complained about missing sensor 4. I couldn't apply any colors. https://imgur.com/a/YJZdk I'll try again tonight using gqrx in my virtualbox which I remember performs better than the one in osx.

Also, what are those other strong signals?

submitted by /u/Oxffff0000
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вот ноа 15 ( 18.10, 61 градус) и 18 ( 18.47 78 градусов) , Выкса , планшет, airspy mini, новый…

вот ноа 15 ( 18.10, 61 градус) и 18 ( 18.47 78 градусов) , Выкса , планшет, airspy mini, новый квадрофиряр (переделал старый) добавлю еще метеор м2 71 градус , время 20:13

снимки за утро. :) Второй день как заменил кабель на шнурок, но хотя бы рабочий….

снимки за утро. :) Второй день как заменил кабель на шнурок, но хотя бы рабочий.

Comment on Using our new Dipole Antenna Kit by Vincent

Thanks admin for this antenna set, I’ve bought it right away:)
I previously bought 2 RTL-SDR from your site, and so screwed the 2 telescopic antennas to where it fits perfectly (3 mm diameter screw). The dipole was then taped into a window. This dipole was the only SMA one I found, so now I’m greatful you provide yours.

Week In SDR 80

How you doing? Anything exciting this week?

Over a years worth of projects, ideas, ridiculous headlines, answered questions, hacks, tweaks, and more located in our Week In SDR Archives

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Comment on Using our new Dipole Antenna Kit by TC

sweet, my old analog tv antenna 🙂

Using our new Dipole Antenna Kit

Over on our store we’ve recently released our new dipole antenna kit which now replaces the older magnetic whip style antennas from the previous kit. This was done for a few reasons including 1) We believe that the dipole kit is much more versatile and will enable beginners to get better reception right of the bat, 2) magnets of any type are no longer welcome on most airmail parcel carriers (though they still get through for now). While the magnetic whip still works perfectly fine, the dipole kit should make it easier to get the antenna outside, and it also allows for a simple v-dipole configuration for satellite reception.

The units are currently in stock at our Chinese warehouse either bundled with an RTL-SDR or as an individual antenna set. The individual antenna set only has a small quantity at the moment, so get in quick if you want them as they’re only $9.95 USD shipped. We expect more stock to be ready in 1-2 months. Amazon USA should also be stocked with these units in about ~2 weeks from this post date.


This post is a guide on how to use the dipole antenna set in various configurations. First we’ll show and explain about what’s included in the set:

  • 1x dipole antenna base with 60cm RG174 cable and SMA Male connector. This is the dipole base where the telescopic antennas connect to. The short run of RG174 is decoupled from the base elements with a ferrite choke. This helps to prevent the feed line from interfering with the dipole radiation pattern. On the inside of the base the two dipole element sides are connected with a 100 kOhm resistor to help bleed off any static. The dipole has a 1/4 inch female screw on the bottom, which allows you to use standard camera mount products for mounting.
  • 1x 3 meter RG174 coax cable extension. This coax cable extension allows you to place the antennas in a place that gets better reception. E.g. outside on a window, or higher up.
  • 2x 23cm to 1 m telescopic antennas. The telescopic dipoles are detachable from the dipole base via a M5 thread which allows for greater portability and the ability to swap them out. These long telescopic antennas cover VHF and to UHF.
  • 2x 5cm to 13cm telescopic antennas. These smaller antennas cover UHF to 1090 MHz ADS-B, and even still work decently up to L-band 1.5 GHz frequencies.
  • 1x flexible Tripod mount with 1/4″ male screw. This mount allows you to mount the dipole on a variety of different locations. E.g. a pole, tree branch, desk, door, window sill. The legs of the tripod are bendy and rubberized so can wrap securely around many objects.
  • 1x suction cup mount with 1/4″ male screw. With this mount you can mount the dipole on the outside of a window, on a wall, car roof/window, or on any other smooth surface. To use first clean the surface with window cleaner or isopropyl alochol. Then place the suction cup on the cleaned surface and close the lever to activate the suction.
What's included in the new Dipole kit
What’s included in the new Dipole kit

Dipole Orientation

Signals are normally transmitted with either horizontal, vertical or right hand/left hand circular polarization (RHCP/LHCP). This is essentially the ‘orientation’ of a signal, and an antenna with the same polarization should be used too for best performance. A dipole can be used in either vertical or horizontal polarization, just by orienting it either vertically or horizontally.

If you mismatch vertical and horizontal polarization or RHCP and LHCP you’ll get an instant 20dB loss. If you mismatch vertical/RHCP, vertical/LHCP, horizontal/RHCP, horizontal/LHCP you’ll only get a 3dB loss.

There are also ways to optimize the radiation pattern with dipoles. For example for LEO VHF satellites you can use a V-dipole configuration. You can also make a somewhat directional antenna by using a bent dipole configuration. Some more examples of dipole configurations can be found on KK4OBI’s page on bent dipoles.

Terrestrial Signal Reception

Most signals broadcast terrestrially (on Earth) are vertically polarized.

To use the dipole for vertically polarized signals, all that you need to do is orient the elements vertically (up and down).

Satellite Reception

The dipole can be used in a V-Dipole configuration for polar orbiting satellite reception. See Adam 9A4QV’s post where he wrote about how he discovered that it was possible to use dipoles in this configuration for excellent satellite reception. The idea is to use the dipole in horizontal polarization. This gives 3dB loss on the RHCP satellite signals, but also nicely gives 20dB loss on terrestrial signals which could be overloading your RTL-SDR.

For 137 MHz satellites like NOAA and Meteor M2 extend the larger antenna elements out to about 53.4 cm each (about 2.5 sections). Angle the dipole so it is horizontal and in a ‘Vee’ shape, at about 120 degrees. Place the dipole in the North-Source direction.

With an appropriate L-band LNA like the Outernet LNA the dipole can also somewhat work to receive L-band satellites. Using the smallest antenna collapsed, use a V-dipole configuration and point it towards the L-band satellite. Ideally use a reflector too. In the image below we used a simple cookie tin as a reflector. A hole was drilled into the center and the mount used to clamp in the antenna. This together with the Outernet LNA was enough to receive AERO and STD-C.

L-band v-dipole with reflector tin

L-band v-dipole with reflector tin

Receiving Inmarsat signals with the Outernet LNA

Receiving Inmarsat signals with the Outernet LNA

Choosing the Antenna Element Length

Like with the whip you can use an online calculator to calculate the optimal length for your frequency of interest. We recommend this dipole calculator. The exact length does not matter too much, but try to get the lengths as close to what the calculator says as you can. With the dipole you want both elements to be the same length.

In reality extending the antenna to almost any random length will work just fine for most strong signals. But if you’re really trying to optimize those weak signals you’ll want to fine tune the lengths.

Basically the longer the antenna, the lower it’s resonant frequency. The shorter the antenna, the higher the resonant frequency. You want to be close to the resonant frequency. Remember that there is about 2cm of metal inside the antenna itself which needs to be added on. Below is a cheat sheet for various lengths and frequencies. Note that the length refers to the length of one side only.

  • Large Antenna, 5 Sections, 100cm + 2cm is resonant @ ~70 MHz
  • Large Antenna, 4 Sections, 80cm + 2cm is resonant @ ~87MHz
  • Large Antenna, 3 Sections, 60cm + 2cm is resonant @ ~115 MHz
  • Large Antenna, 2 Sections, 42cm + 2cm is resonant @ ~162 MHz
  • Large Antenna, 1 Section, 23cm + 2cm is resonant @ ~ 285 MHz
  • Small Antenna, 4 Sections, 14cm + 2cm is resonant @ ~445 MHz
  • Small Antenna, 3 Sections, 11cm + 2cm is resonant @ ~550 MHz
  • Small Antenna, 2 Sections, 8cm + 2cm is resonant @ ~720MHz
  • Small Antenna, 1 Section, 5cm + 2cm is resonant @ ~1030 MHz.

See the SWR plots at the end for a more accurate reading of the resonance points. But in most cases no matter what you extend the length to the SWR should be below 5 at most frequencies which results in 2.5 dB loss or less. More accurate info on VSWR loss graphs can be found in this document from the ARRL “Understanding SWR by Example” (pdf).

Using the Mounts

The mounts and RG174 extension allow you to more easily use the dipole antennas outside. But please note that like our older magnetic whip we do not recommend permanently mounting this antenna outdoors. This antenna is designed to be a portable antenna that you put up and take down at the end of the day – not for permanent outdoor mounting. It is not protected against water, not grounded so cannot handle a lightning strike and could be damaged with dirt and grime build up. For permanent mounting you could conceivably fill the inside and hinges of the dipole with silicon putty or maybe even hot glue and ground the antenna yourself, but we have not tested this. The stainless steel antennas won’t rust, but dirt and grime could gum up the collapsing mechanism.

The suction cup mount allows you to easily place the antenna on a window, or any smooth surface. To use it first clean the surface thoroughly with isopropyl alcohol or glass cleaner. Then apply the suction cup and close the lever to lock it in place. The lever requires some force to push down, and this ensures a strong grip. You can then angle the antenna in the orientation that you need using the ball socket. Once in place close the ring to lock the ball socket in place.

The flexible tripod mount is useful to mounting the dipole to almost everything else. Including tables, doors, poles, trees etc. The legs of the tripod have a flexible wire inside and rubber sheath so they can be bent into a position to grip almost anything.

Some examples of how to use the mounts.
Some examples of how to use the mounts.

Tightening the hinge

Once you’ve got the orientation of the dipoles the way you want, you might want to tighten the hinge so the elements don’t move so easily anymore. To do this simply take a small screwdriver and tighten the screw on the hinge.

Sample VSWR Plots

Small Antenna Collapsed

Small Antenna Collapsed

Small Antenna Extended

Small Antenna Extended

Large Antenna Collapsed

Large Antenna Collapsed

Large Antenna Extended

Large Antenna Extended

RG174 Cable Loss

RG174 Cable Loss

Comment on LocalRadio: A new RTL-SDR App for MacOS by Sauro

Thank you for your answer.
I’ve tested Localradio and use Voice Over on Sierra, I think it’s already quite accessible.
The problem is that I do not know how to recognize my dongle at Localradio.
I’m not SDR expert and I do not know if I need to install specific drivers on OSX, but Localradio does not detect any dongles.
Could I have instructions for a beginner like me?

Thank you.

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