Category: Antennas

Tech Minds: Testing an Inmarsat L-Band Helix for Offset Satellite Dishes

In his latest video, Matt from the TechMinds YouTube channel tests out an LHCP L-band helix feed designed for receiving Inmarsat satellites. Matt pairs the feed with an 85cm satellite dish, an L-band LNA, and an Airspy Mini.

The L-band helix feed comes from a small German engineering company called nolle.engineering. The feed is priced at 94.70 Euros (incl. VAT) (~$102 USD), plus shipping costs. It is a passive antenna so it needs to be combined with an LNA to be usable with a typical SDR.

In the video Matt shows that the reception with the LHCP helix + dish setup is better than expected. He also compares it to a previous test he did with a longer RHCP helix antenna also produced by nolle.engineering. The RHCP antenna is used to be used without a dish, however, as expected the SNR is less than the dish + small LHCP feed setup. Matt then shows some Inmarsat signals being decoded including STD-C and Aero voice.

This L Band Helix Antenna Gives Amazing Performance

Antennas Explained: Finding the Best Antenna for HackRF, RTL-SDR and Other Receivers

Over on YouTube sn0ren has uploaded a well produced video to help beginners to the radio hobby understand antennas. The video explains how antennas work in theory, and how to choose the best antenna for your SDR and application through calculations and use of a Nano VNA.

There is an essential gadget that you will want to get, to get the best antenna performance. But first we need to cover a bit of antenna theory, before we can answer the question of what antenna that is the best one for your HackRF Portapack, or Flipper Zero SubGHZ module, or Meshtastic, Quansheng UV-K5, RTLSDR or other radio devices. This video is covering the bare minimum basics of antenna theory for beginners into the radio hobby.

The best antenna for HackRF Portapack (and Flipper Zero, Meshtastic, Quansheng, RTLSDR, etc.)

Discovery Dish April Manufacturing Update

This was posted over on our Discovery Dish Crowd Supply updates page and we are cross-posting here too.

It’s been over a month since our last update so we thought we’d share some of the recent progress. As mentioned in our last update, during the month of February all manufacturing was shut down due to the Chinese New Year holiday. In early March, staff returned to the factories and began making progress on finishing Discovery Dish.

We have a snazzy new logo, and we are working on obtaining some stickers to include with the feeds.

 

Dish Manufacturing Progress

The molds for the dish stamping machine were successfully created in March and the test stamps have come out great. The manufacturer is still tweaking the secondary mold that stamps the mounting and connecting holes, but we expect that to be completed shortly. Once that is done and tested, we can begin stamping the dish segments en masse.

The Dish mounting system was also finalized and we added 45-degree markers to it, which can help with aligning skew.

We are still awaiting the results of the anodizing tests, but they should be completed by the end of this month. Anodizing the dish is important as the dish must be a dark non-reflective matte color, so that it does not focus hot sunlight onto the feed point plastic head.

Feed Manufacturing Progress

PCB Upgrades

While waiting for the manufacturers to finish up with the molds, we’ve been further refining the PCB feed. Our final version of the PCB has now moved to a PTFE substrate with significantly lower loss at higher frequencies. This has yielded an over 1 dB increase in SNR at the GOES 1.69 MHz frequency.

The change to PTFE was not without problems. An interesting RF engineering problem occurred with the move to PTFE that we wanted to share. When moving to PTFE the only changes to the board layout are PCB trace width changes to keep the impedances matched. Other than that, the boards and layout are essentially identical. However, we discovered that the dual LNA design started oscillating when we moved the PTFE substrate. Oscillations can occur with LNAs when RF essentially bounces back and forth between the two LNAs, which causes undefined behavior in the LNA, such as poor gain, multiple spikes in the spectrum, and unexpected current draw values.

We found this quite odd because oscillations were not occurring in the original FR4 PCB, and the QPL9547 LNA is advertised as ‘unconditionally stable’ which means that it should never oscillate. However, we found that unconditionally stable guarantees may not apply to two-stage designs. In the end, the fix was simple, we just needed to add a damping resistor to one of the inductors on the circuit which reduces its Q-value. It seems that the change from FR4 to PTFE effectively increased the Q-value of this inductor so much, which in turn induced an oscillation in the circuit.

Discovery Dish Feed Head Enclosure

We’ve also refined the entire feed assembly. The feed arm pipe now has a ruler laser etched onto it so that mounting it at the correct distance is easy. A skew angle guide has also been added around the neck. A thumbscrew locking mechanism has been added to the feed head neck too, so that skew can easily be adjusted without the need for a screw driver or Allen wrench to loosen the set screw.

The PCB enclosure has been slightly refined and the injection molding die is currently in production and due to be completed in mid-May. While waiting for the die to be made, we’ve been testing different plastic mixes for the head enclosure to make sure that they are UV stable. The plastic mix has certain strict requirements and choosing the correct mix is crucial. It has to be RF-transparent with a low relative permittivity value, it has to endure direct sun, UV damage, and freezing weather, as well as be water-proof too.

S-Band Feed

Previously as noted in prior updates we were testing an S-band feed with the FR4 substrate. But we found that there was too much loss and the SNR values we got were not great. The move to PTFE substrate means that our experimental S-band feed is now working very well. We will be releasing this in the near future as an additional feed product that can be used with Discovery Dish. This feed will have a frequency range of 2.2 GHz - 2.3 GHz. This covers the main S-band weather satellites, other satellites like Coriolios and JASON as well as the many dump-only S-band satellites that transmit signals only over certain regions.

As requested by most people interested in an S-band feed, the S-band feed will not include a downconverter, so to use it you will either need an SDR like the HackRF which is capable of tuning to the S-band, or a third-party downconverter product.

Discovery Dish Outdoor Metal Enclosure Progress

Our enclosure set is now complete, and the final packing has almost been completed. The user manual can be found here Discovery Dish Outdoor Enclosure User Manual.pdf.

The final set consists of:

  • 1x Metal Enclosure
  • 3x Custom metal cable glands
  • 1x Vent
  • 1x Electronics mounting board
  • 1x Pole mounting set (with hose clamps)
  • 1x Wall/DIN mounting set
  • 1x 10 mm x 10 mm x 8 mm thermal pad (to be placed under the electronics mounting board)
  • 1x 10 mm x 10 mm x 3 mm thermal pad (to be placed under electronics on top of the mounting board)
  • 1x Set of various screws and washers

(Note that there will be some minor changes from this image in sets going out of customers - the hose clamp will be shorter, and the mounting rails will be longer)

Meteor M2-4 Launch

We mentioned in our last update that a new weather satellite Meteor M2-4 was due to launch. The launch was successful and the satellite is now in orbit. The satellite was briefly turned on after launch, and we were able to receive HRPT images from it in the L-band. However, now it is currently in a testing phase so the transmitters are often turned off. We don’t know how much longer it will be in testing, but we assume it won’t be more than a few more months.

GOES-U / GOES-19 Launch Updates

We’ve been keeping an eye on the expected launch date for the next GOES satellite. Currently, it has been delayed from April 30, 2024, to the new date of June 25, 2024, when it will be launched on a Falcon Heavy from Kennedy Space Center, Florida.

Elektro-L4 Updates

In the last update, we mentioned that we were having some problems getting SatDump to receive Elektro L4 properly on computing devices that used ARM processors. After some investigation, we determined that this was a problem with buffer size settings in SatDump and we were able to suggest a fix in https://github.com/SatDump/SatDump/pull/616 which was implemented. New versions of SatDump have this problem fixed.

Driver Tweaks

We have been looking at the RTL-SDR drivers and have found a few tweaks that can improve performance at L-band frequencies. We’ve put a modified version of the librtlsdr/librtlsdr fork up our the rtlsdrblog GitHub at https://github.com/rtlsdrblog/librtlsdr. With this fork and the PTFE feed upgrades, we now get around 5-6 dB of SNR on GOES-18.

Antenna Rotator

The low-cost antenna rotator is finishing up with prototype testing, and we are now working on improving the design’s manufacturability.

Timeline

The ramping of progress from the Chinese New Year holidays to now has been a little slower than expected, but if everything goes perfectly to plan, we will be on time for shipping by the end of June. However, this is currently a best-case scenario. There are still a few manufacturing stages to get through like the final mass production, CE testing and sea freight shipping. Unfortunately, from prior manufacturing experience, there are always setbacks along the way that slow progress, so we are conservatively pushing our advertised timeline back by about 1-2 months. We apologize for any potential delays, but we are working hard to get the product out to you ASAP!

Customer Questions

We have had a few more customer questions over email which we’d like the answer publicly below:

Would it be practical to use this kit indoors to do hydrogen-line astronomy? I ask because I live in a flat in a block of retirement flats, and wouldn’t be able to place an aerial or dish outside, but could find space for a Discovery dish + rotation gear inside.

Unfortunately, indoor Hydrogen line astronomy is out of the question. The hydrogen line signal is just too weak to be seen indoors, and there would most likely be too much interference indoors as well.

What all do i need to purchase and get for the Discovery Dish for Radio Astronomy?

You’ll need these two components from the Discovery Dish Crowd Supply store:

  • Discovery Dish (Dish & Mount Only)
  • Hydrogen Line Discovery Feed

You will also need a software defined radio, such as an RTL-SDR Blog V3/V4 which can be purchased separately, a computer and somewhere to mount your dish (e.g. a mast/tripod etc).

Have you tested this for C-Band / Aero downlink reception?

Currently, we do not have a C-band feed, so we have not tested it for this purpose. Generally, a larger 1.2 m+ dish is required for C-band AERO, so the 70 cm Discovery Dish may not be suitable. We may test this with Discovery Dish in the near future just in case however.

I want to purchase a hydrogen antenna. Where should I buy it? Also, please tell me what is needed to observe seti radio waves.

The Discovery Dish (Dish & Mount) and Hydrogen Line Discovery Feed can be pre-ordered from the Discovery Dish Crowd Supply store. I’m not sure exactly what you are referring to with SETI radio waves. An alien signal could in theory be on any frequency, but the 1.42 GHz Hydrogen line frequency could be a good bet as it’s a universal frequency of interest that any technological civilization would be observing. Realistically the Discovery Dish would be too small to detect potential alien signals unless they were very strong.

I’ve seen a small home made 3D-printed dish called a ‘heliocone dish’ being used for HRPT. How is Discovery Dish different?

The heliocone 3D printer design going around is a great DIY solution for L-Band polar orbiting HRPT satellites. But it has some limitations as it cannot receive the weaker geostationary satellites due to its smaller size and use of a circular polarized feed. It also cannot receive satellites using the opposite circular polarization. It also cannot receive satellites on different frequencies or the Hydrogen Line without designing a new helical feed and using a different LNA+filter combo. Discovery Dish is a more of a general purpose ‘does-it-all’ and ‘ready to use’ out-of-the-box dish. With our dish and feeds you can receive the L-Band polar orbiting HRPT satellites as well as the geostationary satellites. You can quickly swap out the feed for a different feed that covers a different band as well.

 

Testing a WiFi Grid Antenna for L-Band Satellites

Over on YouTube dereksgc has uploaded a video where he tests out a 2.4 GHz WiFi Grid antenna for L-band weather satellite reception. WiFi grid antennas are typically repurposed in the SDR community for L-Band weather satellite reception because they are cheap and mostly work out of the box. They can also be used for hydrogen line radio astronomy. TV dish antennas are an alternative but with them, a custom feed needs to be built. 

In his video, dereksgc tests the WiFi dish on receiving various polar-orbiting L-band satellites including Metop, and Meteor M2. With the polar orbiting satellites the dish needs to point at the satellite as it passes over the sky and so dereksgc recommends using a mount if hand tracking them.

Later in the video he tests some geostationary satellites but finds that the dish is not tuned well enough to receive Elektro-LN3 properly without modifications. He was however able to receive a noisy image from FengYun-2H successfully.

We note that we also currently have our Discovery Dish product available for pre-order, which is similar to the WiFi grid dish, but smaller and lighter weight with a built-in optimized active feed.

I finally got a WiFi grid antenna for satellites

Saveitforparts: Receiving and Decoding L-Band Weather Satellites

Over on his YouTube channel 'saveitforparts' has uploaded a new video showing how he has been successful at receiving and decoding L-band weather satellites using his setup made from scavenged parts. He uses a custom-built helical feed on a scavenged dish, and an automatic pan-tilt rotator built from an old security camera mount. With this setup combined with an RTL-SDR and LNA and filter he is able to receive polar orbiting L-band weather satellites. 

In the video, he shows how his system works and what his software setup looks like. He uses SDR++ to record the pass initially, then SatDump to decode the data into images. We note that SatDump can be used to decode the images live, and can also record the raw radio files too, so SDR++ is not required.

How To Receive And Decode L-Band Weather Satellites

Flipper Zero Starts a Petition To Fight Canada Ban

Back in early February we reported about how the Canadian government is making plans to completely ban the Flipper Zero, and popular pentesting tool. The wording from Dominic LeBlanc, Canada's Minister of Public Safety, also implies that software defined radio devices could also be banned.

The reason for the ban is because the Canadian government claims that Flipper Zero and 'consumer hacking devices' are commonly being used as tools for high tech vehicle theft. However, as mentioned in the previous post, this has been debunked.

The team behind Flipper Zero have recently started a petition on change.org to stop the ban. At the time of this post the petition has already reached over 8,000 signature. The team have also penned a comprehensive "Response to the Canadian government" blog post, explaining why the ban makes no sense. In the post they debunk the myth of Flipper Zero being used for car theft, and show the real way high tech car theft is being done.

Saveitforparts: Building a Satellite Antenna from an Emergency Blanket and a Rotator from an old Security Camera Mount

Over on his YouTube channel, 'saveitforpaarts' has uploaded two new videos. The first shows how he was able to build a very cheap satellite antenna for GOES satellites out of an umbrella and a metallic emergency blanket. The blanket is simply spread over the inside of the umbrella, creating an RF reflective surface. Then a linear feed with LNA and amplifier is placed at the feed point. The makeshift dish works, though the SNR is marginal, and he is only able to receive slightly corrupted images from GOES satellites.

Satellite Antenna Made From Emergency Blanket

In his second video saveitforparts builds a satellite dish rotator out of an old thrown away security camera pan/tilt mount. The mount is hacked to be controllable via an Arduino microcontroller. 

I Built A Cheap Satellite Tracking System From Spare Parts

IndiaRocketGirl Receives NOAA-19 Weather Satellite Images with a Tape Measure Yagi Antenna

Over on her YouTube channel IndiaRocketGirl (@VU3BIZ) has posted a video showing how she was able to receive weather satellite images from the polar orbiting NOAA-19 weather satellite at 137 MHz.

She uses a home made four element Yagi antenna with elements made from a tape measure. This allows the elements to be easily folded down for transportation. A phone running the Heaven's above app is used to help track the satellite in the sky as it passes over, and then SatDump and an RTL-SDR Blog V3 running on a laptop is used to decode the signal into an image.

IndiaRocketGirl notes that in her next video she will show how to make the Yagi antenna that she was using. In a previous post IndiaRocketGirl also showed how she was able to receive geostationary FengYun-2H S-VISSR signals.

How to Receive Real Time Images from Low Earth Orbit Satellites | India Rocket Girl | NOAA-19