Akademisk Radioklubb

LA1K / LA1ARK / LA1UKA

Repairing broken receiver on a USRP N210 WBX40 daughterboard

Kimmo Kansanen at NTNU recently donated some USRP N210 units they no longer had a use for. We have started to use them for various communications experiments, for example estimating the antenna patterns of our VHF/UHF antennas against the LA2VHF and LA2UHF beacons.

While operating one of the N210s we were sudddenly unable to receive the LA2VHF beacon that had previously been easily decodeable. We also saw that the noise floor had increased by 20 dB. Jens, LB6RH, decided to investigate matters further.

Inside the N210 a WBX-40 daughtercard provides the RF-frontend. The device functions as normal, except for in receive mode. The receiver section of the WBX-40 should be a good place to start looking.

The WBX-40 daughterboard after removing coaxial patches that attach to the front panel of the N210.

To further investigate what may be wrong we started investigating the board for any obvious short circuited connections. We were unable to find any such sources. The next step was to probe around the board with a multimeter to check the voltages being generated from the different voltage regulators on the board. Since Ettus Research provides the schematic for the WBX-40 online this process was greatly simplified.

LB6RH found that the 3.3 V rail on the output of voltage regulator U308 was only at 1.2 V. Suspecting that something was wrong with U308, he removed the component and attached a laboratory power-supply to the 3.3 V output pin. After turning on the supply (with the current limit set low, to avoid frying the circuit) he noticed that there was still a short circuit. To identify which component caused the short we borrowed a FLIR thermal imaging camera to check what components got hot when we turned up the current limit on the power-supply.

Unfortunately we did not get a good picture of the thermal test, but the chip that got hottest was the Low Noise Amplifier (LNA) U313. Since our problems are related to poor reception we thought this might be a likely candidate. After removing U313 we turned the power-supply back on, and saw that there was no longer a short, hurray!

A closeup after removing components U313 and U308.

We ordered new components for U308 and U313 from Digikey, and soldered them back in place.

U308 – Analog Devices Inc. ADP3336ARMZ linear regulator

U313 – Broadcom Limited MGA-82563-TR1G MMIC broadband LNA 

Replacements for U308 and U313 have arrived.

The soldering battlestation. A microscope helps when soldering small parts.

 

 

 

 

 

 

 

 

 

 

 

 

 

After replacing the two parts we connected everything back and tried powering on the device again.

We are now able to receive LA2VHF again!

Unified software rotor control over the local network

ARK has recently collected all rotor controllers on a single Raspberry Pi-device and made these available for software control from all Linux machines on the local network. We’ve also enabled rotor control from N1MM on Windows. This post outlines how we did it.

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Field day 2017

Last weekend ARK participated in IARU Region 1 Field Day. In Norway, this contest is more known as National Field Day and is coordinated by the Norwegian Radio Relay League (NRRL). ARK usually treats this as a full three-day social event where we travel to a cabin far away from Trondheim, and treat our members to a nice balance of antenna assembly, food, social exposure and a many new contacts on the radio. This year, we traveled to Fjellvær Gjestegård on Fjellværøya, Hitra.

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License course fall 2017

This years amateur radio license course will start 18:00 Wednesday 06.09.2017 at VE20 Gløshaugen.

An amateur radio license is required in order to participate in the amateur radio hobby. As an amateur radio operator you can learn more about radio communication, build electric circuits that allow you to communicate with people all over the world, and much more. Feel free to show up to the first lecture if you would like a more indepth description of what amateur radio is, and why it is fun.

The course is open to anyone, and will consist of four lectures followed by an exam. Each lecture is approximately two hours long. The lectures are held in VE20 at Gløshaugen. For directions please see this mazemap link.

The lecture plan is:

Date Topics
Wednesday 06.09.17 18:15 to 20:00 Introduction to amateur radio, practical prefixes and units, Ohms law, Passive components, Direct Current
Wednesday 13.09.17 18:15 to 20:00: Alternating current, Active components, Receiver/radio architecture, Modulation
Wednesday 20.09.17 18:15 to 20:00: Antennas and cables, Wave propagation, Digital Communication
Wednesday 27.09.17 18:15 to 20:00 Left over topics, walkthrough of example exam

The course will be held in English or Norwegian, depending on the attendees. The exam will be held Tuesday 03.10.17 at 18.00 in VE20, get in touch with me over email to sign up.

The curriculum for the course is “Veien til internasjonal amatørradiolisens” which can be purchased here. While the book is in Norwegian it is possible to follow the course and take the exam in English.

The course is free, but if you pass the exam there is a license fee of 2000 NOK to the national communications authority (NKOM).

3m parabole dish ready

We have finally finished one of the major goals of the 1 to 10 GHz project. The mast is installed, the rotor is mounted and the 3m parabole is built.

Below is a narrated selection of pictures from the build. You can find the full album here.

Espen Molven, LA2USA, advised that the mast would be easily liftable by two persons.

We barely made it with 4 people.

The mast was easily fitted to the lamp post.

First hoisting of the mast.

The mast hoisting mechanism is really strong. Hydraylic lifting allows us to easily lift a grown man.

The rotor (SPID BIG-RAS/HR) mounted on the mast.

To get the rotor running some outdoors soldering was needed.

The center hub of the parababole fully assembeled.

Two of twelve spokes mounted. The spokes came ready assembeled.

Progress on spoke mounting.

A view of the attachment point of spokes to the center hub.

All spokes in place.

Mounting circular bracing rings around the dish. In the background, you can see our 5.8 GHz wifi link and the four bay array for 144 MHz.

The twelve pieces of mesh that the dish is made of.

One of twelve mesh pieces mounted.

Clamps were very helpful when mounting the mesh.

Half way there. In the background are our homebrewed DK7ZB antennas for 4m and 6m.

We had time to do a re-enactment of the photo from the original 5 m parabole.

Twelve hours after starting mounting the mesh the parabole is complete!

 

A big thanks to everyone who helped make this possible. Stay tuned as we attempt to make our first contacts with the dish, and progress on the RF hardware.

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