Bluetooth PSK31/WSJT/Digital interface for Yaesu FT817 (and a tablet/PC)

I used a bluetooth CAT control with my Yaesu FT817 for quite awhile ($14 on ebay) and was generally happy with it. There is a small lag but one can get used to it. The advantage is no wires between a laptop and transceiver. Also, I could use my HP Stream tablet with it (Win 8) this way.

Given this success, I entertained an idea of making a digital (soundcard) interface wireless too. As the connection would be simplex and mono (1 channel), a regular bluetooth phone headset seemed up to the job.

I happened to have one laying around without much use so the first step was to prove the concept which was very easy. Once paired with the laptop / tablet, the headset became available as a soundcard in HRD DM780 settings. I tried sending some RTTY to it and it worked. I guess now I understand what Alexander Graham Bell felt like when his first phone worked (hi hi).

However, receiving (listening) from the headset did not work. After some googling, I found a hint – set bluetooth headset soundcard as a Default device in the Control Panel -> Sound -> Recording Devices settings. That helped right away so the next step was wiring the headset to the transceiver.

After disassembling the headset, I removed existing battery, speaker and mic and soldered new thin wires to the connecting pads.

Headset with wires

 

For TX (audio out) – I added a 1:25 resistive divider to decrease the output voltage off the speaker wires and to match the voltage requirements of Yaesu; and soldered the speakers wires to it. For RX (audio in), I needed to match Yaesu output to the headset mic. After some experimentation, a combination of two SMD capacitors to both pins and a small resistor in series to avoid overloading and to provide DC isolation finally worked.

Finally, I added a new bigger OEM Li-Ion battery (insulated with black tape) and a USB charger PCB with a switch to improve on portable operation time of the headset.

Li-Ion battery with a charger PCB

The headset, battery, charger, and the existing CAT BT control PCB all managed to fit into a small plastic enclosure. Some hot glue helped to secure them in place.

The boards sit on top of the battery / charger; to isolate the layer I cut a small sheet off a thick polyethylene water jug.

IMG_0789

The enclosure is secured with two small strips of a velcro tape. The battery can be charged via a USB connector; the switch turns on/off the bluetooth headset.

IMG_0788

The PTT is controlled by the software via the CAT control. Now to chase DX with WSJT QRP mode!

 

New Year’s eve building marathon: TNC-Pi APRS gate

I used the New Year’s eve long weekend to finish another project – TNC-Pi kit from Coastal Chipworks. I already experimented with APRS TinyTrak beacon before and noticed bad APRS coverage throughout Toronto, especially, east of DVP so I decided to put my own RX gateway to improve reception in the area.

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New Year’s eve building marathon: Rockmite QRPp 30m transceiver

I was always curios about WARC bands and in particular the 30m band my trusty Kenwood TS-520 lacks. I have it thanks to my FT-817ND but still, in part due to my love of experimentation with radio kits, last spring I ordered a Rockmite 30m kit from Rex W1REX (qrpme.com) and one more 40m version of it. This used to be a very inexpensive kit costing $27 only. These days it’s $45 and comes with a spare pair of crystals. Any mods (AF gain, TX efficiency, etc) are extra. The kit has successfully arrived to Toronto after 5 weeks. During BoM inspection of the 30m kit, I noticed one band capacitor supplied was wrong value and that I got two SA612 mixers and no amplifier IC. Luckily I had enough capacitors of various values ordered from eBay before so finding a replacement was not a problem. The amplifier chip I borrowed from the 40m kit and immediately ordered a pack of 20 on eBay from China for a mere $4 in case I ever need a spare handy… Rex W1REX (from QRPME.com) admitted the kit sorting and handling issues he endured while training a new helper and shortly sent me missing audio amp chip at no charge along with my next order. After finishing sorting components according to the BoM I started building the kit.

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Wired (and wireless) interface for digital modes for Yaesu FT-817ND

I had bought a sound card interface kit (http://foxdelta.com/products/sc2.htm) some time ago which I planned to use with soundcard-based digital modes such as PSK31 and RTTY.

Recently, I finally found time to build it and wire it to my new Yaesu FT817ND radio. Overall, it was an easy and pleasurable build – took me less than an hour. The design is very well thought and easily expandable.

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Chinese QRP VHF-FM radio restoration – continued

The replacement transistors BG1, BG2 (3AA9, 3AA7) are obsolete and next to impossible to find as it’s been 40 years since the radio was built. However, given the known voltage/power/frequency parameters and a friendly help from experienced radio-engineer ham, a reasonable replacement was identified: 2SA1930 from digikey.

Later, I found more data online at http://www.114ic.com/

Model: 3AA7 Model: 3AA9
Manufacturer: China semiconductor companies
Production of materials: Ge-PNP
Nature: RF / high-frequency amplifier (HF), power amplifier (L)
Package: in-line package
Limiting Voltage: 35V
Maximum current allowed values​​: 0.5A
Maximum operating frequency:> 120MHZ
Pins: 2
Beta: 30
Maximum power dissipation: 5W
Possible substitution: B772
Manufacturer: China semiconductor companies
Production of materials: Ge-PNP
Nature: RF / high-frequency amplifier (HF), power amplifier (L)
Package: in-line package
Limiting Voltage: 25V
Maximum current allowed values​​: 0.5A
Maximum operating frequency:> 120MHZ
Pins: 2
Beta: 30
Maximum power dissipation: 5W
Possible substitution: B772

The parameters were exactly as predicted. After installing new transistors, the radio came back to life. However, predictable the output power is too low – less than 100mW.

The bias/feedback seems to be wrong as the bias voltage is different for silicon (0.6V to 0.7V for silicon vs 0.2V to 0.3V for germanium). Also, the operating frequency (50MHz) is too close to the 200MHz limit which also limits the gain.

It may require readjusting the circuit / voltage dividers to ensure proper bias and gain.

While googling the radio, I also found some decent translation of the operating manual: 884_manual_translation

As the radio works on 45-50.1 MHz, it only slightly touches the lowest CW portion of the amateur 6m band. Re-tuning it to 50-55 MHz may not really worth the effort so I may put it on eBay. Would be nice to fix the finals though first.

The full schematics are here:

884_p1

884_p2

 

 

Chinese VHF 6m backpack 884 radio – bad finals (updated)

Had some time today to test the radio. The receiver works – it’s quite loud. It was surprising to find 2-3 very loud music broadcasters on 45-50MHz band. Apparently, there is no volume (AF gain) control on the radio – I even checked the schematics but no, there is no one.

I guess that’s considered normal for army radios?

Everything seems to work fine except there is no RF output! After closer inspection, I noticed that the RF finals transistors are missing:

photo

 

According to the schematic, the RF amplifier uses 2 bipolar germanium PNP transistors: 3AA9 and 3AA7 in TO-3 package:

884 rf finals schematics

 

Hamfest treasures: Chinese VHF 6m backpack 884 radio from the mid-70s

While attending the Durham region hamfest and socializing with OM and YL ham friends, I could not resist grabbing this little green portable radio.

Has anyone had any experience with this radio?

photo 3

Someone appears to tried making some modifications as one panel has been removed:

photo 2

All labels on it and documentation are in Chinese:

884 user manual

Haven’t attempted to try powering it up yet so not sure if it’s in working condition.

According to this blog, the 884 radio operates within 45-50 MHz in a single continues band. It could have 51 channels if the spacing between channels is 100 KHz. It has two modes of operation: FM and CW. The radio itself measures 260 x 220 x 90mm, weight 5.5Kg with batteries. It uses 1.5 meter whip-antenna, operates with 11.5 – 18 V DC and output power is 0.75W. With 1.5 meter antenna, operation distance is 2.5 Km for voice and 5 Km for telegraph under normal battle field condition.

This is how it looked when it was brand new:

Would be interesting to try it with a 6m delta loop on a field day!

73! Paul VA3PAW

 

Are we on a brink of a new technological breakthrough?

There is a short article in the Nature magazine by a Danish team of researchers about ‘Optical detection of radio waves through a nanomechanical transducer’.

In other words, a resonant nano-scale capacitor is fed with a radio signal. A radio signal induced oscillations in this capacitors make it vibrate – like a tiny micro piezo-mechanical quartz. The oscillations are then read using reflected laser light so it works like an up-conversion with optical spectrum used for IF (intermediate frequency) and detection.

I believe, it should be fairly possible to print such up-converters fairly cheap on a silicon wafer – a tiny solid-state laser (LED), photo-diode, and reflecting radio-detecting surface so the application possibilities are endless – e.g. software-defined nano antenna arrays, imaging in gigahertz/terahertz spectrum, highly accurate 3D scanners, ultra sensitive receiver front-ends, etc

See full article about this discovery at U of MD website: http://cmns.umd.edu/news-events/news/1886

HSMM Mesh on Raspberry Pi

Broadband-Hamnet™ (formerly called HSMM-Mesh™)  is a high speed, self discovering, self configuring, fault tolerant, wireless computer network that can run for days from a fully charged car battery, or indefinitely with the addition of a modest solar array or other supplemental power source. The focus is on emergency communications.

In its current form it is built using the Linksys WRT54G/GL/GS wireless routers and operates on channels 1-6 of the 2.4GHz ISM band, which overlaps with the upper portion of the 13cm amateur radio band. Other platforms and bands are in development at this time. Next will be Ubiquiti equipment with others supported as development resources permit.

It’s fairly easy to flash an old Linksys WRT54G router with HSMM-Mesh (now called BroadbandHamnet-v1) firmware. The downside is that the routers are fairly old and not that easy to find anymore. Plus, they are fairly limited in functionality. It would be more interesting to put mesh software on a microcomputer such as Raspberry Pi or BeagleBone which I did.

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WSPR beacon on Raspberry Pi

This was probably one of the easiest fun projects I did. Basically, the software written by Guido PE1NNZ does everything – just download. compile, and run the code. True software-defined radio!

I downloaded the source code from https://github.com/threeme3/WsprryPi and then compiled it on my Raspberry Pi using gcc. I found  instructions coming with  the code very handy.

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