Friday, July 18, 2014

432MHz Solidstate Amplifier Completed

Over 3 years ago I bought a W6PQL 500MHz amplifier module  with the matching LPF/Directional coupler. Before I moved out of the McKinney house I quickly mountedthe modules on a heatsink inside an aliminium chassis to protect it in storage. Over the last few weeks I have finished the metal bashing thanks to WA5YWC and built a PIC controller and LCD display.  The biggest issue was testing it as I no longer had a 432MHz transmitter in the USA. W5LUA kindly offered to let me use the facilities in his shack which included drive source, Power meter and dummy load.
The first thing we learnt was that the RF got everywhere inside the chassis. Initially there was no screening around the PIC board which caused measurement issues. After a trip to the local hobby store for some .015" ali sheet and the donation of many 1nF bolt in feedthroughs by W5LUA that issue went away. It was necessary to put a screening can over the directional coupler (w6pql only suggests it for his 1kW amplifier) as the calibration of the bargraph meter changed dramatically when the cover was put on the box
When completed the amplifier gave 420W for 6W drive when running 17A at 48.0V. Looking at the W6PQL figures I could hit the amplifier harder to get the full 500W but this way I have a safety margin. All harmonics were over 65dB down on the fundamental power.

Monday, July 7, 2014

Fujitsu 251-9735-010 6GHz amplifier fixed

I was given a Fujitsu 251-9735-010 6cm 5W amplifier by WA5VJB about 12 years ago for my Transverter but never got round to trying it out, this weekend was an opportunity. I borrowed a 5760MHz California Microwave brick which gives 16dBm at 5760.000MHz from W5LUA to save needing to retune my DB6NT 5616MHz LO. This needed a -19V supply, provided from my 57A 28V PA supply (yes overkill!) According to Kent's notes the PA needed 4A at 12V and 200mA at -12V for the bias for which two other additional PSUS were found (a variable one and the 13.8V rig supply). Applying the -ve bias the power supply immediately current limited, but the resistance to ground from the bias supply lead was 12kohms. Time to take the lid off. LOTS of screws later the lid was off. The -ve bias supply feeds a 7905 regulator. As a quick test (to avoid more screws) the regulator was cut out and the -5V applied to the regulator output pin. With the 12V supplied 5W was seen. The control board was removed and a new regulator fitted. It still produced 5W. 
The opportunity was taken to measure some voltages and currents. Full output was produced until the positive supply dropped below 12.00V. Full output was produced until the negative bias dropped below -6V, The measured currents were 12V at 3.9A and -12V at 50mA. It was noted that the detected output was a negative voltage. Not good for Microchip PICs! The detector diode was reversed and resistors adjusted so that the detected output was +10V at full output. 

Thursday, June 19, 2014

Hamcom 2014

June brings the annual Hamcom hamfest to Dallas, which, as always clashed with the ARRL June VHF contest.

As in the last four years I volunteered to help man the Elecraft Booth, this year with Eric WA6HHQ and wife Lerma. Their plane got diverted from DFW to AUS as DFW closed for an hour due to bad weather so we didn't start setting up till 5pm Wednesday. 

The trade show exhibitors this year started earlier at 0800 and officially closed at 1800, making a long day. The new item this year was the PX3 Panadaptor for the KX3.
 The K3/0 mini was also in evidence, this time using the software from, to control a K3/KAT500/KPA500 in California. It was great fun on the Saturday afternoon listening to the 6m activity in California during the VHF contest.
 The outside flea market was not too exciting. The most interesting item was a Layafette tube tester without model number. I was told that Lafayette often rebadged other companies products.
 I also got some tube bases, some tubes for my BBC studio-E receiver and a multiband whip for the 2m module

I did get to meet John Langridge. KB5NJD who also operates on LF as WG2XIQ and compare notes from WH2XES. Unfortunately I could not get to his talk.

UPDATE: The Lafayette tube tester is a Accurate Instruments model 157 in disguise

Friday, June 6, 2014

DrugStore Tube tester...every shack should have one!

To help me restore the Country Belle radio I wanted to test the tubes.  I mentioned this to Roger N5PGH at the NTMS Tuesday BBQ meeting. At the next meeting he appeared with a loaner tube tester in the back of his truck. This was a "Seco Electronic Tube Analyser"  It was the type often seen in your local USA drugstore in the tube era so you could test the iffy tubes in your radio receiver and they would sell you a replacement. This one had been previously built into a panel but was now mounted on a undersized box.

It has a meter, switch,  variable load resistor and 92 sockets. It came with a manual of what settings to use for each tube.

All the tubes in the country Belle radio passed with flying colours. along with some other 1930 era tubes I had acquired for future projects.

I had been looking for a 6AF11 audion multistage tube for a while. WA5VJB found me one in the Dayton Hamvention fleamarket. The manual had 3 settings for the tube so decided to test it. Two settings produced good pass results of 120 but the third only produced 20, a big fail. Pity! I then remembered that Roger had mentioned the tube tester can be used as a reconditioner by leaving the tube in its test configuration overnight. Worth a try. The next morning the reading was 100, so I let it be for the rest of the day which restored it to a 120 reading. What a great tool, even if it is so large!  

Restoration Project Country Belle 1956 Radio

Having built a couple of one Tube receivers, a local amateur decided it was time for me to move on to a restoration project. As a challenge he presented me a while ago with his spare Country Belle Radio #556  made by Guild in 1956. This radio was made to look like the old style wall Telephone, but had a 5 tube medium wave receiver Inside. Taking the earpiece of its rest turns the radio on. The Winding crank is the tuning knob, very neat. It had some hardware missing (a bell, the tuning crank and the earpiece rest) but was electrically complete.
The Tubes lineup is the classic "all American Five".  Converter: 12BE6, IF amplifier: 12BA6, Detector: first audio amplifier: 12AV6, Audio power output: 50C5, Rectifier: 35W4. The subtlety of this lineup is that the filament Voltage/Current all add up so you just connect them all in series across the 110V AC (or DC) supply. The 35W4 even has a tap on the filament to drive a dial light (#47)
As the radio is transformerless,  for safety I borrowed an Isolation transformer from WA5VJB. When power was applied, all the heaters lit up, there was some noise but no stations could be tuned in. Tracing the circuitry I found that the grid Transformer of the 12BA6 was open circuit. The Inductor was taken apart and the wire mended. Now when powered up stations were loud and clear. I peaked up the 455kHz IF Transformers, noting that each transformer had an upper AND a lower tuning core.
Next task was the Hardware. Luckily a friend of a friend had a carcass inn their barn which I was given. The wood work was bad but it had all the missing hardware.
The next decision was what do about the woodwork. In the end I decided to sand down all the wood parts (after stripping the fittings) but this removed the Decals. I then sprayed it with Pecan wood stain/Varnish (3 coats). The brass fittings were cleaned with Brasso (which I discovered is sold in the USA) then varnished. It was recommended to spray the other black metal fittings with Black Lacquer, but using it can be challenging. I went to the local Oreilly's autoparts to get some but after explaining what I wanted it for to the Old Guy, he said not to use it but to use Black "Dupli-color Vinyl and Fabric Coating" as It would flake less. This has really worked well
I found a source of replacement decals at These were water based transfers (like I used many years ago for Airfix model aeroplanes) which were a little tricky to apply. When dry the cabinet was sprayed with Varnish
When completely reassembled the radio worked fine and looked very nice, even though I say it myself!

The restored external view


The restored internal Electronics
The good news is that I found a small 240V/120V transformer that will will allow the unit to be used in England, so it has been dismantled ready for shipping


Wednesday, June 4, 2014

NavSpark Arduino compatable GPS receiver

Before Christmas I saw a posting for NavSpark on the crowd funding site  From the web page  "NavSpark is a small, powerful, breadboard-friendly, 32bit development board that is Arduino compatible, with a world class GPS receiver as on-board peripheral, and under $15".  At that price I ordered one, especially as it came with a dual band patch antenna for $19.
It arrived last week, the board looking like an Arduino micro with the dual band active antenna.  Heeding the warning that the U-FL connector can only be used a dozen or so times, I mounted the Board and antenna in a plastic box.

The Arduino IDE, viewing software programming guide and documentation are all at    The USB chip is by Prologix, the unit appearing as a serial port (defaults to 115200Baud). After installing the drivers and software and putting the receiver out on my south facing balcony, it found GPS and GLONASS satelites

The map shows the correct relative position of the satellites, but the map is based on Taiwan (where the units are made) and isn't currently changeable. Not surprising the locked satellites are all to the South with the system on a south facing balcony.


Tuesday, June 3, 2014

Sam Wetterlin Reflection Bridge

Having bought a cheap ($20) Chinese reflection bridge off the internet (NOT ebay) which had appalling directivity (10dB), I decided it was time to build my own to be used with my HPSDR VNA.
A survey of the internet and some recommendations pointed me at the designs by Sam Wetterlin. There were two possible designs, I chose the three bead balun version (mainly on size grounds) This used a Minicircuits transformer and a ferrite bead Balun. I bought some "TC1-1-13" off ebay but these had a pinout different from the Minicircuits catalogue and didn't work well. N1JEZ provided a couple of the genuine articles from his collection which worked perfectly The rest of the parts were bought from Mouser and I designed the two tiny PCB with 0805 components and had them made by ExpressPCB 
Assembly took five minutes. The two PCB are separated by a brass strip which supports the balun.  I had some Glass fibre tape which I used to stop the Balun moving around on the support. I soldered an smt resistor to the PCB as the reference load to save using a 4th SMA for an "external load.
Complete Reflection Bridge
Closer view of the input circuit. The TC1-1-13 is the small square on the right
Directivity was very good, exceeding 30dB from 0.47MHz to 1GHz, more than adequate for my present needs