Thursday, July 28, 2016

Progress on the LDMOS Amplifier

8/10/2016 ~ A Fun Diversion

So OK I am easily distracted and once again I am off topic (only this is not political). Shown below is my beloved SWAN120 Single Band SSB Transceiver built in 1962. Yes, this is an appliance and not a homebrew radio. But there is a real story about the company that manufactured this radio and in particular about this specific radio.
In the late 1950's, Collins Radio came out with an amazing product the KWM-1 a 100 watt, SSB transceiver covering the frequency range from 14 to 30 MHz in 200 kHz slices. This was followed by the KWM-2 which essentially covered the then five major ham bands, 80 through 10 Meters in 200 kHz band segments. This was a major departure from the separate receiver and transmitter that ruled the roost from day one. This opened up a whole new opportunity for mobile and portable operation. It was cutting edge technology with a cutting edge price tag! BTW it is rumored that a KWM-1 was used on Gary Powers' U2 spy plane that was shot down by the Russians. So lots of intrigue here. Other companies were working on "Me Too" transceivers but the Collins rigs were by far ahead of the pack.
In true fashion there were hams working in garages the world over attempting to build a competing less expensive product. One of those visionaries was Herb Johnson, W6QKI (SK) who was living in Benson, Arizona ( a small town in the middle of nowhere not far from Tucson) who built one of those "competing rigs" right in his garage. The urban legend has that he convinced a radio parts supplier in Tucson to provide enough parts to build 10 radios. The concept was to build a single band radio based on operator preference and to concentrate on the portability aspect. In that lot of ten were several 40M and 20M radios. Ultimately the single band radios would operate in the 75, 40 and 20 Meter bands. Units were never commercially produced for the higher bands.
In true ham fashion Johnson bent the metal and painted the units right in his garage. Too bad Oasis Blue was not in the mix at that time. That first lot had an anodized (gold colored) front panel. Instead of a pair of 6146 tubes in the final ala Collins, Johnson used a TV sweep tube, a 6DQ5 which could produce 100 watts of RF. He also used the 7360 for the Balanced Modulator which added an air of cutting edge technology. Another innovation was to use a half lattice crystal filter operating around 5.0 MHz. Thus the same VFO range could yield 75 or 20 Meters. It was a no frills radio lacking refinements such as AGC or an S Meter. The essentially homebrew filter was a bit wide and the VFO was no PTO like in a Collins. But it was about 1/4 the price of a Collins. In addition to being a bit wide they were not as sensitive. But hey you were on SSB!
W6QKI produced several additional runs of radios at his Benson, AZ garage factory; but the popularity of the radio soon caused Herb Johnson to move to Oceanside, CA. The weather was definitely better but so was the availability of skilled electronic assemblers. Well the rest is history.
Now to my specific radio. It was built in Benson, AZ as indicated on the stamping on the back of the radio and is post the initial "gold" faced units but definitely built in the garage. Here is why I can make that claim. Take a good look at silk screen lettering --kinda crude and not well aligned with the controls or openings. The meter is much larger than ones found on later units and in fact later Swan units had a less expensive meter than the Triplett shown in the photo. In later production units to resolve the frequency display Swan used a second meter face that simply fit over the opening in the panel.
This radio was a fortunate find for me as it is in very good cosmetic condition and still works! So it is a keeper and yes I also have a Collins KWM-2.
But there is another story here, one that is perhaps almost as disturbing as the 2016 political process here in the US. Here is my concern. Swan was started by a single individual working out of his garage. He had a vision and that was to put an SSB transceiver in the hands of many hams who simply could not afford a Collins KWM-2. He also used innovations in his design. Ask yourself how many bands do you really work? I find myself spending most of my air time on two bands --40 and 20 Meters. When I operated mobile it was one band. One hundred watts is still one hundred watts whether coming from a pair of 6146's or a 6DQ5.
The disturbing part is spending $7000 for a radio just so you can look at a 27 inch display to see if I have sparkle on my mid-range audio. BTW I can still repair that Swan 120 but not so sure I could tackle the new SDR radios. The disturbing part is, also, that there are very few hams with a soldering iron working out of a garage to produce a low cost radio that will provide endless hours of pleasure. I have a radio built in 1962 that still works in 2016 -- that is 54 years. Where are the Herb Johnson's of today? I can think of a couple (Ashar Farhan comes to mind) but in truth we are losing the skill set to try new ideas and thinking outside box to provide low cost radios that are frequency agile, stabile, and have a display but not a 27 inch screen. And the all important can be had for less than $200.
I am amazed at how well the radio still functions albeit a bit wide, slightly deaf and not too sensitive and did I mention "drifty". Today we can build radios that resolve all of these issues at a mere fraction of the cost of that needed back in 1962.
Pete N6QW



In an earlier post I mention the Power FET Switch from W6PQL. I am now happy to report that the switch arrived and I built the kit. Quite a bargain and as supplied can be wired for a source voltage of 12, 28 or 48VDC. For my build I used the 48 VDC option. The build is straight forward and I soon will be giving it a smoke test. For info purposes shown below is the schematic of the switch and a photo of the actual built switch -- only comment it is small. I now need to locate a heat sink rated at 24 watts.
Pete N6QW


7/30/2016 More Discoveries Continued

Thanks to David GM4JJJ and his suggestion of using a power FET to quickly disconnect the LDMOS amp from the 48 VDC rail that will now be the approach. W6PQL, Jim, has a magnificent website where you can purchase parts for amps and one of his offerings is the FET Power Switch, which can be purchased as a kit or completely assembled. Variants include supply voltages of 12, 28 and 48 VDC. The kit version comes with the parts needed for any of these supply voltages.

The value of the blog is the bidirectional  sharing of information and I am most grateful for any and all inputs.

Pete N6QW

More subsystem testing and discoveries!

The real value of the breadboard test system is that it enables you to find/discover things that were not so obvious.
Currently I have the Start & Stop buttons wired to the Arduino. I also have all six of the Low Pass Filter relays enabling circuits installed and today I installed and used  LED16 which is the  circuit that must be engaged to sense the TR signal from the transceiver. Spent a little time getting LED16 to work properly as I had a bad relay.
Then I decided to use the actual 48 VDC power supply in place of the floor fan connected to the hockey pucks. The supply came on as desired when you punch Key #1 and does go off when you punch the 2 or 3 or 0 Keys. BUT I find that the going "off" condition does not happen instantly. The 48 VDC holds for a second or two and then slowly drifts down to 0 volts. That means the amp could be smoked by the time it gets to 0 volts.
This now requires using something such as a 40 or 50 amp automotive relay that has a 12 VDC coil fed off of the latch rail. This relay would have the 48 VDC fed from the supply  on to the contacts and then fed to the amp. As soon as the latch is broken the supply to the amp would drop. That adds another relay but the voltage "off" would be instantaneous. Had I not used the breadboard and done the testing I could have smoked the LDMOS Amp.

I have been doing some research on the SWR detector and talk about getting "wrapped in a knot". That can happen really quickly. After some inquiries of those who know what they are doing I really don't want to have a built SWR function. I have several external meters to do this including my treasured Drake W4. But what I do want is to detect the "reverse' voltage coming back from a load that is mismatched to the amplifier output impedance of 50 Ohms. Helge Grangberg K7ESO/OH2ZE of Motorola fame wrote two articles in December 1982 and January 1983 QST regarding a 1KW MOSFET RF Power Amp. The protection of his amp was exactly that where a reduced bias would be applied to the amp stages as the Rev voltage increased.

Finally here is a shot of the control board. Additional control functions will be moved to a second board.

Pete N6QW


Monday, July 25, 2016

Yikes -- Another Blue Radio!!

It's compulsive ~ another blue radio.

Today I painted the front panel of the JABOM radio. Blue is good! I swear the blue color makes it work better. This was another 20 minute job.

Pete N6QW

Friday, July 22, 2016

Small Radio --- Big Signal!

A Shirt Pocket SSB Transceiver for 20 Meters!

Several years ago I built a shirt pocket sized SSB transceiver --well actually two of them with the second one being  2X2X4 -- yes that is inches. The overall size was actually dictated by the need to have a front panel. If I had used surface mount it could have been smaller still. The transceiver was the subject of an article in QRP Quarterly. This may be one of the smallest SSB transceivers to be homebrewed. Note for the purists I did not say the smallest!
Recently I made a modification to the driver stage which actually was posted on this blog. I now get about two watts out and driving an outboard amp it is good for about 60 watts PEP. Imagine my surprise the other day when ON8KW was calling CQ and I answered him (60 watts) and he came back to me. I got a 5X8 report. Now keep in mind I am using a beam antenna. So once again a good antenna will level the playing field. The LO is a crystal switched two range VXO that covers from 14.162 to 14.188 and 14.194 to 14.225 MHz or roughly about 60 kHz of 20 Meters. The output device is an IRF510.
Here are a few photos and today I had about 20 minutes so I built and painted blue a case for the rig. Another cool blue radio! By the way the inspiration for this radio was an article written by Ben Vester W3TLN who built a small 20M SSB transceiver that ran off of 6 VDC and put out 200 MW. The 6 VDC was because he had it installed mobile in a 1959 Volkswagen Beetle where pre-1966 Beetles were 6 VDC.
There story here is that you can build an SSB transceiver (large or small) and have meaningful contacts including DX stations. Get off the couch and start building.
Pete N6QW

Saturday, July 16, 2016

Back to the LDMOS Linear RF Amplifier

7/21 The Role of Analog Pin A8

One action that always has a bit of mystery is how to actually put the amp on line? This amp will be used principally for SSB (voice) but the principles would apply to CW or digital modes.

Basically I hear a station or I want other stations to call me and the 1st thing I do is grab the microphone and squeeze the PTT bar. A lot of things have to happen once you key the microphone. Essentially on the amplifier side there has to be a detection that the PTT was closed and then the TR relays are sequenced and the bias applied to the amp.

Part of the TR changeover is hardware and another key piece is software. The software essentially runs some tests such as asking are a set of Low Pass Filters in line? Another is the 48 VDC to 12 VDC DC to DC convertor energized?

Assuming the requirements are met the important pin is Analog Pin A8. If a low (ground connection) is observed on that pin then the amp is in line. A circuit schematic for A8 is shown below.
Not a lot to it but really important.

Pete N6QW

7/19 First Test of the Arduino Control System!

See the Arduino going through its paces.

Pete N6QW


Back to the Amplifier Project ...

I must sound like a broken record when I mention that at times I only have 15 or 20 minutes to work on a project then it is off to my caregiver duties. Well eventually those short periods of working on the project result in something substantive. Starting with wiring up the several power supplies and then moving on to the basic motor starting circuit, I am happy to report that the first tests were very successful.
Using the Keypad and engaging Key #1, I am able to deliver control signals to the "hockey pucks" (Solid State Switches) which  turn on the amplifier power supply (48VDC). Depressing Key #2 (normal Off) drops the control signal. The same applies for Key #3 which is Amplifier By Pass and Key #0 which is Emergency Off. This was a huge proof of concept and reflects the suitability of the Arduino to control the LDMOS Amplifier.

By way of review below is the "Motor Start" circuit I learned about when I worked at Steven Engineering (South San Francisco). This has been around a long time and is used even today. All we have done is to use the Arduino operating via a keypad to simulate the NO and NC momentary pushbutton switches. A new day has dawned!

Then I transitioned to actually controlling a load in this case a large floor mounted pedestal fan. Punch #1 and it goes on and if you punch 2, 3 or 0 it goes off. This is like the Karate Kid Movie ! I can see Mr. Miyagi standing in a corner of my garage chanting "Fan On" "Fan Off". What a great day. Now I will move on to adding the other circuits such as the keypad  selection of the Low Pass Filters and then the supervisory controls such as over temperature and high SWR.

I would like to plug a highly reliable parts supplier and that is Jameco Electronics. Many of the components seen on the above bread board were supplied from Jameco Electronics located in Belmont California and available on the web. I will highlight the Jameco items as we tour the board with the letters JE.

Starting at the upper left corner is a 9.0 VDC power supply with connectors (both JE) This supply is used to power the Arduino Mega 2560. Oh the main power switch is also JE (lower left hand corner). To visually see that 9.0 VDC is available for the Arduino a simple LED with a dropping resistor is connected to the output pins of the 9.0 VDC supply. Next to the 9.0 VDC supply is a 12 VDC supply (JE) and that is used in the Motor Start circuit. Next to the Arduino Mega is the 4X4 Keypad (JE) and the 20X4 from SainSmart.  The board next to the Keypad/LCD will contain many of the key items of electronic hardware . Currently on that board are two small orange relays that simulate the NO and NC momentary switches  and the larger black relay is the latch (American Zettler). The green terminal block (JE) facilitate the interconnections to the Mega 2560 and other parts of the circuit. The two multi-pole barrier type terminal strips on the right hand side are also from Jameco Electronics. They will be used to interface with the Low Pass Filter Relays and the TR Relays. Not currently on this board is the really small 48 VDC to 12 VDC DC to DC convertor (JE) that will solely power the TR relays with the Arduino supplying the sequencing logic.

Stay Tuned,
Pete N6QW

Sunday, July 10, 2016

Squeezing a few more Watts out of the Cool Blue ZIA Transceiver

Getting More Pout of your Rig!

So Ok, we all love to stand on the mountain top and scream I worked a station 12000 miles away on 20M SSB running 100 microwatts. Plausible? Yes! Possible? Yes! Practical on a daily basis? Probably not!
So what do you do to make consistent and reliable contacts? The 1st thing you do is get a decent antenna! A chunk of short wire hiding out in an attic space is not a good start! But a properly designed dipole at 30 feet is much better! Beyond that a beam at 33 feet is even better. So its the antenna for starters.
Next is the rig. You do not need to spend thousands of dollars on an appliance box to have consistent and reliable contacts.  A well designed homebrew transceiver running 5 to 10 watts will result in many contacts. Mating that 5 to 10 watts with an amp can really bore a hole in the ionosphere. I happen to have a really Big Amp -- a 3CPX1500A7 --which will do legal limit with about 45 watts of drive. At 5 to 10 watts it will easily do 400 to 500 watts output. Now that is a signal that can be heard -- keep in mind you are running a QRP transceiver -- only it is on steroids. I also have an SB200 and a couple of 100-150 Watt solid state amps.
In 2015, I built the ZIA Transceiver which has been subsequently updated in 2016 with a new paint job (Cool Blue) and the display has been changed from a Nokia 5110 to a 128X128 TFT. BTW using the Nokia 5110 is like doing brain surgery with a rusty spoon. I am really sorry I ever considered using such a poor device!

If you check my website at you can see the detail of how the ZIA was built. Instead of the usual IRF510 in the output I used a real RF transistor, a Motorola MRF260. This device is really intended for use at VHF but has been employed in this radio as this is what I had in the junk box. It can Pout in the 5 to 10 watt range. On a good day if you squinted properly you could see maybe 5 watts out.
Shown below is the 20M  ZIA parked next to the Nu-Rig (also Cool Blue) built in 2016.
About two weeks ago I tried to squeeze a few more watts out of the ZIA by replacing the MRF260 with a 2SC3133. Well as it turned out the two new "budget priced" 2SC3133's that I got from China were "FAKE" devices and immediately blew up in the circuit. So back to the MRF260. I should note that with the MRF260 the power out using the Solid State Amps (which are lower drive than the SB200) was about 100 Watts PEP. But I felt that 150 Watts should be easily attainable.
So now I went back to "noodling" how to squeeze out more power from the pre-driver and driver stage,  which is a direct lift from EMRFD (2N3904 and 2N3866 ) wherein it was stated that 300 Milliwatts was possible. That was not what I found. I guess this is the EMRFD gas mileage statement.
I made a few changes to that circuit and currently the Pout from the MRF260 is about 8 Watts PEP. I now easily hit 150 Watts out of the Solid State Amp! This past weekend was the IARU world wide contest. With the ZIA and the amp I worked about 30 stations. So much better than 5 or 8 watts alone. The changes to the EMRFD schematic include changing the devices to a 2N2222A and a 2SC2075 as well as the change in the emitter circuit of the 2N2222A. The second photo below shows the actual install in the rig.
This is the case of where we drained the swamp versus raising the bridge. I am very pleased and all the signal reports were excellent. If you look closely in the photo above you can see the 100 NF and the 50 Ohm resistor (actually 2 X 100 Ohms in parallel --what I had in the junk box).

Get more watts out of your rigs --and drive those amps!

Pete N6QW

Tuesday, July 5, 2016

Simpleceiver Revisited

JH8SST/7's Implementation of the Simpleceiver.

For those of you turned off by the LDMOS amplifier project we are making a short detour back to the Simpleceiver project of late 2015 vintage. Jun, JH8SST/7 has built and improved upon the project originally documented on this blog. Kudos to Jun for adding an superb AGC system and by moving around some of the blocks in the project that improve its ability to handle very strong signals. Below is the schematic for Jun's version. Speaking of versions Jun has built both a 40M and 20M version. Linked below are two videos from JH8SST/7 that detail the two versions
Jun also has a blog that shows additional information on his project. Superb craftsmanship is a hallmark of his efforts. Jun's blog is located here.
On my website http://www.n6qw .com is a pdf document that contains the schematic data.
Pete N6QW