Tuesday, November 18, 2008

Aspire One - Bluetooth modification

Acer Aspire One - NetBook

One thing which always bothered me when operating “portable” is the logging process - logging the contacts on paper and then entering them in the computer! Using laptop solves this issue but laptop computers are still relatively big and heavy to carry around and the battery life is limited….until now… Enter the NetBook – new generation of portable computers – UMPC or Ultra Mobile PC.
The Net Book is excellent candidate for logging machine. NetBooks are a relatively new market but with many entries by some “ big boys” – Dell, Asus, Acer, HP etc. I decided on Acer Aspire One!

The version I got is with 160 GB HDD, 1 GB RAM (which I later upgraded to 1.5 GB) and 6 cell Li-ion battery powering the machine for up to 6 hours! The Aspire One is very small and light machine – 2.2 lbs. It is using the new 1.6 GHz Intel Atom CPU. The only thing missing to a full-blown laptop is the CD-ROM/DVD drive – an external USB CD-ROM can be connected if needed. Aspire One is well equipped for connectivity – LAN, WiFi, 3 USB ports, built-in camera and audio card /w microphone (for digital modes).

I got an external “Prolific chipset” based USB-to-RS232 converter for connecting it to the radio via CAT interface. Ham Radio Deluxe runs just fine on this machine. The built-in wi-fi card does a great job connecting the PC to Internet hot-spots (eQSL, propagation, even DX cluster to mention just a few ham applications) . The screen is extremely bright and sharp! One very useful feature of this machine is also the ability to run from solid-state memory module instead of a hard-drive – they sell a different version equipped with solid state memory for those who like better shock-resistance. I decided to go with the hard drive as I needed the storage space – it is nice to have space for pdf manuals, books, music and even a few movies.

The Li-Ion battery is 11.1V /5200 mAh (operating) and DC charging/operating voltage is 19V / 1.58 A. I’ll look into a modification to power it from external battery or solar charger. Another thing I would like to see is a built-in Bluetooth interface which will complete the “interface arsenal”.

Thursday, October 9, 2008


Spotty - the HAM CAT!
"A mouse! On my operating desk?!!
"It is nice to have a callsign! I can dream about DX now!"

"I'll be watching the DX cluster for you!"

"CATuner - solution for high SWR"

"Tuning antennas with manual tuner is exhausting and I have the perfect spot for nap"

Friday, August 22, 2008

LP-100A Integration

Since I started using the LP-100 watt meter some time ago, I have not touched my old Bird 43. The LP-100A is one of the best on the market and it has some very unique features not seen in other meters!
The firmware is user-upgradeable and I am proud to be the originator of a few ideas about the ergonomics and the "SWR Alarm snooze" feature which Larry implemented in the firmware.
There is a great Yahoo Group for technical support and discussions!

Both of my units - LP-100 and LP-100A integrated in my shack. LP-100 (with the green PLED display) is showing the transceiver output (input to the linear amplifier). LP-100A (blue VFD, I actually used gel filter to get the nice blue color out the display) is showing the output of the amplifier.

Looks like the amplifier does a pretty good job. The T-mode is very helpful during tuning!
In vector mode, the meter displays a lot of very useful information about the antenna!

Monday, August 18, 2008

LP100A Vector RF Watt Meter

I finished building my second LP-100 wattmeter - this time it is the LP-100A. LP-100A is the newer version, equipped with nice graphic VFD and it is ready to accept the "Dual channel" option (not released yet). Larry N8LP is doing great job with this watt meter and I cant wait to add the second channel coupler! Hopefully it will be out soon - the enclosure also has extra holes on the back for the BNC connectors of the second channel. Another small change is the addition of a front panel power button. On LP-100 there was none and I had to add it as modification. The PCB is also re-designed. Second processor takes care of the graphic display, extra connector is provided for the dual-channel option, some components values are changed a little bit. LP-100A is most certainly an improvement over LP-100. I like a lot the high contrast and the nice green color of the PLED in LP-100, but the graphic display in LP-100A is also great and provides higher resolution. Luckily I have one of each now! The firmware is also a bit different for each version but the differences are minor and they have more to do with the menus and the calibration.

This is the content of the box. Everything is well packed. All high-quality components and powder-coated aluminum enclosure! Very good kit indeed!

The PCB comes with all of the SMD components factory preinstalled and tested and they are not that many. Here is a picture during the building process with all of the IC sockets installed. I actually replaced the supplied sockets with machined socket type as they are more reliable and provide better contact. The values of all of the discreet components were double-checked!

Picture of the attenuator board located in the coupler! These SMD resistors are pretty big in size and very easy to install! Larry provides some spares should something goes bad during soldering!

One of the unique features of LP-100 is that the power detection is not done in the coupler (as is the case in all other digital wattmeters). Instead, the coupler samples the voltage and the current and the main unit detects the power, which allows for more complex calculations and more data like Z, phase angle, etc. This is a picture of the voltage (left) and the current (right) sample transformers. The transformers are wound in a very specific manner (they are mirror image on each other) on large ferrite toroids. Winding those transformers is probably the most difficult part and requires great precision to achieve for highest possible accuracy! The little piece of silver-teflon coax is the primary winding of the current transformer. Larry provides in the manual exact measurements for cutting and stripping the coaxial and detailed description of how to wind the transformers. Pieces of special self-adhesive tape on the nylon bushings are helping to keep the windings in place and to have proper coverage of the ferrite cores. The windings need to be evenly spread.

The aluminum enclosure of the coupler with connectors and attenuator already installed. The coupler must be build with precision for good accuracy! The instruction in the manual are pretty good and easy to follow. Optional N connectors are sold by TelePost but any standard chassis N connector will work should such connectors are desired.

Picture of the coupler with both transformers in place! The wiring inside the enclosure can be a little tricky. One should not rush thru the building process - this is lab equipment and accuracy of the measurements is essential.

The RF coupler is ready. It has very professional construction and look! Before soldering the primary of the current transformer, the walls of the enclosure have to be pre-tensioned to a specific size, so when the cover is screwed on there is no stress on the connectors and coax.

This is the finished unit. I added another small heat sink (nested inside the main heat sink) to the voltage regulator (on the right). The original heat sink is small and the regulator runs hot. Second heat sink improved the cooling a bit! There is a jumper inside to disable the buzzer of the SWR alarm, leaving the relay fully functional.

Sunday, August 10, 2008

N8LP SteppIR Tuning Relay

I wanted to protect my SteppIR BigIR antenna from accidental Tx while the antenna is tuning. SteppIR antennas can be damaged by high-power TX (>100W) while the antenna element is moving - arcing between the moving antenna tape and the static brush will cause damage to both. The 80m coil for the BigIR Vertical (which I have) is even more vulnerable to damage from high power Tx during tuning. The coil taps are switched by a special Roto-Switch, utilizing copper PCB pads as contact points for the switch(see my BigIR article at http://www.kotarak.net/). Arcing during high-power transmit can damage the copper foil of these contact points! The easiest way to protect the antenna is to inhibit the Tx Key signal going from the transceiver to the amplifier, while the antenna is tuning. It can be done simply by interrupting the Key line signal with a simple switch. Larry, N8LP is selling kit which does exactly that, but it is automatic. It is a very simple device actually, using an Op Amp as basic comparator. The comparator measures the voltage across a shunt resistor (so it measures the current draw by the antenna motor) and compares it to a pre-set value (adjustable via potentiometer). The Antenna controller is powered through the shunt resistor. Normally the stepper motors are always powered with the so called "holding" (idle) voltage, intended to prevent the antenna element from unintentional movement. When the antenna element is tuned by the controller, the current drawn by the stepper motors increases . SteppIR Tuning Relay detects the difference (increase) in the current draw and triggers relay which on the other hand interrupts the KEY signal to the amp. Very simple and easy to do project. The box is just connected in-line with the antenna's power supply and it doesn't need a separate power source.

This is the kit version. It took me about one hour to assemble, test and install it. This project can be done on a universal PCB as well and parts can be substituted. Lately, I just don't have the time to order and collect components and play with universal boards and wires so I went with the kit.

This is the completed SteppIR Tuning Relay. The manual (including schematics) is available at - http://www.telepostinc.com/.
On the front panel there are two LEDs - green, indicating Power to the Tuning Relay (and antenna controller) and red LED indicating that the antenna element is moving. It is a much more visible indication than the blinking asterisk on controller's LCD screen. The blue potentiometer is used to set Sensitivity or in other words the current draw threshold. On the back panel there are two RCA jacks for the PTT line. The pigtail with the power connector goes to the antenna controller's power jack and the power supply for the antenna controller is plugged straight in the Tuning Relay box. The integration in the shack was very quick and easy process and the Tuning Relay works perfectly! Another level of protection (again with the Key signal but this time for the amplifier) is provided by "High-SWR Alarm relay" in LP-100A Vector wattmeter.

Monday, August 4, 2008

Finally - 240V line in the shack

In general, HF power amplifiers (especially those in the kilowatt range) have very high current demand when supplied with 120V AC. They work much better and are more efficient when powered with 220-240V. An added benefit is that the AC current draw drops in half giving less chance for the standard 15A household breaker to trip.
Finally, I found some time to install a 240V line in my shack. It was a bit challenging because I had no available breaker positions in my electrical panel (load center). The electrical panel was really crowded, all breakers were in use and and even separate circuits were sharing common breakers. There was no way that I can free 2 breaker positions for the 240V line so I decided to install a sub-panel. It was time to put on the electrician's hat ;-)

My existing electrical panel - power is supplied to the house by 2 hot wires (single phase) and a neutral wire (which is also grounded in the panel as per NEC) . These are the 3 black heavy wires in the middle of the picture. They are connected straight to the outside service (the electric pole transformer on the street). There are 120V between each hot wire and the neutral (common) wire and 240V across both hot wires. These lines are actually connected to the center-tapped 240V secondary winding of the power transformer outside. Each end of the winding is a "hot" wire and the center-tap is the common.

To install a sub-panel I needed first to install a double-pole breaker in the main panel to serve as a feeder (main) breaker for the sub-panel and bring this way the outside service to the sub-panel thru the double-pole breaker in the main panel.

Piece of plywood was installed next to the existing panel. I used Tapcon screws to attach it to the concrete wall. BTW I did not install the main panel - judging by the angle, whoever did - was obviously drinking at the time :-)

Here is the new sub-panel, attached to the plywood. I installed 8 (16) position 125 Amps sub-panel. This should cover all my future needs. The double-pole 100 Amp breaker is installed at top-right in the main panel. Three AWG #4 stranded copper wires serve as feeder for the sub-panel. Wire size #4 should be able to handle up to 125 Amps (something very unlikely to occur). The green wire (AWG #6) is used to connect sub-panel's Ground to the main panel.

This picture shows the finished sub-panel. I moved some circuits from the main panel including those which I had to disconnect to make room for the sub-panel feeder breaker. I installed also a 20A utility receptacle under the sub-panel. The yellow wire (3- AWG#12) is the 240V line. It is connected to a double-pole 20A breaker at top-left. Safety reasons require the use of a double-pole instead of two single-pole breakers. When using a double-pole breakers, both hot wires will be disconnected even only one is overloaded. (Same reason to use double-pole breakers at the sub-panel feeder line)

This is the 30A in-line RFI filter - Corcom 30VB6. This AC filter is rated at 25A/240V or 30A/120V and provides pretty good attenuation throughout the HF range. The insertion loss is over 50db at 30 MHz. I have similar filters on the line powering the rest of the shack and on the line powering all of my computers. This means that the insertion loss is over 100 db between devices from each group.

To accommodate the filter I used electrical box from a "pull-to-disconnect" device sold for Air Conditioners. It accommodates perfectly the EMI filter and provides the necessary high-voltage safety.

My new 240V/20A AC line is finally operational! As it turns out - I can use it as AC voltage reference :-))

Monday, July 28, 2008

LCD Meters for Elecraft KPA100/KAT100 in EC2

This is an old modifications I did a few years ago. I moved the KPA100 amp of my Elecraft K2 together with the KAT100 antenna tuner into an EC2 enclosure. The front panel of the combo is normally occupied only by the LED indicators and SWR meter of KAT100 and it looks somewhat empty. I decided to install a digital voltmeter showing the voltage of the power supply and a digital thermometer indicating the temperature of the KPA100's heatsink. Both values are important for the proper operation of the amplifier.
K2 has a built-in voltmeter but it shows lower-than-actual value because of the voltage drop across the reverse-polarity protection diode. An accurate voltage is also needed for proper charging of the internal SLA battery. The temperature sensor of KPA100 "knows" only when to turn the fan on, but doesn't display the actual temperature of the finals, which is critical, especially during lengthy CW or digital modes sessions!
I got two LCD meters from Martel Electronics - http://www.marteltesttools.com/products.php?cat=113&action=detail&id=69 - QM-100V (voltmeter 4 - 25V) and QM-110T (thermometer with internal and external sensors, Fahrenheit or Celsius).

Installation is very simple! Each meter requires a single 5.5 mm (7/32") hole in the front panel. I left space in the middle, should I need to install other things on the front panel - switches, LEDs, meters, etc.

I made a custom wiring harness with shielded cable, which powers both meters. Ferrite toroids are installed to suppress any RF noise in the power. Small 3 pin jack is used toconnect the front panel meters to the KPA100 module ( ground, power and external temperature probe). This allows for an easy disconnect and removal of KPA100.
Bypass capacitors are installed on the female jack (KPA100 side)

This is the configuration jumper of the digital thermometer. The meter has two control inputs - when grounded, one is used to switch the display between Celsius and Fahrenheit and the other is used to specify which sensor is in use - internal or external. The meter has an internal sensor but for accurate measurements an external one should be installed. The external sensor is simply a 10 kOhm NTC precision thermistor, attached to the heatsink of the amplifier (near the speaker). I made a small bracket out of thick copper foil to attach the thermistor probe. I applied some thermal compound between the thermistor and the bracket and between the bracket and the heatsink. Small diameter shielded cable (RG-174) connects the thermistor to the female jack. I used thermistor from Mouser - Part# 594-2322-640-63103 (now obsolete part but there are other replacements).

This the final look of the front panel! Now I have an accurate voltmeter displaying the voltage of my bench power supply and thermometer for the finals of the amplifier.

Both meters are splash-proof (there is a thin rubber gasket between the meter and the front panel). They stick out just a little bit (5 mm) from the front face of the panel. On the back of each meter there is a small adjustment screw for calibration. I calibrated the voltmeter using my NIST traceable calibrated Fluke and it is "dead on" accurate now. The thermometer was calibrated using an accurate industrial thermometer. The external temperature sensor must be calibrated for the specific thermistor used to compensate for the manufacturing tolerance! The internal sensor is located in the meter housing and it is factory calibrated (there is calibration adjustment for it as well) - it can be used to show the temperature in the shack (if the radio is powered but not used for Tx). If used as a shack thermometer, there might be a small measurement error if the finals are hot due to proximity of the sensor. Small front panel switch can flip between shack/finals temperature. I don't need a shack thermometer since I already have one in my WavPro Luminator so I didn't install such switch.
I've been using this mod for about 3 years now with no problems!

Shack picture

Finally I am done with the reorganization of my shack. Late last year, I re-did all of the cables, reorganized them and made easier to navigate through the wires on the back. I have connected the Heathkit SB-200 in-line with my dipole antenna and I am almost done! The ACOM 1000 is connected to the vertical. The only things left to install are another LP-100A for more accurate measuring of the output power and an external antenna tuner (most probably Palstar) for my dipole antenna.
Now that I am almost done with the shack, I can focus on my other hobby - flying on Flight Simulator. So far I have 3 Dual-Xeon Pentium 4 machines to serve as render-engines. My plans are for 4 machines and total of 5 or 6 monitors - so much work needs to be done!

This shack perfectly fits my needs for now! It is a result of a couple of years in research for the best equipment/configuration and collecting it. I am really happy with the way it came out. The layout was changed a few times over the years until I got to this final version. This is an old picture of the shack - i'll try to post an updated one soon.

Sunday, July 20, 2008

Mission: Organization

Late last year I went through a complete re-organization of my station. Over the years I was trying to keep it neat and organized but constant modifications, new equipment installations and what not created a big mess behind the operating desk. This is what it looked when I pulled the desk away from the wall:

As one can see it was almost impossible to find or trace cables, especially since there is not much room to work with.

Yet another view of the "wire salad"!

After I disconnected every single cable and made a few custom ones, it took me about a day to create the current, more ergonomic layout of the equipment and reconnect everything.

Now everything is way more organized and accessible. I used huge amount (literally - pounds) of ferrite toroids and split-core ferrite beads to form common-mode current chokes on almost every cable. This resulted in a electrical noise-free environment. Most of the chokes are installed on cables connected to the PC. Right in the middle of the image is visible the copper ground bar. I used wide straps made of copper foil to ground each piece of equipment to the ground bar.

Wednesday, July 16, 2008

Station layout and equipment

Here is a list of some of the equipment I am using. I am really happy with my current configuration and I am not planing any major changes in the near future.
Icom IC-R75 - AM synch detector mod (Rado 2.1), AGC mod, FL-103 (2.8 kHz/9Mhz 2nd IF) and FL-257 (3.3 kHz / 455 kHz 3rd IF) SSB filters, UT-102 voice module. This is my main SWL receiver and station Tx monitor.
Yaesu FT-1000MP Mark V Field - 70 MHz IF amp InRad mod, CW clicks mod, 2nd IF (Yaesu YF-114SN 2kHz / 8.2 MHz) and 3rd IF (InRad #702 -C 2.1 kHz / 455kHz) Narrow SSB filters, 2nd IF (InRad #708 250Hz / 8.2 Mhz) and 3rd IF (InRad #704 250Hz / 455kHz) Narrow CW filters, FH-1 remote keypad. My primary HF SSB transceiver.
Elecraft K2 with KPA100/KAT100 in EC2 enclosure. K2 has all of the options installed - KSB2, K160RX, K60XV, KNB2, KDSP2, KAT2, KIO2, KBT2. The radio is updated will all factory updates and mods. KPA100/KAT100 combo has some extra front panel meters installed (voltage and temperature). This is my primary HF CW radio (also portable/QRP when needed)
Yaesu FT-920 -FM-1 unit, TCXO-7, YF-116A 6kHz AM filter, YF-116C 500Hz CW filter. FT-920 is my secondary/backup HF radio, digital modes and 6 meters tranceiver.
Yaesu FT-100D - cooling fan mods, chasiss ground mod. XF-117A 6kHz AM filter. My VHF/UHF radio and backup portable/mobile radio.
Yaesu FC-20 - external antenna tuner for FT-100D
Palstar AT2K - high power external manual tuner for matching the G5RV
Alinco DM-340MV main power supply (linear) - powers FT-1000MP, K2, KPA100/KAT100 and Yaesu FT-100D.
Alinco DM-330MV secondary power supply (switching) - powers FT-920
Radio Shack 3A linear power supply - powers Icom IC-R75, LED desktop lights and both LP-100 wattmeters.
Telepost LP-100 vector wattmeter - used to monitor amplifier's input RF power.
Telepost LP-100A vector wattmeter - used to monitor amplifier's output RF power.
Bird 43 wattmeter - used to monitor the RF output.
ACOM 1000 - Primary HF+6m linear amplifier
Heathkit SB-200 backup linear amplifier with Palstar DL1500 dummy load.
Tigertronics Signal Link SL-1+ connected to FT-920 for digital modes work.
SteppIR BigIR Mark III /w 80 meter coil vertical antenna and G5RV dipole.
SteppIR antenna controller connected to one of the computer's serial ports.
N8LP SteppIR Tuning Relay - Tx protection for the SteppIR antenna.
2x Diamond CX-210 2-position antenna switches and custom patch pannel for RF signal routing.
4 position RCA audio/video switch for audio routing, 2x 2-position RS232 switches
4x RCA 40-5000 die-cast speakers, Motorola comm speaker and pair of powered Acoustic Designs speakers.
Yaesu MD-100A8X microphone, second homebrewed desktop mic, Sony MDR-2506 headphones.
Begali Signature Edition morse paddle and Bulgarian Military "Voroshilov" straight key.
Griffin PowerMate knob controller.
WavPro Luminator station's master clock.
Pentium 4 / 1.7 GHz computer with nVidia Quadro graphics card anddual monitors, Sound Blaster Audigy 2 audio card and 4 x RS-232 serial ports for tranceiver control . Windows XP Pro.

Tuesday, March 18, 2008

Sad day!

Today one of my favourite science-fiction authors - Sir Arthur C. Clarke passed away. He was 90 years old. Most people know him as the author of 2001: Space Odyssey. My first encounter with Science-Fiction was his 1961 book "A Fall of Moondust". It was given to me by my father when I was at a very young age. After reading the book and especially after reading Clarke's "Rendezvous with Rama", I fell in love with the science-fiction genre and this love never ended. In 1945 Arthur Clarke invented the concept of the communication satellite and in his honour the geostationary orbit is called "Clarke Orbit". He will be dearly missed!!!

Saturday, March 15, 2008

Clipperton Is. DXepedition - disappointment!

TX5C went QRT. This DXepedition was a total disappointment IMHO. No need to say that I didn't have the chance to work it. I cant see what I was doing wrong. My antennas are in top shape - I was able to work meanwhile many and more distant DX contacts. Finally I have the amplifier online - almost 900W out, etc. Due to my schedule I was only able to try to contact TX5C very late in the evening when only the lower bands were open. I blame the failure on the mixture of a bad luck, poor operation from TX5C and the many LIDs (especially on 80 meters), sabotaging the DX. Can't be done much about the luck - it is what it is! On other hand the operation of TX5C was very poor - I just can't list all of the things that were wrong with TX5C! Compared to the 3B7C DXepedition, TX5C left much to be desired!
Some of the french operators were among the worst - they were very slow, running the pileups, they were not announcing their listening frequency for hours, causing many operators to try them on simplex, activating the "frequency police". Sometimes after just a few minutes working NA, they will switch to EU and with almost no stations calling from EU, they will keep asking "Any EU stations?" for good 10-15 minutes, while hundreds in NA wait their turn, and then they'll go QRT with no announcement, leaving people hoping for their return . Sometimes they were spreading the receiving range over 20 kHz and were working only at the very edges of this range, causing everybody to pileup there. At one occasion the LIDs on 80 meters were QRM-ing the DX and instead of ignoring them or changing the frequency, the DX decided to argue with those guys, making the matter only worst and then went QRT for awhile. It goes on and on... Just didn't seem they were capable of controlling the pileup ...Oh well... Next time maybe the sponsors will try to ensure that their money are not wasted like this.
I've been trying to contact them for over a week, 2 hours every evening on 40 and 80 meters with no results. With such a poor operation there, the only thing I had to rely upon was the luck and this time I didn't have it. Maybe this rant is not fair - after all I didn't contribute to the DXepedition - at least I am glad I didn't.

Tuesday, March 11, 2008

New Tubes

I have installed a "Matched Pair" of RF Parts Inc. Taylor 572B tubes in my Heathkit SB-200. As it turned out, one of the original Centron tubes was not performing well - it also had somewhat lower idle current. Those new tubes are probably made in China and just branded under the "Taylor" brand. After installing the new tubes, I left the amp turned ON with no drive for about 4 and a half hours. This serves to condition the tubes and to minimize the chance for flash-over and in general it is a good practice with new tubes and tubes with unknown shelf life. The heat from the filament activates the "getter" which is deposited on the plate. The "getter" is a chemical composition which reacts with any free (gas, metal) molecules in the tube and improves the vacuum.
The tubes are working fine and I am getting over 850W on 80 meters when tuning with pulser. On 40,20 and 15 meters the output is a bit lower - 750+ Watts which is still pretty good for this amp! When I heated the plates with continuous drive, I noticed that one of tubes got a little bit hotter than the other (judging by the plate color). I am planing to buy another pair for spare and will try to re-match them. It is also a good practice to "rotate" the tubes in the amp with the spare ones every year or so and not allow any of the tubes to spend too much time on the shelf. Vacuum tubes don't age well when they are not in use.

The new RF Parts Inc. "Taylor" tubes to replace old Centron tubes. The tubes are from the same factory batch and have writings on the glass envelope with the test results from the "matching" procedure. I cleaned them with alcohol to prevent "hot spots" from forming due to fingerprints. As a side effect the alcohol wiped clean all of the markings along with the red Taylor logo.

Wednesday, March 5, 2008

Heathkit SB-200 Conclusion

The amplifier is finally done! It took me over a month, working a few hours on the weekends. The rebuild is dedicated to my patient and understanding wife (I wouldn't say "supportive" :-) as she wasn't trilled by my activities). I have a lot of spare parts now to address future needs - almost enough actually to rebuild a second one. The only thing left to do is to align the input networks for minimum SWR and to stretch a little bit the coils of the parasitic suppressors. It turned out that the suppressors were heating up at around 28.3 MHz which is somewhat low! By spreading the turns I'll lower the inductance in hope to raise the cut-off frequency towards the upper side of the 10 meter band. Lower power output is expected on 10m but this is normal! On 10m if the band is open you don't need a lot of power anyway - when it is closed, 50-100W more is unlikely to help a lot.

I never cared for the "Heathkit Green" paint. It looks very dated to me. I went for a more sophisticated look for the front panel - I think it came out really sharp. I was going to paint the panel in light grey with black lettering (like the QRO Tech. amps - similar to the "Lab grade equipment" look) but at the end black & white looked pretty good too! The other front panel modifications are the two status LEDs and the "Stand-by/Operate" switch. The left LED is a Bi-color LED displaying the status of the switch - Green for "Stand-By" mode and Red for "Operate" mode. The right LED is a blue color one and indicates the KEY down signal - it goes "on" when the amp is keyed by the exciter (Tx).

The meter is showing the Anode (B+) voltage in HV position of the meter switch. 2400V is "right on the money!" with 110V AC supply. I am planing to build a x100 HV probe for my multimeter. This way I'll be able to calibrate the meter more precisely. The voltage drops to about 1900V when the amp is fully loaded. The plate idle current is 90 mA - exactly where it should be! (with the new tubes)

The amplifier is ready for integration in my shack. I made all of the high-power coaxial jumper cables using RG-393 MIL-spec silver/teflon cable. Diamond 2-position RF Switch will switch the output between the antenna and the dummy load. Bird 43 meter /w 1000H slug will show the amp's output power for now. Later on I am planing to replace it with a Telepost LP-100A vector watt meter. I am already using one (LP-100) to monitor the input RF power. The amplifier will run on 110V until I find time to install the 220V line - most probably in a couple of months.

Tuesday, March 4, 2008

Heathkit SB-200 (Part 2)

As I mentioned before, all of the wiring and most of the components of the amplifier were replaced. These old amps are using carbon-composition resistors. Such resistors change their value from stress and aging. I found that some of the resistors were off by more than 20%. I used precision flame-proof metal-film resistors and ceramic-composite resistors where low inductance is required (grid bias).

This picture shows Wafer C of the band-switch along with the Pi and L input networks, the large filament choke, ALC circuit components and the two valve sockets. The two grid bias resistors are of ceramic-composite type. I also installed bigger (both capacity and max voltage) silver-mica caps in the grid grounding circuit. This will lower the impedance to ground on the lower bands and should result in more output. The original caps can't handle a lot of current and often fail. The length of the leads must be kept to the minimum to avoid extra inductance. A metal-film low-inductance power resistor between the input circuit's rotary switch and the tube's cathode circuit is installed to limit the possibility for over-driving the amp. Before installing the input circuits, I made sure that all of the ferrite cores in the inductors are moving so I can align them later. Extra caution is needed since these cores sometimes get stuck or are glued inside the coils with wax and it is very easy to break the ferrite core when rotated.

Top view of the amp with the RF deck on the right and the HV power supply and power transformer on the left. Both variable capacitors were inspected for signs of arcing, cleaned and lubed. Any signs of arcing and sharp points on the blades must be smoothed with very fine sand paper and cleaned well from the dust afterwards.

Picture of the RF deck. The two original Centron 572B valves seen in the picture were replaced by a matched pair of RF Parts, Inc. 572B Taylor valves. The 10m/15m silver plated tank coil was cleaned with Deoxit D5 solution. Wafers A , B and C of the band-switch were inspected and carefully cleaned with extremely fine (0000 size) steel wool and Deoxit D5 and then treated with Deoxit ProGold. Using steel wool to clean an RF switch requires *very good* washing with alcohol afterwards, as well as using strong magnet and compressed air to get rid of ALL metal particles. The switch should absolutely clean from metal particles and contaminants before installation. After the cleaning, the switch looked almost as new. The output multi-band tank coil was encased in Kapton foil and all leads were inserted in teflon tubing.

The new Low-Q parasitic suppressors designed by Rick Measures, AG6K. The new design includes two sets of suppressors in series (per valve) for an improved performance and amp stability. Resistive Nichrom wire is used to make the inductors - the kit includes silver solder and special (very corrosive!!!) flux for soldering Nichrom. Metal-film resistors used in the suppressor can handle power dissipation in the excess of the rated 3W. An extra 1 Ohm resistor in the anode circuit of each valve serves as fuse in case of a catastrophic valve failure. 572B is a relatively unstable tube when it comes to parasitic VHF oscillations so these suppressors should help a lot.

Another view of the RF deck. I had to repair the plate choke with a new winding. The old one had badly burned wire enamel. The new choke is covered with kapton/silicone adhesive tape. It is barely visible in the top-center of the image. Right next to it is the new blue high-voltage plate filtering capacitor. The door-knob capacitors in the output circuit were inspected and one of them had to be replaced (it was showing signs of arcing). I used a layer of Kapton tape around this capacitor (the red one in the middle of the two variable capacitors) as extra precaution.

Update: I did also some work on correcting the filament voltage. It is posted here.