SSPA for 2 meters - Watercooling

The primary advantage of watercooling is its ability to transport heat away from the source (a transistor) to a secondary cooling surface (a radiator). This allows for large, more optimally designed radiators rather than small fins mounted directly on the heat source.

The disadvantage of watercooling is higher cost and complexity when compared to air cooling.

The picture below shows the components in a watercooled system. In my project, the PA transistor is soldered directly to the copper water block. The radiator is mounted on top of the cabinet and cooled by two large 140 mm fans. The pump and the reservoir is one single unit making the system more compact.

The watercooling system for my SSPA project is about twice as expensive as conventional air cooling. In return, I expect a quiet system which allows high-power transmission and human conversation in the schack at the same time!

OZ1BXM Lars Petersen

Homepage: http://oz1bxm.dk/

SSPA for 2 meters - Cabinet

Building a Solid State Power Amplifier (SSPA) is my project this winter. I have chosen the 1 kW SSPA for 144 MHz as described by F1JRD in DUBUS 4/2010. I'll attempt 2 meter EME later this year, and a powerfull SSPA will become a key component in the set-up.

I have decided to build the cabinet first. I have found DIY alu-frames that can be taylored to many sizes. The cabinet's alu-framework is 30 cm wide, 15 cm high, and 15 cm deep. Furthermore, 2 mm alu-sheets are available from another source, and these sheets fit exactly into the alu-framework. This means no cumbersome cutting and bending of cabinet parts!

The SSPA cabinet.



Another feature of my new SSPA is watercooling. This cooling method is known and used among PC freaks. But as far as I know, only few radio amateurs use that technique. More on watercooling next month.

OZ1BXM Lars Petersen

My homepage: oz1bxm.dk

My latest 10 QSO

Merry Christmas - Happy New Year

It is Winter in Denmark right now. We had a lot of snow this December. As you can see in the picture below, our small garden is totally white!

Outdoor work is not longer possible. It is hazardous to climb a ladder or walk on a roof. So antenna work has to wait for higher temperatures. Indoor activities are at premium. I am waiting for some electronic kits to arrive from USA. I hope they will come before Christmas.

I am taking a 6 month leave from my job. The beginning of 2013 will (hopefully) be relaxing, and some travelling has already been planned. My wife and I would like to visit distant places.

Our garden viewed from the kitchen.

Dear reader. I wish you a Merry Christmas and a Happy new Year 2013! 

OZ1BXM Lars Petersen

My homepage: http://oz1bxm.dk

Homemade 1:2 balun

I need an 1:2 balun
My 20m loop antenna has about 100 ohm impedance at the 14 MHz resonance frequency. My coax-cable is a 50 ohm type. Transforming 100 ohms to 50 ohms can be accomplished by an antenna tuner, or by an HF balun. The inexpensive approach is using a balun.

Figure 1. Balun 1:2. Picture credit: OE7OPJ.

Winding the toroid
Please refer to the drawing by OE7OPJ in figure 1. The red wire begins at the UHF-connector's center pin. The black wire begins at the UHF-connector's ground pin. The two  wires "follow each other" for 6 windings, and then the black wire is connected to one of the output terminals. The red wire continues with 6 more windings and then connected to the UHF-connector's ground pin. Finally, a short wire connects the UHF-connector's center pin to the other output terminal.

Figur 2. The finished 1:2 balun.

My homemade balun can be seen in figure 2. The toroid core is TX36/23/15-4C65 from Ferroxcube. An alternative toroid can be Amidon FT-140-43. The core's outer diameter is 34 mm and the inner diameter is 22 mm (not critical). The teflon wire (AWG18) was purchased from dx-wire.de. The sealed ABS box (item G302) is from Velleman.

Figure 3. The balun is housed inside an ABS box.

Testing the balun
Testing an 1:2 balun is easy. You connect a resistor at the balanced terminals. Then you measure the impedance at the unbalanced port. This impedance should be ½ the resistance at the balanced terminals due to impedance ratio 2:1.

I connected a 50 ohm resistor at the balanced terminals. Then I measured 25 ohms at 14 MHz at the unbalanced end. Conclusion: The balun's impedance transformation is just right!

73 from OZ1BXM Lars Petersen

Visit my homepage: http://oz1bxm.dk

Kenwood TS-850 ALC problem - again

Ten months ago, I fixed the well-known Kenwood TS-850 ALC problem by lowering the resistor values on the DC-DC daughterboard (X59-1100-00) from 22 kohm to 18 kohm. The old horse ran again, and I was happy.

Now exactly the same problem has returned! By visiting Yamada Radio Clinic's archive and reading his article ALC Problem with TS-850 => DC-DC mod I learned that the transistors in the oscillator can degrade over time due to overload. This is probably what happened to my old TS-850 transceiver, which was produced circa 1990.

The new DC-DC board for Kenwood TS-850.



I decided to replace the old oscillator board with a new board using modern components. I followed the idea from Yamada Radio Clinic and made a replacement PCB containing the voltage converter ICL7660 and three more components. The result was satisfying and my Kenwood TS-850 now runs "just like new"!

If you want all details, you can visit my homepage where I've described the task and added more photos and a circuit diagram.

Lars Petersen 

Quad loop antenna

Last month, I told you about my plans for a 20m delta loop antenna. But my plans have changed. The delta loop idea has been discarded, mainly due to the need of a high supporting pole. I prefer two short poles and a square loop.

 The 20m quad loop is supported by 2 poles.

 

All materials for the antenna were purchased in Germany, where Dx-Wire by Peter, DK1RP runs a nice web-shop. The antenna wire is "Dx-Wire UL" (Ultralight). The core consists of 6 thin copper wires and Kevlar reinforcement. The outer jacket is black PE. This wire is only 1.5 mm thick, it is ultra light (4 grams/meter), and the breaking load is 60 kg. 

 

The support lines are Dynema wire made of polyethylene fibre. Dynema lines will stretch only 1.5-3% under tension. The sheath is black 16-stranded polyester. Breaking load is 120 kg.

 

The month of October is dedicated antenna construction. I'll show some antenna photos next month.

 

OZ1BXM Lars Petersen



Vertical delta-loop antenna

This month I would like to share an idea from my sketchpad with you. I am planning to build a vertical delta-loop antenna for 20 meters. The reasons for choosing this design:

• My favourite HF band is 20m
• Delta-loops for 20m are manageable in size
• Loops are quiet on receive
• Vertically polarized loops are well suited for DX

I found the delta-loop overview below at the website of W5SDC:

Delta-loop overview.



My choise of shape will be version D because if offers a low radiation angle, which is necessary for DX. The sketch below shows how I plan to build the antenna:

Delta-loop antenna for 20m.



A delta-loop antenna with ATU was described by WB8IMY and published in QST May 2002: One Stealthy Delta. This article is worth studying if you consider constructing a loop antenna.

OZ1BXM Lars Petersen