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

New blog platform

I have moved to a new blogging platform. The old one was based on text only, and did not provide feeds or a reply function.

This blog will still be updated every month, all year round.

I hope that we can communicate via the reply fields. You are most welcome to leave a reply! You may also consider a subscription to this blog.

The old blog is still available here: Ham radio blog by OZ1BXM (opens in a new window), and my homepage still lives here: A Tiny QRP Page by OZ1BXM

Welcome to my new platform!

OZ1BXM Lars Petersen