mandag den 17. december 2012

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

fredag den 30. november 2012

Homemade 1:2 balun

My loop antenna will show about 100 ohms impedance at the 14 MHz resonance frequency. My coax-cable is a 50 ohm type. Transforming 100 ohms to 50 ohms (and vice versa) can be accomplished by an antenna tuner, or by a HF balun. The inexpensive approach is a balun.

Having searched the Internet for 1:2 baluns, I found two sites describing materials and construction. One is by DH1PLY and the other one is by OE7OPJ. The inner parts of my homemade balun can be seen in this picture. The toroid core (TX36/23/15-4C65 from Ferroxcube) and the teflon wire (AWG18) were purchased from dx-wire.de. The sealed ABS box (G302) is from Velleman.

Homemade 1:2 balun.

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

I connected a 50 ohms 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

mandag den 29. oktober 2012

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 

fredag den 28. september 2012

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


fredag den 31. august 2012

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

onsdag den 15. august 2012

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