vrijdag 25 november 2016

Cylinder dipole in CQ magazine

Cylinder dipole in
CQ Magazine
In the CQ WW WPX CW contest 2016 I used two indoor cylinder dipoles. After I sent in my log for the CQ WPX, Terry N4TZ noticed my soapbox. Terry asked my to send in a picture of my cylinder dipole to include in the write up of CQ Magazine. I thank Terry for the nice and beautiful write up.

Click to read

The CQ WW contests generate a lot of activity.
I use contests to make QSO's with very low power.
And. . it is good opportunity to test your antennas.

Soapbox PA1B in CQ WW WPX CW 2016
X-RADIOS:           FT-817
X-ANTENNAS:    Cylinder dipole
SOAPBOX:            I had great fun with QRP and two cylinder dipoles
SOAPBOX:           On 20m I made 3 QSO's and on 15m 4 QSO's with a 15" cylinder dipole 
SOAPBOX:           On 40m I made 3 QSO's with a 22" cylinder dipole 
SOAPBOX:           The PA1B cylinder dipole consists of two cylinders and a coil
SOAPBOX:           The coil acts as a impedance transformer
SOAPBOX:           The QSB and the good activity, did not make it easy to answer CQ's - hi
SOAPBOX:           Thanks for the activity in the contest

PA1B with cylinder dipole in CQ Magazine
The cylinder dipole shows a large capacity between the cylinders.
Although the coil and the capacity  are tuned to the band of interest, the cylinder dipole can be used as a multi-band antenna. Two taps at the center of the coil provide a low impedance feeding point to connect the twin lead.  Match for a SWR of 1:1 with your symmetrical tuner.

  Energy  Booster  cans or not, a cylinder dipole will radiate better than a wire dipole of the same length.

Thank you, Terry for the very nice write up. 

vrijdag 18 november 2016

36dB Attenuator for 20 W by PH2LB

This beautiful attenuator is designed and built by Lex PH2LB.
0...36 dB attenuator built by PH2LB  -  Click to enlarge the pictures
The attenuator can handle a maximum power of 20 watt and is used to reduce the power of a 5 watt transceiver.
At first I did not realized why Lex designed the attenuator for 20 W. Like many HAMs I thought, that 20 W is QRO. But please notice that 20 W is the Maximum power.  The chosen maximum power of 20 watts for the attenuator is an excellent choice. The attenuator can easily handle a power of 5 watts, without getting hot.

This was an eye-opener for me. hi.
0...36 dB attenuator by PH2LB
with 2 W resistors 
A resistor that  dissipates its maximum power will get very hot.
So it is good practice to choose the maximum power 4 times higher then the continuous power.
Lex choose for  a maximum power of 20 watts, to reduce a power of 5 watts.
The resistors have a maximum power of 2 watts. With a power of 1/4 of the maximum power, the resistors will dissipate about 500 mW each and they will not get hot.

The 20 dB section
Visit the article on the 36 dB attenuator on the web site of Lex PH2LB.

PA1B Power Attenuator Calculator
Lex used the PA1B Power Attenuator Calculator to design his 36 dB attenuator for 20 watts.
This unique spreadsheet in Excel calculates the number of resistors and the values of the resistors from the E12-series for an attenuator section.

In the picture below I show the input values for the section of 20 dB, for a maximum power of 20 watts, that is built with resistors of 2 watts.
PA1B Power Attenuator Calculator - Input values for the 20 dB section
Just download the PA1B Power Attenuator Calculator and play with the values. The calculator has no restriction on the power.

zondag 13 november 2016

Meeting Lex PH2LB

Lex - PH2LB
Last week I visited the HAM convention 2016 - Dag voor de Radioamateur 2016 in Apeldoorn.
I was very pleased to meet Lex PH2LH.
Lex has designed a 0 - 36 dB attenuator for 20 watts, using the
PA1B Power attenuator calculator.

When I approached the stall of Lex, I immediately recognized the 0 - 36 dB Attenuator that Lex has designed and build. Further Lex showed the beautiful build OZ2CPU digital RF mW / dBm / mV meter.
OZ2CPU digital RF mW / dBm / mV meter
   and the  0 - 36 dB attenuator