Simple Morse beacon keyer updated 2014/03/01

W4HBKgrab001

Above is a clip from W4HBK’s 40m grabber today, the signal is VK2OMD running 5W QRSS6 over a 14,700km path. We can infer (Duffy 2012b) from the 15dB S/N in that capture in 0.25Hz noise bandwidth, that in an 800Hz CW filter for say -5dB S/N (threshold of copy) we need 15dB more signal, or 160W for reliable copy. (Less power may be adequate for very short QSOs at the peak of fade cycles.)

Continue reading Simple Morse beacon keyer updated 2014/03/01

Small transmitting loop review

I saw a recent ‘maker’ video describing a small transmitting loop for 40m.

The loop used a 3m length of 19mm copper pipe formed into a circle, and at the gap where the ends almost meet, a tuning capacitance is synthesised using coaxial cable.

Screenshot - 15_02_2014 , 12_06_57

Above is a screen shot from Reg Edwards loop design program. It calculates the radiation resistance at 0.005Ω, loss resistance of the loop at 0.035Ω, capacitance to resonate it of 206pF (Xc=108Ω), and a bandwidth of 3.2kHz.

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ATU voltage verification

I described a method for designing antenna systems to avoid excessive voltages in baluns and ATUs at (Duffy 2011) .

This article reports post implementation measurements of an antenna system designed using that method and using a G5RV Inverted V with tuned feeder and ATR-30 ATU with integral 1:1 current balun. The tuned feeder is a home-made line section of 2mm diameter copper conductors spaced 50mm, and 9m in length. An additional 0.5m of 135Ω line connects from the antenna entrance panel to the ATU.

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A look at internal losses in a typical ATU

This article explores the loss that may be encountered in an ATU in a practical setting.

The load is a G5RV with tuned feeders operating at 3.6MHz. The tuned feeder is 9m of open wire line of characteristic impedance 450Ω, and the impedance seen by the ATU is around 40-j150Ω, this is not a particularly onerous load.

MFJ949E02

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An inexpensive medium power tuner current balun for HF using Jaycar parts

This is a project to design and build a Guanella 1:1 (current) balun suited for up to 100W on HF with wire antennas and an ATU.

For use with a tuner, the most important design criteria are:

  • high voltage withstand;
  • high common mode impedance;
  • power handling.

Continue reading An inexpensive medium power tuner current balun for HF using Jaycar parts

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #3

Third part in the series..

 

Common mode current measurement

Direct measurement of common mode current in an antenna system is the best indicator or whether there is a common mode current problem.

In Common mode current and coaxial feed lines, I mentioned that common mode current is easily measured.

80mIcm

Continue reading Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #3