F5MWW : 2018

2018-12-26

Here is a 2 tones RF generator for 7030 and 7050 kHz, sold by funkamateur.de :

As harmonics are present at the output, a low-pass filter is required.

Good harmonics filters for amateur radio bands can be found at the G-QRP web site, good up to 10 Watts and low insertion loss :

The PCB filter fits in a 80 x 25 x 25 mm enclosure sold by SV1AFN

The filter with 3 x T37-6

The result after tweaking the inductors :

Return loss @ 7050 kHz is 22 dB, SWR = 1.17

Audio is superb, ATU realy amazing

Here is a new toy made with a FT 140-43 and 2 capacitors, total value = 139 pF.

Basically, it's a 28 turns auto transformer with a 3 turns tap

With a 3.3 kOhm between antenna and ground, I obtain the following curves

Return loss

- 19.85 dB @ 7.05 MHz, SWR = 1.22

-19.86 dB @ 10.1 MHz, SWR = 1.22

-18.84 dB @ 14.1 MHz, SWR = 1.26

-15.13 dB @ 21.1 MHz, SWR = 1.42

-11.6 dB @ 24.9 MHz, SWR = 1.71

-8.6 dB @ 28.5 MHz, SWR = 2.18

What about insertion loss ?

To evaluate IL, I made this test circuit

With 2 x FT 140-43, the IL is as follows

Divided by 2, the IL for 1 core is :

0,34 dB @ 7.05 MHz => for 5W input power, 4,62 W go to antenna

0,37 @ 10.1 MHz => 4,59 W to antenna

0.4 dB @ 14.1 MHz => 4,56 W to antenna

1 dB @ 28.5 MHz => 3.9 W to antenna