HOW TO MAKE A BIG COIL

 Here is my 1st attempt to make a big coil.

Needed parts :

- Copper tube, about 4,5 mm OD, 7,6 meters => 16 €.

Search for Copper Nickel Brake Line Tubing on Ebay

- something with a 70 mm diameter and a  corkscrew

- gloves because I don't like to oxidize copper.

Now you must wrap the copper tubing until you are satisfied.

Easy to do because copper is soft.

Insert the corkscrew to give more space between the turns.

The result :

35 cm long - OD 70 mm - Inductance 30 µH

LOW-PASS FILTER FOR 2 TONES GENERATOR

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

https://www.box73.de/product_info.php?products_id=3847

 

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 :

www.gqrp.com/Datasheet_W3NQN.pdf

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

https://www.sv1afn.com/enclosures.html

The filter with 3 x T37-6

The result after tweaking the inductors :

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

KX2 : NEW RIG IN THE SHACK

Audio is superb, ATU realy amazing

EFHW ANTENNA COUPLEUR

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