This is a updated collection of easy to build projects for radio amateurs and swl's. See all my projects in the older posts down this blog.
Have fun.
73 John

Wednesday, June 29, 2011

Z-Match 100 and mini Z-Match

FIRST TEST WITH A  4C65 TOROID, LATER A T200-2 WAS USED

 FINAL VERSION WITH THE T200-6 TOROID
This is a one for all antenna tuner with wide range tuning on all the HF bands. The tuner is based on a G3WQW  design. A T200-6 should give a better Q but the T200-2 was in stock and gave me sufficient tuning range.The final version has the T200-6 toroid and a metal cabinet to provide a better HF isolation. Being a high-pass type it contributes to less receiver noise.  The capacitors are radio types and can be used up to 150 Watts. Using a metal cabinet needs a "floating"mount of the input capacitor. More info about the Z-match design can be found here
Tuning capacitors :http://www.rfparts.com/capacitors/capacitors-antennaload.html

The QRP 160-6 m. mini Z-Match with a T130-2 toroid in a matal cabinet. Polyvaricons are used for tuning within qrp limits. By switching a  270-500 pF capacitor over the left side of C2 (2x 500pF)  the tuning range can be extended. It's possible to tune a doublet antenna on all HF bands. Together with the FT-817 it makes a great qrp combo.
 The mircro Z-Match with 12x5x3 cm ultra portable for 80-6 m. In this tuner a nr. 6 material toroid was used. There is still some room left for a tuning indicator....

QRP tuning indicator . A perfect match is indicated by a bright shining LED , suitible for QRP only. Can be mounted in any QRP tuner at the antenna output. Gives a better reading than the FT-817 internal swr meter.
 THE TUNING AID IN MY MINI Z-MATCH
Another mini Zmatch i made for the field.
VELCRO MOUNTED MICRO Z-MATCH

Travel loop antenna type 40-10 and 80-10

Haunted  as many  others by radio interference and  noise I started looking for a wideband portable antenna . Soon I became focused on a magnetic loop antenna. The only catch was the method of feeding by a Faraday loop , it made the project hand sensitive …. In the Rothammel Antennabook I found a complete different way of feeding made by capacitors .
This was a big  improvement and made a perfect match possible between 6.5 and 30 MHz.
Both tuning capacitors come from old AM radios and because their  sections are switched  in series , they can be used up to 30 Watts without arcing. They interact so it’s wise to make some markings on the front for fast tuning.
The loop is made of RG-213 coax and rests on a cross made of 6 mm. fibreglass rods( kite shop )
Inside the tuner is a shortcut between the centre and the braid of the coax loop to form a solid ring .  By simply adding a second loop with a 5 cm.spacing and a switch to put the loop's in parallel or in series, the antenna becomes a 80-10 m. portable low power loop for travelling. The travelloop was born HI. It has been my travel companion for many years with many qso’s even far over the Atlantic.
Tuning capacitors : http://www.rfparts.com/capacitors/capacitors-antennaload.html

6.5-30 MHz  TRAVEL LOOP

 6.5- 30MHz tuner
3.5- 30 MHz VERSION WITH BANDSWITCH

THE SWITCH SHOWN FROM BEHIND

CAUTION !
Magnetic loop antennas can produce a high voltage that may be harmfull to your health.
Tune your antenna at low power and take a safe distance while operating .

Wednesday, June 01, 2011

20m. end fed halfwave antenna


Working portable demands an easy setup of your antenna. The antenna also has to give enough punch at a low radiation angle without the need of radials.
The vertical end fed half wave antenna is my choice for it’s easy to employ and it's a perfect DX antenna . This antenna is grounded thus giving les static noise to your receiver.
A 20m. version is about 10 m. long and has aprox. 3000 Ohms at the feedpoint. So we need a simple tuner to reduce this to 50 Ohm .
Put 20 turns ( covers half of the toroid ) of 1 - 1.2 mm enamel wire on a T130-2 toroid with a tap at 3 turns from the ground .The first picture shows the first test setup with a 2.5 turn tap. You also need about 25 cm of thin Teflon coax (RG 178 b/u) that will act after tuning as a high voltage capacitor of about 22 pF.
The pictures explain the simple construction. The cabinet is a PVC type G302 made by Velleman.
 TWISTED TAP FOR MORE STABILLETY

 NOTE THE GROUNDSTRIP

ADDING THE CAPACITOR/COAX

HOT GLUE FIXATION

Tuning : The trick to tune this transformer is to find the working frequency first by tuning the capacitor. Then we look for the the 50 Ohm point on the coil .  Connect a 3300 Ohm resistor from the top of the coil to the ground of the antenna plug.
Adjust the length of the open coax line until you reach the lowest VSWR in the centre of the band with an analyser. The coax will be about 23 cm in total resulting in  22pF .
Now remove the resistor and connect the antenna wire of aprox. 10 m. PVC coated copper wire. Tune the antenna for best VSWR by reducing it's length carefully. My antenna is 9.9m. long and is mounted on a 12.5 m. fishing pole. A near 1:1 VSWR  on 14.200 MHz can always be achieved ! Before tuning , fix the toroid with some hot glue and wait fore it to cool off. Beware of the high voltage at the antenna feedpoint , this can rise up to almost 500V at 100 Watts.


10/11m version
For 10/11m band  use 16 turns 1-1.2mm enamelled wire on a T130-6 toroid with a tap at 2-3turns.
A 15 cm piece of coax forms the capacitor. Antennawire length is aprox. 5.5m .

My first DX contact with a vertical half wave end fed antenna was with VK6MV in SSB using the long path, over the north and south pole, with a 5-5 report.
 I was also able to work  Japan,Taiwan, Thailand, India, Indonesia, South-Africa, The Falklands ands. in SSB with good reports. Every end fed / vertical needs some kind of counterpoise to push against and in this case that's the coax , so don't forget a line choke near to your transceiver. 
Good DX !


Disclaimer:I'm not responsable for any damage due to reproduction of my projects.

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