PD7MAA HOMEPAGE

FT-817 mobile mount

2011-08-23T14:49:00.003+02:00

I discovered that the Icom mobile mount type IC-MB10 fits Yaesu's FT-817 .
Just glue in some rubber foam of 50x10 and 50x5 mm to fill the gaps.

No ground antenna for backpackers, balconies or plastic car bodies

2011-07-24T14:20:00.014+02:00

A common problem with backpacker or balcony antennas is finding a good counterpoise. Also cars and caravans with a plasic body are a problem. Althow nothing beats a set of resonant radials, the shown solution offers a 1/4 wave stub that wil create an artificial counterpoise. The mobile antenna mount must be isolated from any metal by a epoxy or plastic plate and a normal T-Connector is used at the antenna feedpoint. Be shore to shortcut the end of the stub. The length of the stub in meters equals 1/4 Lambda x 0.66 (this is the velocity factor of 50 Ohm RG-58 ) or can be calculated by deviding 50 by the frequency .So if you need a stub for 14 MHz the outcome is 3.57 m. but this length is not critical. The setup can be easily mounted on top of a rucksack with the stub stashed inside. On a balcony the stub can be layd on the floor.

Z-Match 100 and mini Z-Match

2011-06-29T23:37:00.010+02:00

FIRST TEST WITH A 4C65 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 gives me sufficient tuning range. Being a high-pass type it contributes to less receiver noise. The capacitors are radio types and can be used up to 150 Watts. I used a plastic cabinet but a metal type would provide better HF isolation. Using a metal cabinet needs a "floating"mount of the input capacitor. More info about the Z-match design can be found here

EASY CONSTRUCTION

The QRP 160-6 m. mini Z-Match with a T130-2 toroid in a matal cabinet. Polyvarcons are used for tuning within qrp limits. By switching a 270-500 pF capacitor between the hot ends 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.

THE TUNING AID IN MY MINI Z-MATCH

VELCRO MOUNTED MICRO Z-MATCH

Travel loop antenna type 40-10 and 80-10

2011-06-29T14:57:00.006+02:00

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.

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 .

Simple antenna analyser 0.1 - 30 MHz

2011-06-25T20:30:00.004+02:00

This is a verry simple but good working swr analyser based on the LTC 1799 smd generator . Tuning is easy: Connect your antenna to the analyser with the meter at full scale and look with the 100K potentiometer for a dip on the meter.
Disconnect the antenna and push the set switch. Now adjust the power for a 1:3 reading on the VSWR meter.Releasing the switch will make the meter jump in to the right corner, but that's normal due to the simple bridgeform . Connect the antenna and read the axact VSWR. The first model had a 6.5 V power suply but this caused the LTC 1799 to warm up and drift. At 5V the current is low and the IC is stable.
Most components are mounted on the back of a little pcb , the rest is soldered directly on to the meter and " point to point ". To expand the range downwards to about 0.1 MHz , just put a switch between pin 4 of the generator and the ground. If you want to use a counter , put a 1K resistor in series with the connector. Those who want to build in a counter can replace the 100 K potmeter by a 10 turns type and omit the presets.A verry small counter is available by Hendricks QRP Kits If you are not using a counter , a tuning scale can be made with the help of digital receiver. By lowering the value of C1 the amplitude can be reduced so a more equal power setting can be obtained over all the bands. The meter should have a 100-200 uA reading. PE1IWT did an interesting mod on this analyser project , you can find it here .It's in Dutch but the pictures explain it all. This versatile instument offers the novice radio amateur a lot of help with his antenna and balun projects .

VFO TUNING OR PRESETS POSSIBLE

MINIMAL COMPONENTS

1:1 PCB

COMPONENTS ARE MOUNTED ON THE COPPER SIDE

NOTE THE GROUNDING OF THE REGULATOR BY A JUMPER

INSIDE VIEUW OF a SECOND MODEL ,MADE FOR AN OTHER HAM
THE PRESET POTENTIOMETERS ARE 10 TURNS TYPES

Not to scale alternative pcb suggesture made by carving with a steel scribe

Wil need 2 jumpers to complete

THE COUNTER BY HENDRICKS QRP KITS
http://www.qrpkits.com/freqcounter.html

The stubloop antenna

2011-06-07T20:57:00.002+02:00

Searching for a new loop antenna project 2 years ago , i found this simple design on the internet.

It’s nothing more than a 1 lambda loop , so if you need a antenna for the 2 meter band your loop has a circumference of about 2 meters . The velocity factor is not used in this design !

I tried a loop for 3 m. (100MHz) and I was amazed by the low VSWR and the large bandwidth. The payoff is a low Q.

The radiation pattern is almost equal to a dipole and by moving the feedpoint to the side it becomes a vertical antenna.

By simply adding a tuning capacitor the loop proved to be a wide range SWL antenna for the HF bands.

There is no gain over a dipole but it’s easy to construct and can be made very weather resistant. Based on today's knowledge , a coaxial stub can be verry lossy but it's fun to play with.

SIMPLE T-CONNECTOR

APROX. 3 M. RG-213 GAVE THIS PERFECT RESULT

THE VARI STUBLOOP FOR SWL'S

JUNKTION BOX FOR FULL LAMDA HF STUBLOOPS

20m. end fed halfwave antenna

2011-06-01T22:20:00.009+02:00

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 3-4 turns from the ground .The 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.

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.

Good DX !

Magnetic windowloop for 20m. no tuning ! Updated november 2011

2010-10-12T08:03:00.036+02:00

A stealth solution for apartments ?
I made a wireloop on the inside of the wooden windowframe in my shack with a circumference of 6,20 meters. The tuning capacitor is made of 20 cm PVC coated copperwire. Feeding is done by a medium size Ferroxcube 4C65 toroid with 1 full turn at the antenna and 2 turns at the coax. For 100 Wats power use only a full size 4C65 or eq. and replace the tuning section by a pice of RG-213 that forms a high voltage capacitor. For 40 m use a pice of aprox 75 cm RG-213. You can even use a double switch to change bands.By means of 4 hand suckers this antenna can be placed on any medium size window.

First contact was made with Bari Itali with 5-7 report.This was followed that day by several qso's with HA, YT , and LZ . All made with 3.5 Watts SSB even S56EQC with a 5-9 report . The antenna needs no tuning for the SWR is lower than 1:1.5 all over the band. This is not a wonder antenna but it gets you on the air for certain. Using 15 mm copper tubing drasticly improves efficiency.
When build as mini deltaloop whith the help of two 2m. fibreglass poles it becomes a nice small field antenna .
Give it a try !

You can find toroids and hamstuff at Haje Electronics

SEVERAL TOROIDS WERE TESTED , THE 4C65 PERFORMS FB

LOOP DATA ALTHOUGH THE BANDWIDTH ( Q-FACTOR ) DOES NOT MATCH

15MM COPPER TUBING LOOP

Magnetic loopantenna calculator by KI6GD : http://www.standpipe.com/w2bri/software/loopcalc.exe
The prog. doesn't have an icon, just klick in the white square above it's name .

DO YOU LIKE TO EXPERIMENT WITH ANTENNAS ?
Here's all you ever wanted to know about VSWR :

http://www.amateurradio.org.za/VSWR%20John%20Fielding%20Final.pdf