inde                                                                    G3VjV

 

G3VjV Station and Magnetic Loop Antennas

(To be continued)

7 x 2 m Loop

80cmLoop

RS232 Stepper Motor Controller

USB Stepper Motor Controller

Software Controller

Noise Nulling

CounterPoise - Radial System

Portable for Top Band and HF

My Station

 

7x2 metre Loop 7x2 metre Loop

Mag Loop Farm

The Big Loop

   
Balun and counter weights Construction

The balanced matching, see radial section for balun.

This loop covers 1.3 MHz to 6.5 MHz.

 

 

 

 

Details of the 7 by 2 metre loop

The 7 x 2 metre loop.

The loop is made from 22mm copper tube the corners are bent with a pipe bender, the joins are made with electronics grade solder and the lower half is strengthened with steel tube, I have used 110 mm plastic waste pipe for support, this slides over a wooden fence post and can easily lowered and raised for servicing, the antenna if fed as a balanced system, rather than a simple gamma match, the intention is to reduce noise pick-up and ensure the minimum amount of R.F. on the centre line of the loop, the balun is made from 30 metres of coiled co-ax.

This loop is constructed from 22 mm tube, the top section is reinforced with fibre glass rod, all other joins are reinforced with 1 metre lengths of 10mm steel tube.

This Loop covers 1.3 to 6.5 MHz so can't be used on 40m but reports suggest it is working very well on 160, 80 and 60m so I think it is worth the loss of 40m

Matching is by balanced tappings via an air spaced Balun..

The bandwidth on 160m is just over 3 KHz so is easier to tune and allows full bandwidth audio.


Vacuum Capacitor
Stepper Motor

The Capacitor:

The capacitor is a 1200 to 10 pf vacuum type, this is driven by a stepper motor via a 5:1 gearbox, the stepper motor is controlled by a pc via a USB port.

 

 

 

 

 

The old serial stepper motor and driver boards were supplied by Maplin, order #: RM75S, Maplin no longer supply this item but it is still advertised on the Milford Web site, see further down for the USB Stepper Motor Controller

Bipolar Stepper Driver Set (#5-595)

Milford House
120 High Street
South Milford
LEEDS LS25 5AQ
ENGLAND
Tel: 01977 683665; Fax: 01977 681465

 


 
Capacitor 2
Little Loop

The 80 cm (Flash Gordon) Loop

This loop covers 10 MHz to 29.7 MHz, the loop itself is from a prototype Catco Antenna but with a new housing, motor and gearbox, (the gear box had not been fitted when the photos below were taken).

The capacitor is at the bottom in this version and is housed in the mounting tube, the tube is 110 mm plastic waste pipe, this antenna is fed with a bal un and has a good SWR on all bands.

The capacitor is 10pf - 500 pf and is really too high a capacitance for 10m, I had to redesign the way it connects to the loop in order to get the thing to resonate above 28.45, on the lower photo you can see the connections are now on the side of the housing.

A single length of co-ax feeds the top, the double image is a shadow.

The completed loop awaiting to go outside.

 

 

 

 

 

 


USB Stepper Motor Controller

The USB Stepper Motor Controller, it consists of a Velleman K8055 USB Experiment Interface Board, this is the same board I use in my Home Control system, if has 8 Digital Outputs, 2 Analog Outputs, 2 Analog Inputs, 5 Digital Inputs per board.

I use 4 of the digital outputs to control the 4 inputs of two L293D Driver chips, another two bits control the Enable pins of each chip, a total of six output lines control the two stepper motors.

This system is faster and more reliable than the previous RS232 controllers, the only downside is the code is more complicated, as I have implemented Ramp Up and Ramp Down to ease the strain on the motor and gearbox.

 

 

 

USB Stepper Circuit
 

The Controller


Software Control

Software full mode

software compact mode

One of the compact modes

 

The software for interacting with the rig, linear and controlling the stepper motor(s).

The yellow needle shows average levels, the purple spot shows the peak Smeter readings.

I use Delphi to write the software.

The image above shows the motor control section at the top.

 

 

 

 

 

Linear Remote Control

Linear Control Page

Linear Control Page:

The program continuously monitors the frequency the rig is tuned to and sets the stepper motor to the correct position, fine tuning of the antenna can be done with the Griffin Controller (on transmit) or the left and right scroll keys.

There is only the basic rig functions implemented, in my view the radio is easier to operate using the front panel controls, I have however implemented an unlimited number of memories, each one can be titled.

The usual scan, priority and memory scan are also implemented in addition any memory can be set as a "Favourite".


Griffin PowerMate USB controller

I have just installed a Griffin PowerMate USB controller (see picture further down) I can really recommend this product, it is a very well made and versatile unit, I will be getting another one for my Video/Sound Editing PC.

I have set-up the Griffin and my software so the Griffin tunes the rig in one Hertz steps, by single clicking the tuning changes to 10 Hz steps, on Transmit the Griffin tunes the Antenna, a single click saves the settings and returns to VFO control, I leave the TenTec VFO on larger steps for quick tuning, it works very well indeed.


Noise -- EMC -- QRN

Like most people using radio I have recently experienced increasing problems of noise from Switch Mode Power Supplies etc. I managed to trace and fix most of the sources from within my own property, the worst offender being my Draytek Router, this transmitted noise from its power supply all round the house via the Cat5 cabling but it is very difficult to deal with noise from adjacent properties, you cure one and then another problem pops from another source!

I decided to try the noise canceling approach, I purchased the MFJ-1025 Noise Canceling Signal Enhancer, this device combines the signals from the Main Antenna and a Noise Pick-up Antenna and by adjusting the phaze and Amplitude it is possible to null out most of the noise, setting up the Noise Pick-up Antenna correctly is crucial, it must pick-up the same noise sources as the main antenna but not too much of the signals you want to hear!

Noise Canceller pic

 

Using the MFJ-1025 in conjunction with a transmitter requires care, the Noise Pick-up Antenna can pick up large amounts of RF from the transmitter and damaged the unit, I have attempted to prevent damage by shorting out the Noise Pick-up Antenna when transmitting, below is a circuit I use, I have included a buffer from the Transceiver T/R line because my Ten-Tec has a maximum current limit of 200ma, the relay in my Linear takes 100ma, the MFJ has a relay and my Antenna muter also has another relay.

I have a RF amplifier to bring the noise levels up to a suitable level and a choice of several Noise Antennas, a 30 cm length of wire stuck to the party wall to pick up my neigbours numerous switched mode PSUs a mag Loop Antenna made from two turns of 10 mm tube and three wire antennas running in different directions some distance from the house.

 

RX Loop

The receiving Loop.

RX Loop

The receiving Loop Window.

 

The Counter-Poise/Radial System

 

Because my loop is too close to the ground there is a large amounted of radiation absorbed by the ground so I have now added a system of radials to my system, this has definitely improved reports on 160 and 80 metres.

I have four radials that are resonated, one for 80 m that is self resonant, one for 160 that has a small inductor to bring it to resonance, one that has a relay switching in inductors for 160 or 80 and another resonated on 160m.

I have one long un resonated radial that runs directly under the antenna and to each side, a total length of over 45 metres.

All the conductors close to the antenna are of old copper pipe, a mixture of 28mm, 22mm and long sections of 10mm, in the picture below there are sections running under the grout between the flags.

 

 

 

 

Radial

The new balun (30m length) and part of the radial system.

 

 

 

 

 

 

 

 

 

80m radial

The last section of a 80m radial runs round the pond.

 

 


 

My Station

The TenTec Jupiter.


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