SWEEP/POWER METER
 Tuesday 31st January 2012

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The DDS VFO KIT Can be used as a simple Sweep Generator by simply changing the software in the PIC16F648A to the SweepGen V2.0x software.

PLEASE NOTE: That this software does not have a trigger output pulse for locking either an Oscilloscope, or display when using the Sweep function. This would be a very useful addition, as many have asked for this to be added to the software.

If anyone is willing to modify the current Sweep software to produce a trigger output pulse, then Mini-Kits will supply the software files to you for free. The agreement is that it must be kept compatible with the DDS VFO hardware, & you must send Mini-Kits a copy of the software so that we can allow others to use it. We are suggesting that one of the spare pin,s either pin 15 or 16 on the PIC16F648A be used as an output.

Most functions of the Sweep software are similar to the DDS VFO software. Please refer to the DDS VFO Kit page for more information.

SWEEP KIT DESCRIPTION

The Sweep Kit uses the DDS VFO Hardware with Sweep software. The DDS VFO is a complete AD9851 DDS, Micro controller, & Sweep software to produce a simple DDS signal & sweep generator, that can be used as a piece of test equipment.

The Kit is for constructors that have some experience in soldering SMD components, with many of the conventional sized SMD components being easily fitted. This Kit may be a challenge for some with soldering the AD9851 chip to the DDS board, so Mini-Kits does offer a service at extra cost to fit just the chip, & also can provide fully built Kits. Some wiring is needed for the header connections between the boards, LCD & Keypad. It is suggested that a suitable crimping tool for 2.5mm header pins be used for reliability, & to save time

The maximum frequency that can be used is 70MHz as this is around a third of the maximum DDS clock frequency for the AD9851 chip. The software allows for a VFO for RX, & a separate VFO for TX that can have the VFO frequencies offset from the displayed frequency. This is useful for receivers or transmitters with an Intermediate Frequency, I/F. So yes it can be used on a receiver that has an e.g. 9MHz I/F by setting the RX display offset by 9MHz. A number of memories frequencies are also available for programming.

DDS chips produce lots of outputs that although many dB under the actual output frequency, can still produce spurious output frequencies when directly fed into a Mixer. For this reason it is suggested that the AD9851 DDS is suitable for simple Radio receiver & signal generator projects. If it is to be used for higher performance applications, then the DDS can be used a a reference for a PLL including a separate VCO oscillator.

 

SWEEP DOCUMENTATION

The first part is to discuss the specifications of the software so that you can determine if Sweep software is suitable for your application.

The PIC Source code may be available for those that may want to change things to suit their own application We ask that any changes to the software be available to all other Ham Radio operators through Mini-Kits for free.

DDS VFO BLOCK DIAGRAM Download Updated 31/1/2012

SweepGen Ver2.0x ( Readme Document for the Sweep Kit ) Download Updated 31/1/2012

SWEEP Ver 2.0x SOFTWARE ( What Will The Software Allow You To Do )

Although no problems have been found with the final Software version 2.0x since November 2007, Mini-Kits takes no responsibility for faults & minor glitches in the Software supplied with Kits. 

Below are the standard specifications for the SweepGen ver2.0x software supplied by Mini-Kits. The PIC Source code may be available for those that may want to change things to suit their own application We ask that any changes to the software be available to all other Ham Radio operators through Mini-Kits for free.

WHAT WILL THE SWEEP GEN SOFTWARE ALLOW YOU TO DO?

Refer to the Software Notes for more detailed information Use, Download the Sweep Readme document.

The Software is designed to be used for a simple signal generator, but also has an inbuilt sweep function with the addition of the Power Head Kit can also measure RF Power in dBm, Watts, Volts. Standard functions are Frequency Tuning, Step Size, Calibrate, Memory, Sweep Direction, Sweep Start Stop, Sweep speed, Fast Sweep, VFO/Sweep mode. The signal generator output can be used at the same time as reading RF from one of the Power Head Kits. So a filters 3dB BW can be measured by tuning the DDS generator by hand looking for the -3dB points of the filter. The Sweep function is only suitable for use with either a Spectrum Analyzer or Oscilloscope with a RF probe as the sweep is too fast for the power head kits to read. Currently there is no trigger pulse available from the sweep generator for locking of an Oscilloscope.

The software does not allow for any display offset or Transceiver Radio functions, as it has been designed to make a useful piece of test equipment.

BASIC SOFTWARE SPECIFICATIONS

1/ Frequency range programmable from a minimum frequency of 1Hz, to a Maximum output frequency of 70MHz,
( Using a Osc4 30MHz osc module & DDS x6 multiplier ).

2/ Variable Rate Tuning & Adjustable Step Size 1Hz, 10Hz, 100Hz, 1kHz, 10kHz, 100kHz, 1MHz, 10MHz, 100MHz, 1GHz etc

3/ Programmed to use a low cost Mechanical Rotary Encoder.

4/ Software fine tuning of the Reference oscillator frequency.

5/ Programmable for various Reference oscillator frequencies & DDS x1 or x6 Multiplier.

6/ Up to 11 Sweep Generator Memories can be programmed, ( Including start & finish frequency, & sweep rate ).

7/ There are two Sweep modes Slow & fast, in each there are 10 sweep speeds. Please refer to the Readme document for more detailed information on the sweep width & speeds.

8/ Memorises the last frequency on power up.

7/ Calibration menu to program optional Power Head Kits.

8/ Programmable menu to set for when using an input attenuator or amplifier on the Power Head.

 

CONSTRUCTION:

 

  The above picture shows the DDS VFO hardware with Sweep software mounted in a Takachi Aluminium Box ( 150x100x120mm ) RS Components 401-8982. The front panel was cut out using a nibbling tool & filed with a very fine metal file.  
     

KIT FAULTS & MODIFICATIONS ( Older EME85 DDS Version Hardware )

1/  Refer to the EME85 DDS Kit webpage for some possible problems.

2/ Most Faults can be traced to poor solder joints, or solder bridges across connections. Check for correct wiring to the control board & LCD display module.

3/ Low RF output on frequencies lower than 15MHz is normally incorrectly fitted 10nF chip capacitors on the input & output of the MAR6 amplifier. Some constructors have accidentally put 10pF capacitors in place.

4/ Some have reported that when using the Power Head kit on the Sweep Kit that the 0.1dB reading flashes erratically on the LCD & cannot be read. The display will normally change between 0.1dB steps as the meter display accuracy is 0.25dB per step but can be quite easily read. Most problems with this, has been traced to a noisy 12 volt supply to the Sweep Kit. Make sure that you use a well regulated 12 volt Power Supply. The problem only shows when using the DDS RF output & is not a problem with another RF signal generator. I suspect that this is due to the MAR6 on the DDS board generating the noise on the RF due to there being no regulator on its supply.

5/ If you are getting erratic letters & numbers, ( Garbage ) on the LCD, disconnect everything from the DDS board excluding the LCD first. If the LCD is still showing the same garbage on the display, then the software in the PIC is probably corrupted & needs reprogramming. There has been one report of this.

 

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