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Archive for the ‘Ham General’ Category

Grid Dip Oscillator

Modern_gdo

Downloading the Marchwood Power Supply link has now been FIXED at the bottom of the page

My name is Dave and live in the Lake District, a little market town Cleator-Moor in west Cumbria, the little village I live in is Wath-Brow

The Homebrew rig covers 80, 20, 40, meters

100 watts output into Auto Atu. I built the Pic-A-Tune designed by G3XJP which was published in a series of articles in Radcom, it turned out to be quite a long winded project which took me 2 years to build but well worth while the effort.

The Digital display that you can see lit up is the G3XJP DDS absolutely brilliant, and that also was featured in Radcom as well which injects +7Dbm into the SBL1 mixer which is just right to turn the diodes fully on in the mixer. I have since built a HMode mixer using Baluns and they are very high performance mixer indeed.

The transceiver I built was from G4CLF’s circuit diagrams

And introduced many other circuits from other magazines to eventually end up with a full blown working transceiver, a labour of love I suppose but I still get a thrill every time I use it.

Below pictures Homebrew Pic-A-Tune designed by G3XJP. I used Mylar sheet for the capacitors which should handle a good 200 watts. I have no problems at up to 150 watts, no flash overs.

The Aerial I use is a Delta Loop with about 210 feet of total wire length and its fed on the bottom leg slightly to one side, a truly very low noise aerial having used it now for about 5 years.

Over the last 45 years plus I have enjoyed making all of my station, the power supply that I use is the Practical Wireless Marchwood design and in actual fact built up 3 of them as they are so reliable 13.8 Volts @ 30 to 40 Amps depending upon the transformer. The Microhone is a cheap homemade electret type but found them to produce very good audio quality if engineered correctly. There is plenty of information out there on the Internet.

This Grid Dip Oscillator design I found on the Internet designed by Al Bloom N1AL. I decided to add it to this site to make it a little easier to find,, I built one up and it works very well indeed, it also dips as it should right down to zero without any hesitation. The only problem that I found was the voltage suggested in the article was 1.5Volts,, this just is not enough so I wrote an email to Al Bloom and he also said that other people had found the same as me,, it requires 3Volts,, 3 x 1.5Volt cells. Just click on the morden_gdo to view the Adobe PDF file and then save it to your computer to print out as required. If you click on the link below it explaines quite well what you can indeed do with the GDO.

73s G4RVH

What-you-can-do-with-a-dip-meter

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IMPORTANT Make sure that your power supply connections are made to the PCB before powering up the device or you will blow the chip. Personally I would prefer to use a small 24 Volt transformer and a small bridge rectifier for the 24V supply but it is a small convenient way of supplying 24V, but far better if you can manage to get hold of a 12V RF relay.

This is a very good solution for switching 24 Volt relays on from a 12 volts supply line or even down as low as 5 Volts,, I have personally tried several circuits to do this job and failed miserably but this little circuit switches any of the high current 24 to 26 volt relays in with a good clunk of the realy contacts. The output volts can be adjusted by altering just a couple of resister values R1 and R2. These values are worked out from a little calculation from the data sheet below. You must use ECR resistors and capacitors and also an ECR inductor or you will run into problems.

Reading the data sheet you need a 4 layer board but I designed a board layout using just the normal 2 layers and had no problems at all. The chip used is an Radio Spares LM2733 which will handle 1 Amp. The part number is 533-5424.

Important If you use these circuits with a power Supply that is sitting at say between 5 to 12 volts and then switch on the circuit you will not have a problem but however if you switch the power supply onto the board from the off state,, as the power supply is quickly going up in voltage the little LM2733 WILL DRAW enough current to blow the device even though the 24 Volt relay is connected.

I have totally tamed this circuit now however by using a Thyristor and it doesn’t matter now, if you switch the 12 Volts onto the circuit with a relay on the output as the Buck Booster circuit is perfectly safe. I have tested the circuit for days on end and now perfectly safe to use without any worries of blowing up the chip. I have actually blown up about 4 of these devices while in development, but that’s electronic development for you as it doesn’t always work out at the first few attempts.

The PDF files of the PCB and the layout are below, just magnify the board layout to see where the parts go.

I designed the board originally in the Eagle CAD program but now have a CNC Cutting machine so design all of my printed circuit boards in 2D Design and then connect my laptop up to the CNC Machine and let the machine make the PCB
printed circuit board while I go for a walk, no more hazardous chemicals like Ferric Chloride, Sodium Hydroxide to do the developing of the board after the light box stage. Also it can be a bit hit and miss using expensive Photo Resist board at probably £10 an A4 sheet size.

lm27313

lm2733

lm27313_layout


Here is another circuit that works well which again produces 24 Volts from 12 Volts DC at up to 1 Amp. The toroid I used has 150 turns of wire on it which gives me 180uH.
I personally prefer the Buck Booster Texas Instruments chip LM27313.

Here are a couple of printed circuit boards that I produced using my CNC Machine so that you can see how powerful they really are once you have mastered driving the machine.

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https://www.qsonet.com/programs.html

This is a Ham only voice over IP system, up to now I am very impressed by the program, I’ve downloaded a copy of the program and have uploaded my license for authentication which is a requirement before you can operate the program at all. Your Licence can be aquired from the Ofcomm Licencing website in PDF format and can all be done on line.

Here is a quick breakdown of the specs:

  • No need to configure router ports.
    This means it can be used from your Laptop
  • Covers 5 HF radio bands – 80, 40, 20, 15 and 10 meter bands.
  • Computer microphone provides voice modulation.
  • Includes built in CW keyer. Simply type on the keyboard to send perfect CW.
  • Spectrum graph shows radio activity within a settable sweep range of 50, 100, 200 and 500 kHz.
  • Call sign, handle, QTH, etc are automatically displayed for current transmitting station.
  • Keyboard “Hot Keys” provide a simple interface for vision impaired operators.
  • “Round-Table” QSO’s are possible because any frequency may have a large number of listeners.

System Requirements:

CQ100 requires Windows 2000, XP or VISTA with sound card, microphone and speakers (or headset).
A reliable internet connection is required with a speed of at least 33.6k dialup.

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This is just a quick note to readers to quickly read a very interesting article that has been written on the Internet about very low phase noise and ultra low jitter in Oscillators which is becoming more important to Radiohams building homebrew projects using high quality ADC`s and FPGA technology (FIELD PROGRAMMABLE GATE ARRAY chips with some of them having 240 pins on one chip. 73s G4RVH

low_jitter_phasenoise

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