Digital modes

It has been a long time since I have used digital mode. So I bought a signalink usbinterface.
Now I can make a restart in digital modes.

An old pentium PC was available for the coding and decoding. The transceiver I use is an old ICOM IC-730. I also have an IC-817 this one works ok but the IC-730 has a better receiver.

A lot of nice freeware programs exists. I have chosen fldigi for most digital modes. Fldigi does not support all modes so I use different programs for modes  WSPR,JT65 and ROS.

For a while I thought that the signallink was partly broken. It worked fine for most programs butI did not see a signal on the right input. It turned out that is was normal as the signallink is a mono device. Unfortunately one of the JT65 programs could not be used because of this. I read that the developer is going to update the program because of this issue. In the mean time I use a different program for JT65.

The modes That I use are: WSPR, PSK31, JT65 and ROS. 

below is a picture of a part of the shack

standard c828m

I bought this radio on a hamfest. It was realy cheap, just 10 euro's. I was told that it still worked.It does not look verry pretty But what can you expect for 10 euro.

Well it did work. The transmitter worked quite well. Output was down to 5 Watts so I realigned it a bit. Now the output is 8 watts. I could get a bit more but then the harmonics are to strong.
All 12 xtal positions were filled. That is a nice bonus. It has some simplex channels , some repeater channels and 144.800.

The receiver had problem, it was deaf. It needed 50 uV for a readable signal.
I found out that the pre amplifier transistor had been replaced by a bf??? I tried to find out what the original transistor should be. Finally I found the manual at mods.dk. The transistor should have been a 2sk19. I had no such device in the junkbox so I tried something else. It turned out that the j310 could be used as  well. Now the sensitivit is ok. It needs 0.3uV for a readable signal. This is acceptable.

dds project

This is my dds project.
On Ebay I found dds pcbs. Those boards contain a 9850 dds chip and an oscillator.
It can be used for a synthesyzer from Hz up to to 40 MHz and more. I bought a few for my projects.
The DDS needs to be programmed. To do that I used a PIC based microcontroller board that I made for my spectrum analyzer project.

Programming the DDS is not that hard. The frequency in the DDS is controlled by writing a value to a 32 bit register. A few control bits must be set and that is it.
The 9850 is a well know chip so some sample code was available.

The biggest Software challenge was to display the frequency correctly. Some floating point calculations had to be done. Unfortunately the double datatype was to small for the calculation so I had to split it up.

Now It works prety good. This project can be the base for projects that need a synthesizer. First candidate is my 70 MHz to cb transverter. I need a 43 MHz signal for it. The DDS can deliver it but the output must be filtered using a bandfilter or a pll. This is needed because of the spurious signals that the DDS generates for signals >30 MHz.

Another project could be a 0-30 MHz CW transmitter. The spurious signals are within legal limits. A lowpass filter however is needed.

70 MHz

A lot of projects are in progress at the same time. One of the projects is a 70 MHz transverter with 27 MHz IF. It uses the same concept as the cb to 40 meter transverter described in one of my blogs.

I made a 43 MHz signal by mixing signals from a 18 MHz Xtal oscillator and a 25 MHz Xtal oscillator. The 18 MHz oscillator is a VXO.
The 43 Mhz signal is amplified by a amplifier using a bfy-90. This signal drives a SBL-1 alike mixer. Signal out of the mixer is filtered by 3 tuned circuits.

TX signal is boosted by a 4 stage amplifier to 1 Watt. It works but I am a bit worried about the stability.

The transverter was pretty deaf so I added a preamplifier using a bfy-90 and 2 tuned circuits in the input. It seems to work. I can hear a 0.1uV signal.
A 0.5 uV signal has a acceptable signal to noise ration.

Pictures and schematics will will be added soon