Topband

Yesterday evening I had WSPR running at 160m. 
WSPR dial: 1.8366 MHz.
With the homemade magnetic loop antenna and 5 Watts RF following unique stations were noticed:

Progress Signal Function Generator

Two blog entries ago I informed you about the Bulgarian function generator.
This morning I was able to finish the circuit:

Some initial tests showed the circuit works. Below you see the generator supplying a nice sawtooth:

Measured upper frequency is appr. 265 kHz. Final steps are the +/- 12Vdc power supply and the casing.

Since I had the oscilloscope, a Handykit HKS130, in front of me, I took the opportunity to apply some contactspray into the potmeters. After all those years they needed this. This type of kits were popular in the 1975-1985 era. It was fun to glance at the contents of the kit and to see how the scope had been designed:

                                        Contents oscilloscope Handykit HKS130

80m WSPR with magnetic loop antenna

This morning I connected my forgotten magnetic loop antenna to the Yaesu FT450 for some WSPR trials on 80m. I made this (muliturn) magnetic loop antenna for 160m and 80m. On top there is a handmade varco to withstand the high voltages. The antenna does not look professional but it works. Tuning of this type of antennas is very critical because of the small bandwidth.

I inserted the well known 80m WSPR frequency of 3.592600 MHz into the Yaesu and the WSPR software. 

After half an hour operating at 5 Watts following stations popped up:

I will have WSPR running today to see how the antenna performs and have a look at changing propagation at 80m.

Update: It is good to see that even with a small indoor antenna and QRP power one can have a lot of radiofun. And even more, my house is 4 meters below sea-level ! Who said antennas must always be at high altitude ?

After a couple of hours WSPR-ing following unique stations have been identified

                                                                                                                 

                                                                   

Bulgarian Signal Function Generator

This DIY design from Bulgaria shows a versatile function generator. The circuit uses an Intersel IC ICL8038. Although it is an old design, this chip performs well and is still available (I ordered two of them at Kent Electronics for under 3 euro each). You can use the output signal for measurements or to modulate your transmitter under test.

The ICL8038 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.001Hz to more than 300kHz using either resistors or capacitors. FM (frequency modulation) and sweeping can be accomplished with an external voltage. The ICL8038 is fabricated with monolithic technology, using Schottky barrier diodes and thin film resistors, and the output is stable over a wide range of temperature and supply variations.

I found a simple design at http://www.constructor.bg/mk/testgen.htm

Google translator was able to convert the Bulgarian text to Dutch for me.  This made it possible to understand the labels.

The circuit uses + and - 12 VDC which you can produce with an 7812 and a 7912 voltage regulator.

Controls are as follows:

Selector switch to R3, R4, R9: Waveform
Selector switch to C3...C7:Frequency Adjustment, coarse
P5 / P1 : Frequency Adjustment, fine
P6 : Output level
P2: Symmetry
P3, P4: Linearity

Component values:

Resistors:  R1 - 56 , R2 - 12 к , R3 - 10 к , R4 - 56 к , R5 - 10 к , R6 - 2.4 к , R7 - 2.4 к ,
R8 - 7.72 M ( 4.3 M + 3.3 M + 120 к ), R9 - 33к , R10 - 18 к , R11 - 20 к , R12 - 680 ,
R13 - 220   
Potmeters: P1 - 1 к , P2 - 1 к , P3 - 100 к , P4 - 100 к , P5 - 10 к , P6 - 100 к .
Capacitors: С3 - 200 pF, С4 - 2.2 nF, С5 - 22 nF, С6 - 220 nF, С7 - 2.2 uF, С8 - 100 nF,  С11 - 100 uF.
Semiconductors: Т3 – 2N3904, Т4 – 2N3904

Generator under development

AM receiver with TA7642

From Kent Electronics l ordered and received some TA7642 Integrated Circuits for 0.75 euro each. These linear circuits in TO92 housing are designed for medium wave AM reception.

The internet provides lots of circuits with the Ferranti TA7642. For example this simple design:

Note: contacts 1 and 3 on TA7642 / contacts 5 and 6 on LM386 swapped

 

What’s possible with this small IC.  How about (V)LF reception or CW/SSB decoding ?

I found some time to solder the circuit above. To be honest, the results were rather dissapointing. Could receive 2 MW stations and in the evening 4. But there was no good separation of the stations (bad selectivity). I used an SMD version of the LM386. It will be hard to discover it on the photo below.

Kent Radio Special magazine

One of the nicest electronics on-line stores in The Netherlands is Kent in Zeeland.
Kent has issued its spring Radio Special catalogue.

This time with good information about interesting components like the TA7642 (Ferranti AM receiver), ICL8038 (Function Generator) and Mini Circuit Mixers. Some complete projects are described as well like the DSP receiver.

Have a look yourself at:

http://www.kent-electronics.nl/

DXCC #129

The postman brought me a nice surprise. QSL from South Africa. April 2011 I made a PSK63 QSO on 28 MHz with Mitch, ZS2DK.

Nice to see the QSO confirmed. This is the first card from ZS and my 129th (confirmed) DXCC.

QTH of Mitch is Port Elizabeth

eAwards

eQSL.cc provides  global electronic QSL card exchange for amateur radio operators and SWLs.  Since 2005 I am using eQSL.cc
This website provides an easy way of swapping digital QSL-cards.
As an eQSL-member you can participate in the eAward program.
There are several eAwards available (e.g. eDX100, ePFX, eWAS).

To my surprise, recently the ePFX300-PSK Award has been introduced.
I have been using the PSK mode often past years since it is an easy and reliable modulation
method for shortwave signals. Apparantly I have exchanged eQSL-cards with radiostations with 342 different prefixes using PSK in the past years.

Another piece of coloured paper to decorate to my "wall of fame" :-)

http://www.eqsl.cc/qslcard/myAwards.cfm

First FM QSO with Iceland

Conditions must have been fine yesterday on 10 m. When Odinn, TF2MSN, replied on my  29.445 MHz FM signal I was really surprised. His signal peaked at 5 dB over 9. 

I used 30 Watts RF from a FT-450.
The URL of Odin: 

http://www.odinn.org/

                  Akranes, QTH of Odinn on the west coast of Iceland. Appr. 6500 inhibitants,

The Shunt Regulated Push-Pull (SRPP)

The SRPP is an elegantly simple circuit, and is really a small output transformerless (OTL) amplifier. It was widely used in TV circuits for delivering significant current into heavy capacitive loads. It was first patented in 1940 by Henry Clough of Marconi, and has returned in many designs since. Interestingly though, it was not referred to as the SRPP until quite recently and instead had a variety of other names like 'bootstrap follower', ‘mu follower’ and 'shunt regulated amplifier'.

Sennheiser HD450

I have used the SRPP principle in a stereo headphone amplifier. The circuit below was made twice (lefthand and righthand channel) and combined with a PSU it forms the amplifier. Allthough the output impedance of the SRPP amp does not exactly match the headphones impedance, the amplifier provides a nice and clear sound to my Sennheiser headphones.
The input comes from a digital source (CD-player, DVD-player or PC soundcard).

                                                       Circuit diagram, 1 channel

                                                     Building in progress, spring 2012