A mini SSB QRP transceiver for 14 MHz (20 meter band) by Peter Rachow (DK7IH) – Pictures

Here are some pictures of my recent project, a very small SSB QRP transceiver (schematics can be found here) that covers the 20 meter band. First let’s have a look to the front panel:

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) - Front view

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) – Front view

And here we go for an inside view:

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) - Inside view

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) – Inside view

Starting on the left you can see the AD 9835 DDS chip on the very compact breakout board by artekit.

The breakout board is mounted on a 2 x 8 pin socket row to have the possibility to change the IC ver quickly in case of damage (I set all ICs into sockets without any exception). Above the DDS there is the ATMega 8 micro. Right from the rf-shield made of brass you can see the 9-MHz local oscillator with the ssb modulator and product detector IC NE 612.

For more information on board layout and part distribution have a cursory glance on this commented picture:

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) - Inside view with board layout

A mini 20-m 14-Mhz SSB Transceiver by Peter Rachow (DK7IH) – Inside view with board layout

By the way: Had some nice contacts today with stations from all over Europe with 5 watts out. The rig is really fun! 🙂

73 de Peter (DK7IH)

Ooops, I did it again: An ultra-compact QRP SSB monoband transceiver for 14 MHz (20 meter band)

Deutsche Version des Artikels

After having finished my last ssb transceiver project I was to a certain degree dissatisfied with the mechanical size of the rig. Even though it performed very well and I did some nice DX with it (including cracking a pile up for a Jordanian station) I wanted to find out, if I could shrink the mechanical dimensions of the device to another significant degree. A pocket-size transceiver with somewhat around 5 watts PEP output was the goal that I wanted to achieve.

First I searched the web for attractive circuitry. I quickly came across the „Kajman Transceiver“ made by SQ7JHM, OM Jurka (Link to schematic). At the first glance the circuit seemed extraordinary simple. But the problem was: The device has been designed for operation on the 80-meter-band. So some extensions and improvements had to be made to make it perform well on 20.

First, the original recveiver seemed to be a problem. The layout is very simple. Above all, there is no rf preamp. This might be OK for the high noise levels on 80 and the relatively high field strength that signals have got there. But for 14 MHz this performed, as I had expected, very poorly as I could easily find out when breadboarding the receiver strip and having it run with a simple VFO. And, in addition, the receiver did not lack only sensitivity, the noise figure was also very poor.

So there were two possibilities to cure this problem: add an rf preamp to the receivers’s front end (to improve noise figure) and maybe add an if amp stage between the two NE612-mixers to improve overall gain.

After having put a dual-gate mosfet rf preamp stage to the receiver it suddenly opened up its ears. Performence now was great compared to that before the modification had been made. With a simple dipole I could listen to VKs ans ZLs in the morning and to state side (even West Coast) in the evening. Being very satisfied with the outcome of this simple measure and strictly sticking to simplicity of cicuitry and limited space I went away from adding an if amplifier. Maybe I’ll give it a try later.

The transmitter had also been modified after a short intensive thinking. I re-constructed my proven 3 stage design with single-ended preamp and driver and two 2SC1306s in push-pull mode as the final. That should deliver 5 watts easily. And, not to drive your tension too high, it finally did.

As Collpits, Hartley and Co. VFO-times are over, I took another AD9835 DDS chip out of my shelf, grabbed into the microcontroller box and an AT Mega 8 microcontroller found its way into the circuit. To have the TTSOP-16-package of the AD9835 on a veroboard I bought a very compact breakout-board for the AD 9835 made by artekit in Italy. Very neat, very compact, very nice. And cheap.

So, enough the talking, here’s the hard stuff, folks! The circuit (not yet finished, but OK as a preview):

A 20 Meter / 14 MHz monoband compact QRP SSB transceiver by Peter Rachow (DK7IH)

A 20 Meter / 14 MHz monoband compact QRP SSB transceiver by Peter Rachow (DK7IH)

The crucial thing is the arrangement of the 2 NE612-mixers involving 2 relays close to them and the 9-MHz-SSB-filter. The relays reverse the signal way between receiving and transmitting. For this purpose I used small print relays made by Finder company.

That’s all so far, the next days I will put in some photos of this neat little 20-Meter-Band-SSB-Transceiver to give more details to the interested reader.

73 the Peter (DK7IH)

20Mtr./14 MHz-SSB Transceiver: The receiver’s front end

Today it’s time to give a presentation about the receiver’s front end. When testing this one with an interfrequency of 9785 kHz I suddenly encountered that I had a strange demodulation phenomenon due to a very strong broadcasting station inside the if channel. After some days of listening and trying to decipher the words in English language I recognized that the „jammer“ was Radio Romania International transmitting on 9783 kHz. OK, folks, right beside the if-channel. Front end selectivity was the problem.

After conceiving about this problem, the conclusion that I drew was that with a receiver front end of only 2 tuned circuits the problem could not be solved to satisfy my demands on receiver purity. But a circuit of 3 LCs should do. So this solved the problem finally. So, here is the circuit of front end, rf preamp and first mixer:

Peter Rachow (DK7IH): The 20 Meter/14MHz SSB  tranceiver:  The receiver's first stages

Peter Rachow (DK7IH): The 20 Meter/14MHz SSB tranceiver: The receiver’s first stages

The circuit on the transceiver’s veroboard:

Peter Rachow (DK7IH): The 20 Meter/14MHz SSB  tranceiver:  The receiver's first stages on board

Peter Rachow (DK7IH): The 20 Meter/14MHz SSB tranceiver: The receiver’s first stages on board

C u soon! 73! De Peter (DK7IH)

Programmierung des AD9835 DDS Chips

Nachdem ich mich nun vertiefter mit der Programmierung des DDS-Bausteins AD9835 von Analog Devices beschäftigte, habe ich auf meiner Webseite unter dem URL

http://peterrachow.scienceontheweb.net/programming-ad9835.htm

eine genauere Anleitung abgelegt, wie die Frequenzeinstellung bei diesem Bauteil vorgenommen wird.

After having explored the AD9835 DDS chip more intesively I posted a detailed description of the neceessary programming procdures for setting frequencies with this device on my website

http://peterrachow.scienceontheweb.net/programming-ad9835.htm

including code examples in C programming language. Unfortunately the article is in German only but code examples are commented in English language.

So, have fun using this essay!

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