QRP CW tcvr DOB80 pre 80 m pásmo

Milan OM3TBG sent us a post, which wants to draw the attention of a wider range of radio amateurs to the successful QRP transceiver DOB80 and to the places, where information about him can be obtained. The device was made by his friend Alex OM3TY from BA. It premiered at the QRP meeting in Chrudim.

The new QRP CW tcvr DOB80 premiered at this year's meeting of OK / OM QRP amateurs in Chrudim. The device was made and brought to the meeting by Alex OM3TY from Bratislava. I was one of the participants in this event, who had the opportunity to get to know the DOB80 better during operation.

We were all surprised by the admirable quality of income. The reception of telegraph signals was extremely pleasant and clean, sensitivity and selectivity excellent.

The transceiver uses a direct-mixing receiver with a phase method of mirror suppression. Unlike the standard connection, this receiver contains two mixers ( BORN 602 ) and NF phaser with quadruple OZ.

The author of the successful project is Leon Williams VK2DOB. An article about him was published in 1997 in Lo-Key magazine, which is published by the Australian CW Operators_ QRP Club. We published an article translated by Jirek OK1DXK in the OK QRP INFO magazine, in double number 43/44 in year 2001. Contains a description and a complete wiring diagram.

Alexa OM3TY was interested in the connection of the transceiver. He contacted Loena VK2DOB directly. He obtained an image of the printed circuit boards of both the receiver and the transmitter from him. In a relatively short time, he built and revived the device. He tested it during the races on 80 m band and was surprised mainly by the quality of the receiver. He has made many nice connections, not just with stations on the European continent. He used an antenna 27 m oblique wire and transmitter with maximum power 5 Watt.

The finished DOB80 device from the OM3TY workshop can be seen in the attached pictures.

Milan OK1IF, also a participant in the QRP amateurs' meeting in Chrudim, posted more information about the transceiver and its comments on QRP on its website. Those interested will also find a scheme with a description of DOB80 on its website and I will receive audio recordings from the band.
The page address is: http://www.qsl.net/ok1if

OM3TY is also preparing with the DOB80 transceiver for a meeting of Slovak QRP amateurs in Vrútky 24. may. He made a promise, that it will publish the implemented adjustments there, which further improved the function of the transceiver.

For those interested in receivers and transceivers of a similar type as DOB80, I can recommend a visit to these websites :

http://www.redhotradio.com – Presentation of QRP transceiver NorCal 30, comparison of excellent parameters of its DC receiver with other radios, including K2 and FT1000MP (.pdf file - 1 MB )

http://www.seboldt.net/k0jd – John Seboldt K0JD website, results of his work and experiments, focused on the construction of high quality DC receivers. Links and links to related sites and articles

http://www.localdial.com/users/lawrence/apf.htm J-TEK All Pass Filter Designer - a program for calculating the values ​​of NF phaser pass components, used in DC receivers ( 2 files, which can be downloaded to a single floppy disk). The program shows in graphical form the magnitude of the phase error in degrees and the level of suppression ( attenuation ) in the selected frequency band depending on the entered frequency values ​​and the number of filters used in each branch.

In the end, you are >your< you can still download a short recording from the reception using the DOB80.

Milan Dostal OM3TBG
BA, 15.4.2003