Milan OM3TBG sent us a contribution in which he wants to draw the attention of a wider circle of radio amateurs to the success QRP the DOB80 transceiver and to places where information about it can be obtained. The device was made by his friend Alex OM3TY from BA. It premiered at the QRP meeting in Chrudim.
At this year's meeting of OK / OM QRP amateurs in Chrudim, the new QRP CW premiered TCVR DOB80. The device was made and brought to the meeting by Alex OM3TY from Bratislava. I was one of the participants of this event who had the opportunity to get to know the DOB80 device more closely during operation.
We were all surprised by the admirable quality of reception. The reception of telegraph signals was unusually pleasant and clear, sensitivity and selectivity excellent.
The transceiver uses direct mixing receiver with the phase method of mirror noise suppression. Compared to the standard connection, this receiver contains two mixers ( NE 602 ) and an NF phaser with a quadruple OZ.
The author of the successful project is Leon Williams VK2DOB. An article about him was published in 1997 in Lo-Key magazine, published by the Australian CW Operators_ QRP Club. We published an article translated by Jirko OK1DXK in the magazine OK QRP INFO, in double number 43/44 in 2001. It contains a description and a complete wiring diagram.
Alexa OM3TY transceiver wiring interested. Contacted Loen VK2DOB directly. He obtained from him an image of both the receiver and the transmitter circuit boards. In a relatively short time, he built and revived the facility. He tested it during competitions on the 80 m band and was surprised mainly by the qualities of the receiver. He made many nice connections and not only with stations on the European continent. He used a 27 m inclined wire antenna and a transmitter with a maximum power of 5 Watts.
Milan OK1IF, also a participant of the QRP amateur meeting in Chrudim, has placed on his website additional information about the said transceiver and his comments about QRP. Those interested can find a diagram and a description of the DOB80 on his website and will receive sound recordings from the band.
The site address is: https://ok1if.hamqth.com
OM3TY is going to the meeting of Slovak QRP amateurs in Vrútky on May 24 with the DOB80 transceiver. He promised that he would publish there the implemented modifications, by which he achieved further improvement of the transceiver's function.
For the attention of those interested in receivers and transceivers of a similar type as the DOB80, I can recommend visiting the following websites:
http://www.redhotradio.com – Presentation of the NorCal 30 QRP transceiver, comparing the excellent parameters of its DC receiver with other radios, including K2 and FT1000MP (.pdf file - 1 MB )
https://www.seboldt.net/k0jd - John Seboldt K0JD's site, the 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 components pass NF phasors used in DC receivers (2 files that can be downloaded on one diskette). The program shows in graphic form the size of the phase error in degrees and the level of suppression (attenuation) in the selected frequency band depending on the specified frequency values and the number of filters used in each branch.
You are at the end >here< you can still download a short recording of the reception using DOB80:
Milan Dostál OM3TBG
BA, 15/04/2003