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ON6BG-antenna coupler





This special callsign was granted by the belgian regulator to our clubstation ON6NB, to celebrate the 900th anniversary of the existence of Belgian's central province (Vlaams-) Brabant.

The call was put to good use for the national SSB fieldday, during the weekend of 2/3 September 2006.
The fieldday site is located at an elevated spot, north of Brussels, in the rural village of Brussegem.
It is in line-of-sight with RVI (Radio Vlaanderen Internationaal), a high power, medium wave transmitter station dedicated for the Flemish people, abroad. More about it, later in this overview.

Two weeks before the event, we decided to provide the RF-equipment  The main parts of the setup are pictured, hereunder:
-Kenwood transceiver TS850D, modified to allow the insertion of filters in the Rx-line
-MFJ voice keyer MFJ432
-Heathkit bandswitch  
-homebrew Rx-filter box with a patch panel configuration
-Drake MN2700, to match the transceiver to the feeder line.

The traditional, single banded, dipoles in inverted V-configuration for 40 and 80m were used.
On 160m, we tried a "military" copy of a Barker & Williamson multiband radiator. An antenna that did not charme many of us.
The 40 and 80m antennas were hung on the lorry tower that also served as mobile shack, kindly provided by ON8CW. (Thanks Walter!)

The special prefix, the setup and the motivation of the ON6NB (Noord-Brabant-Grimbergen) club members paid off considerably.
Very much to our surprise, we easily topped, past club records and worked more than 750 stations and this with just 11 QSO's and 4 multipliers on 160m.
Only one of the handful of "operators" had a rotable beam antenna on shortwave at home, not to speak about the lack of contest experience !!
Amateurs in the true sense of the word!!

Here is a closer view of the homebrew Rx-filter box that contained the filters for 40m, 80m SSB and 160m.

The right hand side of the box provides the controls of a Rohde and Schwarz bandpass filter, originating from an old R&S measurement receiver.
The 40, 80 and 160m bands were selected through a bandswitch. A seperate "fine-tune"-button allowed for setting the filter at the spot, based on the band noise.
The basic performance can be summarized by the following characteristics:
-its -3dB bandwidth being ~ 0.03 f
-its attenuation at 0.1 f ~ 30dB (f being the ferequency of operation)
This commercial unit provides a means of comparison for the performance of the set of homebrew filters.

The left hand side allowed easy "switching" between the bands of interest. I found it easier this way than installing a multi-position bandswitch.
Although, I have to admit that there were abundant BNC jumper cables on hand to provide the selected option...

The 160m filter was built from a design by Tasa, YU1LM whom has been so kind to put his skills to work for us...
After the necessary soldering and "rolling" of the toroids, the unit was measured out on a R&S vector network analyzer.
As can be judged from the article, this homemade bandpassfilter provides not only excellent rejection of the offending 1512kHz MW transmitter (the main RVI transmit frequency)
but also a better than average return loss.

The 40m filter is based on a ceramic 7025kHz Murata filter that was sent to me as a sample, by Murata Europe, 15 years ago. (Thanks!)
The 80m filter is a classic top-coupled dual resonator filter. One for the SSB/DX-portion, the other for the CW-part of the band.

BTW: all the homebrew filters outperformed the reference R&S-bandpass filter. The commercial unit having the advantage to be fully tuneable over all the indicated bands.