RFA through coax                                             

18th May 2008                                                                                                                    

As previously annnounced, enhancement of the Roomcap Antenna continues.
This week I tested successfully an interesting new feature:

The Remote Frequency Adjustment RFA does no longer require a separate
control line.  The control voltage is now sent over the coax by inserting a rf-dc-
separator, one on the transmitter side, and one on the antenna side.
The idea was developed with the magnetic loop antenna, and now adapted to the
specific requirements of the Roomcap antenna.
This week the field test was performed with a 70m long coax line between
and antenna.
Insertion of the two devices produced no detectable attenuation of the system,
with the advantage that the separate control line could be eliminated;
very important: The short distance of the control line to the antenna
created an
rf current on the control line, which had to be filtered.
This problem is now eliminated, as this line is no longer existent.

The next update of the construction guide will contain this new enhancement.

Here are the pictures:

50 ohm dc separator

The black box is the 50 ohm rf/dc separator on the transmitter side (1.8 - 30 MHz)
The white box is the 50 ohm rf/dc separator on the antenna side (1.8 - 30 MHz)