I was asked yesterday if we could bring back our Active V antenna or make an equivalent antenna.

We originally designed the Active V antenna at the request of one of our customers who had some Rohde and Schwartz V antennas from the 1970s and 1980s that were wearing out.

These antennas were designed during the Cold War for use in West Germany to monitor HF radio traffic directly over the border in East Germany.

The original R&S antennas used 3.5 m long elements in an upright V configuration with a central matching transformer unit.

We built the Active V antenna using 1.5 m long stainless steel whips using the high impedance amplifier from our HF Active Antenna. 

This worked very well and due to the short V dipole configuration was excellent for NVIS work with some good reception on vertically polarised ground wave transmissions.

I thought that I could make a similar V antenna using our High Z Antenna Amplifier if the isolation between the coaxial cable and the antenna elements was high enough.

This afternoon I build a test antenna using two 3.5 m elements at a 90 degree angle similar to the original R&S antenna.

This gives a V dipole element with a resonant frequency above 30 MHz so full HF and LF coverage with a predictable pattern should be possible.

I can confirm that the isolation between the coaxial cable and the antenna elements using a transformer and common mode choke in the High Z amplifier is adequate to give good low noise performance.

Using the two 3.5 m elements gives a good RF output from the amplifier and coverage was tested as excellent with low noise from 100 kHz to 30 MHz. The lower 100 kHz limit was due to the test receiver (Yaesu FT-1000MP). It should operate well below that.

It seems to be a feature with V antennas that they don't receive a lot of noise from their local surroundings. I've been experimenting with a NVIS V dipole for a few weeks and that gives a similar low noise performance probably due to the RF pattern optimised for NVIS operation.

I recall being asked if the High Z Antenna Amplifier could make a roof mounted vertical antenna. This did not work well due to the noise collected by the counterpoise ground.

If it was configured as a roof mounted V dipole the performance would be excellent.

Regards,

Chris

Does it have a broadside pattern similar to a dipole? 

The V dipole is elliptically polarised.

For horizontally polarised signals the pattern is broadside similar to a dipole.

Off the ends where you would have a null with a straight dipole it responds to vertically polarised signals.

In practice for use with local vertically polarised ground wave signals you would point the ends of the V dipole at the station for peak signal. For general HF work with varying polarisations coming down from the ionosphere it is effectively omnidirectional.

For it's original purpose the R&S design it was based on was ideal. You would hear any HF signal transmitted on the other side of the border from ground wave vertical to NVIS horizontal or mixed polarisations.

Regards,

Chris