OK, it's up and runnning !
After several weeks of testing I finalized the backyard NVIS antenna, based on the following criteria:
- acceptable RX from 500KHz to 4MHz
- high angle reception for covering distances up to 50-500km circumference
- optimal at upper part MW, 160mtrs and 80mtrs
- minimal visual appearance
My current reference antenna is a 6m tall vertical antenna, tuned to 1830KHz. It receives both groundwave and dx signals very well. I'll make a seperate blog on that later. But its vertical polarisation makes it very susceptible to all local (man-made) noise.
The NVIS needs to act as my 'quiet antenna'.
How I built this one
I used black coated copperclad steel wire from http://www.dx-wire.de/brit/
See at "type A; 0.95mm coated with black polyurethane". It is both stealthy and weatherproof.
The connection box contains a 36:1 x-former (2x glued BN202 #73 binoculairs with 12 and 2 turns). The coax connection has 6pcs "3S4" tubular type ferrites. Inside the shack I have the 2x J-type ferrites with 14 turns coax as a final common mode filter(see picture in the former message below).
The connection box is mounted at 3m20 height in the exact corner of my backyard. See the wooden pole above the red roof, in the background. Both dipole legs are 6m50 long and in a 90 deg horizontal angle. The ends are secured via small porcelan isolators.
It performs great!
This final version shows more output on MW and 160mtrs, which is comfortable when switching back and forth to my vertical reference antenna.
During the evening when the D-layer dissappears, the NVIS is playing well; on par with the vertical and delivering a very comfortable, quiet reception.
I can hear many domestic MW BCB pirate stations between 1600 and 1700KHz coming in and out of the noise, whereas the reference vertical shows strong signals but distorted audio due to man made noise.
160mtrs shows better output, still at a lower level than the vertical but at least now I don't have to both switch on the pre-ampand turn up the AF volume to the maximum.
On 80mtrs the RX is huge; listening to domestic rag-chew rounds I seem to hear every available station no matter how small their antenna /HF output.
Anything left to be desired?
- connection to my remote RX antenna switchbox, which is already available but not wired yet. The NVIS is currently connected to ANT 1 of my ORION.
- adding a pre-amp; this will be mounted in the RX remote control box
- build more RX antennas (you can never have........etc.)