Last Revision: 05 August 2009
The antenna is now working for more than a year without major problems. I only had one bad N-connector on 6m over the winter time. This was repaired easily. After this time the wish came up for some improvement and I decided to stay with the antennas as they are, but add receive preamplifiers for 432 MHz and 50 MHz. You may ask, why an amp for 6m ?? I want to receive some more EME, OK.
I chose a commercial preamplifier which is made by SHF-Elektronik in Germany. As soon as it arrived I took it to my workplace and measured it with the HP8970B noise figure meter. I set it to a gain of 15 dB and saw a noise figure of F = 0,95 dB then, which is OK. The amplifier uses a MOSFET BF980, which has strong signal capabilities. After installation I carefully checked its performance. By switching off AGC in the TS690s receiver and with the use of DL4YHF SpectraLab I could estimate an increase of sensitivity of about 2 dB. But this is only true into directions where noise floor is low. As soon as noise rises, the advantage is gone.
I purchased 2 coaxial relais via ebay for 10€. They looked OK and I put these relais and my very old 70cm GaAs-Fet EME preamplifier into a ruggedized box. The whole thing measured with a gain of 16 dB and a noise figure of 0,65 dB (including the relais). I expected a good improvement and I was not disappointed by its performance. Even sunnoise is clearly detectable. I estimate about 3 .. 4 dB with my two antennas. Cable runs are short (80cm to each af the antennas) and the power splitter is close to the input of the amplifier. Many beacons are audible now and they disappear, when the amplifier is switched off. I estimate an advantage of at least 6 dB if not more.
So on 1 August 2009 the time had come to do some work on the antenna.
The tower is tilt over for the work at the antenna
The 50 MHz preamplifier is mounted close to the feedpoint of the yagi. The connecting cable is a low loss RG400 teflon type.
The main feedline is wound up into a few turns to form a choke against RF on the outer lead of the H2000 cable.
Here are the 432 MHz homemade DK7ZB type antennas with the preamplifier in the plastic box. Note the very short leads to the antennas. I use a 2m power splitter for 70cm which works in 3/4 wave mode. The other preamplifier is the SSB Electronic MV144S for the 2m band.
Here is a full view of the antenna with all preamplifiers and the wind anemometer mounted. The wire antenna is my full size dipole for the 7 MHz band.
Here is another view of the antenna, which principally remained unchanged compared to May 2008.