Its been almost 20 years ago since I made my last QSO on 70cm and a lot has changed with all the digital modes around. The 50MHz band is drying up DXCC wise, have already 2m DXCC so 70cm was next in line.
Here is the new setup::
Main antenna is a stack with 8x 43el by YU1CF http://www.antennas-amplifiers.com/70cm-High-gain-Yagi-432-MHz/70cm-Super-Yagi-EME-antenna-PA432-43-12
Phaselines are 1/2” hardline ( placed along the boom for minimal influence). Array on top of the 24m selfsupporting tower, main feedline for now 7/8" 33m long, but to be replaced by 1-1/4" cable.
Currently (05-11-2017) I have temporary jumper coax giving extra 0.7dB loss.
Antenna central point is at 110m asl. Its the 2nd tower to your left that is used. The antenna H-frame is about 8.1m by 2.7 m and made out of welded steel tubing. Weight is >100kg for the frame, and complete structure is >250kg. The antenna was simulated by YU1CF and I looked through the professional and ham publications on feedline influence of pattern to choose the least influencing cable path to splitters and down to radio. Time will tell if it was right choice.
The SWR plot shown here. Rig used is a TS-2000 chosen for stability and easy split RX/TX. Just need to unplug 1 coax inside to have a separate RX input on 432 MHz.
I swept the connection N connection to RX board and found 10dB loss on the path. No wonder people claim TS2000 is deaf.
I've injected -154dBm straight in RX board and it was still above the noise floor! Only way to get best performance out of TS2000 is to split RX/TX common path.
Preamps works like a charm , first one is NF <0.3dB and gain >20dB and a 2nd one <0.3dB and gain >20dB put at radio end. I use ATT on the rig to compensate for hight preamp gain.
The amplifier, is a LZ2US with GS23 tube, tuned to be able to run 1.5kW JT65 but most of the times I run it at 900 watts.
SWR measurement with HP8752 on 9/9/2017 1.1016:1 on 432.000 MHz and 1.1193 on 432.00 MHz , dip at 432.453 1.0025:1 (this is really good return loss)
Wideband swr measurement 430 to 439 <1.2 to 1, YU1CF really builds great yagis
Just made a "bad" picture of the swr sweep, need to do this again
Total predicted gain is just over 31 dbi.The simulation is for 4wide, 2 high stack. But the desire to be ble to work tropo made me go 2 wide, 4 high, -3dB bandwidth is 7.2 ° this way
As the radiohorizon is excellent (observed on 6 and 2m), almost 360° negative horizon.
From the past (8x38el I0JXX) I could daily work Italy with 50watts over 750km path over the alps, in the last weeks/ months I worked a large number of stations over 750km away and several over 900km.
The antenna is providing a decent signal, after all its 17.28 wavelength long.
For those looking for the full table VE7BQH G/T chart (432MHz) click here
|Electrical Specifications 70 cm|
|Frequency Range:||432 - 434 MHz|
|Free Space Forward Gain:||22.1 dBi|
|Front to Back Ratio:||37 dB|
|3 dB Horizontal Beamwidth:||15.2°|
|3 dB Vertical Beamwidth:||15.4°|
First of all, noise temperature. G/T 16.18dB with a total predicted gain of 31.03dBi.
I haven't found better results anywhere with current manufacturers
PA5Y (ex G0RUZ) suggested I should add a bandpassfilter right after the preamp, this is the one of the ones I got. Its has about 30dB attenuation on 480MHz which is DTV transmitter
Also got one from PA2DOL, over 70dB @480MHz.
Started with a low noise one <0.3dB NF from vhfdesign.
The pictures kinda shows how it looks while putting the array together