Antennas

Last night while operating WSPR @ 475KHz I suddenly hear a hard and broadband noise on one of my receivers. Then I look at the swr meter monitoring the wspr transmitter and discover that it was all over the place. Reason, insulation failure at the base of antenna resulting in arcing.

Here is an active antenna for higher LF and MF frequency range using an U310 N-Channel JFET as amplifier.
Antenna are based on a la8ak (sk) design. It has a decent performance given its small size.
However, on lower LF and VLF range it performs poorly.

A little tip for anyone interesting using this design or similar designs. Do not power it by a noisy switching power supply. Switching noise will go straight into the receiver.

 

Bias tee PCB

Bias tee PCB

 

Left: Remote amp. with telescopic car whip Right: Bias tee

Left: Remote amp. with telescopic car whip Right: Bias tee

 

Remote amp. and antenna

Remote amp. and antenna

 

 

Bias tee mounted in a nice box

Bias tee mounted in a nice box

 

Blue LED in remote amp. shows that power is present. Green LED on bias tee indicates normal current load.

Blue LED in remote amp. shows that power is present. Green LED on bias tee indicates normal current load.

 

Remote antenna amplifier schematic

Remote antenna amplifier schematic

 

Bias tee schematic

Bias tee schematic

 

Here’s some pictures of an antenna I build for a local repeater site a few years back. Its a relative wide band design where VSWR is under 1.5:1 over 30+ MHz and the gain is up to around 7dBi at max. Antenna has worked flawlessly for several years high up on a mountain top in icy and windy conditions.
Antenna are made of TIG welded pipes of square stainless steel.
I have not designed this antenna by my self, its a replica of a commercial product, but with a few modifications when it comes to material used and physical dimension of the antenna and phasing network to lower the frequency a bit.

I’m trowing in a couple of pictures of the FOX DELTA ST2 Antenna Tracking Interface that I have build.
Unit works great, but on the bench for the moment. Antennas ain’t finished yet. 🙁
I’m in the proccess of building a 144Mhz 4×7-Element-Yagi array for EME. ETA not known.