Mini Whip Mod For VLF

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VE3EAR
Posts: 44
Joined: Sat Oct 05, 2019 10:13 pm

Mini Whip Mod For VLF

Post by VE3EAR » Fri Oct 30, 2020 4:08 pm

I've done a mod to the popular PA0RDT Mini Whip antenna, which makes it more effective for receiving signals in the VLF range, 3 kHz. to 30 kHz. Referring to the schematic below, the mod replaces just three components in the Bias-T unit, and one in the antenna unit. In the Bias-T, the toroidal RF isolation trans-former is removed and replaced with an AF transformer having a 1:10 step up, the 470 uH. RF choke with
a 10 mH. RF choke, and the 470 nF. coupling capacitor with a 1 uF. capacitor. In the antenna unit, one component is changed, the 470 uH. RF choke is replaced with a 10 mH. choke.

73, Bruce, VE3EAR
Attachments
PA0RDT Bias-T.png
PA0RDT Bias-T.png (65.81 KiB) Viewed 856 times

snn47
Posts: 223
Joined: Tue Dec 27, 2016 11:00 pm

Re: Mini Whip Mod For VLF

Post by snn47 » Wed Nov 04, 2020 7:54 pm

Hello Bruce,

I am wondering about the benefit of using an isolated BNC connector, because Coax cable and connector are asymetrical
systems. Even if the output connector to the receiver is not grounded, the outer shield of the antenna input of any receiver would be grounded, except for battery powered receiver, .

vy 73

_.. .._. ..... .__. _.__

VE3EAR
Posts: 44
Joined: Sat Oct 05, 2019 10:13 pm

Re: Mini Whip Mod For VLF

Post by VE3EAR » Thu Nov 05, 2020 3:14 pm

I think the primary intention of the isolated Rx connector on the Bias-T is to avoid ground loops, which can be very troublesome, hum wise. All of my Bias-T boxes are built into plastic enclosures, so there is "automatic" isolation. If a metal enclosure is used, then the jack for the receiver would need plastic shoulder washers to isolate it from chassis ground.

73, Bruce, VE3EAR

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