Single Antenna System

This is a Single Antenna 10kHz-30 MHz receiving system - presently a Prototype. A high impedance, high CMRR preamplifier is mounted inside a 3D printed plastic housing near thae middle of a  23' telescoping fiberglass pole and fed with CAT5 cable as shown  below.  This antenna relies on the SWTL model of a dipole and through the use of small .5mm  diameter conductor (not shown)  allows exiting a CAT5 cable (also not shown) along the mast, separated only ~50-100mm from that conductor and finally exiting near the base. This can be done without upsetting antenna balance and symmetry.  Clips are used along the mast to hold the conductor and the CAT5 in proper position.

This system is a larger dipole version of the Field Probe and the original PreampA/2m-dipole projects.  This design is intended to be capable of achieving the ITU "quiet rural" noise floor (noise temperature)  when positioned in a compatible site. 

Like the other broadband rx designs it is a highly symmetrical/differential probe rather than a resonant structure so it can effectively cover from AF into VHF.
The SAPreamp is mounted inside a 3D printed enclosure with antenna wires soldered to pads on the PCB, exiting through the enclosure walls and terminating at the top and near the bottom of the mast. The CAT5 cable exits from the enclosure bottom and is clamped by the enclosure cover which has a silicone gasket. The result is a water resistant housing for the electronics.
There are two versions of the preamp being examinsed,  differing primarily by the CAT5 driver. One uses a LTC6432-15 in a transformerless output configuration while the other uses an ADA4930-1.
As for PreampA, it is connected by a single CAT5/RJ45 connection. and receives 12V and 8V from a redesigned Shack PCB and  delivers balancedRF output over one of the 100 ohm twisted pairs.  A remaining pair is used operate a low-capacitance mechanical relay which can short the dipole terminals to verify CM rejection of the system.

The most promising design version and the Shack Board use an ADA4930 differential amplifier to interface from the input high impedance buffer amplifiers to the CAT5 cable instead of a transformer. This allows  coverage down to ELF,  from AF and well into VHF  while reducing  cost and achieving very much greater CMRR and good IMD performance. The redesigned Shack Board also uses these devices to receive the twisted pairs from the CAT5.
 
The PCB is enclosed in a 3D printed housing and  cover.  Dipole wire connections are made through small holes in the enclosure's wall.  Those holes and a channel in the cover are filled with silicone rubber to help keep the inside dry.  The CAT5 cable is clamped by the cover and  exits from the bottom of the enclosure. The entire assembly is fastened with TyWrap straps to a vertical mast  approximately 24mm in diameter.

In the spectrogram below, note the absence of local QRN signatures and the relatively flat noise floor above mid-HF demonstrating the lack of susceptibility to common mode noise as well as the wide signal dynamic range being tolerated.The periodic interference lines below 5 MHz are actually present within the dipol rather than being coupled into the system by way of common-mode mechanisms as so often the case with ELF-VHF receive systems.
Thus, in this case, "The antenna truly is the antenna".

The trace at the bottom shows the same spectrum with input buffers unbiased  This demonstrates that  feedline and other unwanted ingress  after the preamp  to be greatly smaller than differential signals so do not degrade recovered SNR of received signals.

A second verification method allows shorting the input  at the dipole itself.  This allows the system to be verified for near-field QRN ingress and provides a measurement of total receive system noise temperature. It should be understood that there may still remain mechanismswhich provide coupling to unwanted near-field noise sources when the dipole lies along the gradient of an offending field.


Characteristics - LTC6432 & ADA4930 versions

Blue circles in plot are ITU curve C "quiet rural" output  noise  using a 7m dipole. Green curve is output noise due to preamp.

The Preamp is mounted near the center of the fiberglass pole which can be ground-mounted with a screw mount  for freestanding operation. For permanent use, the pole should  be guyed. I t can also easily be collapsed and moved to a different location.

To achieve the best performance and make full use of the capability of this antenna system's low noise temperature, the candidate area should first be surveyed to find the  lowest noise site. The Field Probe may be a useful tool for doing this.


Material List

What you will need to build this hardware

Item Description

Provider

Source Code

Notes

Approximate Material Cost

(excludes setup fees and shipping)

Assembled SingleAntenna Preamp

Download ADA4930  PCB Kit Files

Download SingleAntenna PCB Source Files

 All of this still prototype !
 in pilot  design phase
 US$xx

3D Preamp Enclosure

 Download SA Enclosure Kit Files

Download SA Enclosure Source Files

  All of this still prototype !
 in pilot  design phase		  

Telescoping Fiberglass Poles

7m Amazon

9.75m Amazon

US$45

US$70

Pole Screw-in Ground Mount

Amazon

US$30



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