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ACTIVE ANTENNA - PA0RDT - Version 1

PA0RDT compact active wide-band receiving antenna for lower frequency bands from 10 kHz to approximately 10MHz.


The antenna is often described as an E-field Probe Antenna as the high impedance front end amplifier measures the potential difference between the antenna plate (E antenna) and the grounded mast or coax screen. For a more comprehensive explanation see the Fundamentals of the MiniWhip antenna - Pieter-Tjerk de Boer, PA3FWM at http://www.pa3fwm.nl/technotes/tn07.html

The active antenna designed by PA0RDT may offer a practical technique for exploring radio frequencies below 500kHz and is reported to offer good performance in the lower frequency bands from 10kHz to at least 10MHz. Slightly modified from the original design to take advantage of available components this active antenna is intended to trial this type of receiving system.  

The MPF102 has similar characteristics to the J310 transistor with the advantage of the later being low noise however with general higher noise levels of the lower frequencies this should not be a problem. 

Fig 1  The compact active wide-band receiving antenna unit schematic. 

 

ID DESCRIPTION QTY
C1, 2, 3 & 5 CAPACITOR, CERAMIC -  470n, 50V 4
L1 INDUCTOR, 470uH 1
R1, 2 & 3 RESISTOR - CARBON   1M, 0.25W 3
R4 RESISTOR - CARBON 680R, 0.25W 1
R5 RESISTOR - CARBON  10k, 0.25W   1
R6 RESISTOR - CARBON   3k3, 0.25W 1
R7 RESISTOR - CARBON  47R, 0.25W 1
R8 RESISTOR - CARBON 330R, 0.25W 1
Q2 TRANSISTOR - 2N3904 - NPN 1
Q1 TRANSISTOR - MPF102 - J-FET 1

Fig 2  List of components.

 

Construction

 

The circuit is assembled on single sided PCB with the copper clad board separated down the middle. The left side forms the antenna and the right side is ground and has a section of Vero-board glued to the back for component connections.

 

The final board is mounted in a section of PVC water pipe for weather protection. The board is connected via a very short section of coax to a male N type connector that is fixed to the base of the water pipe bottom end cap. Constructing antennas around the male N type connector allows for mounting on the standard station Generic Antenna Mount.

 

The active antenna is powered with approximately 12 ~ 15V via the connecting coax cable with the masthead coaxial cable power feed unit.

 

Fig 3  The compact active wide-band receiving antenna board dimensions viewed from the back.

 

 

Photo 1 The compact active wide-band receiving antenna circuit board assembled viewed from the front.

  

Details of the assembly of the board and male N type connector with the water pipe bottom end cap is shown below including the aluminium mounting disc for the N type connector attachment.

 

Photo 2 The active antenna weather cover mounting plate with the N type connector attached. Top view. Photo 3 The active antenna weather cover with the N type connector attached. Bottom view.

 

 

Photo 4 The active antenna circuit board attracted via sort length of coax to the N type connector within the protective weather cover bottom cap.

 

 

Photo 5 The active antenna circuit board attracted via sort length of coax to the N type connector within the protective weather cover bottom cap. Bottom view.

 

 

Photo 6 The active antenna completed assembly.

 

 

Installation:

 

The original mini-whip article by Roelof Bakker, PA0RDT states that the active antenna should be installed on an insulated mast, however there is evidence that the active antenna in fact uses the outside of the coax shield as a ground path there by making the coax shield an integral part of the antenna. With the coax cable entering the radio room it is highly likely that the system will pick up all sorts of noise from equipment such as computers etcetera; therefore in this installation it is intended that the mast will be conductive and electrically connected to ground to encourage a cleaner system. Despite attempts at choking the coax cable with a balun, it yelled no detectable improvement as the antenna is of a very high impedance including the way that the coax shield acts as part of the antenna and there appears no way to isolate the coax shield from being part of the antenna by way of choking.

 

 Fig 4 Active antenna installation details

 

Key installation hardware other than the active antenna are shown below with links to detail pages.

           

Generic Antenna Mount.    Standard antenna mounting for small antennas
Masthead Coax Power Feed Unit. Unit for injecting a 12V supply via the connecting coax cable for masthead equipment.

 

Photo 7 The active antenna installed on stubby mast with out the R.F. choke at this stage. Photo 8 The active antenna installed generic antenna mount details.

 

Photo 9 The masthead coaxial cable power feed unit install in the shack with the computer soundcard interface unit and the TS930 transceiver.

 

 

Performance:

 

First Trial 18/02/2016

 

While this is a bit of a rough comparison it is very encouraging.

 

Comparison set up:

 

Antenna#1: 10m Band Sloper connected directly to the radio with no ATU.

PA0RDT Active Antenna: Was located at the top of an iconic Australian metal cloths line.

Radio: TS930S. The broadcast band (500 ~ 1600kHz) on this radio is deliberately less sensitive at 32uV  

 

Active Antenna in this comparison has demonstrated consistently very good results when compared to the Antenna#1 results. While this appears to be good a results for the active antenna the setup of both antennas is less than optimal, however it is encouraging.

 

STN ID Frequency kHz Antenna#1 Signal PA0RDT Active Antenna Signal Comments
CLK 200 S+20 S+40 NDB Less than 50Watts
JT 281 Nil. noise floor S+10 S+10 Above noise floor. NDB 50Watts
PEA 340 S+10 S+45 NDB 2kW
PH 372 S9 S+45 NDB
6DL 531 S1 S7 BC station, Dalwallinu WA
6WA 558 S2 S7 BC station, Wagin WA
6NM 1214 S+35 S+40 Local BC, Northam 5km away.

 

 

 

Specifications:

 

Frequency rage:              10kHz to 10MHz

 

Power Consumption:        18mA at 12V 

 

Output impedance:          50 ohms approximately

 

 

References:

 

For powering the compact active wide-band receiving antenna via the coax cable. See Masthead coax power feed unit.

 

Details of the generic antenna mount. See: Generic Antenna Mount.

 

Australian aviation non-directional beacon Frequencies. See: NDB Freq

 

WSPR 160m band activity data recorded for a 4 x 24 hour periods 01-04/05/2017:  WSPR_160m 20170504A

Compare the compact active antenna with the main station antenna

 

 

 

Reference articles:

 

Roelof Bakker, PA0RDT mini-whip article. See: http://dl1dbc.net/SAQ/Mwhip/pa0rdt-Mini-Whip.pdf

 

Roelof Bakker, PA0RDT mini-whip article 2006. See: http://www.arimodena.it/tecnica/progetti/mini-whip/doc/article-pa0rdt-mini-whip.pdf

 

Fundamentals of the MiniWhip antenna - Pieter-Tjerk de Boer, PA3FWM. See: http://www.pa3fwm.nl/technotes/tn07.html

 

Grounding of MiniWhip and other active whip antennas - Pieter-Tjerk de Boer, PA3FWM. See: http://www.pa3fwm.nl/technotes/tn09d.html

 

 

 

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Page last revised 01 September 2017  
 

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