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.   

Unlike the Version 1 of this antenna which had used substitute transistors and other minor changes in component values, this version of the PA0RDT active receiving antenna has been constructed verbatim as described by PA0RDT.


Fig 1  The PA0RDT compact active wide-band receiving antenna unit schematic. 


C1, 2, 3 & 4 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  2.2k, 0.25W   1
R6 RESISTOR - CARBON   10k, 0.25W 1
R7 RESISTOR - CARBON  47R, 0.25W 1
Q2 TRANSISTOR - 2N5109  1

Fig 2  List of components.




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 spade crimp connectors to 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. Considerably more effort has been put into the weather proof housing with the view that the active antenna circuit board can be easily replaced with upgraded versions with out the need to replace the complete housing. The weather proof housing also includes an LED light to confirm the unit is powered up.


Fig 4  The active antenna mounting plate


A   3mm Diameter fixing holes
B   3mm Diameter hole for air pressure equalisation. Self tapping screw is installed after assembly.
C   6mm Diameter hole to fit LED panel holder.
D  15mm Diameter hole to attach 'N' type connector




Photo 2 The active antenna mounting plate with the 'N' type connector and indicator LED attached.




Photo 3 The active antenna bottom weather cap with the N type connector attached. The cap, plate and around the 'N' connectors are sealed with silicon to achieve complete air tightness.




Photo 4 The active antenna circuit board attracted via spade connectors and 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 assembly within the accessible weather proof housing. A small amount of grease was lightly coated the cover joining sleave to achieve complete air tightness.



Photo 7 The active antenna completed assembly.





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 5 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 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.





First Trial:  23 August 2017


Active Antenna Version 1 and Active Antenna Version 2 comparative results with a variety of local relatively low frequency sources. 


The two Active Antennas in this comparison have demonstrated consistently very good results with only a very marginal improvement in the Active Antenna Version 2


STN ID Frequency kHz PA0RDT Active Antenna  V1 Signal PA0RDT Active Antenna V2 Signal Comments
JT 281 S+10 S+15 NDB 50Watts
PEA 340 S+60 S+60 NDB 2kW
PH 372 S+50 S+55 NDB
6DL 531 S9 S10 BC station, Dalwallinu WA
6WA 558 S9 S9 BC station, Wagin WA
6NM 1214 S+50 S+50 Local BC, Northam 5km away.



The below graph using WSPR data to compare two versions of the PA0RDT compact active antennas. Antenna#1 was the original designed slightly modified to take advantage of more easily available transistors. Antenna#2 is the PA0RDT compact active antennas constructed with originally specified transistors.


The conclusion is that the two active antennas performance is very similar despite the modified design of the version#1 antenna.

WSPR data has been graphed using Excel. Horizontal axis = UTC Time, Vertical axis = dB below the noise floor.

Antenna#1: Active Antenna V-1 (ORANGE)   21/08/2017 -  22/08/017 UTC

Antenna#2: Active Antenna V-2 (BLUE)        23/08/2017 -  24/08/017 UTC


Distance: 2097km

Grid location: PF94lw

dBm: 33 (2W)

WSPR 630m band activity data recorded for a 4 x 24 hour periods 21~25/08/2017:  WSPR_630m_20170824

Compare the V#1 and V#2 compact active antenna.



WSPR Map for 630m band on 24 August  2017. Active Antenna Version 2 activity.






Frequency rage:              10kHz to 10MHz


Power Consumption:        56mA at 12V 


Output impedance:          50 ohms approximately





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





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





Page last revised 18 October 2017  


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