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Active Antenna Amplifier (model AAA-1C)

106.00 € excl. VAT

The Kit

The amplifier kit consists of the following parts:

  • Amplifier board (mounted and tested)
  • Control board (mounted and tested)
  • 6-pin Female connector for connection of remote control switches
  • Plastic ABS IP55 protected box
  • 3 mounting screws diam. 3.5 mm
  • Load resistor 100 ohms / 2W
  • Short service cable crimped with two RJ45 connectors
  • Spare RJ45 shielded plug connector
  • Spare RJ45 unshielded plug connector

In stock

Product Description

Minimal additional efforts are needed to complete this active antenna project. For more details look at the Active Antenna Amplifier Technical Section.
Please be aware of Active Loop Amplifier knockoffs claiming LZ1AQ design. Read more

This amplifier is intended for construction of small wideband active receiving antennas from LF to upper HF bands. The mechanical construction of the particular loop/dipole antenna must be performed by the user. This amplifier can use two separate small magnetic loops. These two loops are used also as two arms of a small electrical dipole. Thus 3 different antennas can be used. The amplifier has four remotely switched modes: Loop A, Loop B, crossed parallel loops A&B and dipole. Each mode can be switched immediately and this enables us to use the best antenna for the moment.

This kit consists of two SMD mounted PC boards – an amplifier board and a control board. The amplifier has low noise, high dynamic range and wideband properties. It has separate current and voltage amplifiers for the different antennas. It is a balanced design and uses monolithic pairs. The balanced power amplifier uses medium power BJT with very low IMD and can give approximately 75 mW of output power on a 50 ohms load in order to minimize the non-linear distortions. The small antenna frequency response in all modes is flat in a wide frequency range. Usable frequencies are from 20 KHz up to 55 MHz. The antenna gain in the current and voltage mode is set to be approximately the same to avoid striking differences in the gain when the antennas are switched. Every kit set has been tested.


  • 4 remotely switched modes (Loop A, Loop B, crossed parallel loops A&B and dipole)
  • Each mode can be switched immediately
  • Good sensitivity and a flat frequency response
  • High dynamic range
  • Protected input from strong signals
  • High immunity to local noise with balanced amplifiers and balanced feed line
  • Balun transformer coupling for common mode noise reduction
  • Extensive documentation manuals with detailed description how to build your own small antennas

Active antenna kit parts

Control board and cable

The amplifier is connected to the receiver via a control box and an FTP (shielded CAT5E) cable with RJ45 connectors which ensure good balance to avoid common mode noise signals. The cable length can be above 100m. There is a possibility to limit the maximal voltage applied to the receiver input which is needed for some direct sampling SDR. The amplifier has jumpers for setting it to the particular environment. It is of SMD design and is mounted and tested.


The amplifier input is protected from high electromagnetic field intensities – it can be used with magnetic and electric small antenna in the immediate vicinity (20 – 30 m) of transmitting HF antennas even if the power is 1 – 2 KW. The amplifier has input filters to reject the frequencies above 55 MHz to avoid the influence of strong stations in the broadcast FM band (80-108MHz).

Power & Other

The amplifier is powered by a nominal 13.8 V (12.3 – 16 V margins) DC power supply @ 145 mA nominal current. The standard existing power supplies (PS) for the transceivers or receivers can be used. The amplifier is mounted in an ABS plastic (IP55 protected) box. It can be used with any receiver which has sufficient sensitivity and 50 ohms input impedance. This amplifier can be used as a building block for more sophisticated antennas such as phased arrays etc.

Tested parameters in production stage

  • DC operating points
  • Frequency response at 7 points. 0.1, 0.3, 1, 10 , 30, 50 , 100 MHz
  • Output noise power
  • 1 dB output compression point at 10MHz
  • Second harmonic OIP2 at 3.680/7.360 MHz

This set of measurements assures that the amplifier has normal gain, frequency response, noise floor and dynamic range.

Block diagram. Two small loops act also as arms of a small vertical dipole

What the user should prepare

  • Loop antenna
  • FTP cable with crimped RJ45 plugs
  • External DC power supply
  • 3 switches for manual mode control or simple interface for PC control



Output impedance 50 Ohms, BNC connector on control board
Power supply(10) External, 13.8 V, =< 145 mA
Polarity protection & recoverable fuse are on the control board
Maximal output voltage 6V p-p or 4.2 V p-p
Physical size 76 x 76 mm Amplifier board; 32mm x76mm Control board

Current amplifier with 1m diam. loop

Loop diam. 1 m, 1 turn, conductor with 25 mm diameter, 2.4 uH
Antenna Factor Ka 2 dB meters-1 @ 10 MHz
(1 uV/m input signal will give 0.8 uV output voltage)
Ka Frequency response 0.35 – 51 MHz; (within 3dB )
Usable frequency range 0.02 – 55 MHz
MDS @ 10MHz 0.5 uV/m, Noise bandwidth =1KHz
Output noise power at 10MHz -116 dBm
1 dB output compression point +19dBm (5.6 V p-p), equal to +125 dB(uV/m) at input
Second harmonic OIP2 +88dBm to +94dBm
Third harmonic OIP3 +41dBm to +42dBm

Voltage amplifier with dipole arms of 2 x 1 m

Antenna Factor Ka 2 dB meters-1 @ 10 MHz
(1 uV/m input signal will give 0.8 uV output voltage)
Ka Frequency response 0.35 – 55 MHz; (within 3dB)
Usable frequency range 0.02 – 55 MHz
MDS @ 10MHz 0.25 uV/m, Noise bandwidth =1KHz
Output noise power at 10MHz -118 dBm
1 dB output compression point +19dBm (5.6 V p-p) equal to +125 dB(uV/m) at input
Second harmonic OIP2 +94dBm to +103dBm
Third harmonic OIP3 +40dBm to +42dBm


Antenna Factor Ka

Spice simulated antenna factor Ka for loop and dipole. The circular loop is with single turn 1m diam. made with 25mm diam. alum. tube with 2.4 uH inductance. The dipole has two 1 m long arms – effective height is 1 m. .

Active Antenna MDS at 1 KHz BW – Spice Models

Spice simulated input minimal discernible signal (MDS) in [uV/m] for different antennas. The noise bandwidth is 1KHz. First two loops are 1m diam. single turn (thin and fat conductor). 2-crossed loops are loops with 1m diam. circular shape (1.56 m2 total area), each with fat conductor. The dipole is with 2 arms of 1 m. See Antenna section for details. A small loop and dipole models are used which is acceptable up to 10 MHz. For higher frequencies the MDS values might be not reliable.

Measured Output Noise Levels AAA-1C

Output noise levels of the active antenna amplifier measured at 1 KHz bandwidth without antenna. The loop amplifier is measured with 2.4 uH equivalent loop inductance connected to the input. The dipole amplifier is measured with 10 pF equivalent dipole capacitance. The equivalent input noise level of a direct sampling SD receiver is given for comparison. Usually the commercial RX and TRX have similar or lower noise floor. This chart is useful to obtain information for the needed noise floor of the receiver which will be used with this active antenna. A practical rule is that the receiver noise floor should be at least 6 dB bellow the output noise level of the antenna amplifier.

Terms of Sale


The total current price of the kit including any other material which can be downloaded from this site is shown in shopping cart. Each kit content is clearly described in the product description section of this site

Prices are subject to change without notice.

Remark 1: The total price of the Product is formed from the following components: 50% part for the hardware (which is physically send and this price is declared in the parcel) and 50% part for the documentation (including software if such exists) which can be downloaded from this site. The hardware, documentation and software are inseparable parts.

Remark 2: From Oct.22 2021 will begin to charge VAT to EU customers (physical persons). This will be the VAT rate of your country and will be submitted to your country by our tax authorities to your tax authorities. The VAT rate will be set automatically from our shopping cart for the country given in delivery address. We are VAT/OSS registered.

Domestic taxes for the rest of the world (if they exist) are the entire responsibility of the customer. We are not a company with paid personnel and for the moment there is no VAT registration.

Order and Payment

The orders with payment (kit total price plus delivery expenses, no additional Pay Pal fees) should be performed via Pay Pal system through “Add to Cart” button. There is no price discount when buying multiple kits and they will be sent as separate packages each with the corresponding shipping prices. The reason is that we are sending kits as a “small parcel”. When the weight and price increase above certain limits the “normal parcel” category must be used which is more expensive since the minimal price is for 2 kg weight. There are also customs alleviations (for non EU countries) when the price of the parcel is below certain limits. If you want to use other ways of delivery or to send all items into a single parcel you should send an email to and wait for the confirmation from us. Usually in this case we will send a Pay Pal invoice for the due payment. If you want to use other ways of payment (e.g. bank transfer) we will send you a proforma invoice.

For countries in EU we accept bank transfer payments via SEPA. Please send an order to and you will receive a proforma-invoice.

For corporate clients in EU: Send a request to including shipping address and VAT registration number. We will return a proforma invoice for SEPA bank payment.


The price of shipping of a single kit as a “small parcel” (airmail, with priority, not insured, registered mail with tracking) is shown in shopping cart. This price is “flat rate” and is the same all over the world. For multiple kits orders we will send each kit as a separate parcel.

This is the standard international post-office service. The parcel usually needs between 5 and 15 days to arrive for Europe and slightly more for the rest of the world. After the dispatch we will send the parcel tracking number by an email to email address obtained from the PayPal order. Some customers do not use this address for correspondence and rarely read it. Please check your email content after the purchase.

We can track only that the parcel has left Bulgaria. Check at and enter at Post/EMS field your tracking number. The message “Insert item into bag (Otb) ” means that the parcel is ready to be loaded on the airplane to certain destination. This is the last message (with date and time) from this web site. Our commitment for the shipping ends at this point.

In some countries the incoming parcel can also be tracked on the website of the National Postal organization so the next step is to check at your national post site for the arrival. Probably you can do that also on the site of . Choose the destination country from the drop down country list.

All expenses due to any problem with the post office service after the parcel has left Bulgaria are to the customer. In the case of lost parcel we will provide you with proof that the parcel was delivered and with the tracking number that it has left the country – otherwise we will send another kit. There will be no official commitment by us for lost, damaged or delayed parcels after the parcel has left Bulgaria but in any case we will try to solve such problems in informal ham spirit style. If someone wishes to use courier service that can be negotiated with emails to Currently the orders are dispatched from our office within 7 working days.


The return of a functional kit is not possible. In the case of malfunction due to a production defect the customer should inform us with an email to with a brief description of the defect. If the case is a production defect the kit can be returned at the address specified in our confirmation email. The cost of the return shipping of the repaired kit will be at our expenses. The above will be possible within 90 days after the day of the payment. We believe that 3 months is a sufficient period for the most of the production defects (if there are any) to manifest themselves. We are not specifying the usual commercial guarantee period since we are not a company with paid personnel. The kits are low priced and it is difficult for us to give to the customers the usual commercial guarantees. This limited guarantee does not apply to the kits which are visually damaged or repaired by the customer. We will do our best to solve all arising problems in informal ham spirit style.


The Active Antenna Amplifier and Variable Delay Line kits (referred to as the Products) are not intended for professional use or other responsible applications. They are hobby projects and are intended to be used by the amateur radio society. The specifications data are based only on measurements in the designer’s laboratory and model calculations. They are made on random production samples. The designers and producers of this Product will make all the necessary efforts to ensure that the production fulfills the above mentioned specifications. We do not guarantee that the documentation of these Products is free from unintentional errors. Any damages or losses direct or indirect caused to any third party by using the Products and their documentation are entirely the user’s responsibility. The antenna, the cable and the power supply built or supplied by the user should fulfill the requirements of the respective safety standards and regulations.


These Products and associated documents and programs are copyright © of SignaCor EOOD and Chavdar Levkov (LZ1AQ amateur callsign). Commercial use is forbidden without written permission from the copyright holders. Any citation of the text, schematics, photographs and other related materials from these documents can be freely distributed for non-commercial purposes with requirement of written citation of the sources which are or