4 October Shed Workshop

Wellgood loop – a broadband RX only loop

Our recent shed workshop on 4 October was held at Bernard ZL2BD’s QTH at 1 Winsley Tce, Churton Park.

RX Only Magnetic Loops

The workshop summarised further RX Magnetic Loop experiments undertaken by Bernard ZL2XJ and answered the following questions.

Is a broadband RX loop as good as a tuned loop?

No. A tuned loop results in around 6dB better signal/noise ratio and will allow you to hear stations that cannot be heard on a broadband RX magnetic loop antenna. However, the broadband loop has its place in that re-tuning is not required (e.g. in a remote SDR receiver situation). It may also be difficult to tune a single loop across a broad spectrum (e.g. 150kHz to 30MHz).

Do you still get an advantage in using a phasing device to null out noise?

Yes. Phasing two RX antennas will also give you an additional lift in Signal/Noise Ratio.

Would a RX only loop be better than a TX loop for most amateur operators?

A TX loop if designed and built correctly can approach or equal the performance of typical amateur low band antennas (e.g. for 160m and 80m) that will necessarily be sub-optimal in height above ground in urban and sub-urban situations. However, a TX magnetic loop is more demanding to build and an RX loop with a TX/RX switch may be a better solution for most amateur operators.

What do RX loops look like?

The loop above is a broadband loop that will be deployed this summer by RemoteDX in an SDR receiver.

How big does an RX loop need to be to cover100kHz to 30mHz?

Around 600mm to 2 metres in diameter depending on which frequencies you want to cover.

40m TX Magnetic Loop

Bernard also indicated, in following up a comment from Bob ZL2CA in relation to the 40m transmitting magnetic loop, recommends instead of using wire (as demonstrated in the August shed workshop) to connect a fixed capacitor to the plates of the butterfly capacitor it would be better to use copper straps or to add fixed plates to the capacitor. The reason is that a fixed capacitor will carry the majority of the current in a loop (up to 60 amps).

RemoteDX SDR Receiver Project

Bernard outlined in more detail, what was entailed in the RemoteDX Inc SDR receiver project. Documentation will be provided at a later date on the remotedx.nz website. The committee is busy progressing project planning.

Used equipment for sale

Derek ZL2AKS, a long-term member of the club (over 60 years) has asked the club to dispose of quite a collection of used equipment. Bernard ZL2BD is organising the equipment for sale to members, and disposal on TradeMe where there is no interest from members in remaining items. The equipment includes two rarely sighted Yaesu FT One transceivers from the early to mid-1980s. Enquiries to Bernard to view.

Training session on OpenGD77 firmware

Radioddity GD77

Mike ZL1AXG, following the afternoon tea break, provided a training session to attendees in the use of OpenGD77 on Radioddity GD77 and Baofeng 1801/860 handheld transceivers. The meeting concluded around 4.30pm.

Follow on Magnetic Loops Shed Workshop #4

Bernard ZL2BD hosted another shed workshop on Sunday 5 August 2018 from 1pm -3pm at his QTH.  Due to interest in  Small Magnetic Loop antennas, this month’s workshop was a follow on session to assist those committed to construct a loop antenna. Several people purchased Capacitor Kits to make an air spaced butterfly capacitor.  Progress is being made on sourcing LDF4-50 1/2” coax and possibly LDF 5-50 1” coax for the loop material to be made  available to those who want this material.  It’s not too late to order a kit if you haven’t done so. 

Bernard talked about practical matters, such as how to construct the capacitor enclosure and plastic waterpipe housing for the antenna, as well as practical details on putting together the capacitor kit, and selection of motor drivers and gearbox, etc.

Mike ZL1AXG talked to a design that provides for real-time tracking and tuning of a magnetic loop.  A circuit board is available to purchase from North America.    He talked about where to source  components including the processor (Teensy 3.2), a 100 step rotation encoder, 51uH twin coil chokes, the stepper motor driver chips,  and the stepper motor and gearbox.

Bernard provided pre-calculated details for a 2m diameter 40m loop, which most seemed keen to build.   

Shed workshop #3: Magnetic loop antennas

Bernard led off on the third shed workshop for 2018 which was on the topic of “Magnetic loop antennas”.  These antennas are great for getting better signal to noise levels out of typical noisy suburban environments.  They are also compact and can be mounted on a boundary fence or building to blend into an urban environment.  On transmit they are less sensitive to changes in the surrounding environment (e.g. resonance changes observable on wire antennas with wet weather).

Ten members turned out on Sunday 1 July 2018.   A summary of his presentation, theory of magnetic loop antennas and instructions for constructing these antennas can be downloaded here:


Bernard can be seen giving a presentation to kick off:

Several examples of loop antennas were available for inspection including this multiband loop for 15m through 10m:

And a close up of the butterfly tuning capacitor:

The feedpoint and feed system:

And finally, a mag loop controller box that Bernard has constructed (he has several!):

A special price has been worked out for branch members who wish to assemble their own butterfly-style tuning capacitor.  This is required if you wish to make a small magnetic loop for receive and transmit.

Contact Bernard if you would like to order a kit.  A subsequent workshop will focus on assembly of the capacitors, and give further information on other construction details and where to acquire the further parts  required in construction.