EDITORIAL:

• I much enjoy creating these quarterly tomes, but am finding the time taken is a problem. Anyone who can help in some way is welcome to contact me.
• One way in which amateurs can give back a little to the community is to help with WICEN activities. It’s fun, challenging, and character-building. See page 4 for your guide to getting involved in ROSA.
• The April meeting was a great success, with an illuminating talk by Graham Dicker, followed by the official celebration of 25 years of AHARS.
• Jim (VK5JST), ably aided by Barry (VK5ZBQ), has created an excellent 2m beam. See Back Page for details.
• Note that our Mid Year social event will be a luncheon, at our old favourite, the Blackwood RSL.

 John, VK5EMI, Editor and Club President.
 

1.  CLUB PROGRAM    

2.  ODDS AND SODS 
Click HERE to go to Odds and Sods.

 3. TECHNICAL ARTICLE

“An Overview of the Underestimated Magnetic Loop HF Antenna”. 

This article summarises the unique operational characteristics as well as discuss the practical design and key aspects needing to be taken into account for the successful homebrew construction and deployment of the electrically-small magnetic loop antenna when used in both receive and transmit modes.

A small but efficacious HF antenna for restricted space sites is the highly sought after Holy Grail of many an amateur radio enthusiast.  This quest and interest is particularly strong from amateurs having to face the prospect of giving up their much loved hobby as they move from suburban residential lots into smaller restricted space retirement villages and other communities that have strict rules against erecting elevated antenna structures.  These amateurs do have a practical and viable alternative means to actively continue the hobby using a covert in-door or portable outdoor and sympathetically placed small magnetic loop.  The paper shows that such diminutive antennas provide an entirely workable compromise that enable keen amateurs to keep operating their HF station without any need for their previous favourite big towers and beam antennas or unwieldy G5RV’s or their favourite long wire.  The practical difference in station signal strength at worst will be only an S-point or two.  Balanced H-field magnetic loops are also remarkably quiet and provide enhanced SNR on reception.  These were two of the key messages that Professor Mike Underhill also wanted to spread during his recent AHARS lecture that subsequently prompted this follow-up paper. 

Magnetic loops really come into their own on the higher HF bands from say 40m through to 10m; oftentimes with absolutely stunning performance rivalling the best conventional antennas.  Easily field deployable and fixed site loops have been the routine antenna of choice for many years in professional defence, military, diplomatic, and shipboard HF communication links where robust and reliable general coverage radio communication is deemed mandatory.  For 160m top band and even 80m applications, slightly larger diameter up-scaled loops are better suited than the very small ones for the higher bands.

Top band operation at 1.8 MHz is always the hardest challenge for any antenna, small loops (typical dimensions of 0.02λ) included; but their on-air performance is nevertheless authoritative with a commanding signal presence.  There are however no "free lunches" (and few cheap ones) as the free space wavelength has not yet been miniaturized!  Consequently antennas of such diminutive size must always be placed into perspective when compared with the performance attainable from a full-sized λ/2 160m horizontal dipole that most folks haven’t got sufficient real estate block size for and/or mast height in a fraction of wavelength to accommodate so the dipole works properly with a decent radiation efficiency and ability to put its radiated power in a useful direction.  Similarly, reasonably efficient and efficacious Verticals for 160m operation unfortunately exceed the allowed height by a great margin that’s permitted by local council and residential building code regulations. 

As was said in the introduction to Mike’s special guest lecture; magnetic HF loops can be a valid and well founded way to extract a gallon out of a diminutive pint bottle!

Leigh Turner VK5KLT

 NB: For the full text of Leigh’s paper, click HERE 

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Background

Recently, I needed to measure and record the maximum mains voltages at our home to determine the extent that the voltage exceeded the standards. I figured I needed a true RMS meter with AC accuracy of 1% or better. Knowing that none of my meters were good enough, I bought a 3 ¾ digit DMM from Digitech with a stated accuracy of ±1% +5 digits. Unfortunately, I found the meter lacking and therefore consulted some of the AHARS gurus, who recommended Fluke. Subsequently, I purchased a Fluke 289 that is a very accurate true RMS DMM and can log up to 50000 readings.

I logged lots of data from the mains, presented the results to the electricity authority and our mains voltage is now thankfully much lower. With that task completed, I decided to see how well other DMMs performed.  

The Plan

The Fluke 289 is a 50000 count meter with a ¼ VGA screen that has an AC accuracy of ±0.3% + 25 digits from 45 to 65 HZ and a DC accuracy of ±0.025% +25 digits. It is not a calibration standard but may be the next best thing. My idea was to do a consumer report-like comparison of DMMs by measuring AC and DC voltages relative to the Fluke 289.

Measurements were taken during the March AHARS buy and sell, using 12 meters belonging to members, in addition to some of my own. 

The Test Setup

The test setup utilized two regulated DC voltage sources (Heathkit) and a pure sine wave inverter with an autotransformer for a range of AC voltages. A board with multiple binder posts was used to connect the power supplies, the 289 and a test meter for simultaneous measurements. The regulated DC supplies and the battery power inverter assured a stable voltage while the readings were recorded.  A form was prepared to record details about each meter, and the measured readings from the Fluke 289 and the test instrument. The voltages for the comparison were approximately: 

 Each member was given a written record of the measurement results for their meter.

The Meters

Meters from AHARS members included a Fluke 21, DSE Q-1559, Phillips analogue, Fluke 75, Aulec DMM, Brymen BM 727, DSE Q-1419, DT9205A, SOAR ME531, Parameters 7080B, Fluke 8022A, and an unknown DMM.  From my collection, I provided a Heathkit IM-2215, Digitech QM-1536, Digitech QM-1500, Meterman DM78A and Triplett 2030. The age of the tested meters varied from less than 1 year to over 25 years. All were DMMs except the Philips. The Meterman and Triplett are both pocket-sized meters. The QM-1500 is a very basic 3.5 digit DMM costing under $10. The QM-1536 is a 3 ¾ digit true RMS DMM with a specified accuracy of ±0.8%+1 digit and ±1.0% +5 digits for DC and AC respectively. 

RESULTS

All data was entered into an Excel spreadsheet to calculate the percentage difference between the readings of the Fluke 289 and the test meter, and the average of the three AC and DC readings of each. The results were ranked according to the average of the AC and DC measurements as shown in the following table. 

 DISCUSSION

The DC readings of 12 of the DMMs were within ½ % of the readings of the Fluke 289 and within 1 % on AC. I was not able to get specifications for all of the meters and so cannot comment on how each meter performed relative to its specification. Overall, with the exception of the Soar ME531, all of the DMMs appear to be much more accurate than my initial experience with the Digitech QM-1536 would have suggested. The results for the analogue meter are consistent with that technology and clearly indicate the value of DMMs.
 

Robin, VK5ATT. June 2008.

Many thanks to Robin (and XYL Carol, VK5KEY) for their work on this project.
Footnote: Robin hails originally from New Mexico, hence the Wild West connotation! (Ed).

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 5.  BACK   PAGE 

== GENERAL INFORMATION ==

CLUB PROJECTS:
Plenty happening here!
For 2008: SWR Bridge, workshops, and maybe a small loop antenna.
Club Yagi  -  now available. Member’s price - $20. Please pay deposit of $5 to Jim Tregellas ASAP. 

WEBSITE:
Newsletter On-Line:  Log into http://www.qsl.net/vk5bar/      and navigate to Newsletters.

   The on-line Newsletter is much more comprehensive than the hard copy version.
Note also our Resources pages, History, and Club Program, and new Software Downloads sections. 

VK5RAD:
The Repeater Controller is Barry Williams. All enquiries, including requests for access, etc, are to be made through him. Phone 8339 5683 or email [email protected]

Club weekly Net on VK5RAD.
Listen in or join in on Monday nights, from 8 pm to about 9:30 pm local. Receive frequency is 147.00 MHz, with -600 KHz offset. Master of Ceremonies is Jim, VK5JST, or Dean, VK5LB.
All licensed amateurs are welcome. 

 CLUB  MEETINGS:
Third Thursday of the month, starting at 7:30 pm.
Venue: Belair Community Centre, corner of Sheoak Road and Belair Road, Belair.

ARTICLES FOR THE CLUB NEWSLETTER: 
Projects, anecdotes, experiences, ideas, advice, etc, all make interesting and useful reading, and will be much appreciated.  Please forward to the Editor, John Elliott, VK5EMI, phone 8278 1269, or by email (best) to [email protected]

NEXT NEWSLETTER: September.
Article from Ron Lloyd (house fires), our Finnish sister club, and more on Small Loops.           

WICEN :
 Secretary, John Dawes. Email  [email protected]   Phone 8388 2297.
President, Ian Clayton. Email   [email protected]    Phone 8524 5029.

 W.I.A. ADVISORY COMMITTEE:
 Contact person: David Box (VK5OV).
Committee: Peter Reichelt VK5APR, Paul Hoffman VK5PH, and Graham Holman VK5GH.