VE7BQH's Antenna Tables are published by Lionel Edwards VE7BQH and widely circulated for more than the past two decades in a Microsoft Excel spreadsheet format (.xls file). The idea was to promote G/T (strictly G/Ta) as a definitive reference of the overall merit of a yagi antenna, the more positive figure the better a yagi design would be regarded!
EME and DX operators face a bewildering choice when it comes to selecting a suitable antenna for their own particular situation. VE7BQH's Antenna Tables attempts to offer a solution as point of reference, and so to help in making a wise decision.
However, consider that Lionel's tables are produced by computer simulations using a number of antenna modelling programs and so the results may not necessarily be confirmed in real world antenna testing?
During the eighties Radio Amateurs in Sweden at Aneboda would often hold antenna gain competitions and publish their results which were very enlightening because they were real world tests!
Unfortunately the cost of hiring an outdoor antenna test range or anechoic chamber that offers UKAS Accredited Antenna Calibration standards is prohibitive for most Radio Amateurs!
A simplified example of the workings of the table (similar style) are seen below in which WA9XX has lowest temperature and best G/Ta of those listed.
Some yagi designs are better in stacking configurations than others, a clever designer can exploit this fact, particularly when it comes to ranking in the tables!
Formula used in the example table below: G/Ta=Ga-10*log(Ta)
|~ DL6WU OR * Designers stacking||T_sky = 290K whilst T_earth = 5400K (Residential Environment)|
|1 YAGI||< 4 YAGIS >|
|Design ID||λ||Boom (m)||BW Az°||BW El°||Gain (dBi)||F/B (dB)||Ga (dBi)||Ta (K)||G/Ta (dB)||DE||Q-factor|
|~GTV28W||1.78||3.696||40||48||13.36||27.7||19.25||504.0||-7.77||V Split Dipole||17.75|
It is important to consider that the station receiver also has a temperature associated with it, and in its current format the VE7BQH Antenna Tables G/Ta expression does not include the receiver system. Ignoring the total noise power of the system can give rise to the situation where the table overestimates G/Ta. Unfortunately this error can vary in magnitude between different antenna arrangements and render comparisons unreliable.
The original G/Ta proposer for Amateur Radio VHF/UHF use was Rainer DJ9BV who suggested in his work an antenna elevation angle of 30° (the red line) for universal comparison purposes.
Rainer DJ9BV said in DUBUS 4/87: "One should not overemphasize the importance of the calculated G/Ta-ratio. In practical systems one has to add the noise temperature of the receiving system including all baluns and cables (50 - 70 K) to get the overall system temperature."
In the early days Lionel Edwards used Yagi Analysis v3.54 (DOS program) by SM2IEV to calculate yagi antenna G/Ta. However, Pop YU7EF worked with and adopted TANT (also a DOS program) by Sinisa YT1NT/VE3EA which he describes as more precise, particularly when calculating values for a 4 yagi group.
Meanwhile Lionel VE7BQH also moved to TANT and used this exclusively for several years to populate his tables until quite recently that is. However, in the most recent presentations AGTC_lite (runs directly in Windows) by F5FOD/DG7YBN has also been brought into use.
The latest tables feature Interactive Mode in the 50, 144 and 432 sections established by Vladimir UR5EAZ. Interactive mode allows the user of the VE7BQH Antenna Tables to enter T_sky and T_earth values with three suggested local environments: Rural, Residential and City.
In recent times I have observed for myself and reported to Hartmut DG7YBN that at an antenna elevation angle of around 30° both in TANT and AGTC_lite can produce different results (which can be significant) with certain designs and/or stacking distances? Working examples (144MHz and 432MHz) of this anomaly and also optimal stacking distance improvements can be seen below (click on images for full size view)...
|4 x WA26075 in TANT (DL6WU stacking)||4 x WA26075 in TANT (Optimal stacking)||4 x WA26075 in AGTC (Optimal stacking)|
|Anomaly @ 144MHz - Here TANT and AGTC_lite don't agree, which is right?|
|4 x WS718562 in TANT (DL6WU stacking)||4 x WS718562 in TANT (Optimal stacking)||4 x WS718562 in AGTC (Optimal stacking)|
|Anomaly @ 432MHz - Again TANT and AGTC_lite don't agree, which is right?|
The question: Using the VE7BQH Antenna Tables as it currently stands which of these two 432MHz yagis would you choose as the best antenna?
We must first consider that the InnoV 16 LFA has a length of 5.19λ whilst the *M2 432-9WLA has a length of 9.19λ
Surely the much longer antenna must deliver the best G/Ta? Not so in the current tables!
Has the designer become so good he can defy the laws of physics, or is there something wrong with our tool for comparison?
In recent years the VE7BQH Antenna Tables have changed, including interactive features simulating local environments.
So let's put the clock back prior to the changes, here are the original T_earth and T_sky values...
|Corrected T_sky and T_earth numbers mostly in compliance with VK3UM's Calc|
|DUBUS - Notes on VHF/UHF Antenna G/T – (TANT Appendix) Hartmut Klüver, DG7YBN II/22|
|* used originally in VE7BQH Antenna Tables|
Now, I try a test with VE7BQH Antenna Tables. I revert to the original T_sky = 20K and T_earth = 350K. The *M2 432-9WLA becomes the best antenna!...
Next, VE7BQH Antenna Tables set to the new residential values T_sky = 27K and T_earth = 1800.00K. Suddenly InnoV 16 LFA becomes the best antenna?...
There is similar nonsense when comparing InnoV 16 LFA with *M2 432-13WLA... Several other examples can be found across the tables, anomalies like these were not present before the recent changes!
Receiver Noise Temperature or Receiver Noise Figure should be included into the tables, it is noise due to losses of transmission lines, relay, divider, LNA, etc, and with reference to the antenna terminals.
TANT and AGTC_lite do not agree at 30° elevation in several cases tested. Choose one or the other but not both for use in the tables.
It can be argued that antenna manufacturers insisting on their own optimal stacking distances being used in the table can gain an unfair advantage over those designers bound to use less than optimal DL6WU stacking distances.
Also VSWR Bandwidth shown in the tables does not always represent an accurate assessment of antenna Q and the likelyhood to perform as predicted in software model. It would be better perhaps to adopt an average Q-factor value (144-146MHz).
For the table to maintain its integrity and a level playing field all entrants mut be treated exactly the same regardless of who they are!
1. Download link... for the latest official VE7BQH Antenna Tables.gnumeric (Save Link As)
Gnumeric Spreadsheet is an open-source spreadsheet program. It is available cross-platform, for Windows, Linux, and UNIX operating systems. The .gnumeric file format is compressed and allows storage on the server in a much smaller file size than even .zip format!
Windows users can easily use Gnumeric Portable without even fully installing.
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