Justification for Full Antenna Analyser Over a NanoVNA

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G0KDT, Jul 5, 2021.

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  1. W9IQ

    W9IQ Ham Member QRZ Page

    The FCC implementation does have a pre-screening protocol that may allow you to avoid a more detailed analysis. For many, this will greatly reduce the workload. Unfortunately, I have not seen this in any of the templates offered to date.

    I would also point to the extensive field strength database that was already compiled in the ARRL book "RF Exposure and You". This is an excellent resource for hams that cannot model antennas as most garden variety antennas are included showing the controlled and uncontrolled exposure distances for various power levels. It would be nice to see this incorporated into one of the templates.

    It would also be beneficial to push for the antenna manufacturers to supply the data for their antennas. The development of an industry standard data dictionary for this purpose would be a wise investment.

    - Glenn W9IQ
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    If a "catalogue" of common elementary antenna types with modelled or (preferably) measured EMF data could be compiled, it would simplify things considerably.

    Most antennas in practical use by amateurs could be described as a combination of one or two elementary antennas.

    If the EMF densities were normalised to, say, 10 or 100 W of power at the feed-point on the most unfavourable frequency they could easily be scaled to the actual level used.

  3. W9IQ

    W9IQ Ham Member QRZ Page

    The ARRL book I referenced has a quite extensive catalog developed by using NEC. Half-wave dipoles, G5RV, yagis, quarter-wave verticals, half-wave verticals, ground planes and miscellaneous antennas are included. The dataset is designed to show height/distance where the types of maximum allowable exposure occur for various power levels. Unfortunately, it is not in an ideal form for programmatic use.

    What is needed is a standard electronic template in which to communicate this information so that any software that wishes to make use of the data may and anyone that wishes to create new or updated models may. We can than pressure the vendors to our industry to supply this information for their products - particularly when their product does not fit one of the common templates.

    - Glenn W9IQ
  4. KM1H

    KM1H Ham Member QRZ Page

    How many hams have been injured by their own RF using even 1500W?
    OTOH how many have been damaged with an HT regularly buried in their heads?

    Stop trying to add more nanny state crap. Why dont you ask the ARRL to offer that book free to all new licensees? We as hams are supposed to be self policing so promote the book as an aid.

    NO NO NO Keep the damn government out of this as much as possible instead of feeding them more info to mess things up.

    GOOD! This should be for Information Purposes Only

    I hope all hams that read this nonsense pressure you to go back to helping individuals with technical questions and stay out of things that dont need to be fixed.

    WU9I likes this.
  5. W9IQ

    W9IQ Ham Member QRZ Page


    You can download the ARRL book RF Exposure and You to look at their work toward such a catalog. It is a very good start.

    - Glenn W9IQ
  6. SM0AOM

    SM0AOM Ham Member QRZ Page

    I have downloaded the book, and the summary of antennas listed is indeed a very good start. What is missing is a simple way of integrating the antenna models into other structures or systems.

    A 3D graphic visualisation tool for plotting of near-field EMF data points would enhance the information considerably.
    Something along the lines of the far-field visualisation function in 4NEC2 would come a long way.

  7. W9IQ

    W9IQ Ham Member QRZ Page

    I agree Karl-Arne. With a standard data dictionary, it would be easy to show graphic representations.

    - Glenn W9IQ
  8. G0KDT

    G0KDT Ham Member QRZ Page


    Under revised regs here, ALL bands have to have an analysis done, much the same as those described in the ARRL book, but for any Tx power above 10W.

    The current calculator RSGB have takes account of the antenna gain, coax/feeder losses, tx mode and %use in 6mins. Even so it is imposing exclusion zone safety distances of C. 4.7m on 10MHz band even at low power using 1998 ICNIRP Table 7 factors. These are close to the 2020 factors above 10MHz but nothing sorted below 10MHz...
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    If the calculator prescribes an exclusion zone of 4.7 m even at 10 W, it is interpreting the initial conditions wrong. This radius is the "reactive near field zone" within which ordinary far-field calculations fall apart.

    I do not divulge any "Official Secrets" by sharing measurements results from a small naval vessel that I evaluated last year.
    It contained "several" 100 W tactical HF:s and one GMDSS 150 W ship's radio station, in addition to "several" 100 W VHF/UHF radio stations.


    The systems are interlocked so they cannot transmit all at the same time, and the channel occupancy from each, expressed as equivalent key-down power over 6 minutes is conservatively estimated to be 30 %.

    On the roof of the bridge, all antennas and their matching units are placed, and the space on the roof is entirely within the radius of the reactive near field zone.

    Three measurement points were selected, the first at an observation post aft of the mast, one at the base of the mast, and the last about 3 m forward along the centre-line between the two HF antennas.

    The highest E-fields and H-fields measured were from the GMDSS radio at 2182 kHz, but they were still well within the occupational limits according to the 2020 ICNIRP values.

    However, as the Navy safety protocol also recognises "contact currents" which means that the risk of someone getting startled by touching a metal object near the antenna while transmitting is taken into account. This results in a 2/3 reduction of the permitted fields compared to the newer ICNIRP derived limits.

    In the end, it resulted in a sign being attached that the roof should not be entered while transmitting because of the risk of touching a "live" antenna or downlead.

    Experience has shown that "exclusion zones" that are much larger than those necessary to avoid touching the antennas are very seldom necessary at power levels common in both naval and amateur radio.

    US7IGN likes this.
  10. G0KDT

    G0KDT Ham Member QRZ Page

    Last edited: Jul 28, 2021

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