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Author Topic: new "standard" for measuring RF power  (Read 29863 times)
KU7I
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Posts: 122




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« on: September 14, 2013, 01:33:48 AM »

What is the current standard meter all others are referenced to regarding accuracy and reliability? For decades it seems to have been the Bird 43 and the Coaxial Dynamics unit. There seem to be a fair amount of digital meters out there now, what are most folks using now for accurate power measurements? Area of interest is HF from qrp levels up to legal limit amounts. I have a nice Daiwa CN-801 with the large, easy to read big meter but eventually would like to upgrade. Thanks.

Lane Zeitler
Ku7i
JH1JCM
Forward Deployed
US Naval Hospital
Yokosuka Japan
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G3RZP
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Posts: 4625




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« Reply #1 on: September 14, 2013, 03:40:55 AM »

What measurement uncertainty and frequency range are you looking for?
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AD4U
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Posts: 2167




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« Reply #2 on: September 14, 2013, 03:56:38 AM »

Just because any meter (VOM, wattneterm etc) is digital does not mean it is more accurate than an analog meter.  It's the innards that count.

The Bird 43 and similar meters are still the AFFORDABLE standard for HAMs IMO.  They also give enough accuracy 5% for most HAM uses.  There are other meters that cost a lot more that may be more accurate, but their cost is beyond what most HAMs are willing or able to spend.

Dick  AD4U
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WX7G
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« Reply #3 on: September 14, 2013, 04:45:57 AM »

Note that the Bird 43 and the Coaxial Dynamics 83000-A accuracy (measurement uncertainty) is 5% of FULL SCALE and not 5% of measured power.
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AA4PB
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« Reply #4 on: September 14, 2013, 04:57:01 AM »

Just because any meter (VOM, wattneterm etc) is digital does not mean it is more accurate than an analog meter.  It's the innards that count.

Dick  AD4U

That's an important point. It applies to VFOs as well. Just because your transceiver's digital dial reads out to 1Hz doesn't mean that the reading is accurate to 1Hz.
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N3QE
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Posts: 2223




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« Reply #5 on: September 14, 2013, 07:05:01 AM »

In day to day use in well-to-do ham stations in my area, the Array Solutions Powermaster and Powermaster II are ubiquitous. Note, not cheap! But ubiquitous.

Using the Powermaster is truly effortless. Tune up with bargraph for relative measurement, Look at the number for absolute measurement. No reading crossed needles etc.
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K1ZJH
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Posts: 1009




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« Reply #6 on: September 14, 2013, 07:28:02 AM »

Just because any meter (VOM, wattneterm etc) is digital does not mean it is more accurate than an analog meter.  It's the innards that count.

Dick  AD4U

That's an important point. It applies to VFOs as well. Just because your transceiver's digital dial reads out to 1Hz doesn't mean that the reading is accurate to 1Hz.


Indeed. Accuracy, precision and resolution are often incorrectly interchanged.

Pete
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W6RMK
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« Reply #7 on: September 14, 2013, 08:00:27 AM »

Comparing new price against new price, the newer digital units are cheaper, or at least competitive (and generally more accurate).

A new Bird 43 is about $350 and the HF slugs are around $200 (more if you want a 5kW or 10kW slug), or around $500


the LP-100A is $435 from N8LP, and is more accurate than the Bird.  About 3-5% at full scale, but it holds that all the way down to a few watts, unlike a Bird. If all you are doing is "tuning for maximum smoke" then you might not care: go for maximum needle deflection.

It does do a lot of other stuff too: displays Fwd and Return simultaneously, or SWR, or gives you a vector measurement (i.e. mag and phase) so you can use it to adjust your antenna, or look for funkiness in your feedline, etc.

The Array Solutions Powermaster II is in the same price range ($500).

Both of the electronic meters have remote sensing heads, which some find very convenient.  OTOH, if you're carrying it up a tower to test the repeater output and see if lightning fried the antenna, the "single box" of the Bird might be more convenient.

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KD8MJR
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« Reply #8 on: September 14, 2013, 11:01:45 AM »

The LP-100A is this most accurate (Ham) meter you can buy.  Anything better than that is something that costs several thousand dollars and is used for commercial or military purposes.
The LP-100A has a 3% accuracy guarantee but is in fact most of the time closer to 1-2%.
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G3RZP
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Posts: 4625




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« Reply #9 on: September 14, 2013, 11:27:17 AM »

3% of reading or 3% of full scale on that range? It really is accurate to better than 1/8th of a dB over the full frequency range?

That's far better than any of the ISO standards ....What is the measurement uncertainty for an accuracy of 3%?
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W7KKK
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Posts: 374




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« Reply #10 on: September 14, 2013, 12:25:25 PM »

Don't expect precision accuracy by anything that is not a calibrated instrument.
I worked in a type II Cal Lab many years ago for the Navy as we cannot afford to have devices calibrated for 1% or even .1% accuracy on a regular basis. (well I can't anyway  Roll Eyes)
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N6AJR
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Posts: 9908




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« Reply #11 on: September 14, 2013, 12:26:35 PM »

most of the time I need a meter for either finding out where the peak and dip are when tuning an amp, or relative power out when setting up my radio.  %5 is fine with me. I look more for the  reading than the exact amount.  I prefer dual cross needle meters and have them from MFJ, diawa and workman among others, and I am happy with them.  My biggest amp is the alpha 87 a and when it indicates 1000 watts and the meter is around 1000 watts on a solid carrier signal (CW or FM), then I am happy.  good enough for me.
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G3RZP
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Posts: 4625




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« Reply #12 on: September 14, 2013, 01:12:58 PM »

For a 'certificated approved laboratory', the accuracy expected in Europe  for a conducted power measurement to a 95% certainty is +/- 0.75dB - which is in line with international standards.

But only up to 175 watts. For some reason I do not know, the ISO doesn't have certainty limits above that.....

But with those limits at 1kW with +/-0.75 dB, it could be roughly 840 to 1190 watts....so a Bird is theoretically at least, better.

And frankly, what does it matter to better than 1 dB?
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K7KBN
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Posts: 2805




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« Reply #13 on: September 14, 2013, 01:42:25 PM »

For a 'certificated approved laboratory', the accuracy expected in Europe  for a conducted power measurement to a 95% certainty is +/- 0.75dB - which is in line with international standards.

But only up to 175 watts. For some reason I do not know, the ISO doesn't have certainty limits above that.....

But with those limits at 1kW with +/-0.75 dB, it could be roughly 840 to 1190 watts....so a Bird is theoretically at least, better.

And frankly, what does it matter to better than 1 dB?

I like the European wordings for things like meter specifications.  Here in the US, we boast of a meter having "an accuracy of 5%", when that obviously equates to an INACCURACY of 95%.
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73
Pat K7KBN
CWO4 USNR Ret.
W1QJ
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Posts: 1447




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« Reply #14 on: September 14, 2013, 08:05:09 PM »

The LP-100A is this most accurate (Ham) meter you can buy.  Anything better than that is something that costs several thousand dollars and is used for commercial or military purposes.
The LP-100A has a 3% accuracy guarantee but is in fact most of the time closer to 1-2%.


FWIW...... use an LP-100A also.  I bought it for the same reason mentioned above.  A Bird meter is only accurate to their standard at or near full scale.
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