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Author Topic: Which Meter should I trust?  (Read 449 times)

KD9DOG

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Which Meter should I trust?
« on: February 13, 2023, 12:48:43 PM »

I have two meters a MFJ-870 and the MFJ-259C analyzer , when checking SWR I get conflicting reports and I do not know which I should trust.
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KG4RUL

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Re: Which Meter should I trust?
« Reply #1 on: February 13, 2023, 01:53:45 PM »

And if you had three more meters, they would give you different readings.  Lab grade instrumentation and accessories are out of the financial reach of most so, you buy what you can afford and trust that things will not go badly wrong.
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KI5FJ

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Re: Which Meter should I trust?
« Reply #2 on: February 13, 2023, 02:07:50 PM »

James, Please provide more detail. During my 30 Years in the USAF, I was involved in calibration of many types of instruments. Absolute RF power and SWR are very difficult to measure. Accuracy to a NIST traceable standard of ordinary consumer meters is probably +/- 5 % at BEST ! I have several "Meters" in my shack for power /SWR. Please consider the readings approximate and do not attempt to resolve the issue any further. 73 Joe O, K I 5 F J, NNNN
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K8PJM

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Re: Which Meter should I trust?
« Reply #3 on: February 13, 2023, 03:49:48 PM »

I've had many different meters go through my shack and no two of them will give exactly the same readings. I learned not to get to hung up on meter readings in the shack. We are amateur radio operators not a multi million dollar radio station or Motorola service center. Those guys will buy a $10,000 meter without even thinking about it.

The meter that I trust in my shack is the LP-100A by Telepost. It's rather on the pricey side but if you run a solid state amp it might be worth it. I have no interest in Telepost other than liking my meter for what's it worth.

What kind of readings are you getting with your two meters?

The average ham has a price point that we are willing to pay for unlike the commercial world radio users such as government agencies.
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KF4HR

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Re: Which Meter should I trust?
« Reply #4 on: February 13, 2023, 04:15:23 PM »

Most amateur radio RF power meters have an accuracy of plus or minus 10% of their full scale reading which probably accounts for the difference in readings you are seeing between your MFJ RF power meters.  And of course if you are using your antenna as your RF load, any antenna SWR mismatch will negatively affect your power reading accuracy.  As measuring precision increases, so does the cost of the measuring equipment.  MFJ meters are fine if you only need approximate measurements but if you are looking for improved accuracy I suggest purchasing a RF Power Meter with at least plus or minus 5% full scale accuracy.  There are a few out there.  One such meter is the Bird 43 RF Meter.  And for the highest RF measuring accuracy you'll want to use a high quality RF Load (such as a properly rated Bird RF Load).  The Bird 43 meter (or similarly accurate brand meters) will give you a reasonably accurate reading, at a reasonable price.

KF4HR 
« Last Edit: February 13, 2023, 04:22:20 PM by KF4HR »
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NA4IT

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Re: Which Meter should I trust?
« Reply #5 on: February 13, 2023, 04:20:28 PM »

The one closest to the antenna.
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KD9DOG

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Re: Which Meter should I trust?
« Reply #6 on: February 13, 2023, 04:42:53 PM »

I thank you for your candid opinions and will use the MFJ 870 I would use the radio but my site is failing so I must put on binoculars to read it. Hope everyone is going to have a great Spring.
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W1VT

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Re: Which Meter should I trust?
« Reply #7 on: February 13, 2023, 06:34:54 PM »

Plot the SWR readings on a graph.  A Smith chart is a good way of looking at impedance measurements.
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W6MK

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Re: Which Meter should I trust?
« Reply #8 on: February 13, 2023, 06:40:38 PM »

will use the MFJ 870 I would use the radio but my site is failing so I must put on binoculars

You answer your own question quiet logically. The meter you can read is the one to use.
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KE6SLS

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Re: Which Meter should I trust?
« Reply #9 on: February 13, 2023, 10:20:15 PM »


The meters we hams typically use are "relative" in that they give a pretty good approximation of values.

I also have issues trying to see these small meters.  However, I can't say I am a fan of the forward/reverse type meters.  My meters use the twin meter.  One side indicates forward power, the other shows SWR simultaneously. 

I got the luck of the draw as all my meters here tend to agree with each other.

When I first got on HF, my mentor lent me an SWR bridge and an old matchbox.  I discovered that the bridge was quite a bit off after I bought my own and compared them.  The difference of the values intrigued me, so I brought them both back to my mentor's shack and we compared them on a commercial BIRD watt meter.  My new bridge was pretty much spot on, and his loaner was not very accurate.  That was the day he educated me about the idea of "relative" readings :)

I am so grateful to my old mentor -- RIP Shally k6vhp

73
Jaye

https://en.wikipedia.org/wiki/Bird_Technologies
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AI5BC

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Re: Which Meter should I trust?
« Reply #10 on: February 14, 2023, 06:13:56 AM »

Simple you cannot trust any SWR meter. SWR meters are antiquated slot line technology the industry quit using decades ago. Move a SWR meter six inches down the line, and it reads completely different. Like an idiot meter on a car with a check engine light. CB operators are the only ones still using SWR meters. Today the industry uses directional couplers that read Return Loss, a much more detailed and accurate measurement.
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N7EKU

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Re: Which Meter should I trust?
« Reply #11 on: February 14, 2023, 07:14:28 AM »

Hi,

Perhaps the grounding situation is different between the two MJF's.  Try grounding the MFJ-259 to the rig using its grounding post and a short jumper wire and see if the readings become closer.  The other meter will always be grounded to the rig via its coax cable, however the hand-held meter will not.

73,   Mark
« Last Edit: February 14, 2023, 07:16:58 AM by N7EKU »
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Mark -- N7EKU/VE3

KD9DOG

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Re: Which Meter should I trust?
« Reply #12 on: February 14, 2023, 10:21:28 AM »

Thank you for the great info.
&# Jim
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SWMAN

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Re: Which Meter should I trust?
« Reply #13 on: February 14, 2023, 12:35:48 PM »

 Just buy a Bird meter and you won’t ever have to worry about it again.
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HAMHOCK75

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Re: Which Meter should I trust?
« Reply #14 on: February 14, 2023, 02:39:38 PM »

The MFJ 259 should be more accurate since it uses a resistive bridge which can be made very flat with frequency compared to the toroid transformer normally found in most inline swr meter designs.

That said, a lot can go wrong using the MFJ 259 as described here by one of its creators.

https://www.w8ji.com/mfj-259b_calibration.htm
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