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Author Topic: Output Discrepencies  (Read 2162 times)
KB1TJY
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Posts: 257




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« on: June 19, 2013, 08:26:06 PM »

When the power of my Yaesu FT-450D is set to 100W, it's own meter is showing 100W output. However, the Palstar AT2K as well as another external meter are showing 80W. Any idea why this would be? The AT2K just came back from Paul at Palstar and it's 101% functional. (Paul, thanks for the near immediate turnaround!)

Any thoughts?

Thank you,

Lyman
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W8JX
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Posts: 5319




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« Reply #1 on: June 19, 2013, 09:17:44 PM »

No tuner is 100% efficient, there is some power loss. If meter is after tuning section and reading power to antenna it will read lower. Try going using bypass mode on tuner into a dummy load. Also for what it is worth. The difference between 80 and 100 watts is less than 1 db and not noticeable down range.
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KA4POL
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Posts: 1851




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« Reply #2 on: June 19, 2013, 09:44:37 PM »

Why should you trust the indicator in the rig? I just had a Yaesu which the owner claimed to produce reduced power when warming up. The output into a dummy load measured full power. The indicator circuit had a bad diode.
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W9IQ
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Posts: 102




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« Reply #3 on: June 20, 2013, 05:11:57 AM »

Hi Lyman,

Amateur radio grade power and SWR meters are not very accurate instruments for the most part. Expect a +/- 10% error on readings. Meters that are part of a transceiver are often worse in my experience.

- Glenn W9IQ
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WX7G
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« Reply #4 on: June 20, 2013, 06:11:37 AM »

Two meters, one of which was just checked by the manufacturer, indicate 80 watts. You did subtract the reflected power reading from the forward power reading, right? The radio is set to 100 watts. We can reasonably infer that the radio is putting out 80 watts.

Reasons the radio might be putting out 80 watts.

Low DC supply voltage
High VSWR
It is defective
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WB2WIK
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Posts: 20536




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« Reply #5 on: June 20, 2013, 10:31:05 AM »

No tuner is 100% efficient, there is some power loss. If meter is after tuning section and reading power to antenna it will read lower. Try going using bypass mode on tuner into a dummy load. Also for what it is worth. The difference between 80 and 100 watts is less than 1 db and not noticeable down range.

The meter in a tuner would never be in circuit between the tuning elements and the antenna: That makes no sense, since if was located there, the SWR indicated would always be the same no matter how the tuner is adjusted.

The meter is between the "rig" and the tuning elements in the tuner, so it can indicate an SWR dip when tuning.

But a 20% discrepancy isn't bad, and pretty common. 
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WA4NJY
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Posts: 108




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« Reply #6 on: June 20, 2013, 11:43:34 AM »


 Well, I learn something new every day.  I just now checked my IC-746PRO into a good dummy load.  With the internal auto-tuner on,
there is a 10 watt "loss" up to 20 meters.  Above that, about 20 watts, including six meters.

With tuner off, there is a solid 100 watts on all bands.


Thanks,

Ed
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WB6BYU
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« Reply #7 on: June 20, 2013, 12:13:18 PM »

20% is pretty high for tuner loss at 50 ohms.

Using W9CF's handy tuner simulator:  http://fermi.la.asu.edu/w9cf/tuner/tuner.html
the loss for a T network is about 2%, rising to 5% if the capacitors are limited to
100pf.  It may be that the inductor steps are spaced a bit too wide for highest
efficiency on the higher bands.
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AA4PB
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Posts: 12638




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« Reply #8 on: June 20, 2013, 12:30:11 PM »

It sounds to me like something else is going on. I would expect the tuner loss to be greater on the lower frequencies due to the extra wire needed in the inductors for the extra inductance. With a dummy load you are using the tuner to match 50 Ohms to 50 Ohms (its not really doing any impedance changing) and I'm not sure how that might affect loss.

How are you measuring the tuner input power and the output power?
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KB1TJY
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Posts: 257




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« Reply #9 on: July 02, 2013, 05:32:28 PM »

No tuner is 100% efficient, there is some power loss. If meter is after tuning section and reading power to antenna it will read lower. Try going using bypass mode on tuner into a dummy load. Also for what it is worth. The difference between 80 and 100 watts is less than 1 db and not noticeable down range.
Many thanks to everyone who replied to this, greatly appreciated. I take it that the consensus is that this is to some degree to be expected?

On another note, my reason for the late reply was due to my not having received email notifications that posts to my question had been made. Having said that I decided to check in and found all these replies! The email address I have on file is long gone, need to change it and will do so now.

Many thanks to everyone for your input!

73's,

Lyman
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N3HFS
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Posts: 191




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« Reply #10 on: July 02, 2013, 05:40:05 PM »

Are you measuring CW? 

If you're measuring SSB, the peak (PEP) value won't be what you'll find on the external meter.  Few meters read peak power, and those that do make it evident (by name, model, or indication on the scale).  You'll find a typical power meter will read about 70% or so of peak power on SSB.

I'm not sure why most rigs indicate nearly full 100W power on their internal meters, because it's unlikely they're true PEP-reading meters.  Most likely, the meters are compensated to read 100 at full SSB output.
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KB1TJY
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Posts: 257




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« Reply #11 on: July 02, 2013, 06:00:09 PM »

Are you measuring CW? 

If you're measuring SSB, the peak (PEP) value won't be what you'll find on the external meter.  Few meters read peak power, and those that do make it evident (by name, model, or indication on the scale).  You'll find a typical power meter will read about 70% or so of peak power on SSB.

I'm not sure why most rigs indicate nearly full 100W power on their internal meters, because it's unlikely they're true PEP-reading meters.  Most likely, the meters are compensated to read 100 at full SSB output.
Are you measuring CW?

No. When tuning the 450D if I am on 20M I will engage CW, so therefore USB + CW to get the tone I need. The FT-2000 and the Icom-718 would both register 100W on the same meters, but perhaps as you said the design of the 450D provides for the meters being compensated to read 100 at full SSB output.

Thanks!
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W1FBV
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Posts: 25




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« Reply #12 on: July 03, 2013, 11:27:15 AM »

Does the meter on your tuner give you the option of reading peak or average?  If so, it may be set to average.  If it is, try peak.

Jim, W1FBV
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KB1TJY
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Posts: 257




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« Reply #13 on: July 04, 2013, 06:58:20 PM »

Does the meter on your tuner give you the option of reading peak or average?  If so, it may be set to average.  If it is, try peak.

Jim, W1FBV
Thanks Jim. It is set to Peak. I'm really wondering if I should send the 450D into Yaesu and wait for hell to freeze over before it comes back....
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N6AJR
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Posts: 9879




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« Reply #14 on: July 09, 2013, 12:22:09 PM »

nope, use FM if you have it, it gives out full power on transmit with or without any modulation. and most meters are not "calibrated" to exact  measurements. so they are great for peaking the output and give a rough measurement of power out. most meters change  on their accuracy even from band to band. Not to worry, close enough is close enough. enjoy
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