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TOPIC: Different SWR and PWR Readings

Different SWR and PWR Readings 28 May 2021 19:41 #1

Why is there so a big difference between the readings of the internal ExpertSDR2 Software and an external SWR/PWR Meter in PWR and SWR?
Example with 13.8V:
18.100 (100W Carrier), Software says 104W, ext. Meter 78W. SWR internal 1.0, external 1.5
7075 (100W Carrier) , Software says 101W, ext. Meter 82W. SWR internal 1.1, external 1.8
3580 (100W Carrier), Software says 107W, ext. Meter 80W. SWR internal 1.0, external 1.9

The SWR readings from the transceiver are wrong, my external digital SWR and the RigExpert Analyser showing exactly the same values.
I had in the past an Pro and QRP, there was only minimal difference between PWR and SWR readings from the software to the external meters.

Any ideas/solution?
73
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Different SWR and PWR Readings 29 May 2021 02:47 #2

  • VK6NX
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1. Please note that ESDR2 SWR/Power meter is not a scientific precision instrument. And common SWR meter is neither. Those should be taken as "indicative".
2. Taking your example on 7075 - ESDR2 shows you that the carrier of 100W was produced. It does not show you how much was reflected by untuned antenna (this value you can find by switching your external SWR Meter in Reflective mode). SWR (internal) shows 1.1, informing you that SunSDR2 "thinks" its output circuit is close to "comfort zone", and it "thinks" like that because of the distortion caused by external Meter. In this case SWR (internal) gives you the SWR measurements between SunSDR Ant output and Meter Ant input, rather than "full circuit SWR".

There are couple questions for you:
3. If you remove "extras" (like external meter and/or tuner) from the feed line (having in result the circuit SunSDR<->feed line<->antenna), do you have the SWR measurements close enough to what you expect?
4. Did you compare the measurements with transceiver other than SunSDR? What are the results?
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Different SWR and PWR Readings 29 May 2021 12:20 #3

I tested a little bit with and without the external meter.
The results are the internal meter of the "DX" is not usable to tune my antenna (Magloop) to low SWR because the meter says i have 1.1, in real i have 1,9 or something and i have to use an external meter.
I compared the Pro2 and FTDX3000, they show similar results like my digital swr/pwr meter. The DX does not.

The Output of the DX is at 13,8V only around 75W-85W but shows happy 100+ watts internal :D
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Different SWR and PWR Readings 29 May 2021 17:43 #4

  • VK6NX
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TBH, I would be thinking to call Roman if I would have same issues with my SunSDR. May be something wrong with the device itself.
As minimum I would do the full reset of the device and intentionally load Firmware to it. Also check if you do not have any deviations on Options-Device-Expert-Power.
Also - did you check the power output with dummy load? Same 75-85W on full power?

I never thought internal SWR/Power meter is ideal and I never said I like how it works. But I would say it is abnormal if it would demonstrate 20% variation from actual.
Last Edit: 29 May 2021 17:49 by VK6NX.
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Different SWR and PWR Readings 01 Jun 2021 07:10 #5

  • Rome
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Hi, all.
Correct power/SWR measurements should be done with a 50 Ohm dummy load (at least 100W) and never with an antenna.
In case they significantly differ from the internal power meter/SWR-meter readings, we could remotely connect and adjust internal meters.
Роман, Roman
Expert Electronics
Last Edit: 01 Jun 2021 07:43 by Rome.
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Different SWR and PWR Readings 02 Jun 2021 19:55 #6

  • sq3rx
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Hi
For sure measuring output power should be done on dummy load and if it is possible with good quality swr/power meter. :so_happy:

I have additional question about build in SWR metter - What is the refresh rate ? On 160m band I use random wire with CG3000 tunner, which provide low swr for very narrow bandwidth. Sometimes the tuner needs to re-tune antenna match and this provide SWR spike for first second (or even less). Of course I focus to do this with low power. On TS480 this situation was clearly show on SWR metter, on Sun not.

Additional I see that SWR change with power. Don't think this is related with antenna or cable, because I have exactly the same situation with all my antennas. I will do some additional test, but maybe someone has similar observation ?
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