Electronics > RF, Microwave, Ham Radio
CB and Ham Radio Techs Love Their Bird Wattmeters
joeqsmith:
--- Quote from: Wavenode on May 31, 2023, 05:18:27 am ---... We are always happy to provide information and help for inquiries regarding our products. You can reach us at contact@wavenode.com.
--- End quote ---
I took the time to read your PDF but it did not address my question about the LP-1 sensor that was mentioned.
--- Quote ---Ironically, they have a LP-1 sensor that is listed as "20 milliwatts – 60 watts" for HF, but then all their other sensors say 0 to whatever their maximum is.
--- End quote ---
With it connected to your meter as a system if you plot the linearity, what does it look like? Does your meter attempt to correct for the change in slope at the lower levels? If not, why does your company list the part as 20 mW?
Wavenode:
The Wavenode LP-1 sensor will indicate power down to 25 milliwatts, but not within +/- 5% accuracy. Most users would not use this sensor at such low power levels and SWR measurement would be more of concern in normal operation. All Wavenode meters use a 3rd order polynomial to account for detector non-linearity at very low power levels.
All Wavenode products are sold in Europe, and need CE certification for susceptibility to static and ESD, as well as radiated/conducted emissions from the meters. Internal clocks were selected expressly to avoid any harmonic radiation in Amateur Radio bands, a consideration in a long list of engineering do's/don't to survive and operate correctly in the high R.F. fields around a typical Amateur radio antenna, as well as public-service communication towers. These products have matured over a 20 year timespan and survived some brutal conditions in remote communication mountain-top systems. You can find some info about clock selection in our tech document here: https://wavenodedevelop.com/wp-content/uploads/2022/08/Technote-120-R.F.I.-Interface.pdf
73
Wavenode Inc.
joeqsmith:
--- Quote from: Wavenode on May 31, 2023, 06:17:49 pm --- The Wavenode LP-1 sensor will indicate power down to 25 milliwatts, but not within +/- 5% accuracy. Most users would not use this sensor at such low power levels and SWR measurement would be more of concern in normal operation. All Wavenode meters use a 3rd order polynomial to account for detector non-linearity at very low power levels.
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So no data showing the system error over the entire range? Do you have some hard limit where below nWatts, you switch to the polynomial fit or are you using that 3rd order for the entire specified range?
I had to use a fifth order for my display graphics but the actual is point slope only. Took some effort to get the coupler as good as it is but I don't have to deal with that diode detector.
Wavenode:
Operating from memory here since these sensors were devel0ped 20+ years ago. They will remain +/- 5% over 2-60 watt range and +/- 10% down to 1 watt. The polynomial fit is for levels <2 watts, but there is a piecewise linear fit above 50% of the range, which is about 30 watts for the LP-1. All of our sensors are plug/play and not individually calibrated for a particular control box. Other production tolerances come into play to contribute to the +/- 5% spec. A user can purchase our wattmeter today, but add sensors at any time in the future and expect the rated tolerances. A mass produced device can never economically produce the precision results of an HP437B and 8482A sensor that have been calibrated together at a cal lab. The HP units we use for calibration and engineering will always be superior instruments for product development.
73
Wavenode Inc.
xrunner:
--- Quote from: joeqsmith on May 31, 2023, 02:52:44 am ---Curious if they have a detector built in. Guessing with the SMA, it's AC made to drive 50 ohms. Will wait for your report.
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Yea just RF out @ -50dB
Refer to pic for the testing setup I used to check the measurements using a higher power input from my little test transmitter (Baofeng UV-5R).
The actual measured output powers of the UV-5R checked with a hp 436B (no coupler inserted):
VHF low/high Watts: 1.8, 5.1
UHF low/high Watts: 1.4, 4.0
Some years ago I made an SWR test load for calibrating the SWR / power meters on HF transceivers - meaning up to 29 MHz. It uses three 50 ohm RF load resistors and, using a switch, can present SWR 2 or 3 to the transmitter. I used this to check the SWR on 146 and 445 MHz. Given the fact I never designed it for use with VHF and UHF bands it still gave me results that tell me the coupler will work in the application I'm working towards. I need to design a better SWR test load for these higher bands (better shielding and layout for higher frequencies).
Using this SWR test load, I measured the FWD & REV port powers under load conditions that should cause a VSWR of 2 and 3 and so the coupler outputs (FWD & REV) should give us (or a microcontroller) the power levels to calculate it.
Corrected port power used below in dBm (actual port power -50 dB less)
VSWR 2
VHF 146.0 MHz
F 36.4, R 28.4, calculated VSWR 2.4
UHF 445.0 MHz
F 36.7, R 26.8, calculated VSWR 1.9
VSWR 3
VHF 146.0 MHz
F 35.6, R 30.0, calculated VSWR 3.2
UHF 445.0 MHz
F 35.0, R 29.0, calculated VSWR 3.0
In addition to the wideband plot of coupled FWD power output provided in earlier post, I took precise measurements of the advertised -50 dB coupling for each of four ham bands, for use in the software to come later:
6m band (52 MHz): -50.8
2m band ( 146 MHz): -50.8
1.25m band (222 MHz): -51.2
70cm band (445 MHz): -50.4
At this point I'm pretty satisfied that the Putnam dual directional coupler will be satisfactory for this project, so I'll move forward and start collecting some parts I'll need to check it out with a microcontroller.
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