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Power Meter

Homemade

Power Meter

More than a Power Meter for QRP to 1 kW

In the journal FUNKAMATEUR Edition 9/2007 Kurt, DL5MEA has presented an accurate SWR and power meter.
The described variant, and 65 MHz and 1 kW are used, where the tap loss is almost constant.

The circuit board was purchased from the online shop of the radio amateur. The required components from the established professional shipping. The programming software for the microcontroller online.

The aggregation or-build the individual components had influence with the choice of housing.
I chose an aluminum casing similar to that of DL5MEA.

Thanks to Kurt DL5MEA for their friendly support directional coupler.

Year of built 2008


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Power Meter

Briefly describe FUNKAMATEUR 9/2007

  • With the presented combined power and SWR meter is a device available that can be achieved despite high accuracy even with reasonable effort. The presented power meter consists of a simple directional coupler to build the Stockton-principle and one of them separate display unit. Since the display is connected via a shielded cable to the directional coupler, not rigid coaxial cable to the display unit are to be laid - the display can thus be placed anywhere on the station table, while the directional coupler can be inserted at a point in the signal path.


  • With this device can be simultaneously up-and the reflected power, the peak power, the SWR and the average power display digital, with neither performance-based (a few watts to 1 kW) nor the frequency (1-65 MHz) switching is required . By software, the time interval in which the peak is determined, s are set 00-10 - making the adjustment to different operating modes.


  • To make the performance possible frequency, small ripple in the tap loss is optimized, which, however, other properties are not quite so optimal. The higher directivity can be in the range 1-35 MHz have a standing wave ratio (SWR) can be measured by s = 1.07 to 65 MHz and s = 1.12. It was elected a directional coupler with two transformers and optimized for performance measurement. The outputs of FWD and REV were led to sockets. As long as neither of these connectors, the diodes have the terminating resistors are soldered, one can determine the RF characteristics of the object by measuring directional coupler to these jacks exactly.


  • The tap loss varies in the range 1-65 MHz to less than 0.1 dB, the error is on the frequency so that about 2.5%. The result of the measurement is shown in Figure 15. To achieve the low ripple of the tap loss, but the adjustment to a sweep test is required. Radio amateurs who do not have this possibility, by the comparison method described below, try to obtain sufficient accuracy with amateur means are about 0.5 dB can be achieved. For me a few matched with unique measurement diagram is available.


  • The tap loss was chosen so that, without a switch that can measure performance of a few watts to over 1000 Watts. The resolution of the display is better than the performance at higher accuracy, but the decimal value as a trend. It is similar to the second decimal place for the display of the SWR. The calculation of the mean is not valid for all signal types, but you can judge it very well, for example, the recruitment of a speech compressor.


Technical data

Display

 

Envelope peak

0,0.. .999,9 W mit 0.. .9,9 s Time constant

Mean

0,0.. .999,9 W

SWV

1,0.. .99,9

   

Directional couple

 

Power

<= 1000 W

Frequency

1 ... 65 MHz

Tap Loss

~ 26,5 dB mit 0,05 dB Ripple

Directivity

>30 dB bei 1 ... 35 MHz
>25 dB bei 35 ... 65 MHz

Insertion loss

<0,05 dB bei 1 ... 35 MHz
<0,07 dB bei 35 ... 65 MHz

Some pictures of the device

[ CLICK ==> ENLARGE ]

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