Return Loss sweep using IC7410, RL bridge, and RFPM1

This article demonstrates an automated Return Loss scan of an antenna using:

  • IC-7410 transceiver with CIV;
  • 40dB power attenuator;
  • Return Loss Bridge (RLB);
  • RFPM1 with USB data logger (A prototype data logger for RFPM1); and
  • a PC orchestrating the test.

Automation facilitates:

  • measurement of a large number of data points;
  • improved accuracy by reducing the risk of recording errors; and
  • reducing the tedium of a measurement task.

Continue reading Return Loss sweep using IC7410, RL bridge, and RFPM1

A prototype data logger for RFPM1

This project is a data logger accessory for Lou Destefano’s (VK3AQZ) RF Power Meter kit (RFPM1).

The RFPM1 develops an analog signal 0-2000mV corresponding to 0-100dB input power range, -85-16dBm. The module described here produces a digital output scaled -85.0 to 15.0 for 0-2000mV input.

Rrpm1Adc01The hardware is based on a clone of the Digispark ATTiny85 USB development board, about A$3 incl shipping on eBay. Differently to the original Digispark, the board above has a micro USB connector on board. The vero ‘mother board’ carries a resistor and 10t pot for calibration adjustment. Continue reading A prototype data logger for RFPM1

Transmit performance of 2m hand held transceivers – absolute gain estimates

Transmit performance of 2m hand held transceivers reported relative field strength measurements for some transceiver / antenna combinations.

This article documents a more careful measurement of the absolute field strength of one combination, and application of that knowledge to the other results.

Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.

RFPM1-10

Above, the RFPM1 RF power meter.

VhfUhfLoopAbove is the small loop used for field strength measurement. It is 2mm hard drawn round copper wire formed into a circle 185mm in circumference, and a common mode choke is used to connect the loop to the RFPM1 power sensor. The common mode choke is 0.6m of RG58C/U with 0.5m of ferrite sleeves over it and its loss is accounted for in the “Other Loss” item.
Continue reading Transmit performance of 2m hand held transceivers – absolute gain estimates

Transmit performance of 2m hand held transceivers

This article documents measurements of transmit performance of three hand held 2m radio with several antennas.

Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.

RFPM1-VhfLoop

Above, the field strength meter, a RFPM1 with small loop antenna oriented for max gain in the direction of the DUT.  The instrument reads -73.5dBm with no signal, -69.5dBm with the strongest transmitter with the loop removed, and around -30dBm for the various transmitters with the loop in place… so the meter reading is predominantly due to the loop mode pickup.

All three transmitters have different power. The table below reports power into a 50Ω load and does not take account of mismatch with the various antennas.

Screenshot - 06_07_2015 , 12_53_56

Above a comparison of the configurations on a field strength test at 1λ. The relative column factors the different transmitter power and FS to obtain  a comparative figure independent of power. Mismatch is almost certainly a significant part of the explanation of different performance, but it is quite difficult to measure in this sort of application without disrupting the DUT.

BoafengINF641Antenna

It is interesting that there is little difference observed with the Baofeng on two different antennas, when the Boafeng antenna is clearly inefficient, see the thermograph above.

 

Near-field field strength measurements using the RFPM1

Review of Boswell et al paper “Performance of a small loop antenna in the 3-10 MHz band” discussed measurement of near-field field strength for measurement of performance of a small transmitting loop (STL).

This article describes a method of performing near-field field strength measurements using a portable RF power meter (RFPM1) and a small untuned square loop. Continue reading Near-field field strength measurements using the RFPM1

VK3AQZ RF power meter (RFPM1) – filter response example

This article shows use of Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) to plot the response of a 144MHz filter.

RFPM00

Above, the RFPM1 as used.

Screenshot - 24_11_2014 , 10_29_43

Above, the test setup. The filter (DUT) is connected between a standard signal generator (SSG), and the RFPM1 connected to the filter output. A DVM recorded the DC voltage on the ‘CAL’ terminals of the RFPM1. A series of measurements was made from 140 to 148MHz and the results calculated and plotted in Excel. Continue reading VK3AQZ RF power meter (RFPM1) – filter response example