Can a hand held analyser be used to evaluate Insertion VSWR of a VSWR meter?

Some recent articles here used a two port analyser to evaluate Insertion VSWR of some coax switches, and it raises the question about application of a hand held analyser and Insertion VSWR of a VSWR meter.

(Duffy 2007) listed tests for evaluation of a VSWR meter:

Testing a VSWR meter

The tests here need to be interpreted in the context of whether the device under test (DUT) has only calibrated power scales, or a VSWR Set/Reflected mode of measurement, and whether directional coupler scales are identical for both directions.

  1. Connect a calibrated dummy load of the nominal impedance on the instrument output and measure the VSWR at upper and lower limit frequencies and some in between frequencies. The VSWR should be 1. (Checks nominal calibration impedance);
  2. Repeat Test 1 at a selection of test frequencies and for each test, without changing transmitter power, reverse the DUT and verify that repeat the forward/set and reflected readings swap, but are of the same amplitude (checks the symmetry / balance of the detectors under matched line conditions).
  3. Connect a s/c to the instrument output and measure the VSWR at upper and lower limit frequencies and some in between frequencies. The VSWR should be infinite. (Discloses averaging due to excessive sampler length);
  4. Connect an o/c to the instrument output and measure the VSWR at upper and lower limit frequencies and some in between frequencies. The VSWR should be infinite. (Discloses averaging due to excessive sampler length);
  5. Connect a calibrated wattmeter / dummy load of the nominal impedance on the instrument output and measure calibration accuracy of power / ρ / VSWR scales at a range of power levels in both forward and reflected directions (Checks scale shape and absolute power calibration accuracy).
  6. Repeating Test 1 additionally with a calibrated VSWR meter connected to the input to the DUT, and measure the VSWR caused by the DUT at a range of test frequencies (Checks Insertion VSWR).

It is not unusual for low grade instruments to pass Test 1, but to fail Test 6 (and some others, especially Test 3 and Test 4) towards the higher end of their specified frequency range.

Item 6 in the list was to evaluate the Insertion VSWR. Continue reading Can a hand held analyser be used to evaluate Insertion VSWR of a VSWR meter?

Dataflash on NAZE32

The Acro NAZE32 flight controller ships without a dataflash chip, which is so shortsighted of the designer / manufacturer. Many users will not be at all interested in Baro or Magnetometer which come on the deluxe version, but the dataflash is so useful in tuning a copter.

Unfortunately, the designer put pads on the rev5 board for 150mil SOIC-8 chips (SOICN), but lots of dataflash chips are in 208mil packages (SOICW) and all the large capacity chips are SOICW. Rev6 boards appear to have pads that will suit both sizes… but then the Acro comes with dataflash, even if small.

If you are happy to install a 2Mb dataflash chip, buy a SOICN package and your job is easy.

I installed a 64Mb Winbond chip (W25Q64FVSIG), they are easy to find on eBay for a dollar or so. (You will also need a 10nF ceramic 0603 cap).

If you want to install a SOICW package… Continue reading Dataflash on NAZE32

U-BLOX LEA-6T GPS module – for experiments

This article documents a LEA-6T module build for general experiments.

The LEA-6T is an inexpensive GPS module (~$40 at time of purchase, but getting cheaper) that can supply raw pseudo range data.

LEA-6T02

The module above is supplied for use on UAVs of various kinds, and came complete with a plastic radome and cables to suit an APM copter. The module also contains a 3D compass (magnetometer) which is not used here.

LEA-6T03

Above is the internals of the module with a custom cable to pick up just the RS232-TTL signals from the GPS (and supply 5V). The connector is a 8pin Hirose DF13. Continue reading U-BLOX LEA-6T GPS module – for experiments

Coax switches – is shorting unused port necessary for isolation?

At Ratings of coax antenna switches I showed characteristics of a home made switch which has very low InsertionVSWR, but poor isolation.

A couple of correspondents have offered an explanation that the unused port must be shorted to get good isolation.

If that was the case, then we would expect all coax switches that leave the unused port open to have poor isolation.

Let us look at a very good coaxial relay

 

Above is a Dowkey 402 series relay which has good performance to GHz. It does not short the unused port.
Continue reading Coax switches – is shorting unused port necessary for isolation?

Ratings of coax antenna switches

In a recent article I discussed how InsertionLoss implies InsertionVSWR in lossless devices.

This article looks at measurements of a few antenna switches at hand.

Daiwa CS-201G II

It is difficult to find comprehensive data on the very popular Daiwa CS-201 series switches.

CS201spec

Above is the data from the packet of one of these switches, a CS-201G II. The specifications are pretty loose, and one must depend on one’s own measurements.

CS201N01

Above, the CS-201G II, a basic CS-201 series switch with N connectors, advertised as useful to 2000MHz where InsertionLoss is given as 1.2dB (or better?). If there were no TransmissionLoss in the switch, that would imply InsertionVSWR=3.6, but there is probably some significant TransmissionLoss and InsertionVSWR would be somewhat less. Nevertheless, IMHO InsertionLoss=1.2dB indicates it as unsuitable such frequencies. Continue reading Ratings of coax antenna switches

InsertionLoss implies InsertionVSWR in lossless devices

Devices inserted in transmission lines often characterised by one or more of:

  1. Insertion VSWR (the input VSWR when terminated with a matched load);
  2. Return Loss (RL) in dB (20 times the log of the magnitude of the complex reflection coefficient); and
  3. Insertion Loss.

Practitioners often find Insertion VSWR (1) of most use as it indicates whether the device is worse than other system devices, the weak link in the chain if you like. You might see a coax antenna switch specified to have InsertionVSWR<1.2 to 60MHz.

Return Loss (2) is a function of VSWR and vice versa, so it appeals when the designer thinks in terms of Return Loss rather than VSWR (and it is a better metric for VSWR<1.2). You might see a coaxial relay specified to have ReturnLoss>30dB to 500MHz.

Insertion Loss (3) is not so readily compared to the other two which are measures of input reflection with a matched termination. It often yields some numbers that appear very acceptable, but might be deceptively so. You might see a coaxial relay specified to have ReturnLoss>30dB to 500MHz. You might see a coax antenna switch specified to have InsertionLoss<0.2dB to 100MHz. Continue reading InsertionLoss implies InsertionVSWR in lossless devices

Seriously Pro F3 flight controller gyro/acc failure

I purchased an Acro Seriously Pro F3 flight controller (FC) recently and having soldered the connectors on and loaded the current firmware, it was time for a pre-installation checkout.

The article outlines a basic pre-installation test that revealed problems that would prevent effective use of the FC.

Acc/gyro checkout

MPU-6050

Doing no more than an acc calibration and allowing initialisation with a stabilised FC, the FC on the end of a USB cable should deliver acceptable sensor responses in Cleanflight Configurator (CC).

This flight controller has two problems:

  • offset in the gyro z axis (yaw);
  • low acc output in the Y axis (roll).

Continue reading Seriously Pro F3 flight controller gyro/acc failure

Flashing SeriouslyProF3 Cleanflight using ST-LINKV2

Introduction

If for some reason you cannot use the bootloader that reads from the USB port via the CP2102, you can resort to programming the MCU chip using the SWD port and a programmer that supports that protocol.

WARNING: there is potential for damage if you get this stuff wrong. No warranty is offered, if you break it, you get to keep both parts.

Example hardware configuration

FlashCleanflightWithStlink2

Above is the hardware configuration for programming. I have used a LiPo and BEC to supply 5V to the SPF3 board (the target), and a clone ST-LINKV2 (~$4 on eBay) is connected to the Serial Wire Debug (SWD) connector on the SPF3 with a custom cable. Note that you cannot use USART2 concurrently with SWD.
Continue reading Flashing SeriouslyProF3 Cleanflight using ST-LINKV2

Cleanflight – initialisation failure beeps

I spent quite a while chasing down a problem in a Cleanflight v1.13 flight controller which would not start properly, giving a series of beeps that one might expect hinted the problem.

DS1Z_QucikPrint1

Above is a scope capture of the /BEEP signal, five short beeps (50ms ON, 50ms OFF) then four long beeps (250ms ON, 250ms OFF). Continue reading Cleanflight – initialisation failure beeps

A drive test of RTKLIB accurate GPS

Accurate GPS positioning has been of interest in automating data collection in field strength surveys of antennas on HF. To be useful, the positions need to be accurate to 100mm.

RTKLIB is an open source program package for GNSS positioning.

A number of experiments were conducted using a U-Blox LEA-6T assembly with integral small patch antenna (cost ~A$40) and RTKLIB v2.4.3(b8) using a base station feed from Geoscience Australia (with thanks). The test location is about 200km from the reference station at Symonston ACT.

LEA-6T01

Above, the LEA-6T and a RS-232 to USB adapter are strapped to a roof rack bar with stretch film. The high mounting position gives good view of the sky.

 

Screenshot - 30_06_16 , 12_50_35

Above is a position plot of about an hour with the vehicle stationary (though in Kinematic mode) beside the house. Sky view was slightly restricted by the house and a line of tall trees to the west.

firefox 30/06/16 , 15:36:58 http://owenduffy.net/map/20160630.htm 20160630 - Mozilla Firefox

For the most part the track is smooth, but there is one section where the track in a more heavily treed section is markedly jaggy.