Author: Owen

Equivalent noise bandwidth – IC-7300 SSB Rx Filter2 (2400Hz soft)

For a lot of experiments, knowledge of the Equivalent Noise Bandwidth (ENB) of a receiver is necessary. The ENB is the bandwidth of an ideal rectangular filter with the same gain as some reference frequency, 1kHz is usually specified for SSB telephony receiver sensitivity measurement.

Though filters are often specified in terms of bandwidth at x dB down, that metric is of relatively little value, the x is often 6dB but not always, the filters depart significantly from ideal or even common response.

In brief, a white noise source is connected to the receiver input, Filter2 (nominal 2400Hz bandwidth soft response) selected and set to standard PBT, and the audio output captured on a PC based audio spectrum analyser, Spectrogram 16 in this case.

Spectrogram is set to integrate over 30s to average the variations due to the noise excitation. The resulting graph and text spectrum log are saved.

The method is explained in detail at Measure IF Bandwidth.

Above is the spectrum plots, as receivers go this is relatively flat, lacking the usual tapering off above 1kHz (a technique to cheat on sensitivity specs).
Continue reading Equivalent noise bandwidth – IC-7300 SSB Rx Filter2 (2400Hz soft)

Last update: 1st October, 2019, 7:58 PM

GPS antenna plot

I bought an inexpensive GPS antenna on eBay, the requirement was for one that operated from 3-5V to suit both of my GPSDOs. The antenna is mounted in an electrical junction box on conduit above the roof for reliable coverage.

The question was whether the active antenna with 5m of RG174 coax and SMA male connector at A$6 posted was any good.

To map its behaviour, it was attached to a Trimble Thunderbolt GPSDO and Lady Heather used to plot rx signal level over about 30h.

Above is the plot. The pattern is not quite symmetric as there are obstructions in play, in fact some of the dips in performance are explained by specific trees and the roof profile. There is a gap to the south at low elevations, GPS satellites don’t fly there (MEO inclined 55° from the equator) .

Overall, it reaches similar strength at the zenith as other antennas tried.

Overall evaluation, it seems to work ok though the coax is a bit rough.

Last update: 30th August, 2017, 6:25 PM

Inductance of sensorless brushless DC motors

A reader of A Demagnetisation Risk Index for a sensorless brushless DC drive asked whether the inductance of a sensorless brushless DC motor could be measured with one of the inexpensive LC meters available on eBay.

Motor inductance line-line typically ranges from several µH up towards 100µH. Importantly, the fundamental frequency of flux change in the laminated iron core under normal operation is typically less than 2kHz.

Validation of the LC200A

To verify the instrument, a test inductor was made with 3t on a FT-240-43 ferrite core.

Above is an estimate of the expected inductance of the test inductor, 9.65µH. Keep in mind that the tolerance of ferrite is quite wide, 20% variation is not unusual. The test inductor measured 9.1µH at 10kHz on a classic RLC meter.

Above, the LC200A measuring an inductor comprising 3t on a FT240-43 ferrite core, measurement frequency was 670kHz. The measured inductance is 8.98µH, 7% lower than the estimate but well within tolerance of the ferrite core, and less than 2% below the value measure with a classic RLC meter. Continue reading Inductance of sensorless brushless DC motors

Last update: 22nd August, 2017, 9:56 AM

Messi & Paoloni Ultraflex 10 coax cable

Messi & Paoloni Ultraflex 7 coax cable compared M&P UF7 with RG-213. This article does a similar comparison between M&P Ultraflex 10 and LMR400UF.

Both cables are of similar size, ~10mm overall, stranded centre conductor and foil+braid outer conductor. The shield stranding is different and the foil is copper in the UF10, aluminium in the LMR400UF.

Let’s take the loss factors calculated for TLLC and de-construct the conductor and dielectric loss for each line type.

Above is a comparison of the cables. Continue reading Messi & Paoloni Ultraflex 10 coax cable

Last update: 18th August, 2017, 7:14 PM

True balanced tuner

A recent long running thread on QRZ entitled “True balanced auto-tuner” was sure to tease out some pretty woolly thinking… the word “true” was enough to signal the outcome.

There are only three words in the title, we can dismiss “true” as a harbinger of woolly thinking, and though people will argue the toss on the appropriateness of the term “auto-tuner’, most people share an understanding of the meaning. “Balanced” is another problem altogether.

After thirty odd posts, there has been no definition or discussion of the term balanced, or its advantages or disadvantages.

One of the recommendations by several posters is the old is new again solution, the once popular link coupled tuner and the work of W5ZQ featured in one of those recommendations.

W5ZQ and WW8J

Topology

W5ZQ describes a tuner inspired by WW8J. W5ZQ extended the design and provides a writeup on optimising balance.

Above is W5ZQ’s partial circuit. In the article he describes and shows:

  • adjustment of the grounding point of the output tank; and
  • current meters which presumably attach to J2 and J3.

Key to analysis of the topology is that the centre of the output inductor is grounded. This results in the circuit tending towards equal but opposite phase voltages on the output terminals. Continue reading True balanced tuner

Last update: 22nd May, 2020, 12:34 AM

SCT-010-000 current transformer protection

The YHDC SCT-010-000 clip-on or non-invasive current transformer is widely used in DIY energy monitor applications, and is readily available on eBay for A$6 including post.

A key issue with current transformers is that current in the primary winding will cause excessive voltages in the secondary winding unless the secondary winding is suitably loaded. The broad rule of thumb is NEVER disconnect the output connections whilst current flows through the primary.

 

YHDC’s website is typical of Chinese web sites, and I could not find a datasheet for information on the internal circuit and possibly internal protection.
Continue reading SCT-010-000 current transformer protection

Last update: 14th August, 2017, 3:52 PM

Standardised processing of instrument screen captures

I have several instruments and software packages that can create screen captures, and the capture files commonly need some mix of image processing including for example:

  • cropping;
  • scaling;
  • brightness, contrast, gamma adjustment;
  • transparency change;
  • format conversion; and
  • file copy / archive / cleanup.

Above is an example. Though WordPress presents a small image inline, if you click on it, there is a 640×480 image that was created from a QVGA (320×240) screen capture file scaled and gamma adjusted.
Continue reading Standardised processing of instrument screen captures

Last update: 12th August, 2017, 11:18 AM

WSPR – data mining 40m 01/08/2017

I mentioned elsewhere that I dowloaded the WSPR archive for 1/08/2017, and particularly analysed 40m spots.

There were close to 1,000,000 spots for the day, about 340,000 on 40m, and about 20,000 individual transmissions reported during the day (40m).

Tx / Rx mix

Above is a pie chart of the mix of Tx Only, Rx ONLY and Tx/Rx stations. The largest group is Tx Only, 44% of stations do not contribute reception records. Nextly, 30% are Rx Only, and 27% Tx and Rx. Continue reading WSPR – data mining 40m 01/08/2017

Last update: 7th August, 2017, 7:09 PM

WSPR checkout on 30m

On the back of A WSPR experiment for station evaluation I thought I would try a similar experiment on 30m in the quest for some meaningful results.

Given the lack of activity from credible stations on 40m, it seemed worth a checkout on 30m befor committing to the trial run, large download and data analysis.

So, I ran WSPR for a half hour just before 0000Z and observed the activity on WSPRnet map. I should note that my tx power was 0.1W and rx performance was impaired as there was a 20dB attenuator in line to achieve the tx power.

Above, the map after of the half hour of activity.

The encouraging this was that there were 12 stations active. Continue reading WSPR checkout on 30m

Last update: 5th August, 2017, 12:47 PM

A WSPR experiment for station evaluation

An experiment was conducted on 40m using WSPR to compare my own station transmit performance with others relatively close by.

The experiment was conducted around sunset on 01/08/2017, data was collected for the period 0600Z to 0900Z, sunset was at 07:17Z.

The experiment was unannounced as previous experience has been that if the WSPR community becomes aware of activity that does not accord with individual’s opinion of acceptable, the activity can be disrupted.

Data for analysis was fetched by downloading the archive which contained nearly 1,000,000 records for the day, and about 340,000 of those were 40m spots.

Factors shaping experiment design

The following is a discussion of various factors that weighed into experiment design.

Transmitters tend to cluster around the centre of the 200Hz WSPR band.

Above is a frequency distribution of tx frequency, and it is evident that the risk of interference is reduced by choosing a frequency near the upper or lower limit of the band segment. There was some activity just outside the designated band segment which might indicate care and competence of operators.

One wonders if randomising the tx frequency might not reduce collisions and improve decode rates. Continue reading A WSPR experiment for station evaluation

Last update: 4th August, 2017, 6:17 AM