An improvised intake block off adapter for the Husqvarna 372 XP X-TORQ etc

To perform a vacuum and pressure test of the Husqvarna 372 XP X-TORQ chainsaw engine, the intake needs to be blocked off, and the exhaust blocked off.

This is a really important test of two stroke engines as air leaks through crankshaft seals, intake boot, cylinder gaskets, impulse tubes etc can cause them to run lean leading to premature failure of the engine.

The intake boot in the Husqvarna 372 XP X-TORQ has a rubber tongue that projects into slots in the carburettor throat, part of the strato engine.

Above, Husqvarna 578-09-56-01 intake block off adapter for the Husqvarna 372 XP X-TORQ. The open end of the ‘tube’ mates with the rubber intake boot, and the recess accommodates the tongue mentioned. Continue reading An improvised intake block off adapter for the Husqvarna 372 XP X-TORQ etc

Last update: 23rd April, 2024, 12:13 PM

NEC model of 600mm a side square loop for field strength measurement

This article Reconciliation of transmitter power, EIRP, received signal strength, antenna factor, ground wave propagation etc @ 576kHz used a 600mm a side square loop which was originally designed for field strength measurements on the 40m in an effort to understand and document BPL (PLC) emissions.

As part of validation of the antenna, a free space NEC model with external excitation was developed. This article publishes a graphic summary of the antenna characteristic. The model antenna is loaded with 50+j0Ω and includes 10m of RG58A/U which was used for the BPL related measurements with FSM. Continue reading NEC model of 600mm a side square loop for field strength measurement

Last update: 21st April, 2024, 8:00 PM

Crystal substitute using si5351 – part 3

Continuing the Crystal substitute using si5351 series…

Above is an example pair of inexpensive modules, less than $10 for the pair (incl shipping). Both boards are powered from 5V, the left hand module is a ATTiny85 dev board, it has a small 3.3V regulator on board. The dev board uses a DIP chip, so it can easily be programmed in a device programmer and then inserted in the socket. Continue reading Crystal substitute using si5351 – part 3

Last update: 23rd April, 2024, 6:59 AM

Traditional directional wattmeter uncertainty due to coupler Directivity

NanoVNA – how accurate does the LOAD need to be – part 1? discussed the importance of the calibration parts to accuracy of the NanoVNA.

Let’s digress for a moment at look at a directional wattmeter, a traditional way of measuring ReturnLoss and VSWR. This article examines the effect of coupler Directivity alone on uncertainty. There are other contributions to uncertainty, they are outside the scope of this article.

Directivity

Let’s review the meaning of directional coupler Directivity.

Above is a diagram from Mini-circuits. Continue reading Traditional directional wattmeter uncertainty due to coupler Directivity

Last update: 21st April, 2024, 12:24 PM

New e-delay feature in DisLord NanoVNA-H4 firmware v1.2.30

Recent articles discussed the use of e-delay to approximately compensate for cables connecting the DUT to the reference planes.

NanoVNA has had provision for an e-delay compensation for some time, it is a single value that is used to correct the s11 and s21 measurements.

It is very commonly the case that the optimal e-delay values for s11 and s21 compensation are different, so one needed to save a .s2p file for each of the two values and then merge the s11 measurements from its file with the s21 measurements from its file. The requires some work and risk of error.

I recently suggested to DisLord that provision be made in his NanoVNA firmware for specification of separate e-delay values for s11 and s21. He took the suggestion up and with days delivered a beta version with that facility.

This article documents an example use of the facility.

In this article, unless stated otherwise, reference to |s11| and ReturnLoss are to those quantities expressed in dB. Note that |s11|=‑40dB is less than |s11|=‑20dB. ReturnLoss and |s11| are related, ReturnLoss=‑|s11|.

Loss terms used are as defined at Measurement of various loss quantities with a VNA. Continue reading New e-delay feature in DisLord NanoVNA-H4 firmware v1.2.30

Last update: 18th April, 2024, 8:40 AM

NanoVNA – how accurate does the LOAD need to be – part 1?

A reader of EFHW transformer measurement – how accurate does the load need to be? asked whether the discussion applies more generally, in particular to the loads used for calibration and measurement with a VNA.

In this article, unless stated otherwise, reference to |s11| and ReturnLoss are to those quantities expressed in dB. Note that |s11|=-40dB is less than |s11|=-20dB. ReturnLoss and |s11| are related, ReturnLoss=‑|s11|.

Measurement 1

As a basis for discussion, let me offer an example measurement.

Above is a scan of a certain DUT after SOLT calibration of the NanoVNA. Continue reading NanoVNA – how accurate does the LOAD need to be – part 1?

Last update: 17th April, 2024, 6:19 AM

Using the NanoVNA to measure devices that have a UHF series connector – reader challenge

Using the NanoVNA to measure devices that have a UHF series connector left readers with a challenge:

An exercise for the reader: what would the e-delay need to be to compensate an s21 measurement if two identical cables were used to connect a UHF-UHF DUT?

Continue reading Using the NanoVNA to measure devices that have a UHF series connector – reader challenge

Last update: 14th April, 2024, 8:11 AM

EFHW transformer measurement – how accurate does the load need to be?

Several articles on this site use the following technique for measurement of transformer performance, and the question arises, how accurate does the load need to be?

Let’s set some limits on the range of ReturnLoss of interest. Measured ReturnLoss is limited by the instrument, and in the case of a VNA, its noise floor and the accuracy of the calibration parts used are the most common practical limits. That said, in practical DUT like an EFHW transformer, would would typically be interested in measuring ReturnLoss between say 10 and 32dB (equivalent to VSWR=1.05) with error less than say 3dB.

There are many contributions to error, and one of the largest is often the choice of transformer load resistor. This article explores that contribution alone.

2% load error

Let’s say the load resistor used is 2% high, 2450+2%=2499Ω. To measure ReturnLoss with such a resistor is to imply that the transformer is nominally  \(\frac{Z_{pri}}{Z_{sec}}=\frac{51}{2499}\) and ReturnLoss should be measured wrt reference impedance 51Ω.

To measure ReturnLoss wrt 50Ω gives rise to error.

Above is a chart of calculated ReturnLoss wrt Zref=51 (the actual ReturnLoss) and Zref=50 (the indicated ReturnLoss) for a range of load resistances, and the error in assuming RL50 when RL51 is the relevant measure. Continue reading EFHW transformer measurement – how accurate does the load need to be?

Last update: 14th April, 2024, 1:34 PM

Using the NanoVNA to measure devices that have a UHF series connector

From time to time I have a need to measure a device which has UHF series connectors.

UHF series connectors are not suitable for high accuracy measurements, and the problem is not simply that they are not ‘constant through impedance’ connectors, but the availability of reasonably priced calibration parts.

A simple solution when using short interconnecting cables at HF is to: Continue reading Using the NanoVNA to measure devices that have a UHF series connector

Last update: 13th April, 2024, 8:33 AM