Category: Test equipment

Fridge / freezer setup

The operating temperatures of refrigerators and freezers used for food storage is important to safe storage of food and to minimisation of energy costs.

The US FDA recommends the refrigerator should be set to 40F (4.4°) and the freezer to 0F (-17.8°).

Temperatures vary inside the cabinets, and they vary over time with opening and closing doors, and introduction of warmer goods for storage.

Many spot temperature checks are helpful but they don’t provide a very complete picture, and opening the door to make measurements disturbs the very thing being measured. Continue reading Fridge / freezer setup

Last update: 14th March, 2016, 9:51 AM

Chinese 18650 Li-ion cells – Ultrafire capacity test

I purchased a torch (flashlight) on eBay recently. It was described as using CREE T6 LED array, and supplied with two 4200mAh 18650 Li-ion rechargeable batteries with charger for A$25 inc post.

Ultrafire18650Above, the cells are clearly marked 3000mAh, way short of the advertised 4200mAh… but what is their actual capacity.

Screenshot - 04_03_16 , 19_45_49

Above are the results of discharge tests, the first digit is the cell number and the second is the test. The first test is charged with the supplied charger, the second test is with my charger. Continue reading Chinese 18650 Li-ion cells – Ultrafire capacity test

Last update: 4th March, 2016, 8:06 PM

ATU efficiency

Much is written about ATU efficiency, about the need for them or not, and often in subjective terms like “lossy ATU”, and most of it lacking quantitative detail.

The little quantitative detail is almost entirely for purely resistive loads… as if that is typical of real life conditions.

The most common configuration used today is the ‘high pass T match’, but a range of other configurations are seen as being superior… though usually without quantitative evidence.

MFJ claims

More Hams use MFJ-949s than any other antenna tuner in the world! Why? Because the worlds leading antenna tuner has earned a worldwide reputation for being able to match just about anything.

… so let’s make some measurements with a reactive load on a MFJ-949E. Capacitive loads tend to be very common for antenna systems at lower HF, so let’s choose a load of 50Ω with a 100pF silver mica cap in series at 3.6MHz. The reactance of the cap is -442Ω, so the load is 50-j442Ω, and the 50Ω part is a RF power meter (RFPM1).

The test setup then is:

  • a standard signal generator (SSG) on 3.6MHz with 20dB precision attenuator so that we are confident that Zs=50Ω (important to the adjustment of the ATU for maximum power as indication of 50Ω match);
  • MFJ-949E;
  • 100pF silver mica capacitor (low loss);
  • RFPM1

The SSG was adjusted for -10dBm out directly into the RFPM1, then the ATU+cap inserted and ATU adjusted for maximum power indication. Power indicated was 1.4dB lower, so InsertionLoss and TransmissionLoss are both 1.4dB.

Screenshot - 26_02_16 , 19_13_52

Above is a simulation of the T network in RFSim99, component values are adjusted for a match and inductor Q is calibrated to the measured loss of 1.4dB. Continue reading ATU efficiency

Last update: 27th February, 2016, 8:34 PM

RG-6/U for lower HF

RG-6 has become a popular 75Ω transmission line for ham stations, and I have used it to good effect in many applications.

(Duffy 2007) extolled the virtues and gave implementation information, but cautioned:

Some types of RG−6/U use a CCS centre conductor and will have higher loss at low frequencies that shown in Fig 1, depending on the thickness of the copper cladding which may vary from cable to cable.

I have used RG-6/U with solid copper centre conductor widely on HF, and measured performance has always been consistent with expectation.

However, RG-6/U with solid copper centre conductor has become very hard to obtain, and products that remain available such as Belden 1694A are quite expensive.

This article documents measurements at low HF on a 100m roll of Quad shield RG-6/U purchased for UHF TV cabling.

The method used was to measure input impedance of the open circuit terminated 100m line section at a range of resonant and antiresonant frequencies, and from those to calculate Matched Line Loss (MLL) in dB/m.

Screenshot - 25_02_16 , 10_17_41

Above is an example measurement around 3.74MHz. Zin is 213.4Ω at 3.74MHz. In this case I have used an AIMuhf one port analyser, but any instrument that can measure impedance in the range 10-500Ω would suit this particular scenario. Measurement of short low loss cables will yield more extreme impedances and may not be within range of some instruments. Continue reading RG-6/U for lower HF

Last update: 29th July, 2021, 7:35 AM

Measuring common mode choke Zcm using a two port VNA

There are some who insist that it is not possible to make practical measurements of a common mode choke using a one port analyser, and recommend the ‘S21 method’

S21 method

The ‘S21 method’ means different things to different people.

Screenshot - 20_02_16 , 14_31_07
Figure 1.

Above, (Agilent 2009) describe the common methods of impedance measurement using a VNA. The first method is often supported with direct display of R,X, and possibly a Smith chart presentation of Γ. Continue reading Measuring common mode choke Zcm using a two port VNA

Last update: 26th January, 2019, 7:13 PM

Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #4

Fourth part in the series documenting the design and build of a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.

 

Packaging

The prototype fits in a range of standard electrical boxes. The one featured here has a gasket seal (a weep hole would be advisable in a permanent outdoor installation).

AtuBalun201

Above, the exterior of the package with M4 brass screw terminals each side for the open wire feed line, and an N(F) connector for the coax connection. N type is chosen as it is waterproof when mated.

AtuBalun203

The interior shows the layout. The wires use XLPE high temperature, high voltage withstand, moderate RF loss insulation. Two short pieces of 25mm electrical conduit serve to position the balun core against the opposite side of the box, and a piece of resilent packing between lid and core holds the assembly in place.

AtuBalun202

Differently to the example shown in the earlier articles, this prototype uses twisted PTFE insulated wires which have voltage breakdown higher than the XLPE shown earlier.

Clip 124

The self resonant frequency of the built balun was measured as 7.4MHz and the predictive model above calibrated. The balun has high choking impedance on the lower half of HF.

Next installment: Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #5.

Last update: 13th February, 2017, 7:47 AM

Identifying ferrite materials #2

A correspondent wrote about Identifying ferrite materials asking how to use the method on an analyser that does not display X, but displays R and |Z|.

The method described calls for making a winding of the least number of turns for which measurement can reasonably be made, and finding the lowest frequency where R=X.

If your analyser does not display X (or |X|), you can exploit the relationship that |Z|=(R^2+X^2)^0.5. When R=X, |Z|=1.414R… so you would look for the lowest frequency where |Z|=1.414R.

Having found that, compare it with the table given or datasheet graphs to find candidate mixes.

Last update: 9th February, 2016, 10:14 AM

Identifying ferrite materials

This Jan 2012 article has been copied from my VK1OD.net web site which is no longer online. It is for reference from other related articles. The article may contain links to articles on that site and which are no longer available.

One often wants to identify the type of material used in a ferrite core for use at radio frequencies. This article captures advice that the author has offered in online fora stretching back more than a decade, yet it seems uncommon knowledge.

The most common method is to make some measurements to determine the initial permeability µi, usually at audio frequencies, and to compare that to a table of µi for common core materials. This method might well indicate several mixes that have similar µi, but each may be quite different at higher frequencies.

The suitability for use at RF usually depends much more on complex permeability at radio frequencies than it does on µi at say 10kHz.

cf01Above is a plot from the Fair-rite data book showing the complex permeability characteristic of #43 ferrite material. Continue reading Identifying ferrite materials

Last update: 25th October, 2021, 6:06 AM