Posts Tagged ‘Test Equipment’

The Three Laws of Electronic Measurement

On Saturday, I had the privilege of talking to a group of radio amateurs on the topic of electronic measurements. I opened the session with a short discussion of “why do we even need electronic measurements?” This was captured in three “laws” listed below:

Bob’s First Law of Electronic Measurement

With electricity, most of the time we cannot observe what is going on without measuring instruments.

Bob’s Second Law of Electronic Measurement

When we can observe electricity directly, it is often a bad thing.

Bob’s Third Law of Electronic Measurement

Lord Kelvin was right

The post The Three Laws of Electronic Measurement appeared first on The KØNR Radio Site.

RM Ham University – Test and Measurement

The Rocky Mountain Ham Radio group offers an educational series they call RMHAM University. I am honored to be able to present on the topic of Practical Ham Radio Measurements on Saturday morning Dec 15th.

As many of you know, this topic is an intersection of my hobby of amateur radio and 40 years working in the electronic test and measurement industry. I’ve written two books on the electronic measurement and enjoy talking about it.

Here’s the agenda for the class.

Topic Comments Time
1.       Introduction Measurement Concepts, trends in test and measurement 8:00 to 8:30
2.       Digital Multimeters Voltage, current and resistance measurements 8:30 to 9:20
Break
3.       SWR Measurement SWR, reflection coefficient, SWR measurements, antenna analyzers, vector network analyzers 9:30 to 10:20
Break
4.       Oscilloscope measurements Time domain, bandwidth, scope probes 10:30 to 11:00
5.       RF Measurements Frequency domain, spectrum analyzers, SDR receiver, transceiver tests, power measurement 11:00 to 11:30
Discussion and wrap up 11:30 to noon

Location and Registration

Cherry Creek School District Educational Services Center
4700 S. Yosemite St.
Greenwood Village, CO 80111
Please register with the RMHAM web site so we know how many to plan for.  There is no charge for the class.
https://www.rmham.org/wordpress/rmham-university-2018/

The post RM Ham University – Test and Measurement appeared first on The KØNR Radio Site.

Indication versus measurement

The nature of a technical hobby gives way to the ‘buying of stuff’. Sometimes this is the tool required to carry out the crux of the hobby, in our case I’m referring to the transceiver. Sometimes this is the tool required to check that the main tool is working correctly, in our case this could any number of tools such as an antenna analyser.

There are also many hams that like to buy the box, or series of boxes and do the minimal amount of testing to ensure safe operation and there are those that will only operate what they have built themselves. Most of us fit on that spectrum. I certainly do, it just varies on what I’m doing.

For longer than I care to admit I have used an antenna analyser that belongs to my local club. It is free to be loaned but I’ve used it more than my fair share of times. I also like to build the odd antenna. This means I measure the length and then cut the wire and check it’s various characteristics and generally cut it again until I’m happy that I have a suitable compromise. Its a really useful tool. I assume its quite accurate because it cost a lot. But do I really need it?

Separating needs from wants is not that easy, partly because what starts out as a want can quite easily become a need. I made a decision recently, I was going to buy my own analyser. But which one? Que the usual looking through specs and performance criteria, guess what happened next. I started with a small requirement for a HF analyser and ended up looking long and hard at analyser >£300. Reflecting on this it becomes easy to bump up the needs because I never really noted down what I actually wanted.

So what did I actually need? In this case I wanted to ensure that I wasn’t going to damage a transceiver and transmit spurious rubbish (as opposed to my usual cw rubbish). So I didn’t really need a tool to measure, I needed a tool to indicate. But ah ha, I still needed to cut the antenna to the right length, so I did need something to measure but did it need to be really accurate?

It turns out it didn’t. It’ll be a good idea to get a rough idea but to 3 decimal places? nope, it just isn’t that important. So I duly purchased a cheapo SARK analyser off ebay for around £30 and it’s allowed me to measure and get the right length(s) (I built a multiband end fed antenna this time) and use a cheapo end fed tuner and the analyser to get the correct swr and impedance for safe and fairly optimised operation.

The lesson learned is that if I don’t set out the requirements first then I’m going to end up spending 10 times on a product that I probably don’t need.

M328 LCR-T4 an updated version of M328 LCR Transistor tester.


I wrote about the original M328 Chinese kit sometime ago, which I had to build to prove to myself that VK3YE's capacitance offset error problem was a calibration error:


http://g1kqh.blogspot.co.uk/2015/02/building-m328-component-tester-1.html



http://g1kqh.blogspot.co.uk/2015/02/building-m328-component-tester-2.html


However there is now a newer pre built SMD version (M328 LCR-T4) which came into my hands recently, all that you have to do is kit it together with a prebuilt case  and a 9V battery NO SOLDERING: (Cost less than £8 inc case inc delivery).


This version has the advantage of being ready built with ZIF skt, and supports a better LCD full sized display!







I like this for it's ability to identify "any" transistor, or diode, you seem to throw at it.  Displaying the gain figures of, and whatever way around the device is plugged into the ZIF socket, it has the ability to identify the pin out configuration, and if it is PNP or NPN, or even a FET. so you do not have to keep getting the semiconductor book out or downloading the data sheet for the pin data.





I thought this version was so good! I got G4WIF of the GQRP club recently to include it into the new Tribal Knowledge - Test Equipment document here

For those of us who are less technically inclined.

You may be like me. I've been at this hobby for a while now. I've built a ton of kits, made a bunch of antennas, passed all my exams with no problem. I was in the electronics repair biz for over 20 years, trouble shooting and repairing circuit boards down to the component level. But yet, to this day, I can open up a "QRP Quarterly" or a "QST" and look at the technical articles and feel like they are "WHOOSH" - about a mile over my head.

For those of you in the same boat, I would highly recommend the contents of the You Tube channel provided and maintained by Alan Wolke W2AEW. Alan is a fellow member of the Raritan Valley Radio Club. As a VE, I've attended a couple of Ham Crams where Alan was the lead instructor - I can readily testify that Alan knows his stuff, inside and out, upside down and backwards.

Alan has "The Knack" in more ways than one. Not only is he technically gifted, but the also has the ability to take the Greek out of electronics (no offense to my friends from Greece or of Greek decent), and make difficult concepts understandable, in plain English.  And that's a pretty good talent to have when you're a Technical Specialist for Tektronics.

In addition to Alan's You Tube channel, to which I think just about every Amateur Radio op should be subscribed to, Alan gave an excellent interview to Eric on "QSO Today".  You can listen to it here - http://www.qsotoday.com/podcasts/w2aew

Now, I'm not saying that if you watch all of Alan's videos that you'll be able to instantly comprehend every technical article you read in any Amateur Radio publication. But I can tell you that more and more of the content will be understandable and that you won't be totally clueless - like I used to feel. I'm getting better, but still have a long way to go.

72 de Larry W2LJ
QRP - When you care to send the very least!

For those of us who are less technically inclined.

You may be like me. I've been at this hobby for a while now. I've built a ton of kits, made a bunch of antennas, passed all my exams with no problem. I was in the electronics repair biz for over 20 years, trouble shooting and repairing circuit boards down to the component level. But yet, to this day, I can open up a "QRP Quarterly" or a "QST" and look at the technical articles and feel like they are "WHOOSH" - about a mile over my head.

For those of you in the same boat, I would highly recommend the contents of the You Tube channel provided and maintained by Alan Wolke W2AEW. Alan is a fellow member of the Raritan Valley Radio Club. As a VE, I've attended a couple of Ham Crams where Alan was the lead instructor - I can readily testify that Alan knows his stuff, inside and out, upside down and backwards.

Alan has "The Knack" in more ways than one. Not only is he technically gifted, but the also has the ability to take the Greek out of electronics (no offense to my friends from Greece or of Greek decent), and make difficult concepts understandable, in plain English.  And that's a pretty good talent to have when you're a Technical Specialist for Tektronics.

In addition to Alan's You Tube channel, to which I think just about every Amateur Radio op should be subscribed to, Alan gave an excellent interview to Eric on "QSO Today".  You can listen to it here - http://www.qsotoday.com/podcasts/w2aew

Now, I'm not saying that if you watch all of Alan's videos that you'll be able to instantly comprehend every technical article you read in any Amateur Radio publication. But I can tell you that more and more of the content will be understandable and that you won't be totally clueless - like I used to feel. I'm getting better, but still have a long way to go.

72 de Larry W2LJ
QRP - When you care to send the very least!

Antenna testing is hard (II)

This article follows up on this one. The title could also be: doing measurements on hand held radios is hard. Actually, some measurements I did in the past might not be so accurate after all.

Measuring in dBm
If you measure in dBm, what I always did, you assume that the device at the other end is 50 Ohms, just like the manufacturer promises you in the specs. Slowly but surely we are finding out that this is not always the case. As a result I might have to switch to microvolt (µV), a method which doesn’t require a perfect 50 Ohms at the other end.

Can’t we just convert it? 0.5 µV @ 50 ohms = -113 dBm, a piece of cake, right? No. You must know the actual impedance of the receiver if you want to convert from dBm to µV. Erik PE1RQF did some measurements on a few hand held radios to find out the true impedance. The outcome was, well, a bit scary.

Impedance

If a device is 50 Ohms, the SWR should be 1:1. Only a perfect dummy load and the Marconi RF generator are.

What this means for us
What this outcome basically means is that generating cold numbers on sensitivity and antenna performance are nice, but don’t tell the whole story, or could be misleading.

  • Antennas which prove to be the best performers (RX/TX, VSWR), tested under optimal conditions, are not necessarily the best performers on a specific brand/model of hand held radio.
  • There are antennas which aren’t 50 Ohms at all, but could very well outperform everything else on the market because your radio isn’t 50 Ohms either.

Do the test yourself
The best example I can give you is this one: take a Baofeng BF-666S, 777S or 888S, use the stock antenna, and make notes of the performance in the field. Try to hit repeaters which are barely in range. If you have a field strength meter, measure field strength when transmitting.

Remove the stock antenna and replace it by a Nagoya NA-701, NA-771, the $3.79 antenna, or the Baofeng UV-B5 antenna. I tried all of these; just pick whatever 3rd party antenna you have. Repeat the tests.

What happened here is that the short stock antenna was the best of the bunch, all 3rd party antennas had a negative influence on the performance of this specific Baofeng model. The same 3rd party antennas mentioned above did improve the performance of the Baofeng UV-5R, often by a wide margin.

Exception to the rules
The funny thing is that reception suffered greatly too. This is quite uncommon and a sign that hand held radios don’t follow the rules. For example, if you just want to receive on 20 meters and your dipole is 2×6 meters instead of 2×5 meters, you would never notice the difference. With your hand held radio however you will.



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