New affordable EMC probe set at a bargain price - From Ariel Rocholl's lab

[Fraser]

As some may know a really nice chap called Ariel Rocholl designed and produced the RF Explorer handheld spectrum monitor.

Never one to rest on his laurels, Ariel continues to develop accessories for his RF Explorer range. I own two of these pocket Spectrum Monitors and the associated RF signal Generator. It is good to see a product that continues to be developed by its designer. The quality of the products is very good considering their price.

With this in mind, I have no hesitation in highlighting the latest release from the Ariel Rocholl stable. He has just released a set of small H and E field antennas in a nice 4 piece kit. This is intended to be used for EMC type work or where a user wishes to trace a signal up to 6GHz on a piece of equipment or PCB. These antennas are primarily designed for the RF Explorer, I see no reason why such cannot be used with other Spectrum Analysers/monitors or receivers.

I already own a professional EMCO / ETS-Lindgren 7405 E/H Near Field Probe set that cost almost £2K and only officially covers up to around 3GHz.

Ariel previously released a single H field loop and this is now included in the complete kit. The price is $89 for the four probes, the semi rigid coax and the storage box. I have ordered a set today.

If you have a need to detect RF signals up to 6GHz in the near field, you could do a lot worse than buy this set of EMC antennas from SEEED Studio, who are agents for Ariels's products.

Full Disclosure: I have no connection with Ariel Rocholl, his products or SEEED Studio. I am just a very satisfied customer who wants to let others know about what could be useful products for their work.

https://www.seeedstudio.com/RF-Explorer-Near-Field-Antenna-Kit-p-2784.html

I attach a picture of my EMCO 7405 probe set and related datasheet for interest only. They are nice, but very expensive.

Fraser

[Fraser]

For those interested in Ariel's full range of products via SEEED Studio, please look here:

https://www.seeedstudio.com/category/rf%20explorer-c-79.html

https://www.seeedstudio.com/category/rf%20explorer-c-c-79.html?p=1

His earlier H field loop release is here:

https://www.seeedstudio.com/RF-Explorer-H-Loop-Near-Field-Antenna-%28RFEAN25%29-p-2720.html


Another useful product that I bought from Ariel is his nice quality and performance RF Power Limiter/protection unit for analyzers

https://www.seeedstudio.com/Power-Limiter-p-1444.html

Fraser

[tautech]

Nice find Fraser, for $89 that's hard to beat. 

[Fraser]

Just in case anyone thinks these EMC H field antennas are 'just' copper track loops on a PCB substrate, they are somewhat more complex than that  and a lot of development work has gone into them to get the best possible performance out of the design. Achieving a predictable frequency response up to 6GHz is quite an achievement !

Fraser

[nctnico]

Definitely interesting! Thanks for bringing it up 

[Fraser]

Some more details from Ariels email are shown below:

Sadly the Specs link is not working but I saw the previous H Loop spectrum plot and it was more than acceptable. We should see the Antenna response plots soon hopefully. I attach the original RFEAH-25 plot for interest.

Fraser

From Ariels email:

-------------------

Using the same technology of RFEAN25 near field H-Loop antenna, we are happy to announce the availability of the RF Explorer Near Field Antenna Kit at Seeedstudio: link

It is a collection of high performance set of 4 antennas designed for the most demanding RF diagnosis tasks:

RFEAH-25 – 25mm H-Loop

RFEAH-15 – 15mm H-Loop

RFEAH-5 – 5mm H-Loop

RFEAE-10 – 10mm E-Field


The three magnetic H-Loop antennas are very sensitive, compact and easy to use antennas for all sort of radiation sources. As the antenna diameter gets shorter, the antenna increase spatial resolution at the cost of some sensitivity loss; you should select RFEAH-25 for best sensitivity with connectors, large ICs and isolated signal traces, whereas RFEAH-5 works best for very narrow selective work in a populated PCB with close-by signal traces. RFEAH-15 is a good in-between compromise.

The electric field RFEAE-10 is offers a remarkable spatial resolution to determine the exact component in the PCB causing a problem, no matter how small it is.

For more details, please visit Specifications page: link
---------------------------

I have attached the description picture he supplied as well.


Fraser

[amirm]

Thanks.  As it happens I was in the market for a set so just went ahead and ordered these! 

[Fraser]

I almost purchased the first model of H loop that Ariel released but decided to hold out for a complete kit that I knew was in the wings waiting for release. I quite thought it would cost a lot more than $89 though.

The only disappointing thing so far has been the lack of published RF coupling plots to the full 7GHz capability of the kit. It may be that this is included in the paperwork and if so, I will post it here when the kit arrives.

I know Ariel has spent a lot of time developing these EMC loops and they have been through many prototypes to get to the product now on sale.

I have been in contact with Ariel in the past regarding information about the RF Explorer and I am pleased to say that you could not meet a nicer person who genuinely wants to produce a quality product. He originally designed the RF Explorer for his own personal use and realised that there was an opening in the Radio Control model, Radio Mic, ISM band users and similar markets for his unit. He has similarly been guided by his own needs and those of others to produce the accessories such as RF signal/tracking generator, Power limiter and antennas. He has made what I would have liked to make, had I had the time and programming skills (of which I had neither when I bought my RF Explorer)

It is true to say that it is relatively simple to make your own EMC probes using semi rigid, or rigid miniature coax. I have made many for various tasks. They are not optimised however and are just an 'emergency' measure when needing such a probe in the field. Ariel's probes look to have been well optimised for the task of getting up close and personal with PCB's and components. Plus they go much higher in frequency than I have ever built such H field probes for.

Fraser

[joeqsmith]

May be of interest for those interested in making their own.

[Fraser]

There are some more pictures and detail about the RFEA25 H Loop antenna on the news page.......

http://j3.rf-explorer.com/news

I attach the pictures here

Fraser

[plesa]

Can we expect longer probes like Beehive ones?

[Fraser]

No I do not think so.

Ariel designed the probes as a compact 'head' that fits onto a common semi rigid coax that may be bent to the most convenient angle or shape.

The user may make longer probe 'handles' using common rigid coax and SMA connectors. the compact 'heads' will make the kit as versatile as possible so that a head may be used in confined areas with a standard flexible coaxial cable as welll.

Another accessory that is common when using EMC probes is a broadband amplifier that has a relatively linear response and predictable gain across its bandwidth. Thankfully such is not hard to achieve with modern MMIC RF amplifiers. Ariel may, or may not have plans for such an amplifier as he says the loops are already very sensitive.

Fraser

[Fraser]

Ariel has just published a dedicated page to the EMC antenna kit.

URL is :  http://j3.rf-explorer.com/60-rfe/specifications/175-rf-explorer-near-field-antenna-kit

Sadly still no plots of the frequency response. They are clearly stated as "Calibrated" so the plots may come with them.

Fraser

[Fraser]

I have just written to Ariel and asked about the frequency response plots for the antenna kit.

Fraser

[G0HZU]

For home use would it be cheaper (better?)  to just make up a set of classic E and H field probes using semi rigid cable? That's what I did and these seem to work as well as the R&S E/H probe kit we have at work. This kit looks to be the same as your ETS probe kit although it includes a booster amplifier as well.

One critical factor is the rejection/discrimination between the E and H probes. How good are the PCB versions at this?

Note that I don't just use my homemade probes for EMC work, I mainly use them for research work where it is important to get good discrimination between probes when using more than one probe at a time.  This is more important (to me at least) than the frequency response but it's easy to measure the response yourself anyway. A decent set of E and H field probes is a very useful addition to any RF workbench and I think it's hard to beat a simple homebrew probe using semi rigid coax in terms of performance/value for money. The PCB based ones would have to be capable of higher performance than my homebrew ones to make me consider them. But the PCB versions already look very chunky and clumsy to me compared to some skinny semi rigid cable. The PCB E field probe is much fatter than it needs to be and it is too short so it would be hard to poke inside small gaps etc.

[Fraser]

There is nothing wrong with carefully made DIY probes. There have been many articles detailing how to make such with rigid, or semi-rigid coax and I have made a few. As to the performance of the E and H discrimination, I regret I do not have any information on such.

My EMC probe kit had been very useful since I got it. It is a little bulky in some situations though and it is rated up to 3GHz only and some of its probes less than 1GHz.

To me, this is a simple case of whether a user wants to make their own probes or buy a neat compact set that is both convenient and known to perform as expected (yet to be proven by me however).

I also own some very expensive R&S HZ4 active EMC probes that contain an RF amplifier, so I can choose between which I want to use now 

The frequency response can be helpful when monitoring a point on a PCB that displays carries varying frequencies, such as the output of a VCO as compensation may be applied to the readings at different frequencies. As you say, this can be done with an SA and TG, but it would be nice to have the official coupling plots against which to compare. The coupling plot can also provide a means to estimate a signals amplitude without actually directing connecting to the trace or component. Accuracy is unlikely to be great, but adequate for most tasks.

I bought the set as I like its design and, for me, it is a neat and convenient solution without having to experiment with DIY designs. Been there, done that.

Fraser

[Fraser]

This is an interesting H probe web page that covers DIY probes:

http://www.compliance-club.com/archive/old_archive/030718.htm

Fraser

[Fraser]

This is quite interesting as well

https://www.langer-emv.de/en/category/near-field-probes/19

Fraser

[Fraser]

I just found the full data sheet for the RFEAH-25 and it includes the coupling plots. Hopefully we will receive the same for the kits.

[G0HZU]

The response plot for the 2.5cm probe does look a bit unconventional to me. The via patterns in the probe PCB suggest that this is a classic shorted loop. Similar to my homebrew semi rigid probe here. Normally I'd expect to see a corner frequency around 100MHz (which it does have so this is OK) but then I'd expect it to look really flat up to the self resonant frequency that should be just over 1GHz. But this probe has about 6dB ripple/slope from 100-1000MHz.
The other odd thing is that is seems to do 'something' above self resonance (in the 7GHz plot) and most probes are of limited use above the self resonance. Not sure if this is a good thing or not but I'd question how valid it is as an H field probe above resonance. How good is the E field rejection here? Obviously there's something different about these explorer probes that means they do 'something' beyond the self resonance but I'd ideally want to see some proper tests to see how well they perform as H field probes here.

By contrast, my homebrew 2.5cm probe is very flat across 100-1200MHz but is resonant just above this. I would normally switch to a smaller probe to look above 1200MHz. I keep meaning to make one of the balanced (2.5cm) probes with semi rigid because these don't have the resonance at 1.3GHz. I use my homebrew 2.5cm and 1cm probes the most here.

[Fraser]

@G0HZU

Indeed, it is an interesting/unusual response plot. I understand that Ariel has been tweaking the design for some time in order to perfect it. A simple DIY loop would not normally need such. I am willing to give these loops the benefit of the doubt as they are reasonably priced but only practical use will prove them adequate for my needs, or not.

It will be interesting to see the plots for the smaller loops when they are released. Ariel seems to have aimed at maximum sensitivity with the sensitivity dropping with loop diameter, as we would expect. This aim may have resulted in a less conventional coupling plot with greater ripple and variation over the range. Still useful I expect though.

I will have to hunt down the plots on similar PCB construction EMC probes.

Fraser

[G0HZU]

I think a decent set of E and H field probes is a great thing to have if you want to study the nature of EM waves. I use mine quite often to look at transmission lines, transformers, filters and inductors. There's lots of neat tricks you can do with them, eg work out the pF/inch and nH/inch of a tline and compute its characteristic impedance (quite accurately!) and measure the model of an inductor and also investigate various classic printed microstrip structures up at UHF.
These are great tools to have/understand but you need H probes with good performance and decent rejection of the E field in order to do some of this stuff. They can do so much more than just sniff around for EMC problems. I think they probably get used for this the most but they are very versatile learning tools too

[G0HZU]

Here's a quick and dirty VNA plot of my 2.5cm H field probe up to 1GHz. This is a classic shorted loop probe using 0.086" semi rigid cable. You can see it is quite flat from about 150-1000MHz. It's actually flat to nearly 1200MHz but then has a huge resonance at 1300MHz. Above this 1300MHz resonance it is not much use as an H field probe.

[Codemonkey]

Just out of interest, how do you go about making the above measurement ?

I ask since I knocked up a set of probes  (using PCB's rather than semi rigid) a while back to use with a spectrum analyser I got cheap, and I've been curious as to what their response looks like ever since!

I have access to a rather nice 20GHz VNA at work, but i've never used it.

Opportunity for someone to make a video perhaps!

[G0HZU]

I have various E and H field 'playsets'  here to let me look at structures. But for simple stuff like this you can get some idea of the probe response by simply running the VNA port 1 into some (terminated) 50R microstrip on a PCB and then sniffing it with the probe connected to another port on the VNA. I was a bit lazy and didn't bother to calibrate anything for the previous plot. My VNA is pretty good in terms of source flatness and match and response at these frequencies. I'm also using short 18GHz Gore cables for the connections.

I'm lucky to now own a 4 port VNA so I can look at structures using E and H field probes on several ports at the same time. I can use the calibration features on the VNA to normalise the E field and H field responses to both look flat. So I can look at the same place for E and H at the same time. This can be very intuitive when examining certain printed structures on a PCB for example.

But in the raw 2GHz plot below for my 1cm probe there is no calibration or normalising. It's just the flatness of the whole system including the probe. I could probably get a flatter response if I calibrated things but I think this is good enough I need a reasonably flat response because I use the probes as research/diagnostic tools rather than for EMC/interference work.

The plot below is the raw flatness response of my 1cm H field probe. I spent a lot of time carefully making this from skinny semi rigid cable and I spent ages with it under a microscope cutting the tiny split in the cable outer such that it was extremely thin and also symmetrical. It looks pretty flat up to 2GHz but has a big resonance at just under 2.5GHz.