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alenK

An observation at 493MHz.

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Hello,

 I purchased a new RF Explorer that includes VHF as well as UHF ranges. Today I was comparing its performance to my original UHF version.

 

 I learned two things

 

1) The new wider range VHF/UHF unit seems more sluggish than the narrower UHF band unit despite matching all the settings that may be matched.

 

2) My Maytag microwave oven splats bursts of 493MHz RFI. The original RF Explorer shows a large narrow spike repeatedly pop up to -30dBm and disapper. Unfortunately the new VHF/UHF scanner does not display this activity.

 

I thought some may find it interesting that a common household appliance is capable of bursting into the Lectrosonics A1 Band of frequencies, and it may also interest some that this RFI activity may or may not show up on a scanner.

 

 

 

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This is interesting to me or anyone thinking about what RFExplorer version to buy. I'd be curious the setup in detail.

Version of the unit/module and firmware, antennas/filters used, settings, etc.

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The 493 MHz spike may be a spurious response (probably) of the RF Explorer. It is very, very suspicious that one unit shows this spike and the other doesn't. Spectrum Analyzers are like any other piece of gear; you get what you pay for (sometimes).  I would find it more probable that it is a spurious on the unit "showing" the 493 MHz as there, rather than an analyzer just "happens" to suppress a real signal. Tune a transmitter to 493 MHz and see if the "blind" unit suddenly sees it. If it sees the transmitter, then the Maytag is probably innocent, at least at 493.

 

This is not to say the new RF Explorer needs to be shot at sundown; an occasional falsie is still better than having no info about the RF surroundings.

 

Best Regards,

Larry Fisher

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Hi AlenK,

 

The new RF Explorer WSUB1G PLUS is likely the model being presented in this thread as VHF/UHF, and being compared with RF Explorer WSUB1G standard model.

 

If that is correct, please note the new, more advanced model has internal DSP features that, when enabled, may take a few milliseconds longer to complete a sweep by doing a better filtering of <spurs / false signals> which were not filtered by RF Explorer WSUB1G standard model.

 

You can still run the WSUB1G PLUS model in the same way as standard model, if you prefer, being faster: select DSP:Fast mode in the CONFIG MENU. The DSP selection allows you to switch filter / no filter spur signals so you are always in control.

 

More details in the DSP section of the user manual www.rf-explorer.com/manual 

 

Regards

RF Explorer Team

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Hello,

 Thank you for the responses. I apologize for the delayed acknowledgement. I was working on the road and did not have my login info handy.

 

 First I would like to say that I regret having created the impression that I was critical of the RF Explorer devices. Although I see how my original post would appear to focus on the performance of the devices I was and am more interested in having learned that my household appliance may be creating spurious RF.

 Let me explain; I was charging the batteries of the two RF Explorer units which were sitting on the kitchen counter, and I happened to warm up some lunch in my microwave. It was then that I observed the 493MHz spurs. I had not gone looking for them, nor was I actually testing or comparing the RF Explorers, but I did happen to look down and notice some new and unexpected activity on the meter display. To confirm my thoughts I started and stopped the microwave oven several times and saw the 493MHz spurs disappeared with the microwave off. I had never considered the idea before, but I have worked in live kitchens for Cooking Channel segments and in many cafes doing interviews etc. It made me think of the occasions when unexplained gremlins get in the signal.

 That is what I wanted to convey, but I made it more complicated.

 

 LarryF said

"Tune a transmitter to 493 MHz and see if the "blind" unit suddenly sees it. If it sees the transmitter, then the Maytag is probably innocent, at least at 493."

 

 I followed your suggestion and tuned a transmitter to 493MHz and both RF Explorers see the transmitter clearly. I followed the suggestions posted by rfexplorer and tried running the microwave again. The spurs still show up on the Standard model and seem to be unnoticed by the Plus model. When I stop the microwave the spurs cease to occur. I don't disagree that it may be a false reading. I suspect that I do not have the tools to establish a proper protocol for further testing.  

 

rfexplorer said

"The new RF Explorer WSUB1G PLUS is ... being compared with RF Explorer WSUB1G standard model...You can still run the WSUB1G PLUS model in the same way as standard model, if you prefer, being faster: select DSP:Fast mode in the CONFIG MENU."

 

 Yes, you are correct about the two models I now own. Thank you for the suggestion, I have set the PLUS model to fast to make a comparison. The only other potential difference I see is the "Iterations" setting which has a max of 28 in the Standard model and 16 in the Plus model. I have reduced the iterations in the standard model to 16 to match the Plus. I do not mind if the two devices have slightly difference performance as long as they are helpful in the field. It occurred to me to imagine that the requirements for scanning low frequency energy down to 50kHz, as the PLUS model is designed to do, may preclude some characteristic behavior which I have become accustomed to with the relatively narrow band UHF Standard model. In any event, I have found my original RF Explorer to be a very helpful aid when I work, and having recently purchased some Lectrosonics VHF IFB devices, I am eager to use the VHF capable PLUS model as well.

 

 DanieldH said

  "...the setup in detail. Version of the unit/module and firmware, antennas/filters used, settings, etc."

 

That is a lot of typing. :-) I will try to take some screen shots for you to compare.

 

 

Thank you.

 

 

 

 

 

 

 

   

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The microwave oven operates at roughly 2450 MHz. Your Standard RF explorer may be erroneously showing that 2450 as being at 493 MHz. 493 MHz is very close to one fifth of 2450. I'm always suspicious when frequencies are close multiples of one another. In any case, both units are seeing the 493 transmitter correctly so you don't have a blind unit which would be a real problem. You might also try running a wireless receiver at 493 MHz located about 10 feet or so from the microwave to see if there is any energy at 493 MHz. The RF level display should give a reading if there is. You may need to tune the receiver to several frequencies around 493.

 

The RF Explorer is a real bargain if it is even close to the specifications claimed, as lab analyzers are typically between $5k to $50k and up.

Best Regards,

Larry Fisher

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Thanks for the added details, that makes sense.

 

The new WSUB1G+ model has a very effective low pass filter in the RF input stage. This filter prevents any signal higher than 960MHz to produce false intermodulation in the instrument, or saturate sensitive electronics producing spurs. That is not the case with the original simpler WSUB1G model. Therefore what you see is most likely a false reading produced by the strong 2.4GHz signal entering the instrument and creating internal spurs.

 

To test this, you only need an external 1GHz low pass filter connected between the WSUB1G RF port and the antenna, it will behave the same as the WSUB1G+ as far as this signal is concerned.

 

Best,

RF Explorer Team

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Hello,

 I have one last pair of questions to ask:

 

 Is it being proposed that the 490+MHz "spur" does not exist in the "air", but rather only as an inter-modulation artifact within the radio scanner/receiver?

 

 Additionally, is it to be understood that these spurs will only occur within receivers that do not have front end filters designed to protect a receiver from an introduction that may cause inter modulation symptoms?

 

 Thank you.

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On 3/5/2018 at 12:50 PM, alenK said:

Is it being proposed that the 490+MHz "spur" does not exist in the "air", but rather only as an inter-modulation artifact within the radio scanner/receiver?

 

 Additionally, is it to be understood that these spurs will only occur within receivers that do not have front end filters designed to protect a receiver from an introduction that may cause inter modulation symptoms?

 

Yes, in the presence of out-of-band, strong signals such as the one produced by a microwave oven, the signal can produce intermodulation inside a receiver or an instrument.

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