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Author Topic: Spikes @ 8Khz intervals on 80-40m?  (Read 4541 times)
NK7Z
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« Reply #15 on: January 07, 2017, 04:59:46 AM »

Wow! That's some project to have completed in only 2 days! It would have taken me at least four days. I guess I work more slowly than the average person. Or maybe its my lack of a good plan before I start. I usually spend half the time running back and forth getting tools and supplies.
My shack was down, and I am retired, so I was able to spend the entire two days working on it.

When you connected all your equipment to the ground buss, which I assume was then bonded to a ground rod and to the building's electrical service ground rod - did you disconnect the 3rd prong on the power plug to prevent ground loops?
No, that is why I had 99% of everything into a single wall outlet.

I was thinking of using a standard service panel neutral bar as my point of connection inside the shack, but I like your method better. I guess any flat copper bar about 1/2 to 3/4" width would suffice. What exactly did you use for your ground buss?
I square copper rod.  I got it from an old 19 inch rack, they are used as equipment grounds in the racks and are run verticlly.  If you have a broadcast station in your area, get friendly with the Chief Engineer...

I have to try to get some copper braid. I know it's expensive, but I should be able to grab some at a good price on Ebay or at a hamfest.
I got my braid from eBay...  I got the copper connectors from a local fellow that has tones of them, and sells them for fifty cents each.

Same goes for the mix31 ferrites. I'm wondering whether they might solve my EMI issue with the UPS, or whether it is being radiated right out the side of the unit. I have to experiment with aluminum foil first. If it turns out that the EMI is being radiated directly from the UPS, I can purchase some more copper tape and apply it to the UPS just as I did the SDRPlay case.
I replace things like that in my shack.  I might not use the copper tape and opt for a small metal box...  The tape may make things worse if a lot of oxidation forms at the junctions of where the copper from one turn meets another later.  If it were me, the UPS would be parts.

I might be able to detect exactly where the EMI is coming from if I build a "sniffer" antenna, and connect it to the SDR.
I suspect you are correct in this...

My station is much simpler than yours, being that only the SDR is connected to the computer. My rig is an old HW-101, which of course does not have PC connections - actually, I don't think that PC's existed when that rig was made! But it's all I've got as a transceiver for HF at the moment.
I lost a lot of my RFI when I grounded my Computer case...  Also if you have not seen Jim's (K9YC), papers on RFI, you should download them all, and read them.  See:

http://audiosystemsgroup.com/RFI-Ham.pdf

They are the gold standard for RFI reduction.  He has a ton of information available, and has written it all up, and it is wonderful stuff...  If you only have one source for RFI information, I would use Jim's material.  Look especially at the "Pin 1" problem...  I had that on several items, and correcting that on my computer helped a lot.  I ended up connecting the ground buss on the computer to the case, then grounding the case, that removed about 75% of my RFI on the SDR.

I have been a ham for almost 40 years, and yet I feel that I am just learning some of the basics.
Same here, been a ham for the past 50 years as well, and I am still learning, when I stop learning, is when I die.  I am amazed at how much I took for granted.  I was working with a new ham, (very sharp fellow), who wanted to know everything.  Some of his questions forced me to go back and look at some basic physics to be able to answer, questions like why do radio waves propagate...  I was lucky enough that he did not take the stock answer, and we both spend several months reviewing some basic physics videos on Youtube, wonderful stuff...  I finally really do understand the answer to that question at a physics level, not just a radio level.  Things like that are why I became an Amteur Radio oeprator...

Didn't really have to worry too much about EMI back then. No computers, cell phones, SMPS, solar panels, etc, etc to cause problems. I do recall once having a hash type noise on 20m and 15m, and 10m (the only bands I operated), and tracking it down to the small motor that ran the washing machine timer. For some reason, it would keep running after the cycle was finished. I'm not sure why it generated the EMI then, and not during the entire cycle - except that maybe there was a dirty switch contact in the timer preventing it from shutting off. I was able to solve the problem simply by twisting the knob slightly until the motor stopped.
I wish I had my old RFI environment back...  Today, things are really ugly...

I would think that the SDRPlay is much more sensitive than the HW-101's receiver is, so I wouldn't be surprised if, when I get it running (I am about to "recap" the power supply and a few caps in the rig), that I don't hear the noise at all.
I'm going to bookmark your article as well.
You will be surprised...  Lots of RFI using the SDR.
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
KE2KB
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Posts: 527




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« Reply #16 on: January 07, 2017, 07:51:41 AM »

I started by building loops first, they have been much more useful to me over the past 10 years or so, than a probe.  Your local RFI, (in your home), can be located by just killing breakers.  Once you find the offending circuit, unplug each item, one at a time, listening for the RFI to stop.  That will net you a find 99.9% of the time. 

Loops are a blast to build and use.  Just google Loop antenna, you will get tons of loops you can build.  Just built a receiving loop first.  No need to get big heavy vacuum caps unless you want to transmit.

If you just have to build a probe, see the following:
http://www.interferencetechnology.com/wp-content/uploads/2012/04/Wyatt_NA_DDG12.pdf
http://www.emcesd.com/tt120100.htm
http://www.eng.mu.edu/~richiej/seminar/aidi.pdf

Have fun!!
Actually, I think I'll take your advice on killing breakers. I don't have a portable computer on which to run my SDR and connected loop anyway. Last night when I was thinking about RF sniffing, I was already half asleep.
Still, I would like to build some loop antennas for HF. But that's going to need to wait for spring.
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NK7Z
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Posts: 1807


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« Reply #17 on: January 07, 2017, 08:08:52 AM »

I started by building loops first, they have been much more useful to me over the past 10 years or so, than a probe.  Your local RFI, (in your home), can be located by just killing breakers.  Once you find the offending circuit, unplug each item, one at a time, listening for the RFI to stop.  That will net you a find 99.9% of the time. 

Loops are a blast to build and use.  Just google Loop antenna, you will get tons of loops you can build.  Just built a receiving loop first.  No need to get big heavy vacuum caps unless you want to transmit.

If you just have to build a probe, see the following:
http://www.interferencetechnology.com/wp-content/uploads/2012/04/Wyatt_NA_DDG12.pdf
http://www.emcesd.com/tt120100.htm
http://www.eng.mu.edu/~richiej/seminar/aidi.pdf

Have fun!!
Actually, I think I'll take your advice on killing breakers. I don't have a portable computer on which to run my SDR and connected loop anyway. Last night when I was thinking about RF sniffing, I was already half asleep.
Still, I would like to build some loop antennas for HF. But that's going to need to wait for spring.

Build small magnetic loops...  You can make them inside, and they are great for RFI hunting as well!
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
KE2KB
Member

Posts: 527




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« Reply #18 on: January 08, 2017, 08:50:04 AM »

Now I see that I am getting EMI on 20m, up through 10m, but this is not the same as what I get on 80 and 40m. This is a much wider bw, and is on the order of 36Khz intervals on 20 through 15, but on 10m, it's almost 300Khz intervals.
Before I do any sniffing, I think I need to improve my grounding situation. I need to bring in a HQG from the ground rod (and my 2m antenna) to my radio inside. At this point, I'm still using the power line ground for the radio.
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KE2KB
Member

Posts: 527




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« Reply #19 on: January 11, 2017, 07:18:11 PM »

I think I'll be buying a new UPS - probably the APC BR1000G. Does anyone know whether this model is "ham friendly" in that it won't produce EMI that will ruin my HF experience?
I am going to attempt to get this info from APC, but I have my doubts.
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KE2KB
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Posts: 527




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« Reply #20 on: January 13, 2017, 04:23:08 PM »

Here's an excellent source for EMI/RFI solutions & education.
http://audiosystemsgroup.com/RFI-Ham.pdf
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KE2KB
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Posts: 527




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« Reply #21 on: January 15, 2017, 05:05:43 PM »

Just an FYI to finish up this thread, as my problem with the 8Khz spikes has been solved.
It turns out to be the USB cable I was using to connect the SDRPlay to my computer.
Out of my slew of USB cables, I chose this one because it was the only one that had any ferrites installed. This one happened to be shielded, and had a ferrite at each end. It was 6ft long.

After breaking the shield at the PC end and instead connecting the shield to a screw on the case of the computer tower, I found it made no difference compared to the cable shield bonded to the metal shell of the USB-A connector at the PC. It was a bit worse if the shield was left unterminated at the PC end.

Next, I took out all of my USB cables, and checked each one. All but two resulted in EMI on 80 and 40m.
Of the two that did not produce any EMI, one was shielded, with a clear jacket (so I can see that it is shielded) but without any ferrites, and is 10ft or 12ft long. The other is just a 6ft cable with no ferrites - shielding unknown as this cable has an opaque white jacket.
So, I am now using the longer cable without ferrites. I have discarded the ones that caused the EMI.

My speculation is that the cables that do not produce the EMI are twisted pair. There are 4 wires inside the cable I cut the shield on: White, Red, Black, and Green. None of the wires in the cut cable were twisted.

So, in the future, I have to be very careful in buying USB cables. I tend to believe that those rated for USB 3.1 (or maybe 3.0) are going to be the best ones, as they need to handle higher data rates.
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