RFI, KUSB and MFJ-4225
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I am trying to clean RFI on 160m in anticipation of the contest season.
When KUSB is connected to K3, it emits white noise of about 5 Khz BW around 1833. I attributed it to U-verse. The noise is there when KUSB is fully inserted into K3 but no noise when only the grounds are connected. The noise is some 10 db above band noise when using K9AY that is some 100 ft away. A replacement USB adapter is quiet. I used KUSB before it was more RFI proof. Can KUSB be damaged to produce RFI yet be functional as an adapter? MFJ-4225 generates a 10db noise on 160m. Can a simple filter cure the problem or is it better to get a linear PS? Ignacy, NO9E |
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On 10/5/2010 5:38 PM, Ignacy wrote:
> When KUSB is connected to K3, it emits white noise of about 5 Khz BW around > 1833. I attributed it to U-verse. The noise is there when KUSB is fully > inserted into K3 but no noise when only the grounds are connected. The > noise is some 10 db above band noise when using K9AY that is some 100 ft > away. A replacement USB adapter is quiet. I used KUSB before it was more RFI > proof. I'd call that a defective adapter and send it back for a free replacement. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Tnx. It is 1.5 yrs old so no warranty. It took me lots of time to find that KUSB is noisy. No way without SDR-IQ as I would have never suspected a USB adapter.
Ignacy
On Tue, Oct 5, 2010 at 8:46 PM, Jim Brown-10 [via Elecraft] <[hidden email]> wrote: On 10/5/2010 5:38 PM, Ignacy wrote: |
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On 10/5/2010 6:04 PM, Ignacy wrote:
> Tnx. It is 1.5 yrs old so no warranty. It took me lots of time to find that > KUSB is noisy. No way without SDR-IQ as I would have never suspected a USB > adapter. This is not a WARRANTY issue, it is a DEFECTIVE PRODUCT. When a product produces RFI, it is DEFECTIVE.That is especially true when it is INTENDED to be used in a radio system. It may have taken you 1.5 years to figure out that it produces RFI, but that's not your fault. :) 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: RFI, KUSB and MFJ-4225
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In reply to this post by Ignacy
> Can KUSB be damaged to produce RFI yet be functional as an adapter? *ANY* USB adapter will generate a lot of RFI and continue to work properly if the shield of the USB cable is open or the shell of the motherboard USB connector is not properly bonded to the circuit board groundplane. The first thing to try when encountering RFI with a USB adapter or peripheral is to replace the cable. The second thing is to use a #31 mix toroid of the appropriate size and wind the USB cable through it four or five times (preferably one toroid on each end of the cable if the cable is long enough). 73, ... Joe, W4TV On 10/5/2010 8:38 PM, Ignacy wrote: > > I am trying to clean RFI on 160m in anticipation of the contest season. > > When KUSB is connected to K3, it emits white noise of about 5 Khz BW around > 1833. I attributed it to U-verse. The noise is there when KUSB is fully > inserted into K3 but no noise when only the grounds are connected. The > noise is some 10 db above band noise when using K9AY that is some 100 ft > away. A replacement USB adapter is quiet. I used KUSB before it was more RFI > proof. Can KUSB be damaged to produce RFI yet be functional as an adapter? > > MFJ-4225 generates a 10db noise on 160m. Can a simple filter cure the > problem or is it better to get a linear PS? > > Ignacy, NO9E > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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I tried two other adapters and they create no visible noise. The shield in KUSB is all enclosed so hard to see whether it is attached or not. KUSB was immune to QRO while the other adapters were not.
Regarding USB hubs, the ones I tried were not immune to QRO and they did not work after coming back from hibernation. Ignacy |
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In reply to this post by Ignacy
I was surprised to hear of the MFJ-4225 generating noise on 160, since
I use a MFJ-4225MV and work 160 a fair amount, yet hadn't noticed any noise. OTOH, I could I tell if I'm hearing P/S generated noise as opposed to "other" 160 meter band noise? I dug out my homebrew linear supply and decided to use the AFV reading on the K3 for comparisons. With AGC off, antenna connected, K3 tuned to an empty spot on the band with no signals present (daytime). The readings jump around a fair amount with random bursts of noise and possibly QRN crashes, so I jotted down ten or so over a ten second period, first with the MFJ powering the K3, then with the linear P/S, and then back to the MFJ to close the loop. I know this isn't highly rigorous, but it should tell me something. The average readings were MFJ, 146; linear, 168; MFJ, 141. I don't think the differences are significant, that is, I don't think the linear power supply is noisy. So I'd say there's no significant difference. I turned on the MFJ while listening with the K3 powered from the linear P/S and didn't hear any noise increase. The MFJ had long leads attached, going to my IC-706, but not loaded. Looking at the QST product review (January, 2000), they found that the MFJ-4225 was very quiet with some increase in noise between 7.5 and 10 MHz. Maybe there's something wrong with your specific power supply. I guess it's also possible that a change in manufacturing techniques or design has caused the MFJ-4225 to degrade. 73- Nick, WA5BDU On 10/5/2010 7:38 PM, Ignacy wrote: > > MFJ-4225 generates a 10db noise on 160m. Can a simple filter cure the > problem or is it better to get a linear PS? > > Ignacy, NO9E > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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The noise is never high, about 5 db over the morning noise. It occurs in narrow spurs every approx 50 KHz. These move slightly as the output voltage is adjusted.
It is possible that MFJ devices are refined over time. Mine is ca 1999.
Ignacy
On Wed, Oct 6, 2010 at 3:19 PM, Nick-WA5BDU [via Elecraft] <[hidden email]> wrote: I was surprised to hear of the MFJ-4225 generating noise on 160, since |
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In reply to this post by Nick Kennedy
I used to use an MFJ-4125 switching supply, which I believe is the same circuit as the 4225 only sans the meters. I quit using it mostly due to the fan noise (despite trying various circuits to reduce fan noise none that I tried worked acceptably on this unit). But while using it I detected noise on 80m. The noise was coming from the supply and being radiated via the power leads to the rig or antenna. Touching the power leads across a 125 AHr battery would kill the noise. Removing the leads from the battery, so that only the supply was in line, would allow the noise to come through. The battery was acting as a large filter cap filtering out the noise. But it was not broad band noise. Typical of a switcher it only occurred at discrete intervals. I you listened between the birdies there was no noise. If you want to check for switcher noise be sure to scan the band and find the birdies. The observation I would make about the ARRL tests is that while they are OK for comparison of one supply to another, they tell us nothing about whether or not we might expect to hear noise from any of these supplies. The spectrum analyzer charts have a minimum of -80 dB but we know not what the reference is - at least I could not find it in the article. The top of the chart is 0 dB, but we don't know if this is dBw or dBm or something else. If the reference is either dBw or dBm then -80 is still god awful noisy. Remember that the noise floor of a typical RX is around -130 dBm so a supply producing -80 dBm of noise is +50 above the noise floor - or about S9. If the reference is dBw then add 30 dB to that. Plenty loud! They point out in the article that the spectrum analyzer measurements were made under load and that the load on RX is lighter so there will be less noise generated. They ultimately give all but one, the Icom, a passing grade as OK for most installations. But there is no comment about important considerations such as type of antenna and feedline or antenna location. This seems to me to be another case of caveat emptor! One guy could experience bad noise in some situation but might completely clear it with a different antenna or feedline (if there is feedline radiation and pickup). Another might never be able to detect any noise if the antenna is further away and there is no close-by pickup. YMMV. 73 de dave ab9ca/4 On 10/6/10 2:19 PM, Nick-WA5BDU wrote: > I was surprised to hear of the MFJ-4225 generating noise on 160, since > I use a MFJ-4225MV and work 160 a fair amount, yet hadn't noticed any > noise. OTOH, I could I tell if I'm hearing P/S generated noise as > opposed to "other" 160 meter band noise? > > I dug out my homebrew linear supply and decided to use the AFV reading > on the K3 for comparisons. With AGC off, antenna connected, K3 tuned to > an empty spot on the band with no signals present (daytime). The > readings jump around a fair amount with random bursts of noise and > possibly QRN crashes, so I jotted down ten or so over a ten second > period, first with the MFJ powering the K3, then with the linear P/S, > and then back to the MFJ to close the loop. I know this isn't highly > rigorous, but it should tell me something. > > The average readings were MFJ, 146; linear, 168; MFJ, 141. I don't > think the differences are significant, that is, I don't think the linear > power supply is noisy. So I'd say there's no significant difference. I > turned on the MFJ while listening with the K3 powered from the linear > P/S and didn't hear any noise increase. The MFJ had long leads > attached, going to my IC-706, but not loaded. > > Looking at the QST product review (January, 2000), they found that the > MFJ-4225 was very quiet with some increase in noise between 7.5 and 10 MHz. > > Maybe there's something wrong with your specific power supply. I guess > it's also possible that a change in manufacturing techniques or design > has caused the MFJ-4225 to degrade. > > 73- > > Nick, WA5BDU > > > > On 10/5/2010 7:38 PM, Ignacy wrote: >> MFJ-4225 generates a 10db noise on 160m. Can a simple filter cure the >> problem or is it better to get a linear PS? >> >> Ignacy, NO9E >> >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Joe Subich, W4TV-4
I checked KUSB (bought 1.5 years ago) and the shield was not connected to the RS232 plug. After grounding, the white noise decreases dramatically but some noise still remains. Below the band noise on 160m noise with a vertical and above the noise with K9AY.
The other USB adapters that I tried have the grounding and have very low or no noise. Unfortunately they do not come back from hibernation like KUSB does. Elecraft support pointed to a grounding modification of KIO3. My K3 was supposed to have all the mods done when in Aptos earlier this year. I will find out later whether KIO3 was modified. Ignacy <quote author="Joe Subich, W4TV-4"> > Can KUSB be damaged to produce RFI yet be functional as an adapter? *ANY* USB adapter will generate a lot of RFI and continue to work properly if the shield of the USB cable is open or the shell of the motherboard USB connector is not properly bonded to the circuit board groundplane. |
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do you have the details of that mod please?
73 de M0XDF, K3 #174, P3 #108 -- When you want to test the depths of a stream, don't use both feet. -Chinese Proverb On 12 Oct 2010, at 12:34, Ignacy wrote: > > I checked KUSB (bought 1.5 years ago) and the shield was not connected to the > RS232 plug. After grounding, the white noise decreases dramatically but some > noise still remains. Below the band noise on 160m noise with a vertical and > above the noise with K9AY. > > The other USB adapters that I tried have the grounding and have very low or > no noise. Unfortunately they do not come back from hibernation like KUSB > does. > > Elecraft support pointed to a grounding modification of KIO3. My K3 was > supposed to have all the mods done when in Aptos earlier this year. I will > find out later whether KIO3 was modified. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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