[Flexradio] Odd RFI Problem

Sat Dec 5 14:22:19 EST 2009

Here is a nice article from a Far East ham. Now it's included here in
the KC:

http://kc.flex-radio.com/KnowledgebaseArticle50426.aspx

73s-Erik-OZ4KK
> Thanks for the responses Tim, Dudley and Brian.  I apologize as this is a
> longwinded e-mail as I went through some troubleshooting.  The eureka moment
> is near the end, if you would like to skip all the rambling and details.
> Bottom line: RFI causes the printer driver to disconnect the printer from
> the network.  When the printer software re-establishes the connection to the
> printer, it causes PowerSDR to freeze.  RFI source has not been determined.
> Read on (painfully) for details.
>
>  
>
> Well, I did some more detective work.  I moved my choke outside my shack.
> It was right in the shack before the feedline went outside.  The choke I am
> using as a Balun Designs 1115ud.  The details of which are at:
>
> http://www.balundesigns.com/servlet/the-63/balun-designs-1-cln-1-Isolation/D
> etail
>
> The choke is now about 15 feet away from the shack.  Probably about 20 feet
> from the amp as the coax runs.  This made no difference.  So I added a
> second 1115u (not D version) choke back inside the shack.  This also had no
> effect, but I am choked to the max to stop any common mode, that is certain!
>
>  
>
> For the record, the antenna in use is a Butternut HF9V-X that is about 100
> feet from the shack/house.  The shack is in the basement below grade.  The
> feedline is pulled through conduit underground below the very extensive
> radial field; 64 radials 40 feet long.  I use 9913 foam (RG-8U) coax
> throughout my system.
>
>  
>
> I do use the DPC latency checker.  My latency never gets above 100 uS under
> the most busy clicking sessions.  The machine is built for quality and
> speed.  Even under this dropping of communications with the Flex post TX,
> the latency doesn't rise, so that has been ruled out.
>
>  
>
> I have added another ferrite choke to the firewire cable that was large
> enough to loop the cable through twice.  This was no help.  I put this at
> the computer end, as the two on the stock Flex provided firewire cable are
> at the rig end currently.
>
>  
>
> Another observation of note; The TX must be in excess of 20-30 seconds for
> the problem to occur.  On a short TX, the problem doesn't occur, even at PEP
> 750 watts out on RTTY.  The networked printer I mentioned doesn't lose
> communications for until at least that 20 second mark is reached also.  It
> is as if the RFI has to build up.  Seems odd.
>
>  
>
> Certainly, going to a better grade firewire cable is a good idea and I may
> do this.  But I will work on getting the RF out of the shack first, as I
> should.  I want to try nipping it at the source.  I need to get myself a RF
> sniffer in here or build something capable of doing it.
>
>  
>
> I changed a 2 foot coax jumper between the transmatch and the SO-239 on the
> wall to a 60 foot cable I had lying around.  No change.  So feedline length
> had no effect.  I changed back to the 2 footer.
>
>  
>
> As far as grounding the computer to the station, I read the article and was
> hesitant at doing this.  WAS is the operative word there.  I have taken some
> care to insure that the house AC line grounds are not common with the RF
> grounds and my metal sealtight conduit that runs up the wall and out of the
> shack.  My thoughts would have been before this that by grounding the
> stations RF ground to the computer, I am making the computer the common
> point between the house ground and my station's RF ground.  I would have
> thought it would be necessary to use a converter plug to lift the ground of
> the computer from the house's AC ground circuit.  But upon further
> consideration, I got out what schematics I have of equipment.  I noted right
> off in the schematic for my AL-80B that the AC ground is common with the RF
> ground of the SO connectors ,at least by its schematic.  Hmm.  I do not have
> the schematic for the Flex-3000, as it is not in the manual.  But looking
> under the hood, (and correct me if I am wrong) it would appear that the AC
> ground is common with the BNC connector's ground, making RF and AC grounds
> common in this too.  So while we all take great care to try to eliminate
> ground loops, it would appear that the standard practice (probably due to UL
> and NEC requirements) in ham gear is for the AC ground to be common with the
> RF ground point on the back.  So while I have tried to isolate my house
> ground system from my RF ground system, those efforts would appear to be for
> naught, as it is all made common through the rig and amp anyway.  What does
> it mean?  Probably nothing.  This was just a revelation that I didn't
> realize and from an engineering standpoint and something I hadn't considered
> before now.
>
>  
>
> The big weakness in my shack is the length of the my main ground strap with
> runs to my RF ground system.  It too is 15 feet long and runs out that
> conduit along with my feedlines.  All components attach to the strap it in a
> star pattern with equal length braided 1" wide conductors.  The entire
> ground strap is a 1" braided strap.  Not ideal.  One theory would be that I
> have gotten to a situation that a resonance/high impedance is set up on it
> and now that more power is added, it is rearing its ugly head.  Looks like I
> could be drilling into the basement floor.  Still a few things to try, but
> it's not looking good for the home team in avoiding that intensive bit of
> labor and expense.  If I do so, 3-4 copper pipes and 3" wide copper strap
> will be involved.
>
>  
>
> So now to drill a hole in the back of the computer and add a strap and
> grounding screw.  Such fun.  But maybe I'll get lucky and this will solve
> the problem and I won't have to reinvent my RF ground system.
>
>  
>
> I added a big snap-on MFJ ferrite to the printer's network cable at the
> printer end with the cable through it 4 times.  No change on helping the
> printer's connection.  At this point, I almost overlooked that fact that
> when I plug the printer back into the network that the PowerSDR will freeze!
> PowerSDR isn't doing anything but sitting there idling in RX mode.  There is
> no rise in DPC during this.  So I watched closely after a TX and it is true
> that PowerSDR only freezes when the printer re-establishing its connection
> with the computer's driver.  (It's an HP Officejet 7310 running their Hp
> Solution center driver software)  If I leave the computer unconnected from
> the network where it doesn't lose communications because it isn't connected
> in the first place, then PowerSDR never freezes!!!!  Just turning it off
> works too.  Eureka!  So it seems I need to get rid of the RFI to keep some
> parts of the network from having problems that then stops the printer driver
> and then freezes PowerSDR upon reconnect!  But in the short term, I can at
> least unplug the printer/turn off and keep using RTTY on 20M and not have
> any PowerSDR freezes.
>
>  
>
> So I can now conclude that something about the printer software
> re-establishing communications with the printer after being interrupted by
> RFI causes PowerSDR to freeze, even though there is no DPC latency issue.
>
>  
>
> There are some of the network wires that run through the wall within 4 feet
> of the coax conduit run.  I estimate that the conduit runs within 3 feet of
> the data closet where the DSL modem, router and switch reside.  I have now
> tried ferrite chokes on every part of the printers network cable, tried it
> on different wall connections and put ferrite on the printer's power supply
> cable, both on the high voltage and low voltage side.  No changes.  I must
> now look for the source of the RFI.
>
>  
>
> Ok, I'm now officially mentally exhausted for the day with this one but I
> can now operate RTTY with the amp on 20M without PowerSDR freezes.  Now to
> sniff out where the RFI comes from exactly.
>
>  
>
> 73,
>
> Scott AC8DE
>
> _______________________________________________
> FlexRadio Systems Mailing List
> FlexRadio at flex-radio.biz
> http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
> Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/
> Knowledge Base: http://kc.flex-radio.com/  Homepage: http://www.flex-radio.com/
> Message delivered to eja at urbakken.dk
>
>   