P3 Spurii and a cure.
Locked
 
|
I have had 2 problems with my P3 Panadapter, both were the subject of comment on the Reflector.
The first was spurii radiated from the P3 DC cord and picked by my nearby antenna on 144 MHz. This problem was largely solved by fitting a commercial RFI filter in the DC cord and ensuring that all panels were clear of paint in the corners where the connections are made. The second problem was the occurrence of wideband noise humps which drift across the display from time to time obliterating the genuine signals. I dubbed the characteristic doubled-humped noise signature as my noise monster. Experiment showed that these spurii and noise products were being generated in the P3 itself. It was not possible to precisely pin-point the source of these signals inside the P3 using a small pick-up loop. The signals were strong everywhere inside the P3 box, but, perhaps, were strongest near the processor chips. This would seem to make sense, but not everyone has these problems, so clearly the mechanism for producing this hash, varies from chip to chip. Thanks to everyone who responded. I am now able to report I have found a complete cure for these problems which works in my case, but, of course, I can not guarantee it will work in every similar case. The cure involves the use of conductive foam. This is the black foam that ICs are normally pushed into when they are delivered. It is carbon impregnated. You can tell the difference between this conductive foam and ordinary foam using an ohmmeter. Pressing the probes against the conductive foam will give a reading of a few Kohms. Ordinary foam will be open circuit. This foam is available from many electronic suppliers. I bought my foam from Farnell Electronics (Now called Element 14 in Australia), order code 168-7846. The cost is 89 cents for a sheet about the size of the P3 side panel. I cut the foam to form compartments to completely isolate the front panel, IF input board, and IO board. I even put foam between the folds of the ribbon cable. In doing this I was carefully not to allow the foam to actually touch any components or bare wires, otherwise a circuit would be formed. I cut the foam panels deliberately oversize vertically, so that when the lid was screwed down, ther e was pressure to make sure the foam had a conduction path to ground. The result of this work was that all spurii have disappeared and my noise monster has never shown its face again. My theory is that the foam is effective because it actually absorbs the RF signals and turns them harmlessly into minute amounts of heat. The problem with metal screening and chokes/capacitors is that these devices simply reflex the RF back. But back to where? The whole P3 box is already abuzz with these signals and they will try to get out anyway they can. The foam kills them dead. That's my theory anyway. If you have these or similar problems, give it a go. 73 Roger, VK4YB ______________________________________________________________ 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 |
|
|
Perhaps it was for the SVGA adapter, but I remember instructions to secure the cable closely along side the cabinet to prevent a problem of interference/radiation.
Dick, n0ce ----- Original Message ----- From: Roger Crofts To: elecraft reflector Sent: Monday, August 26, 2013 5:57 PM Subject: [Elecraft] P3 Spurii and a cure. I have had 2 problems with my P3 Panadapter, both were the subject of comment on the Reflector. The first was spurii radiated from the P3 DC cord and picked by my nearby antenna on 144 MHz. This problem was largely solved by fitting a commercial RFI filter in the DC cord and ensuring that all panels were clear of paint in the corners where the connections are made. The second problem was the occurrence of wideband noise humps which drift across the display from time to time obliterating the genuine signals. I dubbed the characteristic doubled-humped noise signature as my noise monster. Experiment showed that these spurii and noise products were being generated in the P3 itself. It was not possible to precisely pin-point the source of these signals inside the P3 using a small pick-up loop. The signals were strong everywhere inside the P3 box, but, perhaps, were strongest near the processor chips. This would seem to make sense, but not everyone has these problems, so clearly the mechanism for producing this hash, varies from chip to chip. Thanks to everyone who responded. I am now able to report I have found a complete cure for these problems which works in my case, but, of course, I can not guarantee it will work in every similar case. The cure involves the use of conductive foam. This is the black foam that ICs are normally pushed into when they are delivered. It is carbon impregnated. You can tell the difference between this conductive foam and ordinary foam using an ohmmeter. Pressing the probes against the conductive foam will give a reading of a few Kohms. Ordinary foam will be open circuit. This foam is available from many electronic suppliers. I bought my foam from Farnell Electronics (Now called Element 14 in Australia), order code 168-7846. The cost is 89 cents for a sheet about the size of the P3 side panel. I cut the foam to form compartments to completely isolate the front panel, IF input board, and IO board. I even put foam between the folds of the ribbon cable. In doing this I was carefully not to allow the foam to actually touch any components or bare wires, otherwise a circuit would be formed. I cut the foam panels deliberately oversize vertically, so that when the lid was screwed down, th er e was pressure to make sure the foam had a conduction path to ground. The result of this work was that all spurii have disappeared and my noise monster has never shown its face again. My theory is that the foam is effective because it actually absorbs the RF signals and turns them harmlessly into minute amounts of heat. The problem with metal screening and chokes/capacitors is that these devices simply reflex the RF back. But back to where? The whole P3 box is already abuzz with these signals and they will try to get out anyway they can. The foam kills them dead. That's my theory anyway. If you have these or similar problems, give it a go. 73 Roger, VK4YB ______________________________________________________________ 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 |
|
|
In reply to this post by Roger Crofts
Regarding the hump monster appearing on the screen of the P3:
I had this to a severe degree with my P3 when I first put it into service. Here are the results of my quick tests: 1. humps vanish when the P3 has no patch cord attached to it. 2. using a different BNC patch cord from the P3 to the K3 caused the humps to vary in intensity: a. using a 20 year old mil-spec BNC patch cord removed the humps completely. b. using a replacement from Elecraft improved the situation with smaller humps. c. using a different replacement from Elecraft also reduced the humps. As a result of the above, I use my 20 year old mil-spec BNC patch cord and am very happy. Not a big deal to me, it was easily fixed, and I am very happy with my P3. Bill W2BLC a happy K-line owner ______________________________________________________________ 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 |
|
|
Huh, I just noticed I have them too.
So, given that regular cables don't always remove these, how does one build a mil-spec bnc cable? Tom Sent from my iPhone On 2013-08-27, at 9:43 AM, Bill <[hidden email]> wrote: > Regarding the hump monster appearing on the screen of the P3: > > I had this to a severe degree with my P3 when I first put it into service. Here are the results of my quick tests: > > 1. humps vanish when the P3 has no patch cord attached to it. > 2. using a different BNC patch cord from the P3 to the K3 caused the humps to vary in intensity: > a. using a 20 year old mil-spec BNC patch cord removed the humps completely. > b. using a replacement from Elecraft improved the situation with smaller humps. > c. using a different replacement from Elecraft also reduced the humps. > > As a result of the above, I use my 20 year old mil-spec BNC patch cord and am very happy. > > Not a big deal to me, it was easily fixed, and I am very happy with my P3. > > Bill W2BLC a happy K-line owner > > ______________________________________________________________ > 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 |
|
|
On 8/27/2013 9:06 AM, Tom wrote:
> how does one build a mil-spec bnc cable? What's apparently causing the problem is poor quality of the coax, or the connectors, or the termination of those connectors by the third-party vendor. This is a VERY old problem -- my first P3, a fairly early serial number, came with a bad cable that didn't even have continuity! Bill is simply saying that he grabbed a decent cable, with good connectors, properly installed, from his junk box and it worked. 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 |
|
|
In reply to this post by tomb18
So a Pasterack bnc male to bnc male using 24" of RG58 is 23.90 + shipping
Not so bad if it fixes the problem. Is it supposed to be rg58? Thanks Sent from my iPhone On 2013-08-27, at 12:31 PM, George Danner <[hidden email]> wrote: > Tom, > Try Pasternack or Bracke. > > I've used their patch cables from audio up to 18 GHz. Both manufacture have > quality components & assembly. Prepare yourself for sticker shock! Quality > does cost. > > For my P3, I made my jumper with a piece of old RG-58 and double crimp BNC > connectors. That solved my issue. As an early P3 user (first group of kits), > the issue was not yet identified. During my experimenting others had found > the solution. My experimenting indicated there was a ground loop due to poor > shield connections. The Elecraft cable was crimped to a foil/braid shield. > > BTW - Poor full shield connections were an issue identified many years ago > in broadcasting when we switched from UHF connectors to BNC connectors. The > full shield coax that used a foil were (are) especially prone to ground > loops by not having a good connection at both connectors. I'm sure there is > a way to use this cable with BNCs, but we were never successful. We quite > using foil coax & non-crimped shields about 30 years ago. Analog video in a > broadcast plant needs to pass DC to at least 6 MHz. > > 73 > George > AI4VZ > > > -----Original Message----- > From: Tom > Sent: Tuesday, August 27, 2013 12:06 PM > To: Bill > Cc: [hidden email] > Subject: Re: [Elecraft] P3 Spurii and a cure. > > Huh, I just noticed I have them too. > So, given that regular cables don't always remove these, how does one build > a mil-spec bnc cable? > Tom > > Sent from my iPhone > > On 2013-08-27, at 9:43 AM, Bill <[hidden email]> wrote: > >> Regarding the hump monster appearing on the screen of the P3: >> >> I had this to a severe degree with my P3 when I first put it into service. >> Here are the results of my quick tests: >> >> 1. humps vanish when the P3 has no patch cord attached to it. >> 2. using a different BNC patch cord from the P3 to the K3 caused the humps >> to vary in intensity: >> a. using a 20 year old mil-spec BNC patch cord removed the humps >> completely. >> b. using a replacement from Elecraft improved the situation with >> smaller humps. >> c. using a different replacement from Elecraft also reduced the humps. >> >> As a result of the above, I use my 20 year old mil-spec BNC patch cord and >> am very happy. >> >> Not a big deal to me, it was easily fixed, and I am very happy with my P3. >> >> Bill W2BLC a happy K-line owner >> >> ______________________________________________________________ >> 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 > 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 |
|
|
On 8/27/2013 1:51 PM, Tom wrote:
> The > >full shield coax that used a foil were (are) especially prone to ground > >loops by not having a good connection at both connectors. While I agree with your analysis that the problem was a bad shield connection to a crummy cable, there's a bit more to understanding what's going on. Coax (and other transmission lines) reject noise and crosstalk by providing a low impedance, low reactance path for return current. That is, the current in the center conductor returns in the shield, so the total field outside the coax is zero, and no external field can couple into the transmission line. When that return connection is not there, the current returns by whatever path mother nature finds, a large magnetic field is generated that is proportional to the loop area, and any RF current near that loop is coupled into the circuit. Yes, one solution is to buy a decent cable. Another is to take a short piece of RG58 (or any coax with a copper braid shield -- the cable is far too short for Zo to matter) and put BNC connectors on each end. If you have a decent crimper for BNCs and some connectors, that's easy. If you don't, it's a bit more work. :) 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: P3 Spurii and a cure.
|
Administrator
|
In reply to this post by Jim Brown-10
We upgraded these BNC cables to much better quality versions some time ago.
73, Eric elecraft.com On 8/27/2013 11:36 AM, Jim Brown wrote: > On 8/27/2013 9:06 AM, Tom wrote: >> how does one build a mil-spec bnc cable? > > What's apparently causing the problem is poor quality of the coax, or the > connectors, or the termination of those connectors by the third-party vendor. > This is a VERY old problem -- my first P3, a fairly early serial number, came > with a bad cable that didn't even have continuity! > > Bill is simply saying that he grabbed a decent cable, with good connectors, > properly installed, from his junk box and it worked. > > 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 ______________________________________________________________ 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 |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |