[Elecraft] P3 Hash

[Jack Smith]

If you look at an HP/Agilent 75 ohm BNC connector you will find it has 
no supporting insulation, just the bare spring finger in the female 
version or the outer metal shell in the male version.

As far as I have been able to determine from checking dimensional 
drawings, BNC 50 and 75 ohm connectors will mechanically mate without 
damage. There will be, of course, a bump in the line that may or may not 
be of concern.

There may have been some very old BNCs - 1940's vintage - for which the 
pins are different diameter but that seems not to be the case for 
anything made in recent times.

50 and 75 ohm N connectors, in contrast, do not physically mate as the 
75 ohm male pin is smaller diameter than the 50 ohm version. If mated 
with a 50 ohm female, the center pin will not make reliable contact. 
Worse yet, a  50 ohm male N will splay out the spring fingers in a 75 
ohm female connector and damage it.

Jack K8ZOA


On 8/17/2012 3:20 PM, Brian Alsop wrote:
> There are 50 ohm and 72 ohm BNC's.  They look the same.  They differ in
> the pin details and dielectric used.
>
> See for example:
> http://www.milestek.com/blog/index.php/2011/04/50-ohm-vs-75-ohm-bnc-connectors-explained/
>
> They supposedly can be plugged in to the "other type" without damage.
> I'm not sure just what that means.
>
> 73 de Brian/K3KO
>
> On 8/17/2012 17:15, Rowland R Johnson wrote:
>> I had the same problem. Replacing the BNC coax cable (between the P3 and
>> K3) with one I had lying around fixed it. Howard at Elecraft tech
>> support then sent a new cable that arrived 36 hours after I talked to
>> him. This new cable from Elecraft worked fine, for a while, but then
>> started having the same kinds of problems. I put my old cable that I had
>> lying around back on and it's worked for several months now.
>>
>> I haven't pursued getting a second replacement from Elecraft because it
>> hardly seems worthwhile. In addition, it's not 100% clear to me that the
>> problem is the cable. With the 2 Elecraft cables I've noticed some
>> difficulty in connecting the BNC plug to the BNC receptacle on the back
>> of the P3. Not so with my old cable. The supposition being that the
>> physical dimensions of BNC receptacle on the P3 aren't quite right.
>> Whereas the new cables have a problem fitting, my old cable may be worn
>> enough that it fits anyway.
>>
>>
>> On 8/17/2012 9:00 AM, Gene Trasti wrote:
>>>> P3 with svga
>>>>
>>>> I have a considerable amount of "hash" on my panadapter screen.  It tracks the same spot on all bands.  All my equipment is very well grounded.  I have measured my shack for RFI-it is very clean.  I swapped out my switching power supply for a highly filtered one.  I even purchased a pretty expensive ac terminal strip with isolation transformers.  I have been through the house and have virtually switched off and unplugged everything-nothing seems to help.  This hash takes up a pretty healthy portion of the bandwidth.  Any sugestions would be appreciated.  Is it possible that this could be a problem with the P3 or K3 they are both factory built-although I added the svga board using a wrist ground..
>>>>
>>>>
>>>> Gene. W6jmp
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