[hpsdr] Mercury Spurious Emissions

[Helmut Oeller]

Hi,

I'm really wondering at the discussion: An 'ancient' law says that each RF
device should operate in a metallic closure, only reasonably opened for
shielded connectors and may be ventilation through a metallic grid. If you
follow this recommendation you will have no problems. Forget every checks
with a handheld FM rig near the open closure.

All the spurs of my 2 mercuries directly connected with the spectrum
analyzer via BNC are below -80 dBm.

Don't worry, enjoy HPSDR

73 Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Jeremy McDermond
Gesendet: Sonntag, 11. September 2011 06:26
An: Joe Martin K5SO
Cc: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] Mercury Spurious Emissions

***** High Performance Software Defined Radio Discussion List *****

On Sep 10, 2011, at 4:54 PM, Joe Martin K5SO wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> On Sep 9, 2011, at 5:52 PM, Jeremy McDermond wrote:
> 
>> It seems as if Mercury is radiating spurious signals into the antenna
connector.  The symptom is showing up on 144.390 MHz.
> 
> Using my IC910 with a whip antenna a few feet from my HPSDR enclosure
(Antec) I too can see a signal at about S3-S4 strength showing up at 144.390
(or image thereof) when my three Mercs are running.  However, the signal is
NOT being radiated from the Mercury antenna connector.  In fact, when I
directly connect the input of the IC-910 to the Mercury antenna connector
the signal appearing at 144.390 MHz (or it's image, of course) actually goes
away.  The emissions you are seeing are coming from the bus or the boards
and not being output through the antenna connector, it seems.

I'm not seeing the same thing on my system.  If I disconnect the antenna
connector from the system, I do see the S3-S4 signal, which isn't such a big
deal.  If I connect the antenna to the system it becomes at least an S9
signal, if not more.  Without the antenna connector it isn't noticeable on
the mobile that's like 20 ft away.  With the antenna connector on, it's S9
on that mobile.  Interestingly if I merely touch the shields of the BNC, I
see this behavior.  This seems to indicate that it's coming through the
ground side connection.

> That such VHF signals are present in the immediate vicinity of the HPSDR
rig is not very surprising of course, no more so than similar type signals
emanating from any bus-driven computer system, since the bus has relatively
large amplitude square wave signals on it.   I was concerned that something
was being radiated via the Mercury antenna connection, as was initially
suggested...or at least I that's what I thought that's what the suggestion
was.  Well, it isn't, in any case.

I'm not necessarily suggesting that this is a design issue or a general
issue with Mercury in general.  I do know that the behavior of mine differs
when I have the antenna ground connected.  I'm just trying to figure out
whether I have a problem with my particular Mercury.  Of note is that my
portable antenna is only around 10 feet away from the radio and there are no
walls between the radio and the antenna.  So, proximity could be an issue,
but it certainly seems for me that the antenna makes a difference.

I made a quick and dirty video showing the issue:

http://www.youtube.com/watch?v=BxJJFe9PjFc

> In this case it seems that standard, or perhaps elaborate, rf shielding
techniques should be able to reduce the bus or board emissions to an
acceptable level in the vicinity of the HPSDR rig, as has been already
suggested.  Anyway, no wonder I didn't see much with the spectrum analyzer
except for the 122.88MHz clock and it's harmonics when I connected directly
to the BNC connector on Mercury earlier.  The problem you see isn't coming
from there, clearly.
> 
> For your demos, in which folks may have handhelds right up next tot the
HPSDR rig you may need to simply have a super shielded setup and not run
with the covers off, but that hardly is conducive to showing people what the
rig looks like.  At least I think you by now have a good idea what the issue
actually is, right?
> 
> 73,  Joe K5SO

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com



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