[hank alrich]

Back in Austin at the dance studio I've started looking into a problem
with one of the Sennheiser EW100 G2 units. Sometimes the receiver puts
out a lot of trash; other times is works as intended.

I've just discovered that this is coming from the Gemini CDX-601 player
immediately above it in the rack, and that the level of the interference
is dependent on the amount of bass info in the CD being played!

Not only that, but if the CD player is powered-up and there is no CD in
the drive the RF is very strong.

I've not yet run through all available channels to see if this happens
accross the spectrum, but this seems very weird, and suggests the Gemini
probably does not meet FCC standards for lack of spurious emissions.

--
ha
shut up and play your guitar

[Scott Dorsey]

hank alrich wrote:

I've not yet run through all available channels to see if this happens
accross the spectrum, but this seems very weird, and suggests the Gemini
probably does not meet FCC standards for lack of spurious emissions.

This is about typical for consumer electronics these days. But it's possible
that it may actually meet Part 15 requirements, which are pretty slack.

It's expensive to build quiet switching supplies.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Chris Hornbeck]

On Wed, 3 Dec 2008 17:18:46 -0600, (hank alrich)
wrote:

Back in Austin at the dance studio I've started looking into a problem
with one of the Sennheiser EW100 G2 units. Sometimes the receiver puts
out a lot of trash; other times is works as intended.

I've just discovered that this is coming from the Gemini CDX-601 player
immediately above it in the rack, and that the level of the interference
is dependent on the amount of bass info in the CD being played!

Not only that, but if the CD player is powered-up and there is no CD in
the drive the RF is very strong.

I've not yet run through all available channels to see if this happens
across the spectrum, but this seems very weird, and suggests the Gemini
probably does not meet FCC standards for lack of spurious emissions.

Scott and Bob have already said everything really interesting, and
I can only add the obvious: It's wierd, isn't it?

RF interference is one of the strangest things that we deal with
"in these days of modern times" with its lack of generality and
its maddening threshold effects, intermittancy and lack of FCC
oversight. But that's why we get the Big Bux. Arf.


Much thanks, as always,
Chris Hornbeck
And, FWIW, it's much, much more fun than a computer virus. Be Happy!

[Richard Crowley]

"hank alrich" wrote...
Back in Austin at the dance studio I've started looking into a problem
with one of the Sennheiser EW100 G2 units. Sometimes the receiver puts
out a lot of trash; other times is works as intended.

I've just discovered that this is coming from the Gemini CDX-601 player
immediately above it in the rack, and that the level of the interference
is dependent on the amount of bass info in the CD being played!

Not only that, but if the CD player is powered-up and there is no CD in
the drive the RF is very strong.

I've not yet run through all available channels to see if this happens
accross the spectrum, but this seems very weird, and suggests the Gemini
probably does not meet FCC standards for lack of spurious emissions.

Putting a sensitive receiver right next to any digital device
may be beyond what the Part15 specs allow for.

Are the antenna(s?) right on the back of the receiver, or are
they mounted at least a few feet away?

What happens if you swap the position of some of the rack
equipment to put something between the CD player and the
receiver? Metal rack?

[Ralf R. Radermacher]

hank alrich wrote:

Not only that, but if the CD player is powered-up and there is no CD in
the drive the RF is very strong.

Reminds me of a friend's stereo amplifier that broadcast its input
signal five blocks down the street in the 49 m band.

Ralf

--
Ralf R. Radermacher - DL9KCG - Köln/Cologne, Germany
private homepage: http://www.fotoralf.de
manual cameras and photo galleries - updated Jan. 10, 2005
Contarex - Kiev 60 - Horizon 202 - P6 mount lenses

[philper]

On Dec 4, 1:22 am, (Ralf R. Radermacher) wrote:
hank alrich wrote:
Not only that, but if the CD player is powered-up and there is no CD in
the drive the RF is very strong.

Reminds me of a friend's stereo amplifier that broadcast its input
signal five blocks down the street in the 49 m band.

Ralf

--
Ralf R. Radermacher - DL9KCG - Köln/Cologne, Germany
private homepage:http://www.fotoralf.de
manual cameras and photo galleries - updated Jan. 10, 2005
Contarex - Kiev 60 - Horizon 202 - P6 mount lenses

In my experience Gemini occupies the lowest rung of Chinese
electronics manufacturing--the worst design, lowest quality, most
problem prone and least supported. But they are cheap! You could
move the RX away from the player, maybe find some other device to put
in the rack between the two, grab some lead sheeting (or mu metal,
except that that's expensive) and see if any of that makes a diff.
Remoting the antennas from the RX might help as well--it certainly
does on my sound cart--get them up away from the local hash.

Philip Perkins

[Richard Crowley]

Phillip Perkins wrote ...
... You could
move the RX away from the player, maybe find some other device to put
in the rack between the two,

Excellent advice.

grab some lead sheeting (or mu metal,
except that that's expensive) and see if any of that makes a diff.

Simple aluminum foil would do the job here (for RF).

Lead is needed only if you need to block ionizing radiation
(e.g. x-rays, etc.). Or for blocking acoustic transmission
(such as lead sheets in walls, etc.)

Mu-metal is useful in blocking magnetic radiation (as from
a CRT, etc.), but we are talking about RF here. It is also
frightfully expensive and difficult to use.

Anything conductive will block RF (as in this case). While lead
and Mu-metal would work, they are vast overkill and much more
expensive than aluminum-foil. Of course, whatever the metal you
use, it must be grounded to the chassis of the CD player at some
point, or else it just becomes an antenna element itself.

Remoting the antennas from the RX might help as well--it certainly
does on my sound cart--get them up away from the local hash.

Absolutely. And especially if the equipment is in a metal rack
(which will *shield* the antennas from the desired signal (the
microphone transmitter), while *enhancing* the ability to
"receive" the hash from inside the rack.