[TenTec] Re: Orion - Jupiter Microphone Connections

Sun Apr 18 18:55:04 EDT 2004

John is correct with regard to grounding.  There's 3 kinds, each different
in its requirements.
(a) the power or AC ground, specifically for safety reasons.  Easy to obtain
by a driven rod at the main power entrance to the structure.  Connected to
the neutral side of the AC lines as provided by the power company.  Most
equipment has a 3rd pin ground (unless removed) for safety reasons.  I do
not suggest removing 3rd pin ground in any circumstance.

(b) RF ground, as stated to ground RF. However, we need to look at this one
closely.  Remember any distance between the radio and RF ground is some
portion of a wavelength at some frequency.  Realizing this, then a
"conceived RF ground" that is some 9 ft in length is 1/4 wave at 10 meters.
At 1/4 wave one sees a maximum of RF voltage.  I really wouldn't consider
this as RF ground even though it may measure a few tenths of an ohm.  The
reactive value is quite high.  Using a large surface copper straps does
reduce inductance but keep in mind, RF ground must be very short distance
with regard to the RF frequency in question.  By all means, stay away from
1/4 wave and 3/4 wave increments for RF ground.

(c) lightning ground, designed to dissipate large amounts of energy as
generated by a lightning strike.  Best located at the base of the tower.
Many different methods are effective.  However, one thing often overlooked
is to be sure that all things on the tower, antennas, feedlines, rotors,
masts and such have a solid bond to the tower.  To that end, in most cases,
we never get actually struck by lightning.  We do get however see the
results of near strikes and this is where the problem arises.  A nearby
strike produces a "step voltage" which is dissipated across the surface of
the earth.  Analyze this:  two grounds, AC ground and tower ground separated
by some 50 feet.  There is a difference in potential between the two during
a nearby strike.  Answer this;  is your radio equipment connected to both?
If so, then the likely hood of damage to the radio equipment is quite great
due to difference in potential between the two.

While many will argue this, the safest method is to securely bond ALL
grounds together to minimize the difference in potential between any of
them.  This is the safest method for the structure, the tower and the
associated electronics.  Yes, tie all grounds together with as big of a
conductor as your can afford and install.

Keep this in mind,  due to the excessive energy in a lightning strike, and
in the unlikelihood of a direct lightning strike.........nothing helps
except not being where lightning strikes.  Bottom line, something is going
to fry!  However, by using safe, effective grounding schemes we can minimize
the damage and that is to be sure all grounds are securely bonded together.

If you would like to read more on lightning grounding and structure
protection as electronic safety, a return e-mail will get a Microsoft Word
document on the topic.

As to internal grounding, microphone connections and RF, I suspect that
radiation back into the associated equipment or cables is the culprit.
Grounding won't solve it unless one is at the electrical end of a 1/4 wave
or 3/4 wave ground pole.  As to inserting a transformer, this is simply a
frequency limiting device (it won't pass RF) so the RF induced into the mike
cable won't get into the rig. I don't advise this approach as impedance
matching, common mode rejection, and associated humm pickup may prevail.

73
Bob, K4TAX

----- Original Message ----- 
From: <N0KHQ at aol.com>
To: <tentec at contesting.com>
Sent: Sunday, April 18, 2004 8:53 AM
Subject: [TenTec] Re: Orion - Jupiter Microphone Connections

> The microphone connections on both rigs are unbalanced ( mic + and -
Grnd).
> Now there is nothing wrong with this setup mfrs. have been doing this
forever.
>
> The Orion, Jupiter and Peg are computers in a transceiver case and in an
RF
> environment. Standard RF grounding techniques do not apply. All computer
> systems not only require special grounding techniques but also require
special power
> supply techniques.
> The NEC is concerned with safety not quality. (see balanced power systems
vs.
> standard power systems)
>
> Where a lot of hams go wrong is when they try to use (1) ground for
> everything and its just not going to work. This may work on standard rigs
but isn't
> going to work on computer designed rigs.
>
> There are (3) types of grounds that should be considered:
>
> AC Ground (from the service panel outdoors to a grounding rod)
> RF Ground
> Lightning Ground (at towers)
>
> And contrary to some on this list these grounds are separate and not
> interchangeable. Each ground is a "special purpose" ground. (see broadcast
engineering
> grounding)
>
> If you are experiencing RF in your rig, it is not the rig that's at fault.
>
> It is true, that if you take an ohm meter and measure the resistance from
the
> ground lug on the back of the Orion or Jupiter to the ground pin on the
> microphone plug you will see approximately 3 to 4 ohms of resistance, this
is a
> no..no and can be easily corrected. Any resistance here looks like a path
for RF.
>
> The Orion is a great radio and should not be confused with other mfrs.
rigs.
> Lets compare apples to apples and not oranges to apples.
>
> There is only one other rig on the market today that is based on the same
> technology as the Orion / Jupiter / Peg, and that is the SDR-1000
(FlexRadio).
> (that I'm aware)
>
> To help cure RF in the audio chain one might add an isolation transformer
at
> the mic input. (Jenson xfmrs)
>
> My hat is off to Ten-Tec for always leading the way and not following.
There
> are just a few things in your stations construction that may have to be
> modified.
>
> I like my Jupiter, and not because its the prettiest thing I ever saw.
(wish
> it was black)
>
> I also like my IC-756Proll, but like I said, lets compare apples to
apples.
>
> Just my $ 0.02
>
> 73
> John / N0KHQ / St. Louis
>
> Always on 18.130
>
> Antennas:
>
> You can build 'em better than you can buy 'em
> Please visit the sites below:
> http://www.hamuniverse.com/17mcoaxmox.html
> http://www.cebik.com/n0khq.html
> http://www.ssb-audio.com/forum/
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>