DVP Hum

[W8JITom at aol.com]

In a message dated 96-09-18 21:46:24 EDT, you write:

>
>At this point, I don't even know for sure that the hum isn't the result of a
>cable shield being PROPERLY connected, rather than an open or something
>else.  Before I spend an afternoon scrambling around behind my computer,
>under my operating desk, can anyone tell me whether a 1:1 isolation
>transformer in the headphone line would solve the problem, and might even be
>the most reliable protection against a recurrence?
>
>Thanks, all...  
>
>73, Pete Smith N4ZR
That's a big problem with any external audio accessory. I have that problem
with a VOMAX audio processor.

Sometimes the problem can be eliminated by direct grounding of the accessory
to the rig's cabinet. At times you need to cut the shield at one end of the
path (only when the equipment has another very good ground path), and at
times a 1:1 isolation transformer is required to eliminate hum.

If the computer has a three prong plug be sure it's plugged into the same
outlet or outlet strip as the rig. The ground loop voltage usually comes from
the neutral of the power line, a tiny voltage difference betwwen the cabinets
from the tiny difference at the outlets sets up a small common mode current
in the unbalanced audio cable .

73 Tom

>From sm3bdz at pobox.com (Lars Harlin)  Thu Sep 19 17:40:57 1996
From: sm3bdz at pobox.com (Lars Harlin) (Lars Harlin)
Date: Thu, 19 Sep 1996 18:40:57 +0200
Subject: 80m 4-square owners...
Message-ID: <199609191640.SAA17385 at www.itz.se>

                                                                             
At 06.05 1996-09-19 -0500, you wrote:
>At 05:44 PM 9/17/96 +0200, you wrote:
>
>>Talking about efficiency, I mean that there are two
>>kinds. RADIATION-efficiency and REFLECTION-
>>efficiency. To benefit from both I guess that there
>>is no substitute for 100 radials, elevated or
>>on the ground.
>>
>>Still, as I ve no room for 100 radials I use elevated
>>radials so that I at least can get good RADIATION
>>efficiency, and I must say that so far it s the best
>>antenna I ve had for 80!
>>
>>
>>73 s de Lars / SM3BDZ
>
>After seeing and hearing 4-Squares on 80M. They only have about 3 DB signal
>advantage
>over an inverted vee antennaas, and some good front to back ratio.
>
>No one I have talked to has ever tried a Mono pole vertical and for that=
 matter
>a 4 square made up using them.  Sure the feed pint at the base of a single
>vertical
>is 300 ohms but can be used to your advantage.

Sri Jim, but I disagree. You wont get 300 ohm feedimpedance with that
arrangement.
A folded vertical works as a impedance-transformer with 1:4 ratio. Then if
you have a perfect=20
groundplane the transformation will be 4 times 36 ohms =3D 144 ohms.=20
=20
>No need for 100 radials because the ground return path on this antenna is
>much better
>thus have better effecancy.  The monopole is a quater wave antenna folded
>over.

Wrong again. Even if you have impedance-transformation you will still have
THE SAME
radiationresistans so that the groundloss/rad.res. ratio will remain=
 unchanged!


>At least try one and see if it makes a difference.  Seams to not couple=
 into
>the sorroundings, and acts more like what an antenna should with no
>compromises.  You
>should have about 300 KHZ band width if you use it.

That I doubt! But on the other hand a good dummyload has almost infinite
bandwith !.... :-)

>73es Jim WA9YSD
>Family of J. A. Borowski's  All at jabruski at execpc.com
>Joan, XYL=20
>Juli
>Janice
>Justin
>Jim, WA9YSD, OM
>

73=B4s de Lars/SM3BDZ