Hi JC,
Very good webinar presentation (I watched the recorded version this past
weekend), and I always enjoy hearing what you have done, and your on the
air results are always very impressive.
I would like to comment about the statement you just made regarding "metal
box, not aluminum that allows magnetic field through".
Aluminum can't block a static magnetic field, but when we are talking about
RF the magnetic field is not static (it's amplitude is time varying).
Because it's amplitude is time varying, aluminum or any other metal can
provide an effective shield based on the skin effect principal (you just
have to factor in the resistivity of the material and operating frequency
to determine how thick the material must be to become an effective shield).
Aluminum and copper actually have resistivity values close to each other
compared with stainless steel which has much higher resistivity. Therefore
for a given thickness, aluminum and copper are much better shields than
stainless steel (as an example).
*Resistivity Values*
Copper: 1.7 uohm-cm
Aluminum: 2.7 uohm-cm
304 Stainless: 72 uohm-cm
Just FYI,
Don (wd8dsb)
On Tue, Mar 8, 2016 at 5:43 AM, JC <n4is@comcast.net> wrote:
> Hi Folks
>
>
>
> I have been working to improve my RX systems for several years. I ‘ve got
> good results using good practice on grounding shielding and detuning my TX
> antennas.
>
>
>
> I heard this several times from different hams, I need to update my system
> to the REAL WORLD, my station is close to perfection .. Well let me tell
> what is happening when I am installing WF. I am personally involve on the
> first 50 WF TOP-BEAM installations to make sure this thing about REAL WORLD
> is part of my RX system.
>
>
>
> With permission from PT9ZE let me explain what I found there . Zé Alfredo
> lives in a farm, not any rural location. The farm is near Brazil Bolivia
> and
> Paraguay border, the first city I hundreds of miles away.
>
>
>
> Would you imagine a quieter place to install a HAM radio Station?
>
>
>
> PT9ZE has an impressive station, 3 towers 120 ft. self-standing 500ft
> apart
> , 1st 3 elements YAGI on 80m + 15m, 2nd 4 elements full size for 40m +15m
> ,
> both 70 ft. boom, 3rd long 10m +6m.
>
>
>
> We installed the WF on the tower #2 below the 10 m 7 elements. UNREAL
> right!!
>
>
>
> PT9ZE noise was very REAL due these REAL things.
>
>
>
> 1- LG top line refrigerator, It uses a VFD motor and scream RF like
> crazy.
>
> 2- Siemens AC center unit. The noise sounds like 10 cw spark station
> in contest.
>
> 3- WiFi router
>
> 4- LED lamps
>
> 5- UPS
>
> 6- Cable/Satellite TV box.
>
> 7- Wall power supply for cellphone, computer and wireless telephone
> extension.
>
>
>
> And the list of noise devices we found goes on and on..
>
>
>
> The station have an extensive ground system, all cables buried. Just
> perfect. It was necessary to choke all those devices , I mean heavily choke
> all wires in and out the devices.
>
>
>
> Well …..welcome to REAL word, the ham radio practices from the last
> century,
> unfortunately few years ago are no longer enough or apply for REAL WROLD.
>
>
>
> The REAL WORLD we live today brought the noise inside our homes. We need to
> adapt fast if we want to keep enjoying radio.
>
>
>
> Things I presented on the Webnair unfortunately is very real, grounding,
> shielding using metal box, not aluminum that allows magnetic field through
> .
> Run RX lines for receiving antenna inside metal conduit to avoid common
> mode
> noise from inside and outside your hone.
>
>
>
> One single connector with bad contact between coaxial braid and the PL259
> was enough to allow s4 of noise into the receiver and this was after the
> preamplifier.
>
>
>
> I think the real world is here to stay and we need to review our best
> practice for low band stations.
>
>
>
> A SWL AM/SSB portable radio to sniff the new source of noise is a very
> important tool for the Real World.
>
>
>
>
>
> 73’s
>
> JC
>
> N4IS
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
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