SV: [AMPS] Re: Static discharge caused NOISE

[sm5ki]

No Tom I dont think so: When you use an antenna tuner you have ceramic
material in the discharge path and do you not get piezoelectric effects?
Making a lot of noise? I have much practical experience with a copy of the
old Johnsson Matchbox together with a very long longwire. The antenna was
connected to the variable capacitive divider in the matchbox and had no DC
connection to ground. In summertime I had very often a high noise level that
disappeared as soon as soon as I connected my NATIONAL R-175 choke from
antenna to ground. Without this choke there was often flash-overs as soon as
a thunderstorm was coming up.

sooner .......... Hans
----------
>Från: "Tom Rauch" <w8ji@contesting.com>
>Till: "Amps Reflector" <amps@contesting.com>, "Carl Clawson" <ws7l@arrl.net>
>Ämne: Re: [AMPS] Re: Static discharge caused NOISE
>Datum: lör 11 mar 2000 17.59
>

>
> 
>> > All antennas should be DC shorted to ground at the receiver input
>> > because
>> of
>> > another reason: a sometimes much lower level of receiving back-ground
>> noise.
>> > de Hans
>
>DC grounded antennas are no different in noise level that DC leak 
>antennas, or DC floating antennas with one exception.
>
>If the antenna charges up enough to arc something over, you will 
>hear a loud POP in the receiver. Other than that, they are just as 
>"quiet".
>
>My lowest noise receiving antenna for 160 meters are arrays of 
>eight verticals and four verticals that are NOT dc grounded in any 
>way at all. They are quieter than my arrays of Beverages, which are 
>dc grounded. 
>
>The reason the choke makes no difference is because the noise 
>outside the frequencies where the receiver is tuned does not make 
>it through the receiver, unless the receiver is very poorly designed. 
>At the operating frequency, the coke is a high impedance and so it 
>doesn't affect noise at that frequency at all.  
>
>> And we certainly need to keep the choke on the tank side of the output
>> relay. Otherwise the tank floats during receive. With HV on there are
>> probably enough ions to charge it up and cause arcs.
>
>Yep, that annoying tick tic as the leakage in the blocking cap 
>allows the variables to charge until the flash over! That can be 
>shocking.
>
>> It makes sense to put the rf choke at the output side of the relay 
>so that
>> it shorts anything that is not supposed to be there to ground - 
>and, as
>> Hans has suggested, improve receiving back-ground noise.  
>There is one
>> minor caution, though, in that the rf choke will drop in impedance 
>at some
>> point and affect received signals.  A 2.5 mh choke would be fine 
>through
>> 160 meters when using a low impedance antenna - but suppose 
>you also use
>
>A 100 microhenry choke is enough for 160 meters in a 50 ohm line. 
> 
>> Sorry to digress, but it really has to do with design of power 
>amplifiers
>> - and whether the rf choke should be hung on the output side of 
>the relay.
>
>A choke should always be used on the tank circuit end of the relay.
>
>
>73, Tom W8JI
>w8ji@contesting.com
>
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