[RFI] Maintaining 50 Ohms...

[Grant Saviers]

For Tx antennas the power rating of the resistor is the limiting factor. 
  For "nominal" QRO @ 50 ohms, about 300 volts RF so 68K ohms would 
dissipate 1.32 watts @ 100% duty cycle.  Allen Bradley 2w carbon 
composition resistors still can be found on ebay, and having very low 
inductance and high surge resistance, are my go to choice.

Elevated radials have a lot of capture area for coupling to the ground 
and field transient from nearby strikes, so a bleeder is important IMO.

Grant KZ1W

On 9/17/2021 17:54, David Eckhardt wrote:
> I have lost too many preamps due to near-by lightning and static
> discharge.  After the last (expensive) MMIC failure, I have made a practice
> of installing a resistor to return (chassis or "ground") across the input
> coaxial connector.  The value is anything over 10 kohms.  The disturbance
> to the 50-ohm impedance is completely negligible.  The rule-of-thumb on the
> resistor value is something over 10X the system impedance.  I've even used
> 1k successfully.  Go for it !!
> 
> Dave - WØLEV
> 
> On Fri, Sep 17, 2021 at 10:36 PM Dave <dave at nk7z.net> wrote:
> 
>> Hi,
>>
>> I am building a static bleed resistor, (5 Mohm), inserter, and want to
>> place it on the transceiver output, not at the feedpoint of the antenna...
>>
>> I have not seen this done in this way before, which may indicate there
>> is something bad about doing it this way...
>>
>> Does anyone know why this might be a bad idea, assuming I can maintain
>> 50 ohms while adding 5 Mohms to ground off the center of the coax?
>>
>> --
>> 73, and thanks,
>> Dave (NK7Z)
>> https://www.nk7z.net
>> ARRL Volunteer Examiner
>> ARRL Technical Specialist, RFI
>> ARRL Asst. Director, NW Division, Technical Resources
>> _______________________________________________
>> RFI mailing list
>> RFI at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
> 
>