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@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
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