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Grounding of Active Antennas Like The Mini-Whip

Posted: Thu Feb 22, 2018 6:50 pm
by Aries
I've been reading about the grounding of active mini-whip antennas to improve the signal, and I have a query about grounding when using a non-conductive mast.

Dr Boer at the University of Twente says that you can mount these mini-whip antennas on a conductive or non-conductive mast.
http://www.pa3fwm.nl/technotes/tn07.html
Whether the mast is conductive or not hardly matters for the reception.
What if the mast is not conductive? The amplifier will still measure the potential difference between the plate and the "ground" of the amplifier circuit. If the mast is not conductive, then the only thing connected to the circuit ground is the shield of the coaxial cable. In that case, the potential difference will be measured between the plate and whatever that cable shield goes to. If the cable shield is solidly connected to ground somewhere further on, it will work just as well as with a grounded mast.
He further goes on to say
if the mast is non-conductive, making a connection between the cable's shielding braid and a ground electrode.
http://www.pa3fwm.nl/technotes/tn09d.html

Would I be right in thinking the grounding of the cable's shielding would be done from the bottom of the non-conductive mast?
i.e. the coax runs from the antenna down the non-conductive mast, then at the bottom of the mast I ground the cable shielding with an earth stake?

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Fri Feb 23, 2018 4:17 pm
by hotpaw2
A mini-whip likely uses either the outer coax shield or the mast as part of the antenna (the counterpose), so it likely doesn't matter as long as both are far away from noise sources (e.g. up high).

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Sat Feb 24, 2018 6:52 pm
by snn47
Lightning protection is imho a reson for using a a grounded (for lightning) conducting antenna mast .

For reception grounding will have a minute impact, since actice antennas are not resonant at their operating frequency unlike antennas that can be used for transmit and receive. Actice antennas are short to most wavelength it supports.

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Mon Mar 05, 2018 11:05 pm
by phil
I have a mini whip i use for long wave in a rural environment, and grounding does make a difference here. The noise floor is lower with the antenna earthed at the base ( 4 ft star picket driven down so only about 3 inches show).

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Thu Mar 08, 2018 3:00 pm
by Aries
phil wrote:
Mon Mar 05, 2018 11:05 pm
I have a mini whip i use for long wave in a rural environment, and grounding does make a difference here. The noise floor is lower with the antenna earthed at the base ( 4 ft star picket driven down so only about 3 inches show).
How exactly have you got your grounding set-up?

I live about 3 miles from the nearest town, and located my antenna on a 15ft mast about 70ft from the house. The noise floor on it is incredibly high. I can see lots of signals, but the noise is drowning them out.
I tried attaching a ground line from the coax to a 4ft copper grounding rod and it made no difference at all.

The University of Twente have their mini-whip antenna located in an urban area, and they get an excellent signal with good grounding, so it should in theory be possible to get a good S/N ratio in my environment.

I'm using a linear power supply, so that shouldn't be causing much interference.

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Thu Mar 08, 2018 9:58 pm
by phil
I suppose it may come down to what type of soil you have, i have read in some scenarios several earth points have been used in poor conductive soils.

Mine's pretty crude, i just split the RG-58 at the base of the mast (4M galv. pole with a 1M pvc tube at the top). The braid on both ends has a crimped eyelet and bolt arrangement which goes through the stake. The centres of the coax are joined with small single terminal block. This is all located right next to the house.

I have into looked the info provided by the University of Twente about their setup in an effort to gain better reception above 5MHz (theirs is excellent right through HF, but here, my random wire in an "L" configuration leaves the mini-whip in the dust.

Re: Grounding of Active Antennas Like The Mini-Whip

Posted: Mon May 07, 2018 3:06 pm
by illllm
I do grounding for 4 feet this way: 6inch circumference hole , 4 feet long . Grounding rod in middle then first I pour in 1 foot of charcoal, one pound rock salt on that. Then I add I foot of dirt. Then one feet of coal, then one pound rock salt on that. Cover it all with dirt. Works perfectly.