Shorter Ground wire

[am1670acr]

From what I have read on this board and others, traditionally power and audio are sent up to the transmitter and from there, the transmitter is grounded back to earth ground.

Assuming we are dealing with a DC powered transmitter, has anyone tried to ground the power and audio first to an earth ground and then send the power and audio up to the transmitter. This would eliminate the need for another wire or large conductor run back down to the earth ground. The connection to ground would most likely be to the center of radial spokes and an 8 foot ground rod.

Would there be any noticeable difference in the signal by grounding it this way?

 

[pbolyn]

The importance of a very good ground system for part 15 AM transmitters cannot be overemphaized. A very good ground system is your best opportunity to increase your range. A less than perfect ground causes a large portion of your output power to be lost through disipation in any greater-than-zero ground resistance.

What you are proposing would work to an extent, but the ground path through your probably long audio and power feed wires would not be very good. A shorter, and best-conductance ground path to a system of long buried radial wires will yield the lowest ground resistance without the added resistance and RF impedance of a longer run of smaller wire from the audio/power feed source.

Phil B


> From what I have read on this board and others,
> traditionally power and audio are sent up to the transmitter
> and from there, the transmitter is grounded back to earth
> ground.
>
> Assuming we are dealing with a DC powered transmitter, has
> anyone tried to ground the power and audio first to an earth
> ground and then send the power and audio up to the
> transmitter. This would eliminate the need for another wire
> or large conductor run back down to the earth ground. The
> connection to ground would most likely be to the center of
> radial spokes and an 8 foot ground rod.
>
> Would there be any noticeable difference in the signal by
> grounding it this way?
>
<P ID="signature">______________
Phil B
</P>

 

[part15guru]

> The importance of a very good ground system for part 15 AM
> transmitters cannot be overemphaized. A very good ground
> system is your best opportunity to increase your range. A
> less than perfect ground causes a large portion of your
> output power to be lost through disipation in any
> greater-than-zero ground resistance.
>
> What you are proposing would work to an extent, but the
> ground path through your probably long audio and power feed
> wires would not be very good. A shorter, and
> best-conductance ground path to a system of long buried
> radial wires will yield the lowest ground resistance without
> the added resistance and RF impedance of a longer run of
> smaller wire from the audio/power feed source.
>
> Phil B
>
>
> > From what I have read on this board and others,
> > traditionally power and audio are sent up to the
> transmitter
> > and from there, the transmitter is grounded back to earth
> > ground.
> >
> > Assuming we are dealing with a DC powered transmitter, has
>
> > anyone tried to ground the power and audio first to an
> earth
> > ground and then send the power and audio up to the
> > transmitter. This would eliminate the need for another
> wire
> > or large conductor run back down to the earth ground. The
> > connection to ground would most likely be to the center of
>
> > radial spokes and an 8 foot ground rod.
> >
> > Would there be any noticeable difference in the signal by
> > grounding it this way?
> >
>

While you are absolutely correct in stating that a GOOD ground system is essential for AM transmitting antenna systems, unfortunately, the FCC rules state the following: The antenna, feedline and ground system CANNOT exceed 3 meters in length! So elevated radials, spoke-type radials on the roof, etc are ALL illegal under part 15 rules. I feel your pain!

Part15Guru

 

[wcummings]

The FCC to my knowledge has never enforced the ambiguous rule that the ground lead length be a part of the antenna and antenna feedline length calculation.

In fact, the FCC has blessed part 15 AM installations using Hamilton transmitters that were mounted on top of large metal structures such as a roadside billboard.

One could argue that since the transmitter is elevated 100 feet above ground on top of the billboard's metal frame, that the length of the frame's electrical path to ground should be considered in the 3 metre rule. The FCC did not see it that way. (BTW, I personally knew of this FCC blessed transmitter that was located on Hwy 99 near Stockton, CA on top of a billboard. Range was about 4 miles.)

The poorly written rule is ambiguous on many levels.

>
> While you are absolutely correct in stating that a GOOD
> ground system is essential for AM transmitting antenna
> systems, unfortunately, the FCC rules state the following:
> The antenna, feedline and ground system CANNOT exceed 3
> meters in length! So elevated radials, spoke-type radials
> on the roof, etc are ALL illegal under part 15 rules. I
> feel your pain!
>
> Part15Guru
>