On Thu, 18 Aug 2005 10:54:21 -0500, (Richard
Harrison) wrote:
Thank-you Richard for the prompt reply, which I am afraid I understood
little of (! my fault not yours)


Stephen Parry wrote:
"I drive a truck on the continent of Europe, and would love to listen to
this service on the road for cricket."

The Blau Punkt in my Karman Ghia got such signals all over the
continent, and I`m just one of millions.

Mr Parry did not say if his truck is Diesel powered as most European
trucks are.
Yes Diesel power, so no HT coil, plugs, distributor etc
If so, he is free of his own ignition noise, usually the
hardest to suppress.
Ok.
He still may have alternator whine (perhaps a bad
diode)
Yes I think I do have alternator noise could you explain what I might
do ?
and he may have static discharges from things which rotate. Some
are under the hood, and their radiation should be kept under the hood by
the metal surrounding them. All such metal pieces should be bonded
together to keep the trap they form closed.

All conductors coming through or under the firewall should be well
grounded or bypassed with capacitors at the firewall. The exhausr pipe
may need bonding here also.
I think we might have been divided by our common language! My truck
has no "hood" as such http://www.duet-duda.mojagielda.pl/?9

Maybe there is a gasoline powered rerfrigeration compressor generating
ignition noise. Standard resistance wires, capacitors, and bondibg
should silence that.
No 'fridge
Springs can be used in wheel hubs to ground out static.
I did not understand this part

All the metal parts of the truck may have to be bonded together.
Or this

My Blau Punkt was equipped with a good sized choke coil in its battery
lead. It also had an internal "spark-plate" capacitor, and these rid the
power source of radio noise.
Or this

The telescoping antenna (about 50 years ago) could be extended to about
100 inches, which made the Karman Ghia quite a sight, but it worked. The
antenna cable was the standard high-impedance small inner-wire coaxial
type. This must be intact and perfect to keep the signal on track and
the noise out. Though German, it used Motorola connectors.

Radio frequencies decline very rapidly near their source. This is your
friend when the source causes interference.
Sorry, this too!
Keep the antenna away from
and shielded from sources of interferebce.
When you say "bonding" I am guessing this means a clean earth return
to battery?

In 1935, Alfred A, Ghirardi (E.E.) wrote:
"---an aerial must be installed in (or on) the roof, under the running
boards or chassis of the car, or in some other locations.
---Considerable attention must be given to the ignition and other
electrical wiring of the car in order to eliminate all electrical
interference which it produces in the receiver."

Noise problems are more often caused by the vehicle than by the receiver
but some receivers may not be shielded and filtered well enough. If the
truck cab has its pieces bonded together and all pass-through conductors
are well bonded or bypassed, it should be electrically quiet. You should
be able to use a portable radio in there with proper placement or an
outside antenna.

Ghirardi devotes an entire chapter to automobile radio installation in
"Modern Radio Servicing". Car radios are hot in the summer months while
home radios are not.

Best regards, Richard Harrison, KB5WZI

Stephen Parry wrote:
"Yes I think I do have alternator noise could you explain what I might
do?"

Often the first sign of diode failure is a whine in the loudspeaker of
your radio which varies in pitch with engine speed.

Alternators have no commutator but use silicon diodes to make d-c from
the a-c they generate. It`s usually 3-phase, using (6) diodes in (2)
groups of 3 each in a full-wave rectifier. These are located inside the
alternator. If any of the diodes fails, at least one of the 3 pahases
quits contributing to the alternator output. Maximum output is reduced.
Replace the diodes. The whine goes away and full output is restored to
the alternator when required.

Stephan also wrote:
"I think we might have been divided by our common language!"

What Americans call a hood, I believe, is what the English call a
bonnet. The effectiveness of a screened enclosure depends on good
connections between its pieces.

In a modern diesel truck there may be noise generating electrical
fuel-injection control, rotating belts which generate static discharge
noise, electrical relays and contactors, and other sources of radio
frequency noise.

Noise containment is one goal of the bonnet. The hinge which holds the
bonnet and the latch which locks it are often inadequate in r-f
continuity. Their electrical contact is not good enough.

Wheels rotate on stationary spindles and axles. Rotation can produce
charge which repeatedly arcs across wheel bearings or other points.
Spiral springs are made with a large diameter on one end to rest on a
stationary part of the wheel assembly. The spring tapers down to a small
diameter or point on its other end. This point makes contact with a
hammer-on cap over the nut which holds the wheel on its spindle. The cap
rotates with the wheel. So we have a conducting connection between the
wheel and the non-rotating parts of the vehicle. Only extreme noise
cases require these springs.

Stephen also questioned what I meant by perfect antenna cables. I once
repaired rafios and my experience is that most noisy automobile
receivers got that way from defective antennas and antenna cables.

The base of the antenna needs a good connection to the vehicle body,
which is the other half of the antenna. The vehicle body is the
connection for the cable shield. The shield needs to be continuous to
carry the signal rather than having the body carrying the signal where
it may be exposed to noise currents.

I wrote:
"Keep the antenna away from and shielded from sources of interference."

When one installs an antenna, it should be placed in a quiet receiving
location if possible. It should not be installed on the same side of a
screen as wires carrying interference. The antenna should be installed
on the outside of the truck cab where it has large exposure to the
signal.

When I said bonding, I did mean a clean earth return but I was not
thinking of battery current. I was thinking of r-f currents, signal and
noise.

Radio frequencies don`t penetrate deeply into metal but travel on the
surface. Large surface area is needed for low r-f impedance. Battery
current uses the entire cross section of the metal.

Wires slung under running boards and the chassis are not much used now.
Other noisy conductors may be nearby Broadcast ground waves are
vertically polarized. It makes sense to use a vertical whip for
reception, though almost any wire works.

Stephen`s portable likely has a loop antenna inside which makes it
somewhat bidirectional in azimuth. A vehicle mey be found in any
position. This makes an antenna which is nondirectional in azimuth
desirable.

Best regards, Richard Harrison, KB5WZI