KB6NU's Ham Radio Blog

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2016 Extra Class study guide: E4E - Noise

Posted: 15 Mar 2016 05:01 PM PDT
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E4E Noise suppression: system noise; electrical appliance noise; line
noise; locating noise sources; DSP noise reduction; noise blankers;
grounding for signals

Noise is often a real problem for radio amateurs. Fortunately, by
understanding how noise is generated and how to reduce or eliminate it,
noise can be tamed.

Atmospheric noise is naturally-occurring noise. Thunderstorms are a major
cause of atmospheric static. (E4E06) There’s not much you can do to
eliminate, but you can often use a receiver’s noise blanker to help you
copy signals better. Signals which appear across a wide bandwidth (like
atmospheric noise) are the types of signals that a receiver noise blanker
might be able to remove from desired signals. (E4E03) Ignition noise is one
type of receiver noise that can often be reduced by use of a receiver noise
blanker. (E4E01)

One undesirable effect that can occur when using an IF noise blanker is
that nearby signals may appear to be excessively wide even if they meet
emission standards. (E4E09)

Many modern receivers now use digital signal processing (DSP) filters to
eliminate noise. All of these choices are correct when talking about types
of receiver noise can often be reduced with a DSP noise filter (E4E02):

Broadband white noise
Ignition noise
Power line noise


One disadvantage of using some types of automatic DSP notch-filters when
attempting to copy CW signals is that the DSP filter can remove the desired
signal at the same time as it removes interfering signals. (E4E12)

While filters can be very effective at reducing noise, it is often better
to figure out what is generating the noise and taking steps to reduce or
eliminate the amount of noise generated in the first place. For example,
one way you can determine if line noise interference is being generated
within your home is by turning off the AC power line main circuit breaker
and listening on a battery operated radio. (E4E07) If by doing this you
determine that an electric motor is a problem, noise from an electric motor
can be suppressed by installing a brute-force AC-line filter in series with
the motor leads. (E4E05)

All of these choices are correct when it comes to the cause of a loud
roaring or buzzing AC line interference that comes and goes at intervals
(E4E13):

Arcing contacts in a thermostatically controlled device
A defective doorbell or doorbell transformer inside a nearby residence
A malfunctioning illuminated advertising display


Sometimes your own equipment may be the cause of received noise. Cables in
an amateur radio station, for example, can radiate or pick up interference.
Common mode currents are the culprits. Common mode currents on the shield
and conductors can cause shielded cables to radiate or receive
interference. (E4E15) To eliminate this interference, make sure to ground
the shield at one end of the cable. Common-mode current flows equally on
all conductors of an unshielded multi-conductor cable. (E4E16)

Electrical wiring may also pick up interference. A common-mode signal at
the frequency of the radio transmitter is sometimes picked up by electrical
wiring near a radio antenna. (E4E08)

The main source of noise in an automobile is the alternator. Conducted and
radiated noise caused by an automobile alternator be suppressed by
connecting the radios power leads directly to the battery and by installing
coaxial capacitors in line with the alternator leads. (E4E04)

Personal computer and other digital devices can also generate noise. One
type of electrical interference that might be caused by the operation of a
nearby personal computer is the appearance of unstable modulated or
unmodulated signals at specific frequencies. (E4E14) All of these choices
are correct when talking about common characteristics of interference
caused by a touch controlled electrical device: (E4E10)

The interfering signal sounds like AC hum on an AM receiver or a carrier
modulated by 60 Hz hum on a SSB or CW receiver
The interfering signal may drift slowly across the HF spectrum
The interfering signal can be several kHz in width and usually repeats at
regular intervals across a HF band


Noise can even be generated by the most unlikely things. For example, it is
mostly likely that nearby corroded metal joints are mixing and re-radiating
the broadcast signals if you are hearing combinations of local AM broadcast
signals within one or more of the MF or HF ham bands. (E4E11)

The post 2016 Extra Class study guide: E4E Noise appeared first on KB6NUs
Ham Radio Blog.


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Operating notes: CW edition

Posted: 15 Mar 2016 11:35 AM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Recently, I tweeted:




kb6nu@kb6nu

Getting decent spots on 30m, but no calls.
and got this reply:

Charlie M0PZT @M0PZT

QRS much?!


In the subsequent conversation, I said that I always slow down if someone
replies at a slower speed or asks me to QRS, but Charlie pointed out that
sending CQ at a relatively high speed might be scaring guys away.

I must admit that he has a point, but honestly slower operators should not
be afraid to reply to fast CQs. After all, the guys not sending CQ HIGH
SPEED ONLY. If you dont want to have a high-speed contact, reply at
whatever speed youre comfortable with, and the faster op will slow down for
you.


I know that I will. Id rather have a 15 wpm QSO than none at all.
Still working on R, L, F, C

Im still working on sending these characters iambically. Im getting better
at sending the characters, but still have to make a conscious effort to do
so. Every once in a while, I find myself sending an R without thinking
about it, but I still need more practice.
CW at Dayton!

Ill be speaking about CW at Dayton!

On Friday, May 20, at 9:15 am, Ill be giving a talk about CW at Dayton. It
will be pretty basic. I plan to talk about why you might want to operate
CW, some ways to learn Morse Code, what key to select, and how to make
on-air contacts.Â*Im not sure what room Ill be in yet, but Ill pass on the
info as soon as I know it.


Id love to hear about what youd like me to talk about. Please leave a
comment here or e-mail me directly.



The post Operating notes: CW edition appeared first on KB6NUs Ham Radio
Blog.