Hi Bob,
I don't find the airplane comparison to be reasonable. In my example the
penalty for choosing the wrong power supply from a very limited choice,
with little information about the performance of the available choices,
is a week at the cabin without being able to hear weak signals on your
radio. In your example the penalty of piloting an unsafe aircraft could
be death.
I devised a hypothetical situation in which a person has limited time,
information and resources to select a power supply. I think anyone in
this situation who is experienced with HF radio and DC power supplies of
both the linear and switched mode varieties would chose the linear mode
supply. Even those of us who know that "properly engineered" switched
mode power supplies do exist, are aware that the chances of getting RF
noise from a switched mode power supply are much greater than from a
linear mode one.
DE N6KB
On 1/20/2014 5:21 PM, Bob McGraw - K4TAX wrote:
I would never pilot an airplane unless I performed a proper and
complete ground inspection while using a check-list.
I would never buy a power supply unless I perfromed a proper
evaluation but first knowing the needed power requirements.
73
Bob, K4TAX
----- Original Message ----- From: "Ken Brown"
<ken.d.brown@hawaiiantel.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Monday, January 20, 2014 8:19 PM
Subject: Re: [TenTec] Power supply types
They are both commonly available and they can both be used to power
typical HF transceivers. I think it is a reasonable comparison to make.
Here is another question: What kind of power supply did you first see
reviews in QST in which the subject of RF noise generation was even
mentioned?
Yes, switched mode power supplies CAN be made that do not generate
(and radiate) RF noise. And switched mode power supplies are
generally more energy efficient.:
How about we state the question this way:
Suppose you're on vacation and you brought your mobile rig along with
you, which runs on 12 VDC. You planned on only operating from your
vehicle, so you did not bring a power supply for use from 120 VAC.
You are offered an opportunity to stay for free in a nice vacation
rental cabin for a week. The cabin has all the conveniences,
including grid power. There are tall trees and you have a spool of
skinny copper wire and an antenna tuner in your vehicle. You think it
will be a great opportunity to get on the air from a remote location,
with hopefully not a lot of RF noise. Before you head up into the
mountains to the go to the cabin you see a store which sells two
kinds of power supplies that have the right voltage and current
rating to power your rig. One of the power supplies is very
lightweight and the label say it is super efficient and uses
switching mode technology. The other power supply is heavier, and you
can see it has a laminated iron core transformer and a big
electrolytic capacitor in it. The prices of the two power supplies
are identical and they both appear to be well constructed. You cannot
find any other data about these power supplies. The drive to the
cabin is long, and you don't intend to drive back to town until you
have finished your stay at the cabin. If you buy both power supplies,
you won't have enough money left to buy the wrist rocket slingshot
you intend to use to send the skinny wire up into the tall trees.
Which power supply would you buy?
DE N6KB
On 1/20/2014 3:41 PM, Kim Elmore wrote:
This is an apples vs pecans question.
Better-stated questions:
What's the probability that a properly-designed and engineered
linear power supply will radiate RF noise of sufficient amplitude
to be bothersome?
What's the probability that a properly-designed and engineered
switching power supply will radiate RF noise of sufficient
amplitude to be bothersome?
Answer: unknown. likely small but equal.
Kim N5OP
On 1/20/2014 7:13 PM, Ken Brown wrote:
What is the probability that a transformer/rectifier/capacitor
filter/linear regulated power supply will generate and radiate
(through AC power input or DC power output leads) RF noise of
sufficient amplitude to be bothersome? That probability may not be
zero.
What is that probability that a switched mode regulated power
supply will be not "properly engineered" and generate and radiate
RF noise of sufficient amplitude to be bothersome?
How do those two probabilities compare?
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