Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: Prev 1 2 3 [4]   Go Down
  Print  
Author Topic: QST Magazine Technical Articles  (Read 11583 times)
G3RZP
Member

Posts: 4731




Ignore
« Reply #45 on: December 29, 2011, 08:57:49 AM »

I took the exam on my 14th birthday. 4 questions on licencing, 4 out of 8 on theory. A 2 hour exam. Questions like 'draw the circuit diagram of a VFO suitable for an amateur transmitter, describe its operation, and show suitable component values for an amateur band. What precautions need to be taken to ensure frequency stability and pulling from transmitter loading.'

and a simple one ' describe the construction of a half wave dipole aerial for the 14 Mc/s amateur band. Show the method of feeder connection and wht precautions should be taken in connecting the feeder'.  Which meant you had to say why (or why not!) you would use a balun, what impedance cable you would use and why, and how you would waterproof the connection.

3 years later I was taking professional exams in radio that were only harder because there was more math involved.....which I've never been good at!

Much harder to cover that much ground in a 'vote for joe' exam.

Multiple choice exams (aka 'vote for Joe') are cheap to mark with a computer. N2EY points out that 'less government = less money= less service. Same everywhere, except he didn't add 'more tax'!
Logged
W6EM
Member

Posts: 820




Ignore
« Reply #46 on: December 29, 2011, 06:51:38 PM »

The recent, and there have been several, poorly edited and checked technical articles in QST are the tip of the iceberg.

Several articles? Name some, besides the filament-voltage article in October 2011?


Hello, Jim.

Not entering this foray to carp, but frankly, I think often of the need for someone to more closely review QST article submittals.  One I happened upon several months back was a portable, battery-toting plastic tool box.  The lacking concern to me was missing overcurrent/short circuit protection for the two 7AH sealed lead acid batteries inside the box.  A rather simple paralleling switch was part of the project. And, lack of detail on how to secure/anchor the batteries inside the box to keep them from banging into each other further aggravated my safety concerns.

After pointing this out to QST, they sent my email to the author.  I don't recall seeing anything suggesting the addition of two small fuses near the battery terminals or clarification on an anchoring method published.

Mention of the issue to ARRL officials at a hamfest awhile later also got some nodding agreement, but no "strays" mention.

First and foremost there should be an editor scan of submitted article material for safety concerns.  It wouldn't have to be rocket science.  ARRL's Laboratory has some very astute, capable people who could, in a few minutes time, make precursory reviews to at least see that what is submitted for publication is reasonably safe for amateurs to build and use.

73,

Lee
W6EM 
Logged
AD7XN
Member

Posts: 36




Ignore
« Reply #47 on: December 30, 2011, 12:50:57 AM »

One thing I have discovered about ham related articles in print,on web sites,or forums is that you will get many opinions in how to do something.  And it can very frustrating trying to do the correct (safe) operation when EE's and very experienced techs say to do it like this and they are at odd's with each other.
Take for instance grounding and lightening protection-please take it !!!  I have read every thing I can find in print, and on the web about this seemingly simple subject from very athoratative (EE's) to very experienced hams.
I still have reservations about how to do it properly.   I know in every form of recreation there are ways of doing  things differently that work as well as the rest, but when it comes to grounding and lightning protection there must be a standard that is inscrutable .  Yes there are two types of grounding
systems-electrical and RF so lets get that out of the way and continue. Grounding conductors are supposed to be short for low impedance, but when you have an electrical entry box 50 feet from your antenna, according to one EE, you might just as well give the antenna it's own ground as the impedance will be to high to be of any use- I thought the antenna was to have its own ground anyway !!. Yet I have been told by two EE's to run a ground wire from the antenna to the electrical entry box ground- from an antenna that will be 60 feet away.  If according to one opinion that is to far to be effective then how effective will a ground wire from said electrical entrance be at 100+ feet to the station ground.  I have been told never to run a ground from the antenna directly to the station ground by EE,s, but have read that what is supposed to be done.
I live in a very high lightning area during the summer and I have become perinoid about puting up a vertical that will be 34' high thanks to all this differance of opinion.  I read where one ham had his antenna about 150 feet from the entry box, and the electrical contractor put ground rods every 8 feet to the station ground.  I know there is no protection from a direct lightning hit so maybe it' a mote point anyway, but good engineering practice demands it so the litrature shoud be agreed upon by all .

 
Logged
KD5NDQ
Member

Posts: 21




Ignore
« Reply #48 on: December 30, 2011, 06:16:09 AM »

Late getting into this thread (which I find fascinating by the way!), and new to doing anything in ham radio even though I've had the licenses for years, but I have a sort of off-topic question about this:

Someone I know offered me their collection of QST magazines dating back 60 or 70 years along with some ARRL project books..  I thought they would be great for looking at projects to build and learn from.  After reading this thread though I'm now considering it's not such a good idea anymore!  Any ideas on that either way, or what's the best place to find projects to build to learn from!?  He's looking to unload these magazines..should I just chuck them in the bin?

73,
Robert Opalko
KD5NDQ

Logged
K8AXW
Member

Posts: 3906




Ignore
« Reply #49 on: December 30, 2011, 08:23:57 AM »

XN:  This is the reason why I no longer ask questions about amplifiers on the Amplifier Forum, eHam.com.  Instead of getting a simple as possible, straight forward answer, I get all kinds of technical BS that never answers the basic question. 

I understand there are many different circumstances that require different solutions but when you phrase a specific question with an accurate description and still get a highly technical answer which in turn starts an argument that goes on and on.  The original answer never gets answered.


Logged
W6EM
Member

Posts: 820




Ignore
« Reply #50 on: December 30, 2011, 09:28:43 AM »

One thing I have discovered about ham related articles in print,on web sites,or forums is that you will get many opinions in how to do something.  And it can very frustrating trying to do the correct (safe) operation when EE's and very experienced techs say to do it like this and they are at odd's with each other.
Take for instance grounding and lightening protection-please take it !!!  I have read every thing I can find in print, and on the web about this seemingly simple subject from very athoratative (EE's) to very experienced hams.
I still have reservations about how to do it properly.   I know in every form of recreation there are ways of doing  things differently that work as well as the rest, but when it comes to grounding and lightning protection there must be a standard that is inscrutable .  Yes there are two types of grounding
systems-electrical and RF so lets get that out of the way and continue. Grounding conductors are supposed to be short for low impedance, but when you have an electrical entry box 50 feet from your antenna, according to one EE, you might just as well give the antenna it's own ground as the impedance will be to high to be of any use- I thought the antenna was to have its own ground anyway !!. Yet I have been told by two EE's to run a ground wire from the antenna to the electrical entry box ground- from an antenna that will be 60 feet away.  If according to one opinion that is to far to be effective then how effective will a ground wire from said electrical entrance be at 100+ feet to the station ground.  I have been told never to run a ground from the antenna directly to the station ground by EE,s, but have read that what is supposed to be done.
I live in a very high lightning area during the summer and I have become perinoid about puting up a vertical that will be 34' high thanks to all this differance of opinion.  I read where one ham had his antenna about 150 feet from the entry box, and the electrical contractor put ground rods every 8 feet to the station ground.  I know there is no protection from a direct lightning hit so maybe it' a mote point anyway, but good engineering practice demands it so the litrature shoud be agreed upon by all .

 

The lightning issues you present here aren't simply a "one size fits all."

Case 1.  Direct strike.

Only a very low impedance ground from a very heavy duty grounding electrode and grounding electrode condutor will route most all of the current away from other grounded paths.  Especially ground loops formed by conductive paths grounded at multiple points like your ham gear grounding via coax and the power cord to the outlet.  (This is why the National Electric Code requires all residential incoming utilities to be grounded at one point only.)

The best thing you can do is to draw from the NEC's requirement to protect yourself from unequal potentials created by heavy direct strike current.  Single point grounding (from either a very good grounding electrode or several connected in parallel) is safest from a personal safety perspective as whatever you have connected to the grounding conductor and electrode will be elevated substantially above ground potential due to even a very small electrode resistance.  No, the NEC maximum permissible grounding electrode resistance of 25 Ohms is NOT a good ground.  Lightning currents can be as much as 50,000A or more.  So, simple Ohm's law, say through a 0.5 Ohm grounding electrode, will elevate everything tied to it to a mere 25kV!!!

So, you want EVERYTHING in your residence, including your ham gear, coax, etc., raised to whatever that elevated level is so that there won't be any potential difference between anything in your residence that is supposed to be grounded.  You can't escape it, so you simply join it in being elevated to whatever lightning decides to raise it all to.

Case 2.
Indirect strikes.

Large potential gradients are created by a nearby strike since, like I said above, a huge voltage rise occurs at the direct strike point.  So, the voltage (and secondary currents) flow in the ground and conductive objects as a result.  A strike to a poor ground really causes a huge potential gradient plane.  Simple example: why golfers get electrocuted from nearby strikes to trees while standing on the course.   General rule for golfers: get away from clubs and kneel down and grab your ankles keeping feet together to minimize earth voltage gradients if a strike is imminent (body hair effects, leader sparks, etc.)

Now, to help keep the currents and high voltage from nearby strikes from flowing in coax, etc., you want to make your coax a high impedance path to common mode currents as well as, as noted above, single point ground it to your residence ground.  Hard to avoid a ground loop from incidental grounding at the antenna though.  To raise coax common mode Z and not effect characteristic Z and differential current, (this is what you want to remain  unperturbed) either use a few slip on ferrite toroids over the coax at the antenna and shack entrance point or make small coils of multiple wraps of coax and tape the coils up.  You can also use a gap or combination gap/mov arrester at the point of entrance from outdoors, but it, too, should be connected at that point to your residence grounding system.  Of course, you should disconnect it from your gear as well.  Not much you can do with balanced line (twin lead or ladder line) as anything you do to it will disturb its impedance significantly.....like putting toroids over it or wrapping up coils of it.

Hope this helps.

I'm one who believes that lightning rods tend to make attractive points for lightning strikes.  But, if you have something like 2/0 copper running from each to a substantial grounding electrode system with everything bonded to it, you won't be affected very much by a direct strike.

Moral of the story:  side mount verticals on towers.  Or, you might try a static potential diffuser (inverted metallic brush) atop a capacity hat on top.  :-)

Don't know if Yagi aluminum will approximate a flat enough surface to avoid leader discharges.

73,

Lee
W6EM

Logged
G3RZP
Member

Posts: 4731




Ignore
« Reply #51 on: January 01, 2012, 05:20:16 AM »

>Simple example: why golfers get electrocuted from nearby strikes to trees while standing on the course<

It's even worse for cows. They are very susceptible to voltages between front and back legs, and it's not that uncommon for them to be electrocuted by the differential voltage along the ground caused a close strike. I read somewhere of a case where a cow on the bank of a river got electrocuted, while one standing 6 feet away with all legs in the river was OK.
Logged
K1CJS
Member

Posts: 6045




Ignore
« Reply #52 on: January 01, 2012, 06:10:33 AM »

... Soon it will come to the point ... where you WILL need a surface mount workstation just to replace a resistor or a diode.

That's an interesting statement. Why do you say that? Are the sizes or designs of SMD components going to change that much?

I say that not because of the parts or the equipment themselves, I say that because of the age of the people who want to take the time to actually work on their own equipment is steadily rising.  I don't know about you, but my eyesight is getting worse, and my ability (and patience) to take the time and effort to replace those miniscule components is also diminishing.  I like the smell of hot silder/flux and the feeling I get when I get something working again, but all too many younger people today have the attitude "If its not working, get rid of it and get another."

Do you disagree?
Logged
K1CJS
Member

Posts: 6045




Ignore
« Reply #53 on: January 01, 2012, 06:28:18 AM »

Only a very low impedance ground from a very heavy duty grounding electrode and grounding electrode condutor will route most all of the current away from other grounded paths.  Especially ground loops formed by conductive paths grounded at multiple points like your ham gear grounding via coax and the power cord to the outlet.  (This is why the National Electric Code requires all residential incoming utilities to be grounded at one point only.)

The best thing you can do is to draw from the NEC's requirement to protect yourself from unequal potentials created by heavy direct strike current.  Single point grounding (from either a very good grounding electrode or several connected in parallel) is safest from a personal safety perspective as whatever you have connected to the grounding conductor and electrode will be elevated substantially above ground potential due to even a very small electrode resistance....

First, I apologise for dragging this thread off its course, but I have seen some statements on grounding in QST that are stretching the definition of single point grounding, and Lee has been good enough to remind us of those here.

Lee doesn't seem to understand the concept of single point grounding at all.  Single point grounding doesn't require just one ground rod.  Single point grounding requires that all ground rods be at one grounding potential.  That is why the code in the US requires that all ground rods at a building be bonded together--that in itself brings all grounding points to that one potential.  In reality, every mast and tower should have a grounding system at its base and those INDIVIDUAL GROUNDING POINTS MUST BE BONDED TOGETHER BY NUMBER SIX CABLE.  That is the correct concept of single point grounding, not what Lee promoted in his post--and not what some others have stated in their articles either.
Logged
W6EM
Member

Posts: 820




Ignore
« Reply #54 on: January 01, 2012, 06:03:17 PM »

....Lee doesn't seem to understand the concept of single point grounding at all.  Single point grounding doesn't require just one ground rod.  Single point grounding requires that all ground rods be at one grounding potential.  That is why the code in the US requires that all ground rods at a building be bonded together--that in itself brings all grounding points to that one potential.

That only becomes true when currents flowing between the ground rods in an interconnecting matrix produce NO voltage rise or drop.  Essentially, when currents are zero.  Or, the IR product is very, very small.  AWG 6 Cu is not sufficient if the interchange current is high enough to fuse the AWG 6 conductor.

Why isn't AWG 6 the minimum size necessary for air terminals (lightning rods)?  Short answer:  Very likely, 6 would fuse (or melt) with a direct strike.  I don't have an I squared t table handy or I'd look up what it will take to melt it.

The key, my friend, is to shunt high currents through very very low resistance conductor.  And, BOND everything with low/no current in the bonding conductor to create an equi-potential plane. 

Now, since you hang your hat on the NEC, what say you to a "NEC-satisfactory" ground rod earth resistance of 25 Ohms?  Do the math with a mere 10KA mild direct strike and see how high your ground rod or tied-together rods rise above true ground.



 
Quote
 In reality, every mast and tower should have a grounding system at its base and those INDIVIDUAL GROUNDING POINTS MUST BE BONDED TOGETHER BY NUMBER SIX CABLE.  That is the correct concept of single point grounding, not what Lee promoted in his post--and not what some others have stated in their articles either.

Your antenna, if it suffers a direct strike, will likely quickly separate that number 6, and your coax and whatever is connected to it will be toast.

An antenna and its structure, at more than a few feet from your attempted equipotential plane will not be safely included in it.  You should discourage any lightning current flow through lumped common mode reactance.

Like I said, single point grounding doesn't guarantee no voltage rise above ground from lightning current.  If done adequately, then all things will rise to the same level.  If not, toaster time.

Also, I'd suggest that in any conductor used for bonding smaller than AWG 2 should be bare solid, not stranded cable.  Definitely not insulated if it is stranded so that the strands can be visually inspected from time to time.
Logged
Pages: Prev 1 2 3 [4]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!