[TowerTalk] Re:1, 2, 5 dB Value

[K7GCO@aol.com]

 There have been many opinions of the value of 1, 2 or 5 dB.  Although 1 dB 
  is just perceptible on an S-meter, in a contest of heavy QRM it will result 
  in more points.  One needs to be a "dB Loss Detective" and the coax joint 
  area is good place to check for heat as it's centralized.  Loss in a 100' 
  length of coax is distributed full length and it has to be really over 
loaded 
  to feel it at any spot.  
   
   N4KG posted a simple way to check coax loss with a dummy load and watt 
meter 
  which is a great test I do every year.  There is another way of just 
shorting 
  the end of a coax or leaving it open (infinite SWR) and using low power (A 
CB 
  rig is ideal), measure the SWR, divide 9 by the SWR and it equals the dB 
loss 
  of the length.  It's accurate for high SWR's down to about 2:1 and then 
it's 
  accuracy starts to decrease.  As a comparison data test every year using 
the 
  same power level, bridge and shorted or unshorted (I use the latter with it 
  disconnected from the antenna.  It eliminates the need to take the DL and 
wattmeter to the top of the tower), it gives valuable comparative data year 
to 
  year along with a fairly accurate dB loss data comparable to the dummy load 
  test previously described.  I had an article on this very coax loss test in 
  CQ about 30 years ago.  My copies are packed.  It shows up coax loss due to 
  water entry and all the other loss factors which I keep a log on.  
   
   I don't test open wire line, I just inspect it visually as that is all 
that is needed. 
  I don't even have solder joints as I bend the wire around the clamping bolt 
and 
  coat it with silicone grease.  It's the most trouble and test free no worry 
feed 
  system there is which I have recommended several times.  It costs about 
20-30
  dB less $$$ also.  If ceramic insulators are used it will last your 
lifetime (don't use 
  wooden dowels boiled in wax).  It eliminates all worry of initial loss as 
  it's the lowest of all, stays that way and only the heat test is needed in 
  the Antenna Tuner as has been described by w8ji and myself.  
   
   I described in TT a very simple technique to cover 3.5-4 MHz with a dipole 
  using a 1/2 WL of open wire line and a BC Variable Xc in series with one 
leg 
  of open wire line connected to the coax switch ground side (rotor) and the 
  other lead to the center conductor.  Balanced feed to an unbalanced input 
is not the sin in the shack as an unblanced feed line to a balanced feedpoint 
is at the antenna.  There are a few tricks and guide lines in it's proper use 
and I've recommended the Johnson Match Box with my modifications.  This 
system will transfer more RF to any antenna than any other system.  Art 
Collins set RF transfer efficiently back with his Pie/L outputs and coax 
cable.  Visit the articles and books written in the last century for more 
info.  Coax is not your RF efficiency and financial friend from the shack to 
the antenna.  It will bleed you RF and financially broke.  It is needed 
inside the shack. 
   
   To get down to some "Silver Plated Brass Tacks" to increase Intellectual 
  Conductivity, consider the following comparisons in regard to the value of 
1, 
  2 or 5 dB gain that has NOT been touched in any post so far.  Many gave 
their 
  opinion from a standpoint of personal experience like K3BU winning contests 
  with quads which I like compared to the "Theory Merchants" only.  They 
spend 
  too much time finding fault with observations many give from actual 
  experience and they deserve the respect at least of checking out the claims 
  and data before the "CCC"--Constant Critical Comments (who often never 
check out anything).  They seldom if ever ask the person for his data but can 
find all kinds of fault with it.  We have all kinds of advanced communication 
techniques like ham radio, telephone, letters, Fax, in person, and then there 
is "E-Mail--the fastest and easiest of all.  What I call the "Appliance 
Critics", they often use it only to find fault not facts, new trends or break 
throughs.  I request data all the time if a claim doesn't seem right.  If 
someone has a hot antenna I try and get the details and make my comments 
after evaluating it.
   
  In DX Magazine there was a statement that in a SweepStakes Contest, the 1 
KW 
  scores were 40% higher than the 100W scores--which would be expected.  
  Therefore for a strictly linear comparison, each dB increase is worth 4 % 
  higher score.  I feel it's more like the pyramid layers in advantage.
   
   In Quality Assurance Statistical Process Control (SPC), there is a process 
  where one wants to see what the affect of a small change is on tolerance 
run 
  out.  The "Taguchi Procedure" is to make a large change comparable in power 
of 
  100W to 1 KW in the previous example so a large affect can bee seen.  From 
  this one can accurately predict the affect of a small change even in the 
mist 
  of other variables.  In mechanical tolerance control the results are 
usually 
  linear.  I used a Taguchi version of this in Bench Rest Rifle Shooting to 
  determine the affect of variables in bolt lug pressure caused by neck 
  resizing only.  I added strips of scotch tape on the bases of the cases.  
It 
  showed it clearly in the presence of other variables.
   
   No one have ever touched on this point.  1, 2 or 5 dB increase can be 
  obtained in 2 ways--a power increase or an antenna gain increase which 
every 
  one knows.  They are not the same however in this respect.  Antenna 
software 
  doesn't really show how strong you will be at the DX station with changes 
of 
  antenna gain--the DX S-Meter does.  Software shows you only what free space 
  gain is or the take off gain and angle is--not the typical or actual dB 
  difference at the other end that is the result of a beam gain increase and 
  the resulting vertical pattern change.  
   
   I and many others have run tests with DX of different gain beams at the 
same 
  height and the affect of stacked beams with the typical 3 dB line of sight 
  gain increase from a sharpening of the vertical pattern and the different 
angles
  of radiation.  They often don't give the same line of sight gain difference 
from differences in the angle and other factors--it's usually more.  As I 
recall the previous posts didn't delineate which increase method was 
used--power or antenna gain from stacking or collinear gain increase.  If a 
higher gain beam is installed the gain is obtained by sharpening of the E&H 
planes.  If the E or horizontal plane is sharper, it reduces the square miles 
of signal coverage on transmit and receiving just with 1 or more dB gain.  It 
can work for and against you with reduction in QRM and making the signals 
stronger where it is dominate.  It can work in different 
ways by requiring more changes in the beam orientation.  Increased gain can 
lower F/B also and the advantage or disadvantage of that can go either way.  
I have a 3 element yagi on 10M on a 12' boom or .35 WL that is tuned for max 
gain of 10.2 dBi, it has 8 dB F/B and I like the pattern.  The bandwidth is 
narrow but I came up with an easy way to widen it.  
   
   With increased gain the H or vertical pattern also sharpens.  I never hear 
  or read of anyone addressing this concept anywhere.  Here a knowledge of 
  Reflection Factors is needed to illustrate the overall effect other than 
just 
  more line of sight gain.  I've not read one discussion of this on TT. If 
you 
  can stack 2 beams horizontally and also have 2 stacked vertically both with 
  the same gain, you will see the difference on DX. You will be able to speak 
  with some real authority instead of being painted with theoretical 
  limitations only.  There are different kinds of dB's. The line of sight FS 
  Meter doesn't know how the gain was obtained--by E or H Plane sharpening.  
A 
  DX station will be able to tell you which one you used.  I gave good 
  illustrative example of this in an article in CQ about 35 years ago.  
   
   I had mentioned in TT that I hadn't seen the Reflection Factors printed in 
  the Antenna Manuals for many years.  Only one TT'er E Mailed me that they 
did 
  occur in a recent issue I hadn't seen.  They show the only angles RF can be 
  directed into for horizontal and vertical polarization's for certain 
heights 
  for all antennas due to ground reflections.  In the case of perfect ground, 
  up to 6 dB reflection gains is obtained over the free space gain at certain 
  angles if the free space pattern and Reflection Factors are pointing in the 
  same directions.  As the ground losses increases the reflection gain 
decreases and the nulls fill in.  In the case of a "perfectly lossy ground" 
(no reflections), only the top half of the free space pattern radiates right 
on the horizon up starting a 0 degrees.  
 
  The worst conditions are when a high gain antenna is low to 
  the ground.  The Reflection Factor lobe for a low horizontal beam is at a 
  high angle like about 30 degrees for 1/2 WL high and a high gain free space 
  vertical pattern is fairly sharp pointing on the horizon where the lower 
half 
  reflects off the ground and the other goes into free space to combine at 
  certain angles with the reflected wave or lobe or create a null.  The - 3 
dB points 
  of the vertical free space pattern may be at around 30 and or - 30 degrees. 
 
  If 1/2 WL high the amount of RF directed at 30 degrees is far less than say 
a 
  2 element beam with -3 dB points at around +/- 50-60 degrees.  The 2 
element 
  beam will out perform the higher gain beam when both are 1/2 WL high.  It's 
a 
  common practice to mount high gain beams 1 or more WL higher where the free 
  space pattern properly covers the favorable low angle Reflection Factors 
for 
  those heights.  This is why 2 element beams work well close to the ground.  
  It can be graphically drawn out to see the affect and the final pattern.  
The 
  free space pattern is graphically multiplied by the reflection factor.  
Before computers this was the way it was done to see what you had.  
   
   NOTE! I should like to point out very clearly I only claim that 2 element 
  beams with wide vertical patterns have a "Special Nitch" close to the 
ground 
  where they can give UNUSUAL PERFORMANCE into the higher angles which are 
very often very beneficial contrary to a lot of brain washing by those 
educated beyond their intelligence. Over the years I've had many drop in on 
me trying to catch me running excessive power as I could beat the higher gain 
beams in the US.  I'VE BEEN EVEN ASKED IF I VIOLATED SOME RF LAWS.  Their 
beams were too high.  The world of low beams is almost a best kept secret.  
10'-15' high on 6M does a great job. One ham brought it up 30 years later 
asking me just what the hell I had for a beam on 20M to do so well on the 
East coast at 35' high.  I HAVE NEVER EVER CLAIMED MORE GAIN FROM A CERTAIN 
BOOM LENGTH THAN POSSIBLE AND SUGGEST MY STATEMENTS NOT BE REVISED.  JUST THE 
READ THE REASONS FOR MAXIMIZING THE PERFORMANCE THAT I DO AND TRY IT YOURSELF 
BEFORE MISSTATING WHAT I SAID.  IF IT DON'T WORK FOR YOU, YOU MIGHT EVEN CALL 
ME ON THE PHONE AND ASK WHAT YOU ARE DOING WRONG!  
   
   FURTHER MORE THERE IS MORE OF A DIFFERENCE OF PERFORMANCE OF A QUAD OR 
YAGI IF TUNED FOR MAX GAIN OR F/B INSOFAR AS THE SHARPNESS OF THE VERTICAL 
PATTERN WHEN MOUNTED CLOSE TO THE GROUND COMPARED TO HIGHER.  ONE SHOULD 
CRANK THAT IN TO THE EVALUATION EQUATION OF ANY ONES ANTENNA.  THESE ARE SOME 
OF THE FINER POINTS THAT ARE OFTEN NEGLECTED IN ALL THE HIGH POWERED ANTENNA 
EVALUATIONS I READ.  JUST GET ALL THE FACTS.  I HAVE A 3 ELEMENT YAGI ON A 
.35 WL BOOM TUNED FOR BEST F/B THAT HAS THE SAME VERTICAL PATTERN -3 dB 
POINTS AS A 2 ELEMENT QUAD ON A .12 WL BOOM TUNED FOR F/B ON 20M.  BOTH ARE 
GREAT ANTENNAS AT 1/2 WL HIGH AT 1500-3000 MILES AND EVEN DO A GREAT JOB ON 
DX WITH 100W.  ON 20M THE QUAD SAVES ME 16' OF BOOM AND ONE ELEMENT.  ON 40M 
THAT'S 32' OF BOOM SAVED OVER A 3 ELEMENT YAGI AND IT REALLY FILLS THE HIGH 
ANGLE REFLECTION FACTORS FULLY WITH TYPICAL BEAM HEIGHTS THAT IS NO VIOLATION 
OF THE GAIN THEORY.  I JUST USE IT BETTER.  THE RAIBEAM  DOESN'T NEED A 
REFLECTOR FOR IT'S 3-5 ELEMENT BEAMS AND JUST USES THE BOOM LENGTH MORE 
EFFICIENTLY--ONE MORE DIRECTOR ON THE SAME LENGTH.  WHY IS THAT SO HARD FOR 
SO MANY TO UNDERSTAND?  THESE BEAMS HAVE BIG SIGNALS.WITH THE LEAST HARDWARE, 
COST AND ARE TOTALLY IMMUE TO ALL THE CRITICS.
     
   Another benefit of the sharp vertical pattern is that it directs less RF 
  into the 2nd and 3rd level Reflection Factor Lobes of the higher angles 
when mounted 1 WL or higher and therefore tends to reduce QSB on transmit.  
On receive it can reduce the signals coming in at the higher angles which can 
be a disadvantage.  I have a simple switching technique so that the top, 
bottom or both beams can be selected even with additional bandwidth.  
Comparative "DX Gain" differences are often more than the line of sight gains 
which is related to the vertical pattern sharpness differences.  
   
   A 2 element beam 1 or more WL high will also work very well into the same 
  low angle Reflection Factors for the most part with slightly less gain for 
a lot less cost and is easy to install and maintain.  I have platforms on my 
towers so I can 
  reach the elements of 2 element quads if I ever have to. It will however 
  almost completely fill the higher angle lobes also which can be a definite 
  advantage closer on transmit in a contest or not.  It will put more RF into 
  more areas and perhaps have a bit more QSB.  2 element beams like the Quad, 
  Raibeam, Hexbeam and Moxon using a .12WL boom are great antennas at any 
  height for the cost. The low cost communication world of properly designed 
and properly installed 2 element beams is one that many have never 
experienced.  
   
   << Virtually all of the biggest amateur stations in the world use yagi's, 
    and virtually of the commercial services that use parasitic arrays 
    use yagi's. It's actually quite a compliment to be considered on-par 
    with a workhorse like a yagi, not an insult.  >>
   
   If they haven't discovered what "properly designed quads" will do is not a 
  technical compliment to their antenna intellect.  Many have to be dragged, 
  kicking and screaming into higher levels of performance.  Some do it just 
by 
  observing how well quads work with no RF spill over feed systems and 
without 
  electrical deterioration and maintenance as they have just one permanently 
  soldered zero resistance joint per element.  One of the dumbest designs 
I've 
  ever seen was the 2 element 2M quagi which was fed with unbalanced coax 
  directly.  A potential design improvement was crippled by a hot feedline 
  shield with the "Dreaded RF Spill Over" all over it.  The Hexbeam doesn't 
  even have any joints--except the feedpoint.  When properly designed 
  mechanically quads stay up.  Take a look at Antenna Mart Quads.  There have 
  been too many compromise and junk manufacturers that cater to the low 
budget 
  crowd.  There are Special Ovens in Hell for these manufacturers.  K7GCO
   
    

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