Tuesday, November 25, 2014

Power or Antennas - When Less is More?

Opinion Piece by Ariel Jacala NY4G

The following has been included in Chapter 6 of the new book with added content:

The Dxer's Companion

Having been a QRP operator and having started my amateur radio career from among the ranks of QRP operators, you will be able to instantly tell my bias for antennas.  From the standpoint of economics, you will get the most signal strength for your dollar by investing in antenna systems (when you can) as opposed to investing in power.  There are many folks who are limited in the ability to put up effective antennas by Homeowners Association (HOA) restrictions.  There is a move afoot in Congress called the Parity Act, HR-4969 , that will allow radio amateurs to legally fight the HOA's.  However, this bill has not been signed into law, as of the time of this writing. Back to the subject of antennas, a little knowledge about antenna theory will go a long way towards improving your signal up to 18 dB or 3S units.

Signal Strength in Relative Versus Absolute Terms

RF performance of both amplifiers and antennas are most easily talked about in relative terms than in absolute terms.  It is here that most hams get lost in the jargon.  Here are the standards.  An S9 signal is created by inputting a 50 microvolt signal into the antenna ports of a receiver.  Six whole dB down from S9 is S8 which is a sound power level factor of 4 (or 1/4 the power), S7 is a power factor of 1/16, S6 is a power factor of 1/64, S5 is a power factor of 256, S4 is 1/1024 and so forth.

Let us consider a RF path from South Carolina to California - some 3000 miles away.  An amateur in California is transmitting at 1 kW and is being received by an operator in SC at S9 - a really strong signal and the SC operator copies him well.  The SC operator has a QRP rig capable of producing 5 watts of RF.  The difference in power level is a factor of 200 or 23 dB (10log200).  The California operator will see the signal of the the SC operator at a tad over S5 (provided his S-meter is calibrated).  The copy by the CA operator of the SC signal is still excellent provided S5 provided the noise floor is well below S5.  In the high bands, provided you have a quiet receiver, the atmospheric noise is typically low.  In the high bands, high power amplifiers are typically overkill, provided propagation conditions are decent.

50.00mv S9+60
15.81mv S9+50
5.00mv S9+40
1.581mv S9+30
500uv S9+20
158.1uv S9+10
50uv S9
25uv S8
12.5uv S7
6.3uv S6
3.2uv S5
1.6uv S4
0.8uv S3
0.4uv S2
0.2uv S1

Signal levels higher than 83 dB over S9 has the potential to damage receivers.  Front end limiters must be used if that possibility exists.

The Half Wavelength Rule

For the high bands - that is 30m to 10m, the standard bearer is the dipole.  The dipole is a very simple antenna to construct and understand and will give you the highest value in cost effectiveness.  The dipole at a minimum half wavelength height above ground will give you 6+ dB of gain due to ground reflection relative to an isotropic radiator at 0 dBi as a reference, at the radiation lobe at typically 40 degree angle.  Above and below this arrival angle, there is attenuation.  A general purpose dipole will do well at half a wavelength.  A dipole meant for DX will need that radiation lobe maximum at lower takeoff angles - typically 5-8 degrees and will need to be more than a half wavelength high above ground.  At these heights, radio amateurs typically employ beam antennas that provide more forward gain than a dipole, and provide the additional benefit of front to back ratio - enhancing signal to noise ratio. I can go into a whole dissertation on antenna design and modeling but I won't, I will relate what I have produced from experience as an avid DX chaser that learning about antennas and applying what I have learned has given me in a little over a year almost 700 band points towards the ARRL Challenge award.  One needs 1000 band points to qualify for this award and I have line of sight to over 900 in my short 4 year career as an amateur.  Fully 700 of those have been in the last year and a half through the judicious application of antenna theory and of input power.  For the low bands, the antenna of choice is the vertical since it is near impossible to get a dipole high enough to get good takeoff angles in the low bands - 160m, 80m.  A 40m dipole at 50-60 feet is very good compromise and a very versatile antenna for both DX and regional communications.

Verticals and Ground Planes

Verticals typically require an effective ground plane to be effective.  The main advantage of the vertical is the low take off angle of the radiation pattern which makes it suitable for DX work.  Forward gain however, is much lower compared to a dipole unless the vertical is over sea water or has an extensive ground system.  For example, on 160m, over 25000 (48 wavelengths) feet of radials is required to maximize the antenna efficiency when laid on the ground.  That is according to the ARRL handbook.  Anything less than 48 wavelengths of radials will have reduced efficiency, when the radials are laid on the ground.

The Place for Power

Power has a definite place and it is not desired or even necessary to be used all the time.  One of the ethical principles of amateur radio is to apply the least power to make the communication possible.  Sometimes, the least power to make that communication possible is 1 kW or even 1.5kW.  Take marginal conditions for example, - low signal levels in a high noise environment, or poor propagation, or compromise antennas.  Power becomes a bigger factor precisely for the above reasons on the low bands, 160m, 80m, or even 40m.  Low band operators, and typically the good ones, milk their stations of every bit of efficiency on the antenna side (both RX and TX) and typically run power.  According to ON4UN, typical low band DX'r on top band will run 800W to a kW.

Skill Versus Brute Force

The desirability of having lower power forces one to develop and hone operating skills, understand and employ techniques to improve signal to noise ratio.  This is the David and Goliath analogy. Taken to the extreme, any idiot can fire up a water cooled Voice of America transmitter and generate a huge signal.  I place hams who take this approach in the same category as the guys who burn rubber on their 500 hp Mustangs.  Impressive indeed, but is it necessary.  On the other hand, if you align yourself with the "Davids" of the world, substituting skill for brute force, you will be in better company - to the like of Stew Perry - and you will be upholding the tenets of the Amateur Radio service.

Hams treading the middle ground are concerned about others—hams, neighbors, family members, etc. They try to fit in, to get along, to accommodate a community of interests in addition to their own. They practice the Golden Rule Do unto others as you would have them do unto you (reasonable variations notwithstanding).

As hams who comprise a federally licensed emergency service, we enjoy certain protections from unreasonable local restriction.  These privileges are welcome and necessary as a whole, but they can be easily abused.

Just because we can transmit a 1500-W signal doesn’t mean we should. Just because we can erect a 200-foot-high antenna tower doesn’t mean we should. Hams who follow the Golden Rule integrate their radio pursuits with the pursuits of others—not because they have to, but because they want to!
Governments can’t legislate common sense. That’s up to us.

Case in Point - Knowledge is Power

To start, let’s assume that you have a typical shack. A 100-W transceiver graces your operating desk and "talks" to a coax-fed dipole (or two) through a 300-W antenna tuner. Thanks to the tuner, your rig can happily put out full power regardless of actual antenna/feed line SWRs on the various bands you work.  You have erected a 260 foot Carolina Windom with both ends at 35 feet above ground level (as the reference).  EZNEC models indicate that DX coming in at 5 degrees or less are 15 dB down from the max lobe or about -11dB net.   Let's say that you are avid DX'r and want to get more DX in your log, especially in the low bands. You now acquire knowledge that if you raise the Windom to 66 feet, you gain an average of 6 dB on 160m relative to the 35 ft reference antenna .  If you now employ an inverted L for the low bands and increase your efficiency by 12 dB in the 160m (by going from-11dB to +1 dB),

Let's see how the balance tips.  The great thing about improving your antenna system is that you get the improvement both ways - on receive and transmit.  Let's ignore the receive benefit for the moment and just look at the transmit trade:

Inverted L
Cost: $50 in wire from Lowes, and additional $50 for NEMA boxes, SO239, and and additional $100 in good quality coaxial cables - total outlay $200
Transmit gain increase 12 dB or 2 S units on DX

Raisng the dipole to 60 feet:
Cost: additional rope $20
Transmit gain is 6 dB on 160m DX

Cost of Power (relative to barefoot 100W) - costs are rough numbers
11.8 dB or 1500W - approximately $4000 (ACOM 2000)
10 dB or 1000W - $800-$1200 for a used tube amplifier Drake L4B or Heathkit SB220
$2500 for a new ACOM1000
7 dB or 500W  -  $2500 for an Elecraft KPA500
$1100 for an Ameritron AL811

It is a "no brainer" to figure out that improving the antenna system is the more cost effective and signal effective way to go.

Hidden Costs of Power

Don’t think you can get away with just an amplifier! The power output curve is often deceptive. For example, above 300 W outputor so, you’ll need a beefier antenna tuner. Expect to spend up to $500 for a good one.  And don’t forget about the ac mains, either. You can probably get away with running a 500-W output amplifier on 120 V ac, but beyond that, it’s 240 V all the way. (Don’t believe me? A 500-W output amplifier runs about 1000 W input power. That’s 8.5 A at 120 V. With your rig added in, that’s more than 10 A. Believe me, the lights in your house will "jump" to the rhythm of your code key or your spoken words!)

Chances are good that you won’t know how (or won’t want) install that 240-V line yourself, either. The materials and an electrician to install them likely will total $300 to $500. Many first-time amplifier users don’t consider their beast’s power supply requirements until they’ve set up the amp and started "browning out" the rest of their house! If this is you, you’ll be lucky if you don’t trash your TV set or your home computer in the process of "modulating" your 120-V power feed!

If you live in an urban setting, don’t neglect the potential "public relations" costs of firing up a beast of signal in the midst of all thoseconsumer electronics devices. I know...you can legally stand on the solid rock of FCC-mandated power output limits— but be warned - that you may be shunned by your neighbors.

A Better Way - A Balanced Middle Ground 

To maintain good relations with your neighbors, XYL, fellow hams, and to keep your wallet full and not have to modify your house wiring, consider improving your antenna system before investing in an amplifier. Here are some ideas to get you started

One almost universal way to get out more signal is to get your antenna(s) farther up in the air (your present antenna or a new. Build a taller mast, find a taller tree or put up a tower.

If that dipole just isn’t cutting it, put up a contest-winning and DX-catching secret weapon a full-wave horizontal loop for 40 or 80 meters (up as high as possible, of course!). Feed it with coax and use a tuner on bands above the fundamental frequency. That’s a "cheap ‘n’ dirty" way to snag an extra 2 to 10 dB, depending on frequency.

For less than the price of an entry-level 1000W amplifier you can buy or make a multiband hexagonal beam antenna and a decent rotator. This dynamic duo, mounted reasonably high, (I mean 25-35 feet) will offer a noticeable and steerable improvement to your signal. Remember amplifiers only boost your transmitted signal and do nothing to improve reception. By rotating a directional antenna you can often achieve a double benefit — boosting the signal you’re trying to receive while attenuating signals that are unwanted. For example, if I’m working a European ham from my South Carolina QTH, a potentially interfering signal from an op in Florida—located in the side null of my directional antenna—may drop 20 dB or more! The difference, more than 30 dB of signal enhancement, could never be achieved by a lone amplifier.  I constructed a hexagonal beam antenna for less than $300.  I used a push up mast and fabricated my own pilot bearings and thrust bearings for another $250.  I purchased a used but rugged rotator for $200.  Now I have 3dBd gain over a dipole, a a front to back ratio of 18-25dB, on 6 bands - 20-6m all for less than $1000.  Don't get me wrong, the LPDA at 60-80 feet will perform better, but at what price?  Anything over 40 feet requires some sort of a tower structure.

Let me come clean and admit the cold hard truth now.  I am a DX'r and there are marginal conditions that require power.  There is a time and place for power. My first amplifier was a well used Drake L4B that was kept in museum condition by its previous owner.  It would put out 10 dB additional signal. I seldom drive with more than 80 watts on it and so I can only realistically get only 300 watts more than my second 500 watt amplifier, a reliable Elecraft KPA500.  Those additional watts which is less than half an S unit meant the difference for me in snagging FT4TA Tromelin and E30FB Eritrea, two DX entities that only come around every 15 years or so.  It also helped me snag VU4KV Andaman which I venture to guess would not have been possible on my 500W amplifier.  Remember, I am also  competing against power, and I am using all my skills in timing (optimum propagation), putting my transmitter VFO to where the DX station is listening, and lining up my beam on the ideal RF path.

On SSB, learn the correct use of your rig’s speech processor. There’s another 3-dB (or more) improvement, this time in the modulation department! No purchase necessary!  Learn to use your rigs signal equalizer and boost the midrange 16dB and roll off the highs and lows.  This will serve to attenuate low and high frequency noise and boost the mid-range where the ear has been given the God given gift of sensitivity to begin with.   Noise devices and receive antennas are relatively cheap and home brewable.

So, where has this middle ground taken me?  Admittedly, I have had to use power occasionally and sparingly.  On 80m, I was able to get DXCC in one year.  I was able to get 5 band DXCC and DXCC on 17m.  That only leaves 12m, 30m and 160m.  Given the choice, of only one, I will take the "killer" antenna versus the "rock crusher" amplifier.  Take it from a guy whose second DXCC award is QRP-DXCC.  They say life is too short for QRP.  I say QRO is a lot more fun and productive after you have learned the skills derived from QRP operation and apply them to QRO operation.

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