[HCARC] DEE-BEE's, Amps and Antennas

[Gary and Arlene Johnson]

Kerry,

Sorry about the Dee-Bee's - I saw it the other day in one of the ARRL pubs 
and just thought it was fun.  I have read about the differences of dBi and 
dBm - hadn't heard about dBV - will need to read about that sometime.  What 
I did ask was is the dB increase that you get as a result of the increase in 
wattage out of the amplifier additive to whatever increase you get with a 
directional antenna.  And yes I do understand the cost of antennas and 
towers and rotators - I have a tower and the rotator is coming, but alas no 
antenna for it yet.  As for getting the station on the air, the ditching for 
the coax comes next weekend (God and my wife willing).  Without the ditching 
I can't get to the other side of the road to where the antenna needs to go. 
My house and garage/shack are built virtually on my Northern property line 
with a road bisecting them from the rest of the property - I have figured it 
wouldn't be good for coax to run my truck over it repeatedly.

BTW, how well do solid state amps work vs tube ones??  BTW, you don't know 
me very well if you think that I believe statisics and theoretical 
measurements are nothing more than semi-educated guesses.

As for PSK-31 and amplifiers - I thought that you weren't supposed to run 
PSK-31 with much over 20 watts anyway.

As far as DX and Contesting - I don't know about the contesting, but as far 
as DX is concerned, there are some places in the world like the South Pole 
and McMurdo Station (places I have been to) that I am going to talk to one 
day regardless and I would like to make the occurance more than a rare 
occurance.

Sorry if you feel that asking questions if "Fooling Around" - one has to 
learn it somewhere!!!  And BTW, once the station is up and running the 
questions will probably increase vs decrease.

Gary J
N5BAA
HCARC Secretary 2013


----- Original Message ----- 
From: "Kerry Sandstrom" <kerryk5ks at hughes.net>
To: "Gary and Arlene Johnson" <qltfnish at omniglobal.net>; 
<hcarc at mailman.qth.net>
Sent: Saturday, February 16, 2013 4:57 PM
Subject: Re: [HCARC] DEE-BEE's, Amps and Antennas


> No Gary, there isn't a conspiracy.  Instead of fooling around on the 
> internet asking questions, everyone else is operating and gaining 
> experience!
>
> By the way, you really know how to irritate me.  It isn't DeeBees its dB, 
> never plural, and it stands for deci Bel.  The basic unit is the Bel, 
> named after Alexander Graham Bell.  It is a logarithmic unit for ratios. 
> Again it is never plural.  It was originally used in acoustics but it can 
> be used anywhere you are dealing with ratios.  There are numerous similar 
> units you will come accross such as dBm and dBV.  dBm is an absolute power 
> referenced to 1 milliWatt.  For instance 0 dBm = 1 milliWatt.  o tells you 
> the ratio is 1 and m tells you the reference is milliWatts.  20 dBm is 100 
> milliWatts. 20 dB tells you the ratio is 100 and m again tells you it is 
> referenced to 1 milliWatt.  For dBV, the reference is 1 Volt and 20 dBV is 
> 10 Volts (Yes, that is 10 V and is not a typo).  dB is a power ratio.  For 
> voltage, remember that power goes as the square of the voltage so if your 
> impedance is constant, 10 times the voltage is 100 times the power.
>
> The power output of amplifiers and/or the gain of antennas must be used 
> with extreme caution.  This may be difficult to believe, but the 
> manufacturers stretch the truth whenever they give numbers like power 
> output and antenna gain.  I don't believe any manufacturer of ham antennas 
> has a real antenna range.  A real antenna range for HF requires a couple 
> of hill top locations several miles apart looking accross a deep valley. 
> Anything less will produce gains corrupted by ground reflections.  Even if 
> the gains were measured accurately, something I really doubt, unless you 
> put ypur antenna up in the same relationship to other conducting 
> structures like the ground, you will have different results.   Until a few 
> years ago QST would not allow manufacturers to publish antenna gain 
> figures in their QST ads because they were so misleading.  The other ham 
> magazines had no qualms about gain figures in their ads, but that doesn't 
> mean they were any less misleading. More recently QST has started 
> publishing gains.  That doesn't make it right, it only shows how far the 
> league has strayed from their original intent. They make there money from 
> advertising not from being honest!
>
> Amplifier power outputs are equally misleading.  There are really three 
> numbers that count: peak power output, intermodulation distortion at that 
> output, and average plate dissipation.  Typical grounded grid amplifiers 
> have about 10 dB gain.  If you want 500 Watts out, you probably need 50 
> Watts to drive the amplifier.  Grounded cathode amplifiers can be designed 
> to have more gain, but instead of getting more output, you actually 
> require less driving power.  The standard 3rd order IMD level for ham 
> amplifiers has been -30 dB or so.  If not carefully operated, the IMD 
> level can rise quickly to -25 dB or higher.  This is not good.  Some modes 
> like PSK 31 require better than -30 dB IMD levels so you don't see people 
> running amplifiers with PSK 31.  The average plate dissipation is a 
> critical factor in tube life.  Once you exceed the manufacturers average 
> plate dissipation rating for the type of service, you are cutting into 
> tube life.
>
> Some years ago there were several articles on station design.  What was 
> true then and is still true now, is the cheapest dB are those from going 
> to the maximum legal power.  The initial 5-6 db for an antenna are also 
> relatively cheap, but once you've got them, adding 3 dB at a time by 
> increasing the antenna size (proportional to gain, you need to double the 
> antenna size for 3 db of gain) or antenna height gets very pricey very 
> quickly.  The advantage of the antenna is it helps you on both transmit 
> and receive so you can hear the station your trying to work better. There 
> is no similar advantage on receive from adding a more powerful amplifier.
>
> No you haven't made any math mistakes.  I think you will find that the 
> cost of an antenna is more than you think when you consider the tower, 
> rotator and the antenna.  Also you must be very wary of published gain 
> numbers.  I don't believe any tribander has 8.9 db of gain when installed 
> in a typical ham ststion.  I'm sure others will have other opinions, but 
> that's mine. You can have a lot of fun with a standard 100W XCVR and a 
> good dipole or vertical and you can get on now!  You won't be a big 
> contest station or a big DX'er but I'm not sure either one of those is a 
> worthy goal.
>
> Kerry
>
>
>
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