[Boatanchors] 120 - 240vac and output
Gary Schafer
garyschafer at comcast.net
Fri Nov 26 20:43:39 EST 2004
Well Ray, now that you have defined what you mean by "doubling the
signal strength" I have to say that is a very liberal S meter you are
dealing with there!
That may be so on some S meters. But that would make the calibration of
the S meter just a little over 1 DB per S unit!
By the way the difference between 1000 watts and 1200 watts is about .8
db. So on that S meter with 1 DB per S unit, you could see 1 S unit
difference in that change of power.
The old standard was 6 DB per S unit. That would make the meter go up by
1 S unit if you increased your power by 4 times.
Unfortunately most receivers are not set up to that standard today. Some
are a little over 1 DB per S unit on the low end of the scale to around
5 DB or so per S unit as you approach S9. There are a few that conform
to the 6 DB per S unit standard.
So you really can't go much by what someone tells you they read on an S
meter when you increase your power.
But what you can count on is that if you double your power your signal
will increase by 3 DB. If you double it again it will increase another 3
DB. So increasing it by 4 times gains you 6 DB. On a real S meter that
would be 1 S unit.
I am not sure what you were getting at when you said the other guy would
notice a difference only if you were running into a 9 db gain beam?
It sounds like you are saying that there will be a greater difference in
your signal strength when increasing from 1000 watts to 1200 watts if
you are feeding that beam verses feeding a no gain antenna like a dipole?
If that is what you mean, then that is not correct. If you had a 9 db
gain antenna and you double your power from say 100 watts to 200 watts,
that is still a 3 db increase in signal strength on that same antenna.
Increasing power by 3 db again to 400 watts gives you a 6 db increase
over the 100 watts you first had. 1 S unit again.
It always takes 2 times the power to increase signal strength by 3 db.
No matter how much gain you have in the antenna or anywhere else.
Now if you are saying that that extra 200 watts from 1000 watts to 1200
watts may make a difference in poor signal conditions, I would agree
with you. If you are almost readable with 1000 watts, 1200 watts may be
enough difference to be heard but not by much. It would be almost
immeasurable at the other end. Well, the difference is .8 db between
1000 watts and 1200 watts. If someone has a 1 db per S unit meter then
he will probably see the difference.
73
Gary K4FMX
Ray Friess wrote:
> The 4x power to double signal strength that I was referring to was the
> power output of the
> transmitter or linear.. In other words, if I want to double the S
> meter reading on the other
> guys receiver from, say, S 4 to about S 9, and I am running 100 watts
> .... then I generally need
> to go to 400 watts to get double that reading on his S meter. Again,
> increasing my power
> output from my linear from 1000 watts up to 1200 watts is not going to
> make me one bit strong
> in the other guys receiver or his S meter.... GENERALLY.
> I say generally because if I am running that extra 200 watts into a
> beam with a 9 db gain...
> while he wont see a doubling of my signal strength over 1000 watts into
> that same beam, he may
> see an S unit difference, which can make the difference between a
> contact or no contact...
> especially in a pileup.... Still, to me it wouldnt be worth the worry
> or extra effort to run 220
> into my shack just for my linears. I would, and do, use 115....
>
>
>
> Gary Schafer wrote:
>
>> Sometimes it's nice to have information police. It is good for
>> entertainment value if nothing else. :>)
>>
>> I wonder what the transfer curves look like for 3-500Z's in an SB200?
>> I believe that was the amplifier being discussed. Maybe there are
>> transfer curves for the filaments too? I believe that was being
>> discussed.
>>
>> The 2X and 4X is a way to get in the ball park with differences as
>> there is 2X the current in a 120 volt circuit from what there is in a
>> 240 volt circuit and there is 2X the voltage step up in the HV
>> transformer in a 120 volt circuit compared to a 240 volt circuit for a
>> given amount of power. If we know the primary voltage drop on the 120
>> volt mains we can figure what it is on 240 volts without too much
>> trouble. Much easier than trying to figure out what the resistance of
>> the mains in your house all the way back to the pole just so you can
>> use I squared R to calculate. Vic is on the mark here.
>>
>> This was I thought more of a generic discussion on 120 Volts verses
>> 240 volts and how it affects voltage drop. We did not get into
>> transformer losses either which play in the problem.
>>
>> Part of the discussion was about tube life on 120 verses 240 volts. I
>> assumed that arose from the question of filament voltage-- so my
>> simple answer about that.
>>
>> As far as signal strength doubling with 4 times the power, that can be
>> correct. It all depends on what your perspective is on what double the
>> signal strength is. If it is one of 2X the power then 3 db of course
>> would be correct. If it is one of 2X the voltage then 6 db or 4X the
>> power would be correct. Without qualifying your statements you are no
>> more correct than Ray was.
>>
>> It is not always necessary to write reams of information to answer a
>> question. It can always be elaborated to death and no one wants to
>> read it anymore.
>>
>> However you do add another perspective which I would think is of value
>> too.
>>
>> Happy thanksgiving,
>> Gary K4FMX
>>
>>
>>
>> Ron wrote:
>>
>>> Sometimes I sit and read these posts and just shake my head.
>>> The one great thing about the internet is that information can be
>>> available to a great number of people quickly. The worst thing is
>>> that the wrong information can be passed just as easily.
>>>
>>> I made no comment during the 2x 4x discussion but now with the 4
>>> times your power to double your signal strength .....well ...that's
>>> enough.
>>>
>>> Primary loss is calculated from I *2 x R not 2x or 4x. In this case
>>> I is doubled and 2 squared is 4 so for this specific case , 4x is
>>> correct ......but losses are from the square of the current. All the
>>> assumptions so far assume that the secondary side or the high voltage
>>> transformer acts as a resistive linear load and that is not so. Take
>>> a look at the transfer curves for a 3-500z and you will see what
>>> currents it draws 2KV compared to 2.2 or 2.4KV. Current drawn in the
>>> secondary is reflected to the primary . When you work this problem ,
>>> you work it from the secondary back to the primary ...not primary to
>>> secondary.
>>>
>>> As far as the 4x power to double signal strength ...it ain't so.
>>> Doubling signal strength will add 3 dB to your signal strength. I
>>> suppose if your signal is 1/2 S unit then adding 3dB would double it
>>> but when your signal strength is S7 , doubling your power gives you a
>>> signal of S7.5 as an S unit is 6 dB.
>>> I'll agree about the extra 200 watts ....it won't make a difference.
>>>
>>> Come on guys, if your going to post information , remember that a lot
>>> of fellows will read your stuff and then pass it on.
>>> I can't tell you how many guys will sit and argue a point about some
>>> information gleaned from some post they read a week or two years ago
>>> that was just wrong.
>>> ---
>>> Ron
>>>
>>>
>>>
>>>
>>> Ray Friess wrote:
>>>
>>>> What Vic says is true.... AND another thing to remember along with
>>>> it is that that extra
>>>> 200 watt difference is not going to make a BIT of difference in your
>>>> signal strength. The
>>>> receiving station wouldnt be able to tell the difference in your
>>>> signal if you went from 1000
>>>> watts to 1200 watts. In fact, the scientific fact is that in
>>>> order to DOUBLE your signal
>>>> strength.. you have to FOUR TIMES your power.. so adding an
>>>> additional 200 watts to a
>>>> 1000 watt signal is not going to make a bit of difference.... even
>>>> in the worst of QRM or
>>>> band conditions....
>>>>
>>>>
>>>> Vic Rosenthal wrote:
>>>>
>>>>> Gary Schafer wrote:
>>>>>
>>>>>> Think about this for a minute and you should be able to figure it
>>>>>> out yourself. The only thing that changes in the amp whether it is
>>>>>> run on 120 or 240 is the primary configuration of the transformer.
>>>>>> The rest of the amp knows nothing of the difference. Filament
>>>>>> voltage is the same and plate voltage is the same.
>>>>>>
>>>>>> With a however here, The plate voltage may be a little better
>>>>>> regulated (may not drop quite as much) because of a little less
>>>>>> voltage drop on the house wiring on 240 volts.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> But keep in mind that the reduction in plate voltage due to primary
>>>>> voltage drop will be FOUR TIMES greater on 120V than 240V. The
>>>>> primary voltage drop will be twice as great, since the current is
>>>>> double (given the same wire size, etc.). Since the transformer will
>>>>> need to multiply the voltage 2X more, the drop will be 4X what it
>>>>> was. If you have a 120V circuit using no. 8 wire going directly to
>>>>> the service entrance, the effect will be much smaller; but most
>>>>> 120v circuits are not like this.
>>>>>
>>>>> This explains why people say they get 1200 watts with 240 V and
>>>>> only 1000 watts on 120, for example.
>>>>>
>>>>
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>>>> ** List Administrator - Duane Fischer, W8DBF/W9WZE ** ** For
>>>> Assistance: dfischer at usol.com ** $$ For vintage radio info,
>>>> see the HCI web site $$ http://www.w9wze.org
>>>
>>>
>>>
>>>
>>>
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