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Just a thought...

Discussion in 'Discussions, Opinions & Editorials' started by AF5ID, Feb 3, 2013.

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  1. AF5ID

    AF5ID Ham Member QRZ Page

    I'm thinking about buying an amplifier for legal limit and they all say 1500W PEP. I was wonder what that is not in PEP and how do I calculate pep.

    73's DE AF5ID
     
  2. KL7AJ

    KL7AJ Ham Member QRZ Page


    Hi Josh:

    If you plan on "crowding the limit" with a 1.5 KW amp, you'd better have an accurate way of MEASURING the power, rather than relying on calculating it. Fortunately there are some very good and inexpensive PEP meters around now...though I still prefer an oscilloscope.

    As a rough rule of thumb, if you are NOT using audio processing, your PEP will be about 6 times the AVERAGE power, if you've got a typical male voice. (Female voices have MUCH lower PEP to average ratios...which is why they punch through QRM like they do). If you use some really strident processing, you can probably safely run 1KW average power.....but don't count on it. Whenever using a linear amplifier, always use SOME reliable means of measuring PEP.

    Eric
     
  3. KJ4VTH

    KJ4VTH Subscriber QRZ Page

    Don't worry about it, many lids don't. :(
     
  4. KQ9J

    KQ9J Subscriber QRZ Page

    Get yourself a 1500 watt PEP rated amp, and a good peak reading wattmeter. The wattmeter needs to have active circuitry to read true PEP. Then drive the amp to only 1000 watts or less, WHEN needed. It will last forever, and no one will notice the difference between that and a full 1500 watts. Do a LOT of studying first, though. And the money a legal limit amp costs these days is really better applied to the antenna system FIRST. :)
     
  5. N0AZZ

    N0AZZ Ham Member QRZ Page

    Well there are legal limit amps and then there are legal limit amps. Some say rated 1500w intermintent use and some say key down legal limit forever there is a great deal of difference in these amps in construction and price.

    In new American made amps the 2 largest (there are many small shops and custom made ones) one are Amertron the AL-1200 and the 1500 costing up to about $3500 for the 1500. The other is top of the line Alpha from RF Concepts the manual tune 8410 for $5400 and the fully auto tune 9500 at $8000 both are capable of 3000+w and full duty cycle forever. I have ran mine in several RTTY contests with back to back contacts and never a problem @ 1500w with my Alpha for about 8 hrs that is all I could last LOL.

    Both amps are a good value for the money.
     
  6. KA9JLM

    KA9JLM Platinum Subscriber QRZ Page


    I must have fallen asleep in the new school Electronics Class.

    Is there a new way of calculating PEP now ?

    I came from old school.

    Sorry if my question is stupid, I would just like the new formula.

    Please include the formula for a Female voice also.

    Thank You.
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Since power is regulated by output and not input, it's not calculated; it's measured. No requirement to accurately measure it at all, although if you're right up against the legal limit I suppose some degree of measurement accuracy is implied.

    Also since FCC has exhibited zero desire to closely regulate the amateur radio service with respect to field inspections and such -- who cares?:p
     
  8. KA9JLM

    KA9JLM Platinum Subscriber QRZ Page

    I agree.

    Measured or guessing 6 X does not seem close to me.

    I would like to see how 6X is even close to some outcome.
     
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    On my own SSB transmitters, which number "several," if I use a non-powered standard-issue Wattmeter (like a Bird 43 or any number of variants), the difference between what the meter indicates and actual PEP runs from about 4x to about 10x depending on the transmitter.

    My Jupiter with the processor engaged and set to "50" (I have no background noise at all), the difference is only about 4x; i.e., a Bird will read 25W when the real PEP is 100W as indicated on a scope or true PEP meter. But I was just using my Drake TR-7 over the weekend and noted the difference is closer to 10x: Bird indicated 10W and PEP meter 100W. The Drake hasn't any real speech processing.

    Thus, IMO it varies all over the place.:p
     
  10. KA9JLM

    KA9JLM Platinum Subscriber QRZ Page

    Ok.

    I thought P-P was different than PEP.

    I guess I was mistaken.
     
  11. W4PG

    W4PG Super Moderator Staff Member QRZ Page

    I was wondering if you could help me with a new homebrew amp. It has four 4-1000As and I wasn't quite sure whether class C was the correct mode or not.

    .............Bob
     
  12. KL7AJ

    KL7AJ Ham Member QRZ Page

    These are rules of thumb...not calculations. Female voices are MUCH less "spiky" than male voices on the average....easily visible on an oscilloscope. But the 6:1 general rule was even described in my old Hallicrafters Ht-32 manual....which of course didn't have any compression! Always safer to overestimate the peak to average power in any case. HI!
     
  13. WA9SVD

    WA9SVD Ham Member QRZ Page

    That's NOT something to which you should admit in public...
     
  14. AB1QP

    AB1QP Premium Subscriber QRZ Page

    Maybe irony and sarcasm have both gone QRT at QRZ.
     
  15. WA7PRC

    WA7PRC Ham Member QRZ Page

    Only people who are curious about ways to measure it. Everyone else doesn't care any more than the FCC does. There are bigger fish to fry.
    I use an inexpensive and easy to use oscilloscope to ensure my SSB signal isn't flat-topping. I care little about the peak value.
     
  16. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think you mean, "Classy," it's all one word.

    Yeah, four 4-1000s is pretty Classy and if you use screening rather than solid metal for the upper enclosure, you won't need any other room lighting.
     
  17. KA9JLM

    KA9JLM Platinum Subscriber QRZ Page


    Or Heating...
     
  18. AF6LJ

    AF6LJ Ham Member QRZ Page

    I was thinking of chicken wire laminated between sheets of glass. Bob could drive the grids with about forty watts and get something around the legal limit plus or minus six DB.
    Close enough.

    Bob;
    If you really want to impress, build the power supply in a enclosureless form factor.
    Just bet some chain link fence polls and for effect razor wire to go across the top.
    Add a small gate with a big heave Medco lock.
    Rig an interlock to the gate for safety.
    And by all means use the biggest loudest contactors you can afford.
    You want your neighbors to know when you are transmitting. :)
     
  19. KB3LIX

    KB3LIX Ham Member QRZ Page

    Or a room heat source !
     
  20. W5BIB

    W5BIB Premium Subscriber QRZ Page

    Hi JOSH. It's not "legal limit" but I have a SWAN-1200X amp that will match the SWAN-260 CYGNET I "gave you" (including insured shipping). You must have received some insurance monies to be able to purchase a "legal amp". I feel like quoting P.T. Barnum,... but will refrain. :(
     
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