[Elecraft] Product Suggestion - 500W Dummy Load

Bob McGraw - K4TAX rmcgraw at blomand.net
Fri Sep 18 16:57:21 EDT 2015


Well ...........it seems pretty clear.

Part 97.3 states: "(6) PEP (peak envelope power). The average power 
supplied to the antenna transmission line by a transmitter during one RF 
cycle at the crest of the modulation envelope taken under normal 
operating conditions."

Part 97. 313 states "(b) No station may transmit with a transmitter 
power exceeding 1.5 kW PEP"     There are specific lower power limits as 
applied to certain bands, i.e. 30M and 60M etc.

73
Bob, K4TAX
K3S s/n 10,163

On 9/18/2015 3:36 PM, Wes (N7WS) wrote:
> The power limit for most hams and ham bands is 1.5 KW PEP output. The 
> rules don't state where the output is measured.  I assume it's at the 
> antenna since the transmission line is part of my transmitter's 
> matching system.  With lossy lines, 2.5 KW at the line input doesn't 
> seem unreasonable.
>
> On 9/18/2015 1:10 PM, Bob McGraw - K4TAX wrote:
>> Who runs 2.5K ?   Uh, isn't that just a wee bit over the legal limit?
>>
>> 73
>> Bob, K4TAX
>> K3S s/n 10,163
>>
>> On 9/18/2015 1:54 PM, mfsj wrote:
>>> I can tell you this there is a world of difference between 800w and 
>>> 2.5k or even 1.5k for that matter. I am in 0 land and very hard to 
>>> break the coasts on a good day at times so a little extra helps 
>>> break those pile ups.
>>> Fred  N0AZZ
>>>
>>>
>>> Sent via the Samsung Galaxy S6 edge+, an AT&T 4G LTE 
>>> smartphone-------- Original message --------From: 
>>> ae4pb at carolinaheli.com Date: 09/18/2015  1:16 PM  (GMT-06:00) To: 
>>> 'Edward R Cole' <kl7uw at acsalaska.net>, Elecraft at mailman.qth.net 
>>> Subject: Re: [Elecraft] Product Suggestion - 500W Dummy Load
>>> Forgive me in advance if this is a stupid question.
>>>
>>> Is there any reason you have to tune at full power? It seems to me that
>>> tuning can be accomplished easily with much lower power. The same 
>>> thing goes
>>> for the ATU to the antenna. I don't see why we need more than a few 
>>> MW at
>>> most for the ATU to Antenna link.
>>>
>>>
>>>
>>> Rightly or wrongly when I was in the hobby the first time I ran a 
>>> TS-850
>>> into an SB-220 to an MFJ roller tuner connected to an antenna switch
>>> feeding: 80m inverted V, 30m/40m rotatable dipoles, and a triband beam.
>>> Whenever I tuned on the inverted V or outer band limits of where my 
>>> antennas
>>> where tuned I ended up putting labels on the ATU on cap position and a
>>> number/clock combo that represented a roller inductor position for 
>>> each band
>>> area I cared about. It ended up I rarely had to tune up anything one 
>>> the air
>>> because I knew where the antenna tuning was using just the Rig and ATU;
>>> tuned the APM into a paintcan MFJ load then switch it inline. I was 
>>> all set
>>> and never had issues when I needed to kick in the horses.
>>>
>>> Now my debate is 500w vs 800w... there's a larger difference between 
>>> 500w
>>> and 800w than between 800w and 2.5kw signal wise if I understand
>>> correctly...
>>>
>>>
>>> Jerry Moore
>>> AE4PB, K3S - S.N. 010324
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf 
>>> Of Edward
>>> R Cole
>>> Sent: Friday, September 18, 2015 2:00 PM
>>> To: Elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] Product Suggestion - 500W Dummy Load
>>>
>>> Don't have much to say:
>>>
>>> Had a Cantenna from Heath in the 60's - knocked over; spilt mineral 
>>> oil on
>>> the floor, threw can away!
>>>
>>> I have acquired "dry" loads over the years rated into UHF and 
>>> sometimes to
>>> mw at flea markets and swaps.  My highest power load is 500w Sierra 
>>> with
>>> power meter and switch for 150 or 500w (probably good to 1000-MHz).  
>>> Have a
>>> couple Bird terminations rated 50w.  Most can handled double their 
>>> rating
>>> for short duration.
>>>
>>> The hardest duty on my loads is when optimizing the output of a new 
>>> unit
>>> where I'm keyed up longer than I should.
>>>
>>> But I do have a question on how adjusting a tuner into a 50-ohm load 
>>> saves
>>> one from transmitting a signal once the tuner is connected to an 
>>> antenna
>>> that may not be 50-ohms.  On 600m my inverted-L is Z = 0.8
>>> +j680.  Tuning into a 50-ohm load does nothing to help match the
>>> antenna.  The amplifier is solid state with input and output 
>>> transformers
>>> (no adjustment).
>>>
>>> I think, unless you use a high power tetrode or triode, that no one 
>>> tunes
>>> amplifiers anymore.  Solid state amps are broadband and need LP 
>>> filters to
>>> keep from amplifying harmonics.  BTW my 2m-8877 is capable of 2000w* RF
>>> output so pretty hard to find a dummy load to take that. Fortunately 
>>> the
>>> amp does not change much so very little tuning is ever needed (of 
>>> course I
>>> am on a small segment of one band about 200-KHz wide).  Of course 
>>> the answer
>>> is to tune antenna at lower power and hope the High Power amp will 
>>> always be
>>> looking at 50-ohms.
>>>
>>> I do not have a QRO 2m antenna tuner but the antenna SWR < 1.25 so 
>>> only the
>>> anode tuning needs a light adjustment occasionally (loading has not be
>>> adjusted for 8 years).  My "dummy load" has 19.2 dBd gain and 
>>> radiates well.
>>>
>>> *I operate at 1365w CW which allows for about 9% variance in meter 
>>> accuracy
>>> to stay legal.
>>>
>>> 73, Ed - KL7UW
>>> http://www.kl7uw.com
>>>       "Kits made by KL7UW"
>>> Dubus Mag business:
>>>       dubususa at gmail.com
>>>
>
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