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Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?



 
 
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  #1  
Old August 17th 08, 10:36 PM posted to rec.radio.amateur.antenna
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Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?

My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

Dave WB3DWE Temple, TX
  #2  
Old August 17th 08, 11:07 PM posted to rec.radio.amateur.antenna
Ed Cregger
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Posts: 238
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?


wrote in message
...
My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

Dave WB3DWE Temple, TX


--------------

The old tube rigs used power input to finals as their customary metric.
Considerably less power was output as RF power, which is all that the dummy
load is concerned with - assuming that you have a sentient dummy load. 8)

A standard 200 watt air cooled dummy load will suffice.

Ed, NM2K


  #3  
Old August 17th 08, 11:09 PM posted to rec.radio.amateur.antenna
Richard Clark
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Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?

On Sun, 17 Aug 2008 16:36:42 -0500, wrote:

My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .


Hi Dave,

DC? (Yes, I know, straight from the specification sheet, but
nonetheless: DC?)

Whats the minimum dummy load requirement to tune it ?


Add 50% for safety factor. Or simply ask yourself, do you need to
tune up with full power? Kenwood is usually engineered well enough
not to demand this.

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?


Sure. Better question to ask is "can I trust the claims of this kit?"

Are there standards as to how the rating of a dummy load
is to be interpreted ?


Something short of:
1. throwing the solder of the connections (a temperature under the
eutectic point if 61/39 tin/lead).
2. ignition;
3. personal harm.

The dummy load's rating can be extended through cooling by forced air
or immersion - so its environment is as much a part of the
specification as anything (it doesn't work as well inside a stove as
it does a refrigerator).

If you are building your own (implied by your reference to a kit);
then it behooves you to maintain the lowest heat path resistance
between the load (the resistor) and the coolant. This generally means
a very tight gas-free bond between the load (the resistor) and the
heat sink and the absence of insulating air on the heat sink surface
(either in the form of an air pocket, poor circulation, or a bubble).

Last of all, how sure are you that the load is actually the Ohmic
value you need? The harder you push it, the less likely it will be
that value. In that case, derating to 25% to 50% is called for.
Frequency can be an issue too.

Caddock's MP9100 50 Ohm resistors are a useful jumping off point for
building your own load.

73's
Richard Clark, KB7QHC
  #4  
Old August 17th 08, 11:48 PM posted to rec.radio.amateur.antenna
Highland Ham
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Posts: 250
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB?

My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

====================================
Professional dummy loads are normally rated for continuous use .
They often have cooling fins with the actual resistor being of the thin
film type on a heat sinking tab.

I have made my own dummy loads (for HF and lower VHF) from 20 pcs 1KOhm
2watts ,resistor ,so good for 40Watts as is ,but when immersed in motor
oil capable of handling 100+Watts for 10-15 minutes.
I used carbon film resistors ,but metal oxide ones are perhaps better.
The advantage of using many resistors (in parallel) is a very low
inductance.
I fitted the resistors (sandwiched between 2 jam jar lids with leads
just long enough to solder to lids through holes) inside a cylindrical
metal can with a SO239 connector fitted in centre of its lid.
To prevent oil 'swetting' from can I covered the seams with solder on
the inside. Even after many years ,resistance was 50.6 Ohms or about.
A simple but effective homebrew project.

Frank GM0CSZ / KN6WH
  #5  
Old August 18th 08, 12:46 AM posted to rec.radio.amateur.antenna
Ralph Mowery
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Posts: 426
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?


wrote in message
...
My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

Dave WB3DWE Temple, TX


The numbers you have are the input to the final tubes. The rig will put out
around 100 to 120 watts CW.

Dummy loads are usually rated for so much power for so long of a time. Some
will be good for 100 watts continious and maybe 300 or 500 for a short time
such as 30 seconds , with a cooling off period of 5 minuits.

I have a comercial one that is built with a pl259 on the end. The dummy
load is about 3 inches long and 2 inches in diameter. It is rated for 15
watts continious and 100 watts for 15 seconds with a cooling off period of
so long. I have ran a 100 watt rig into it for a short period of time. It
does get very hot after a few seconds. The old Heathkit dummy I have is a
resistor in a gallon 'paint can'. It is full of oil and can take a KW for a
short period of time.

I picked up some dummy loads at a hamfest that are good for about 50 watts
and not sure how long or how much power they will take. I did hit they
with around 100 watts for about 30 seconds to check out a rig and they took
it,but they did get very warm.

For the ts520 you can use a 100 watt light bulb. I would not recommend it
for any rig with transistors for the output, but it is fine for the tube
rigs. Just use about a foot of coax to the light bulb. They will radiate
a small ammount of power, but not enough to both most stations.
You just tune for maximum brightness. If you have a wattmeter, it will
probably not be accurate into the light bulb as it is not 50 ohms, but good
enough to tune the rig to see if the power out is around 100 watts.


  #6  
Old August 18th 08, 02:56 AM posted to rec.radio.amateur.antenna
John Smith
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Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB?

Richard Clark wrote:

Whats the minimum dummy load requirement ...


73's
Richard Clark, KB7QHC


Richard in the back of my pickup?

Regards,
JS
  #7  
Old August 18th 08, 03:04 AM posted to rec.radio.amateur.antenna
John Smith
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Posts: 2,915
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB?

John Smith wrote:
Richard Clark wrote:

Whats the minimum dummy load requirement ...


8-)

....
  #8  
Old August 21st 08, 07:54 PM posted to rec.radio.amateur.antenna
JB[_3_]
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Posts: 543
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?

wrote in message
...
My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .
Whats the minimum dummy load requirement to tune it ?

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?

Are there standards as to how the rating of a dummy load
is to be interpreted ?

Dave WB3DWE Temple, TX


For ham goodies look at the specs. Ham stuff usually needs to be more
bulletproof than commercial but it aint'. You would probably be all right
with the 100 watt kit for quick tune-ups unless the fine print says 100w for
10 seconds. It isn't the 200w pep to worry about, it's the 160 w CW and FM
and how long you lean on it. Five seconds on and off three times should be
all you need to get it tuned or get a reading.

I have an old Bird Termaline, oil filled, rated for 20 watts that I have
used for years on barefoot rigs. I would never go smaller than that because
the heat may rise too fast and burn the oil and anneal the contacts of the
load resistor. I have used a big 500 watt Bird for continuous burn-in
(weeks) of 100 watt FM repeaters and Base transmitters though. It is all
about duty cycle and whether the heat can me moved out fast enough to
prevent damage to the resistors and contacts.

Dry dummy loads are a different story. Don't put more than double the
rating even for brief periods unless they are well heat sinked..


  #9  
Old August 24th 08, 07:03 PM posted to rec.radio.amateur.antenna
Robert Smits
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Posts: 17
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?

JB wrote:

For ham goodies look at the specs. Ham stuff usually needs to be more
bulletproof than commercial but it aint'. You would probably be all right
with the 100 watt kit for quick tune-ups unless the fine print says 100w
for
10 seconds. It isn't the 200w pep to worry about, it's the 160 w CW and
FM
and how long you lean on it. Five seconds on and off three times should
be all you need to get it tuned or get a reading.

I have an old Bird Termaline, oil filled, rated for 20 watts that I have
used for years on barefoot rigs. I would never go smaller than that
because the heat may rise too fast and burn the oil and anneal the
contacts of the
load resistor. I have used a big 500 watt Bird for continuous burn-in
(weeks) of 100 watt FM repeaters and Base transmitters though. It is all
about duty cycle and whether the heat can me moved out fast enough to
prevent damage to the resistors and contacts.

Dry dummy loads are a different story. Don't put more than double the
rating even for brief periods unless they are well heat sinked..



I concur. Unless you're going to leave the transmitter keyed up for minutes
or hours even a 50 watt dummy load is quite sufficient to tune up my TS
820S, which has essentially the same finals. Done it for years.
--
(Robert Smits, Ladysmith BC)

"I'm not one of those who think Bill Gates is the devil. I simply suspect
that if Microsoft ever met up with the devil, it wouldn't need an
interpreter." - Nicholas Petreley

 




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