Re: [Elecraft] Dummy Load recommendation

[CUTTER DAVID via Elecraft]

Don
Thanks for those further notes.  I'm also thinking of the best we can do with 
the most primitive equipment.  Amateurs have been making RF probes forever and 
now we have cheap digital multimeters with >1Mohm input impedance it should be 
even easier to get a good estimate of power using the method you outline but 
without a scope, which itself has to be expensively calibrated and you still 
have to interpret an analogue display.  
I wonder just how good we could make and calibrate an RF probe. 
David G3UNA

> On 31 July 2019 at 16:28 Don Wilhelm  wrote:
> 
> 
> David,
> 
> Your question about "what is good enough" is an informative one.
> When I was doing repair/alignment work for others, it was important to 
> me to have tools that had traceable calibration info.  I had some good 
> 50 ohm dummy loads that were good to 1 GHz, and an LP-100A that was 
> calibrated to NIST standards (which I used as a sanity check for other 
> power measurement instruments).  Having those calibrated tools were 
> important to maintain my customer's trust.
> 
> In amateur practice, such care is not necessarily needed, but the 
> K3/KX2/KX3 TX gain calibration does require a good 50 ohm load up to 50 
> MHz.  That is easily checked by sweeping it with an antenna analyzer.
> 
> As for the power measurement, once you have a good 50 ohm dummy load, it 
> is easy to use a 'scope (with a 10X probe) connected across that dummy 
> load (use a TEE adapter to gain access to the coax center conductor). 
> Then you can measure the RF voltage (peak to peak shown on the 'scope), 
> and use the formula Vp-p squared then divided by 400 to quickly obtain 
> an accurate calculation of the power.  Nothing really expensive except 
> for the 'scope (which can be borrowed in many cases).
> 
> So what you need first is a good 50 ohm dummy load, and secondly, access 
> to a 'scope having reasonable calibration for the vertical deflection at 
> the frequency of interest.
> 
> With that combination, you can check the error in other in-line power 
> measurement equipment.
> 
> In most cases a 10% or 20% error is not going to make a big difference 
> in on-the-air performance - anywhere in the ballpark is usually OK.
> 
> You are correct that we have become complacent because of digital 
> displays.  Take a 4 digit display in an instrument having accuracy of 
> 10% - the difference between a display of 10.41 and 9.37 or 11.45 is 
> meaningless given the 10% accuracy of the instrument itself.  You should 
> round that reading to 10 volts.  Analog readouts automatically do that 
> compensation because you cannot read the meter scale with 4 digit 
> accuracy.  Even my 12 inch slide rule in college was limited to 3 
> significant digits.
> 
> There is a difference between doing it "good enough" and with greater 
> accuracy depends on the purposes of your measurements.
> 
> 73,
> Don W3FPR
> 
> On 7/23/2019 11:38 AM, CUTTER DAVID via Elecraft wrote:
> > I agree with all that has been said and suspect a lot of responders on this 
> > list are or were engineers who are used to using precision equipment.  I 
> > think it can be misleading to look at some instruments built into a 
> > transceiver for instance, but it never seemed to matter, until Elecraft 
> > came along.  I did my calibration with a Bird power meter and a Bird 500W 
> > load but I have no idea when they were last calibrated, so, what value do I 
> > put on the measurements?  Well, it's good enough for me. But calibration is 
> > a special case and I'd never heard of amateurs calibrating for power before 
> > Elecraft.  Accurate power meters are costly to buy and maintain if you are 
> > in business, but for me now I'm retired it doesn't matter so much because 
> > I'm not doing it for a paying customer.  I think we are misled by the easy 
> > precision of the digital multimeter which for a few £ or $ is ten times as 
> > good as what we previously thought were good analogue instruments.  In 
> > short, I think technology can cause us to bite our finger nails 
> > unnecessarily.  10% or 20% power error is hardly noticeable to the guy on 
> > the other side of the world.
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Re: [Elecraft] Dummy Load recommendation

[Don Wilhelm]

David,

Your question about "what is good enough" is an informative one.
When I was doing repair/alignment work for others, it was important to 
me to have tools that had traceable calibration info.  I had some good 
50 ohm dummy loads that were good to 1 GHz, and an LP-100A that was 
calibrated to NIST standards (which I used as a sanity check for other 
power measurement instruments).  Having those calibrated tools were 
important to maintain my customer's trust.


In amateur practice, such care is not necessarily needed, but the 
K3/KX2/KX3 TX gain calibration does require a good 50 ohm load up to 50 
MHz.  That is easily checked by sweeping it with an antenna analyzer.


As for the power measurement, once you have a good 50 ohm dummy load, it 
is easy to use a 'scope (with a 10X probe) connected across that dummy 
load (use a TEE adapter to gain access to the coax center conductor). 
Then you can measure the RF voltage (peak to peak shown on the 'scope), 
and use the formula Vp-p squared then divided by 400 to quickly obtain 
an accurate calculation of the power.  Nothing really expensive except 
for the 'scope (which can be borrowed in many cases).


So what you need first is a good 50 ohm dummy load, and secondly, access 
to a 'scope having reasonable calibration for the vertical deflection at 
the frequency of interest.


With that combination, you can check the error in other in-line power 
measurement equipment.


In most cases a 10% or 20% error is not going to make a big difference 
in on-the-air performance - anywhere in the ballpark is usually OK.


You are correct that we have become complacent because of digital 
displays.  Take a 4 digit display in an instrument having accuracy of 
10% - the difference between a display of 10.41 and 9.37 or 11.45 is 
meaningless given the 10% accuracy of the instrument itself.  You should 
round that reading to 10 volts.  Analog readouts automatically do that 
compensation because you cannot read the meter scale with 4 digit 
accuracy.  Even my 12 inch slide rule in college was limited to 3 
significant digits.


There is a difference between doing it "good enough" and with greater 
accuracy depends on the purposes of your measurements.


73,
Don W3FPR

On 7/23/2019 11:38 AM, CUTTER DAVID via Elecraft wrote:

I agree with all that has been said and suspect a lot of responders on this 
list are or were engineers who are used to using precision equipment.  I think 
it can be misleading to look at some instruments built into a transceiver for 
instance, but it never seemed to matter, until Elecraft came along.  I did my 
calibration with a Bird power meter and a Bird 500W load but I have no idea 
when they were last calibrated, so, what value do I put on the measurements?  
Well, it's good enough for me. But calibration is a special case and I'd never 
heard of amateurs calibrating for power before Elecraft.  Accurate power meters 
are costly to buy and maintain if you are in business, but for me now I'm 
retired it doesn't matter so much because I'm not doing it for a paying 
customer.  I think we are misled by the easy precision of the digital 
multimeter which for a few £ or $ is ten times as good as what we previously 
thought were good analogue instruments.  In short, I think technology can cause 
us to bite our finger nails unnecessarily.  10% or 20% power error is hardly 
noticeable to the guy on the other side of the world.

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[Elecraft] Dummy Load Recommendation

[Mark Murray via Elecraft]

The previously described RFL-100 $50 resistor dummy load kit (also available
pre-built) is perfect.  With a very nice cabinet, choice of UHF connectors,
and very nice price.

For those who experiment with very small RF Termination Resistor devices,
the microwave company Anaren, Inc., of East Syracuse, NY now manufactures
(overseas) a tiny 450-watt RF termination device that measures roughly
1-inch x 1/2-inch.  DC-through 1.7-GHz.  $24.00 from Mouser.com.  Model #
G450N50W4.  AiN device, 50-Ohms +/-2%.   Two flange holes for mounting on
heat sink.  See spec sheet for temperature limits.  Even at 100-watts
dissipation you'll need a good heat sink and cooling fan; likewise when
wiring up four.  Recommended for experimenters. 
// Mark W2OR
~~ ~~ ~~



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Re: [Elecraft] Dummy Load recommendation

[Fred Jensen]

Recalls to mind Tom Schiller, N6BT, and his "Phased Illuminator."

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 7/23/2019 1:42 PM, Jim Ragsdale wrote:
I quit using 60 W light bulbs when I worked a station in New Jersey 
from Memphis, Tennessee!

Jim W5LA ex K4QG ex WA4BAC ex WN4BAC


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Re: [Elecraft] Dummy Load recommendation

[Jim Ragsdale]

I quit using 60 W light bulbs when I worked a station in New Jersey from 
Memphis, Tennessee!

Jim W5LA ex K4QG ex WA4BAC ex WN4BAC

On 07/23/19 3:03 PM, Grant Youngman wrote:

As a new ham (1958-9) my "dummy load" was a 60 watt light bulb.  Even made a 
few local contacts with it.  Couldn’t afford anything else.  A good pi-network could load 
most anything, anyway .. :-)

Grant NQ5T
K3 #2091 KX3 #8342


But as a new young ham (1960's) I bought a cantenna (paint can filled with 
mineral oil and resistor load immersed) for HF stuff and a Knight-Kit SWR 
meter.  But as I got older and had more cash I got better stuff.


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Re: [Elecraft] Dummy Load recommendation

[Grant Youngman]

As a new ham (1958-9) my "dummy load" was a 60 watt light bulb.  Even made a 
few local contacts with it.  Couldn’t afford anything else.  A good pi-network 
could load most anything, anyway .. :-)

Grant NQ5T
K3 #2091 KX3 #8342

> 
> But as a new young ham (1960's) I bought a cantenna (paint can filled with 
> mineral oil and resistor load immersed) for HF stuff and a Knight-Kit SWR 
> meter.  But as I got older and had more cash I got better stuff.
> 

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Re: [Elecraft] Dummy Load recommendation

[Edward R Cole]

This discussion reminds me that most on this list are HFers and never 
go above 30mcs (MHz).  Or buy all their ham stuff and believe the 
mfrs specs or meters without question.  Probably do not build 
homebrew equipment so never had to measure if such-an-such actually 
is working (and at what level).

By now I should have made a few of you angry at my post.   Good!

For most arm-chair operators a Bird and Bird load will be more than 
adequate to determine power and SWR to +/- 5% full scale reading.  It 
was my main antenna meter when working as a professional 
technician.  Rugged, fairly accurate, dependable (don't drop it off the tower).


A good non-inductive 50-ohm resistive load and a scope able to 
measure over 50-MHz will do better.


Next some better directional couplers will give more accurate return 
loss (SWR).


My "standard" is using better than good directional couplers (>20 dB) 
with my HP-432A mw power meter using  up to 10 mw signal 
sources.  This is usable to 18 GHz.  With use of high power coax 
attenuators, I can measure power as high as the rating of the 
attenuator.  I use 50-dB directional couplers on 1296 to measure my 
600w amp (58 dBm).


XG3 is a good 1mw source (0 dBm) up to 200-MHz, though not real 
accurate in frequency (which is not that important for 
power/reflected power).  But harmonic energy exists unless you use a 
filter since the output is a square wave.


I recently bought a used Bird HP 8202 500w load (good to 2500-MHz) 
which I can use with amps up to 1500w (as long as transmission is 
kept short - less than a minute; most tests take only a few 
seconds).  I have a Bird 25w load which I have used up to 150w for 
short measurements.  If it feels hot stop  until cool again.


But as a new young ham (1960's) I bought a cantenna (paint can filled 
with mineral oil and resistor load immersed) for HF stuff and a 
Knight-Kit SWR meter.  But as I got older and had more cash I got better stuff.


A dummy load that you can trust to be SWR 1:1 is good thing to check 
those SWR meters or antenna analyzers with.  Handy when measurements 
seem to be "all over the map".  Use it to test coax cables, for instance.


73, Ed - KL7UW
  http://www.kl7uw.com
Dubus-NA Business mail:
  dubus...@gmail.com 


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Re: [Elecraft] Dummy Load recommendation

[john]

I have a 500 watt and 1000 watt Bird dummy loads and they are well  
made.  These are not toys. I believe that they are rated for average  
continuous power and I do not agree that they need to be rated for 2X+  
the transmitted power, especially for intermittent use like most of us  
do.


John KK9A



Bob McGraw K4TAX wrote:
I agree that Bird dummy loads are some of the best.  Be sure to get  
one rated for at least your maximum power anticipated.  And do allow a  
margin of safety. I use 2x, thus for 100 watts I use a 250 watt rated  
load.


I purchase all of my power measurement equipment from NM3E.COM.

Bob, K4TAX

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Re: [Elecraft] Dummy Load recommendation

[Charlie T]

The secret to using wire-wound resistors for a 50Ω load is to use a lot of them 
in parallel as the inductance divides just as the value does for the number of 
resistors.
Of course, this is only reasonable if you already have a pawful to start with.  
Otherwise, RF rated, big 50Ω non-inductive resistors are available from many 
sources.
I had a lot of 1200 Ω, 10 watt (light blue??) wire-wound resistors, so 24 of 
them between two pieces of G-10 made a decent HF dummy load with a good safety 
factor at 100 watts.

Another handy load, is one that will show 2:1 (100Ω) or 3:1 (150Ω) SWR.  It 
wouldn't have to take much power as you'd only be using it to check an SWR 
readout, etc.
I made a few out of a couple 2W resistors. They'll take reasonable power for a 
very short  (½ second??) check time.

73, Charlie k3ICH



-Original Message-
From: elecraft-boun...@mailman.qth.net  On 
Behalf Of CUTTER DAVID via Elecraft
Sent: Tuesday, July 23, 2019 6:44 AM
To: hawley, charles j jr ; Art Nienhouse 

Cc: Elecraft@mailman.qth.net
Subject: Re: [Elecraft] Dummy Load recommendation)

I often wonder just how useful a precision dummy load really is in the amateur 
service.  I picked up home brew dummy load at the club the other day.  It 
measured 57ohms dc and comprises 4 wire-wound resistors attached in a cluster 
across the end of the coax.  After lots of disparaging remarks I put it on the 
VNA and it didn't look at all bad out to 30MHz: nothing over 1.5:1 and no 
spikes or dips to indicate resonances. I'll have to do it again and make a 
print-out for posterity. 
I've heard that salt water in a bucket works after a fashion.  
So the question is: how good do you need it to be?
David G3UNA 

 

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Re: [Elecraft] Dummy Load recommendation

[CUTTER DAVID via Elecraft]

I agree with all that has been said and suspect a lot of responders on this 
list are or were engineers who are used to using precision equipment.  I think 
it can be misleading to look at some instruments built into a transceiver for 
instance, but it never seemed to matter, until Elecraft came along.  I did my 
calibration with a Bird power meter and a Bird 500W load but I have no idea 
when they were last calibrated, so, what value do I put on the measurements?  
Well, it's good enough for me. But calibration is a special case and I'd never 
heard of amateurs calibrating for power before Elecraft.  Accurate power meters 
are costly to buy and maintain if you are in business, but for me now I'm 
retired it doesn't matter so much because I'm not doing it for a paying 
customer.  I think we are misled by the easy precision of the digital 
multimeter which for a few £ or $ is ten times as good as what we previously 
thought were good analogue instruments.  In short, I think technology can cause 
us to bite our finger nails unnecessarily.  10% or 20% power error is hardly 
noticeable to the guy on the other side of the world.  

David G3UNA


> On 23 July 2019 at 16:16 Bob McGraw K4TAX  wrote:
> 
> 
> Yes a calorimeter is the better way to measure power.   Not inexpensive 
> however. 
> 
> Bob, K4TAX
> 
> 
> Sent from my iPhone
> 
> > On Jul 23, 2019, at 10:07 AM, W2xj  wrote:
> > 
> > If you really want precision, use a water cooled load. Measure the flow 
> > rate and input and output temperature. You can precisely calculate power. 
> > 
> > Sent from my iPad
> > 
> >> On Jul 23, 2019, at 9:38 AM, Bob McGraw K4TAX  wrote:
> >> 
> >> Since power meter systems are calibrated at a known impedance {usually 50 
> >> ohms}, and they are voltage sensing devices, any deviation from the 
> >> calibration value will introduce an error in power indication.  It just 
> >> depends on how precise one prefers to be with power measurements.
> >> 
> >> 100 watts into 50 ohms is 70.71 volts
> >> 
> >> 100 watts into 55 ohms is 74.16 volts
> >> 
> >> 100 watts into 45 ohms is 67.08 volts
> >> 
> >> 73
> >> 
> >> Bob, K4TAX
> >> 
> >> 
> >>> On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:
> >>> I often wonder just how useful a precision dummy load really is in the 
> >>> amateur service.  I picked up home brew dummy load at the club the other 
> >>> day.  It measured 57ohms dc and comprises 4 wire-wound resistors attached 
> >>> in a cluster across the end of the coax.  After lots of disparaging 
> >>> remarks I put it on the VNA and it didn't look at all bad out to 30MHz: 
> >>> nothing over 1.5:1 and no spikes or dips to indicate resonances. I'll 
> >>> have to do it again and make a print-out for posterity.
> >>> I've heard that salt water in a bucket works after a fashion.
> >>> So the question is: how good do you need it to be?
> >>> David G3UNA
> >>> 
> >>> 
>  On 22 July 2019 at 23:58 "hawley, charles j jr"  
>  wrote:
>  
>  
>  Used Bird Attenuator is a good deal.
>  
>  https://nm3e.com/AttenuatorSampler.htm
>  
>  Then you’ll have a sample to plug into your counter or scope
>  
>  Chuck Jack Hawley
>  KE9UW
>  
> >>> __
> >>> Elecraft mailing list
> >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> >>> Help: http://mailman.qth.net/mmfaq.htm
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> >>> 
> >>> This list hosted by: http://www.qsl.net
> >>> Please help support this email list: http://www.qsl.net/donate.html
> >>> Message delivered to rmcg...@blomand.net
> >> 
> >> __
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> > 
> > 
> 
> 
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Re: [Elecraft] Dummy Load recommendation

[W2xj]

It doesn’t have to be that expensive. I have built several. DIY is as good as 
buying the finished product. 

Sent from my iPad

> On Jul 23, 2019, at 11:16 AM, Bob McGraw K4TAX  wrote:
> 
> Yes a calorimeter is the better way to measure power.   Not inexpensive 
> however. 
> 
> Bob, K4TAX
> 
> 
> Sent from my iPhone
> 
>> On Jul 23, 2019, at 10:07 AM, W2xj  wrote:
>> 
>> If you really want precision, use a water cooled load. Measure the flow rate 
>> and input and output temperature. You can precisely calculate power. 
>> 
>> Sent from my iPad
>> 
>>> On Jul 23, 2019, at 9:38 AM, Bob McGraw K4TAX  wrote:
>>> 
>>> Since power meter systems are calibrated at a known impedance {usually 50 
>>> ohms}, and they are voltage sensing devices, any deviation from the 
>>> calibration value will introduce an error in power indication.  It just 
>>> depends on how precise one prefers to be with power measurements.
>>> 
>>> 100 watts into 50 ohms is 70.71 volts
>>> 
>>> 100 watts into 55 ohms is 74.16 volts
>>> 
>>> 100 watts into 45 ohms is 67.08 volts
>>> 
>>> 73
>>> 
>>> Bob, K4TAX
>>> 
>>> 
 On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:
 I often wonder just how useful a precision dummy load really is in the 
 amateur service.  I picked up home brew dummy load at the club the other 
 day.  It measured 57ohms dc and comprises 4 wire-wound resistors attached 
 in a cluster across the end of the coax.  After lots of disparaging 
 remarks I put it on the VNA and it didn't look at all bad out to 30MHz: 
 nothing over 1.5:1 and no spikes or dips to indicate resonances. I'll have 
 to do it again and make a print-out for posterity.
 I've heard that salt water in a bucket works after a fashion.
 So the question is: how good do you need it to be?
 David G3UNA
 
 
> On 22 July 2019 at 23:58 "hawley, charles j jr"  
> wrote:
> 
> 
> Used Bird Attenuator is a good deal.
> 
> https://nm3e.com/AttenuatorSampler.htm
> 
> Then you’ll have a sample to plug into your counter or scope
> 
> Chuck Jack Hawley
> KE9UW
> 
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 Message delivered to rmcg...@blomand.net
>>> 
>>> __
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>>> Message delivered to w...@w2xj.net
>> 
>> 
> 
> 
> 

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Re: [Elecraft] Dummy Load recommendation

[Bob McGraw K4TAX]

Yes a calorimeter is the better way to measure power.   Not inexpensive 
however. 

Bob, K4TAX


Sent from my iPhone

> On Jul 23, 2019, at 10:07 AM, W2xj  wrote:
> 
> If you really want precision, use a water cooled load. Measure the flow rate 
> and input and output temperature. You can precisely calculate power. 
> 
> Sent from my iPad
> 
>> On Jul 23, 2019, at 9:38 AM, Bob McGraw K4TAX  wrote:
>> 
>> Since power meter systems are calibrated at a known impedance {usually 50 
>> ohms}, and they are voltage sensing devices, any deviation from the 
>> calibration value will introduce an error in power indication.  It just 
>> depends on how precise one prefers to be with power measurements.
>> 
>> 100 watts into 50 ohms is 70.71 volts
>> 
>> 100 watts into 55 ohms is 74.16 volts
>> 
>> 100 watts into 45 ohms is 67.08 volts
>> 
>> 73
>> 
>> Bob, K4TAX
>> 
>> 
>>> On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:
>>> I often wonder just how useful a precision dummy load really is in the 
>>> amateur service.  I picked up home brew dummy load at the club the other 
>>> day.  It measured 57ohms dc and comprises 4 wire-wound resistors attached 
>>> in a cluster across the end of the coax.  After lots of disparaging remarks 
>>> I put it on the VNA and it didn't look at all bad out to 30MHz: nothing 
>>> over 1.5:1 and no spikes or dips to indicate resonances. I'll have to do it 
>>> again and make a print-out for posterity.
>>> I've heard that salt water in a bucket works after a fashion.
>>> So the question is: how good do you need it to be?
>>> David G3UNA
>>> 
>>> 
 On 22 July 2019 at 23:58 "hawley, charles j jr"  
 wrote:
 
 
 Used Bird Attenuator is a good deal.
 
 https://nm3e.com/AttenuatorSampler.htm
 
 Then you’ll have a sample to plug into your counter or scope
 
 Chuck Jack Hawley
 KE9UW
 
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>> 
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> 


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Re: [Elecraft] Dummy Load recommendation

[W2xj]

If you really want precision, use a water cooled load. Measure the flow rate 
and input and output temperature. You can precisely calculate power. 

Sent from my iPad

> On Jul 23, 2019, at 9:38 AM, Bob McGraw K4TAX  wrote:
> 
> Since power meter systems are calibrated at a known impedance {usually 50 
> ohms}, and they are voltage sensing devices, any deviation from the 
> calibration value will introduce an error in power indication.  It just 
> depends on how precise one prefers to be with power measurements.
> 
> 100 watts into 50 ohms is 70.71 volts
> 
> 100 watts into 55 ohms is 74.16 volts
> 
> 100 watts into 45 ohms is 67.08 volts
> 
> 73
> 
> Bob, K4TAX
> 
> 
>> On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:
>> I often wonder just how useful a precision dummy load really is in the 
>> amateur service.  I picked up home brew dummy load at the club the other 
>> day.  It measured 57ohms dc and comprises 4 wire-wound resistors attached in 
>> a cluster across the end of the coax.  After lots of disparaging remarks I 
>> put it on the VNA and it didn't look at all bad out to 30MHz: nothing over 
>> 1.5:1 and no spikes or dips to indicate resonances. I'll have to do it again 
>> and make a print-out for posterity.
>> I've heard that salt water in a bucket works after a fashion.
>> So the question is: how good do you need it to be?
>> David G3UNA
>> 
>> 
>>> On 22 July 2019 at 23:58 "hawley, charles j jr"  
>>> wrote:
>>> 
>>> 
>>> Used Bird Attenuator is a good deal.
>>> 
>>> https://nm3e.com/AttenuatorSampler.htm
>>> 
>>> Then you’ll have a sample to plug into your counter or scope
>>> 
>>> Chuck Jack Hawley
>>> KE9UW
>>> 
>> __
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Re: [Elecraft] Dummy Load recommendation

[Don Wilhelm]

David,

If your use of the dummy load is only to provide a load to the 
transmitter for things like a quick "does it work" check, then precision 
is not necessary.  Anything that presents an SWR of 1.5 or less would be 
adequate.


OTOH, if you want to do things like the TX Gain Calibration of the K3 or 
KX2/3, or do measurements with a 'scope (or other measuring device) 
across the dummy load, then better precision is required if one expects 
the results to be meaningful and accurate.


In other words, if your expectation of measurement accuracy is a range 
of +/-50%, then using a load with a 1.5 SWR is acceptable.  If your 
expectation requires an error of less than 10%, then more precision is 
required.  That goes for not only dummy loads, but any other measurement 
instrument.


Parallel non-reactive resistors in a can of mineral oil can be used 
effectively up to 200 watts in a quart can, while up to the legal limit 
can be obtained in a gallon can of oil (Heathkit Cantenna style).  Those 
can be easily homebrewed and the amount of precision depends on the 
resistors used and the care with construction.


73,
Don W3FPR

On 7/23/2019 6:43 AM, CUTTER DAVID via Elecraft wrote:

I often wonder just how useful a precision dummy load really is in the amateur 
service.  I picked up home brew dummy load at the club the other day.  It 
measured 57ohms dc and comprises 4 wire-wound resistors attached in a cluster 
across the end of the coax.  After lots of disparaging remarks I put it on the 
VNA and it didn't look at all bad out to 30MHz: nothing over 1.5:1 and no 
spikes or dips to indicate resonances. I'll have to do it again and make a 
print-out for posterity.

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[Elecraft] Dummy Load recommendation

[Ron Durie]

Very well stated, Bob.  
I like precision loads especially for calibrations and repairs.  
I am surprised at how many Hams that do not even own a Load; let alone a
good one.  
A good Load is one of the most important troubleshooting aids in the Ham
Shack.  73's 

Ron Durie
WB4OOA
Elecraft K-Line



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Re: [Elecraft] Dummy Load recommendation

[Bob McGraw K4TAX]

Since power meter systems are calibrated at a known impedance {usually 
50 ohms}, and they are voltage sensing devices, any deviation from the 
calibration value will introduce an error in power indication.  It just 
depends on how precise one prefers to be with power measurements.


100 watts into 50 ohms is 70.71 volts

100 watts into 55 ohms is 74.16 volts

100 watts into 45 ohms is 67.08 volts

73

Bob, K4TAX


On 7/23/2019 5:43 AM, CUTTER DAVID via Elecraft wrote:

I often wonder just how useful a precision dummy load really is in the amateur 
service.  I picked up home brew dummy load at the club the other day.  It 
measured 57ohms dc and comprises 4 wire-wound resistors attached in a cluster 
across the end of the coax.  After lots of disparaging remarks I put it on the 
VNA and it didn't look at all bad out to 30MHz: nothing over 1.5:1 and no 
spikes or dips to indicate resonances. I'll have to do it again and make a 
print-out for posterity.
I've heard that salt water in a bucket works after a fashion.
So the question is: how good do you need it to be?
David G3UNA



On 22 July 2019 at 23:58 "hawley, charles j jr"  wrote:


Used Bird Attenuator is a good deal.

https://nm3e.com/AttenuatorSampler.htm

Then you’ll have a sample to plug into your counter or scope

Chuck Jack Hawley
KE9UW


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Re: [Elecraft] Dummy Load recommendation

[CUTTER DAVID via Elecraft]

I often wonder just how useful a precision dummy load really is in the amateur 
service.  I picked up home brew dummy load at the club the other day.  It 
measured 57ohms dc and comprises 4 wire-wound resistors attached in a cluster 
across the end of the coax.  After lots of disparaging remarks I put it on the 
VNA and it didn't look at all bad out to 30MHz: nothing over 1.5:1 and no 
spikes or dips to indicate resonances. I'll have to do it again and make a 
print-out for posterity. 
I've heard that salt water in a bucket works after a fashion.  
So the question is: how good do you need it to be?
David G3UNA 


> On 22 July 2019 at 23:58 "hawley, charles j jr"  wrote:
> 
> 
> Used Bird Attenuator is a good deal.
> 
> https://nm3e.com/AttenuatorSampler.htm
> 
> Then you’ll have a sample to plug into your counter or scope
> 
> Chuck Jack Hawley
> KE9UW
>
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[Elecraft] Dummy Load recommendation

[Ken G Kopp]

I'll second this recommendation ...

73!

Ken Kopp - K0PP

On Mon, Jul 22, 2019, 17:08 Walter Underwood  wrote:

> If you can solder, or would like to learn, I recommend the RFL-100 kit
> from Oak Hills Research. Simple kit, large parts for easy soldering. It
> will support 100 W continuous. I used their BNC/UHF converter so it would
> have a BNC jack. Nice deal for $50.
>
> http://www.ohr.com/rfl100.htm
>
> Here are some photos from my RFL-100 build.
>
> https://observer.wunderwood.org/2016/12/31/building-a-dummy-load/
>
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
>
> > On Jul 22, 2019, at 3:58 PM, hawley, charles j jr 
> wrote:
> >
> > Used Bird Attenuator is a good deal.
> >
> > https://nm3e.com/AttenuatorSampler.htm
> >
> > Then you’ll have a sample to plug into your counter or scope
> >
> > Chuck Jack Hawley
> > KE9UW
> >
> > Sent from my iPhone, cjack
> >
> > On Jul 22, 2019, at 4:59 PM, Art Nienhouse  ka9...@gmail.com>> wrote:
> >
> >
> > __
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Re: [Elecraft] Dummy Load recommendation

[Bob McGraw K4TAX]

I agree that Bird dummy loads are some of the best.  Be sure to get one rated 
for at least your maximum power anticipated.  And do allow a margin of safety. 
I use 2x, thus for 100 watts I use a 250 watt rated load. 

I purchase all of my power measurement equipment from NM3E.COM.  

Bob, K4TAX


Sent from my iPhone

> On Jul 22, 2019, at 5:58 PM, hawley, charles j jr  
> wrote:
> 
> Used Bird Attenuator is a good deal.
> 
> https://nm3e.com/AttenuatorSampler.htm
> 
> Then you’ll have a sample to plug into your counter or scope
> 
> Chuck Jack Hawley
> KE9UW
> 
> Sent from my iPhone, cjack
> 
> On Jul 22, 2019, at 4:59 PM, Art Nienhouse 
> mailto:ka9...@gmail.com>> wrote:
> 
> 
> __
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Re: [Elecraft] Dummy Load recommendation

[Walter Underwood]

If you can solder, or would like to learn, I recommend the RFL-100 kit from Oak 
Hills Research. Simple kit, large parts for easy soldering. It will support 100 
W continuous. I used their BNC/UHF converter so it would have a BNC jack. Nice 
deal for $50.

http://www.ohr.com/rfl100.htm

Here are some photos from my RFL-100 build.

https://observer.wunderwood.org/2016/12/31/building-a-dummy-load/

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Jul 22, 2019, at 3:58 PM, hawley, charles j jr  
> wrote:
> 
> Used Bird Attenuator is a good deal.
> 
> https://nm3e.com/AttenuatorSampler.htm
> 
> Then you’ll have a sample to plug into your counter or scope
> 
> Chuck Jack Hawley
> KE9UW
> 
> Sent from my iPhone, cjack
> 
> On Jul 22, 2019, at 4:59 PM, Art Nienhouse 
> mailto:ka9...@gmail.com>> wrote:
> 
> 
> __
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Re: [Elecraft] Dummy Load recommendation

[hawley, charles j jr]

Used Bird Attenuator is a good deal.

https://nm3e.com/AttenuatorSampler.htm

Then you’ll have a sample to plug into your counter or scope

Chuck Jack Hawley
KE9UW

Sent from my iPhone, cjack

On Jul 22, 2019, at 4:59 PM, Art Nienhouse 
mailto:ka9...@gmail.com>> wrote:


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Re: [Elecraft] Dummy Load recommendation

[Lynn W. Taylor, WB6UUT]

If you had an HTML dummy load, it'd be invisible.

Set your mail client to send E-Mail in plain text, please.

On 7/22/2019 2:58 PM, Art Nienhouse wrote:


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[Elecraft] Dummy Load recommendation

[Art Nienhouse]

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