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FW: K2/100 SWR accuracy

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WA7CS

FW: K2/100 SWR accuracy

My K2/100, SN 3777 works great. No complaints

However, I am a bit leery of the indicated SWR.

The indicated SWR seems to tell me that my antenna match is better in
nearly all cases than several other SWR and power meters I have
laying around.

When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird
43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher
than that shown on the K2.

For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other
meters all consistently indicate a value significantly higher - lets
say 1.4:1

If I happily ignore the other SWR measurement tools, and only use the K2
SWR indications, everything still works great, I make lotsa contacts and
all is well.

However, at the home QTH, I do have a fairly well matched antenna, and I
do know that it is resonant in the band segments that I work.

Taking he K2 into the field is another question altogether. At this
point, I don't trust the K2 SWR readings and have been dragging along
other SWR meters when loading a temporary or unknown antenna.

Please advise.

Carl
WA7CS

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John Huffman-2

Re: FW: K2/100 SWR accuracy

Carl -

You might want to adjust the KPA100's R26 and R27 to agree with your external
meters.

73 de NA8M
John

----- Original Message -----
From: "Carl Strode" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, December 14, 2005 6:58 PM
Subject: [Elecraft] FW: K2/100 SWR accuracy

> My K2/100, SN 3777 works great. No complaints
>
> However, I am a bit leery of the indicated SWR.
>
> The indicated SWR seems to tell me that my antenna match is better in
> nearly all cases than several other SWR and power meters I have
> laying around.
>
> When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird
> 43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher
> than that shown on the K2.
>
> For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other
> meters all consistently indicate a value significantly higher - lets
> say 1.4:1
>
> If I happily ignore the other SWR measurement tools, and only use the K2
> SWR indications, everything still works great, I make lotsa contacts and
> all is well.
>
> However, at the home QTH, I do have a fairly well matched antenna, and I
> do know that it is resonant in the band segments that I work.
>
> Taking he K2 into the field is another question altogether. At this
> point, I don't trust the K2 SWR readings and have been dragging along
> other SWR meters when loading a temporary or unknown antenna.
>
> Please advise.
>
> Carl
> WA7CS
>
>
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> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
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>

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Don Wilhelm-3

RE: FW: K2/100 SWR accuracy

In reply to this post by WA7CS

Carl,

You may want to re-calibrate your KPA100 wattmeter (and also check the
calibration of your other meters). If you have a good non-reactive dummy
load, it is really easy, but check your dummy load with an antenna analyzer
first to be certain that it will do th ejob properly at the frequency where
you will do the calibration.

Wattmeter calibration is a subject for extended discussion - just be aware
that no matter what the advertizement implies, many wattmeters can be off by
a great deal. Look at the specs and you will normally see something like
+/-10% of full scale - what that means is on a 200 watt scale, the reading
can be off by as much as 40 watts!!! and that applies to the entire scale
too, not just the upper end. Most are not really that bad, but some are,
and SWR can be proportionally incorrect.

I calibrate the forward power in a wattmeter by driving a non-reactive 50
ohm dummy load and measuring the RF Voltage across that load - my calculator
then tells me what the K2 display should be showing for forward power -
adjust until it agrees with the actual power calculated. I would be willing
to wager that the resulting setting will be as accurate as the best external
wattmeter you can find on the ham market (Bird included).

After setting the forward power, I calibrate SWR on the KPA100, KAT2 and
KAT100 wattmeters with my pair of 2:1 SWR dummy loads - I have a
non-reactive 25 ohm dummy load and a 100 ohm dummy load. I switch between
them and to check the null capacitor adjustment first, the SWR reading
should be the same for both loads - if not, I adjust it slightly until it is
the same - then I set the REF pot so the K2 displays the SWR as 2.0. This
method works fine, and I believe it was first suggested by Don Brown. The
settings for the KPA100 and KAT100 will not be veery far away from th
einitial setting suggested in the manual, but for some reason that I have
yet to explain, every KAT2 requires that the REF pot be set much higher than
the FWD pot to achieve a 2:1 display with the SWR=2 loads.

Since the KPA100 reduces power when an SWR>2 is encountered, it is
informative to know when that is likely to happen and take steps to avoid
it.

73,
Don W3FPR

> -----Original Message-----
>
> My K2/100, SN 3777 works great. No complaints
>
> However, I am a bit leery of the indicated SWR.
>
> The indicated SWR seems to tell me that my antenna match is better in
> nearly all cases than several other SWR and power meters I have
> laying around.
>
> When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird
> 43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher
> than that shown on the K2.
>
> For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other
> meters all consistently indicate a value significantly higher - lets
> say 1.4:1
>
> If I happily ignore the other SWR measurement tools, and only use the K2
> SWR indications, everything still works great, I make lotsa contacts and
> all is well.
>
> However, at the home QTH, I do have a fairly well matched antenna, and I
> do know that it is resonant in the band segments that I work.
>
> Taking he K2 into the field is another question altogether. At this
> point, I don't trust the K2 SWR readings and have been dragging along
> other SWR meters when loading a temporary or unknown antenna.
>
> Please advise.
>
> Carl
> WA7CS
>
>

Dan Barker

RE: FW: K2/100 SWR accuracy

In reply to this post by John Huffman-2

Be sure you are talking Apples and Apples here. There may be an Orange in
the mix!

The responses you've gotten for calabrating your SWR to match the external
meters are assuming you are putting your tuner in bypass mode. You didn't
say that, and may not be doing so. What you said was "press[] TUNE". The K2
SWR meter will normally read the SWR between the Radio and the Tuner. Your
external meters will read the SWR between the Tuner and the Antenna.

There may be nothing wrong at all.

Dan / WG4S / K2 #2456

<snip>
You might want to adjust the KPA100's R26 and R27 to agree with your
external
meters.
</snip>

<snip>
> When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird
> 43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher
> than that shown on the K2.
>
> For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other
> meters all consistently indicate a value significantly higher - lets
> say 1.4:1
</snip>

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WA7CS

Re: FW: K2/100 SWR accuracy

In reply to this post by Don Wilhelm-3

Here is a bit of follow up info, and preliminary results.

I got a bunch of input and suggestions - all are appreciated.

The covers are off, and the K2/100 is spread out all over my shack. The
setting of C1 was checked, and I do now recall that the "sweet spot" is
really hard to find using the first method in the manual. The range
over which an indicated 1.0 SWR is displayed is much to large. I used
the alternate method of measuring the TP4 null voltage, and seem to have
a bit better results. My first choice of a DVM was one with 2-1/2 digit
resolution (e.g. the smallest digit displayed is an integer millivolt).
Then I tried a higher-end Fluke meter with two orders of magnitude
better resolution. I found the adjustment of C1 could be significantly
improved. This is not possible using the K2 SWR indication only, or
using a cheap DVM with typical hardware store accuracy

I am still awaiting the arrival of some non-inductive resistors so my
wattmeter settings can be refined. In the meantime, I have been
tweaking R26 and R27 in an attempt to get things working a bit better.
The one problem I am still rassling with is the K2s tendency to change
its power output in the tune mode. Just as I am about to zero in on a
power setting - lets say 30 watts as indicated by an external and
trusted wattmeter, the actual power output from the K2 jumps around - up
and down, back and forth - by several watts. I am left chasing the
setting allover the place from 20 to 40 watts.

This is really driving me nuts! I suspect this is what may have led
me to buttoning the K2 up a couple of years ago before I had done my
best calibrating power output and SWR indications.

Carl WA7CS
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Don Wilhelm-3

RE: FW: K2/100 SWR accuracy

Carl,

Yes, the ALC power leveling will cause jumps in TUNE mode, I try to work
fast enough to work with it - it will settle down after a bit, but try that
only at lower power levels (35 watts and below) where the KPA100 is rated
for continuous duty cycle.

Make up a graph of RF voltage vs. calculated power and put it at your work
area - that way you can monitor the RF Voltage and determine the actual
power at a glance (make it a big chart so it can be easily seen). If you
are using an RF Probe, enter the RMS voltage values, but if you are using a
'scope, enter the peak to peak voltages.

Formulas: Vrms^2/R = Power
Vpp^2/8R = Power or for a 50 ohm load Power = Vpp^2/400

73,
Don W3FPR

> -----Original Message-----

>
> Here is a bit of follow up info, and preliminary results.
>
> I got a bunch of input and suggestions - all are appreciated.
>
> The covers are off, and the K2/100 is spread out all over my shack. The
> setting of C1 was checked, and I do now recall that the "sweet spot" is
> really hard to find using the first method in the manual. The range
> over which an indicated 1.0 SWR is displayed is much to large. I used
> the alternate method of measuring the TP4 null voltage, and seem to have
> a bit better results. My first choice of a DVM was one with 2-1/2 digit
> resolution (e.g. the smallest digit displayed is an integer millivolt).
> Then I tried a higher-end Fluke meter with two orders of magnitude
> better resolution. I found the adjustment of C1 could be significantly
> improved. This is not possible using the K2 SWR indication only, or
> using a cheap DVM with typical hardware store accuracy
>
> I am still awaiting the arrival of some non-inductive resistors so my
> wattmeter settings can be refined. In the meantime, I have been
> tweaking R26 and R27 in an attempt to get things working a bit better.
> The one problem I am still rassling with is the K2s tendency to change
> its power output in the tune mode. Just as I am about to zero in on a
> power setting - lets say 30 watts as indicated by an external and
> trusted wattmeter, the actual power output from the K2 jumps around - up
> and down, back and forth - by several watts. I am left chasing the
> setting allover the place from 20 to 40 watts.
>
> This is really driving me nuts! I suspect this is what may have led
> me to buttoning the K2 up a couple of years ago before I had done my
> best calibrating power output and SWR indications.
>
> Carl WA7CS
>
>

WA7CS

Re: FW: K2/100 SWR accuracy

In reply to this post by WA7CS

Don,

My resistors arrived yesterday.

Today I hacked up a piece of aluminum for a heat sink - about 3/16"
thick, 1-1/2", wide and 3" long.

Drilled four little holes and bolted the resistors on.

Two resistors wired in parallel for 25 ohms, two resistors wired in
series for 100 ohms.

A phono jack was attached to each network.

I used a short piece for coax with a PL-259 on one end and a phono plug
on the other end to connect the K2 antenna output to the dummy load.

It worked like a charm!

The C1 null adjustments I had made using a good quality voltmeter were
about 1.4:1 with 25 ohms, and 2.0:1 with 100 ohms. Tweaking C1 got both
values to read the same (1.7:1), and adjusting the REF pot brought the
SWR indication right on the money at 2:1.

This technique works very very well. Thanks a million!

Carl
WA7CS

Here is a photo of the SWR tuning dummy load

http://webpages.charter.net/crstrode/Photos/dummy.jpg

Don Wilhelm wrote:

> Carl,
>
> If you want good resistors for dummy loads, try the power thick film
> resistors. I have had good luck with the Ohmite 35 watt jobs, but
> they do not have a 50 ohm value - 51 ohms is available and close to
> what you need. The Caddock brand is good too, but I have found that
> only the 50 ohm units are reliably non-reactive - yes they are
> non-inductive, but I have found ones that are capacitive, and that is
> just as bad. The Caddock are available from Mouser and I would
> recommend the 30 watt resistors - you can series parallel connect 4 of
> them for a 120 watt load if you want that capacity, otherwise one will
> handle 30 watts for lower power. The Mouser number is 684-MP930-50,
> currently $3.55 for one or $2.85 each if you order 10. I use 2 in
> parallel for my 25 ohm load and 2 in parallel for my 100 ohm load.
> Checks with several antenna analyzers indicate that they can be used
> up to 30 MHz, but are really on the money at 7 thru 10 MHz, and I do
> most of my calibration at either 40 or 30 meters.
>
> These resistors do have to be mounted on a heat sink, but that is easy
> since they are TO-220 packages and heat sinks from defunct computers
> are plentiful - just drill and tap a hole and mount them with short
> leads to a BNC or SO239 chassis mount connector. Use short leads for
> best high frequency performance - Hint, if you use 4 of them, mount
> them like spokes of a wagon wheel so all connections are in the center.
>
> 73,
> Don W3FPR
>
> -----Original Message-----
> *From:* Carl Strode [mailto:[hidden email]]
> *Sent:* Wednesday, December 14, 2005 9:12 PM
> *To:* [hidden email]
> *Subject:* Re: [Elecraft] FW: K2/100 SWR accuracy
>
> Don,
>
> Thanks for your very interesting comment.
>
> Believe it or not, I was rummaging about in my junk box last night
> looking for some big fat resistors to do just what you have suggested!
>
> However, I'm gonna probably need to surf Ebay a bit to find some
> good ones. It seems that the only candidates I could fine in my
> shack were either way to small (power dissipation), or were of the
> wire wound variety.
>
> Now, I am charging full speed ahead with the knowledge that my
> proposed method has actually been used by an expert - You!
>
> Thanks again for the advice.
> 73
> Carl
> WA7CS
>
> Don Wilhelm wrote:
>
>>Carl,
>>
>>You may want to re-calibrate your KPA100 wattmeter (and also check the
>>calibration of your other meters). If you have a good non-reactive dummy
>>load, it is really easy, but check your dummy load with an antenna analyzer
>>first to be certain that it will do th ejob properly at the frequency where
>>you will do the calibration.
>>
>>Wattmeter calibration is a subject for extended discussion - just be aware
>>that no matter what the advertizement implies, many wattmeters can be off by
>>a great deal. Look at the specs and you will normally see something like
>>+/-10% of full scale - what that means is on a 200 watt scale, the reading
>>can be off by as much as 40 watts!!! and that applies to the entire scale
>>too, not just the upper end. Most are not really that bad, but some are,
>>and SWR can be proportionally incorrect.
>>
>>I calibrate the forward power in a wattmeter by driving a non-reactive 50
>>ohm dummy load and measuring the RF Voltage across that load - my calculator
>>then tells me what the K2 display should be showing for forward power -
>>adjust until it agrees with the actual power calculated. I would be willing
>>to wager that the resulting setting will be as accurate as the best external
>>wattmeter you can find on the ham market (Bird included).
>>
>>After setting the forward power, I calibrate SWR on the KPA100, KAT2 and
>>KAT100 wattmeters with my pair of 2:1 SWR dummy loads - I have a
>>non-reactive 25 ohm dummy load and a 100 ohm dummy load. I switch between
>>them and to check the null capacitor adjustment first, the SWR reading
>>should be the same for both loads - if not, I adjust it slightly until it is
>>the same - then I set the REF pot so the K2 displays the SWR as 2.0. This
>>method works fine, and I believe it was first suggested by Don Brown. The
>>settings for the KPA100 and KAT100 will not be veery far away from th
>>einitial setting suggested in the manual, but for some reason that I have
>>yet to explain, every KAT2 requires that the REF pot be set much higher than
>>the FWD pot to achieve a 2:1 display with the SWR=2 loads.
>>
>>Since the KPA100 reduces power when an SWR>2 is encountered, it is
>>informative to know when that is likely to happen and take steps to avoid
>>it.
>>
>>73,
>>Don W3FPR
>>
>>
>>
>>>-----Original Message-----
>>>
>>>My K2/100, SN 3777 works great. No complaints
>>>
>>>However, I am a bit leery of the indicated SWR.
>>>
>>>The indicated SWR seems to tell me that my antenna match is better in
>>>nearly all cases than several other SWR and power meters I have
>>>laying around.
>>>
>>>When SWR is measured using a MFJ 962 tuner, a Daiwa 101N meter, a Bird
>>>43, Autek RF-1, or a MFJ 249 analyzer, the indicated SWR is always higher
>>>than that shown on the K2.
>>>
>>>For example, pressing TUNE on the K2 may indicate a 1.0:1, but the other
>>>meters all consistently indicate a value significantly higher - lets
>>>say 1.4:1
>>>
>>>If I happily ignore the other SWR measurement tools, and only use the K2
>>>SWR indications, everything still works great, I make lotsa contacts and
>>>all is well.
>>>
>>>However, at the home QTH, I do have a fairly well matched antenna, and I
>>>do know that it is resonant in the band segments that I work.
>>>
>>>Taking he K2 into the field is another question altogether. At this
>>>point, I don't trust the K2 SWR readings and have been dragging along
>>>other SWR meters when loading a temporary or unknown antenna.
>>>
>>>Please advise.
>>>
>>>Carl
>>>WA7CS
>>>
>>>
>>>
>>>
>>
>>
>>
>>