If u scroll through the messages... u will see that # 863 has been
blown out ! I responded to it last night... then it comes back
as "message 863 can't be retrieved" Did the fellow blow it out
himself... or was it censored... or what ?

The fellow was commenting on the fact that 3rd order IMD products
don't tell the entire story. Most of the xcvr's will show
pretty good 3rd order specs... then the 5-7-9-11th distortion
products flatline.... and don't improve very much.... and it's the
higher order products that create all the off freq QRM.

The 2 tone test is flawed, and isn't used anymore in the
commercial world. By juggling the spacing of the 2 x tones, you
can hit a .."sweet spot" and come up with really good IMD numbers.

They all use the noise test these days... pump the xcvr with
bandwidth limited white noise.... that will drive the xcvr to full
pep output.... and simulate voice or many data tones. In the
commercial world, it's common to use 4 x multiplexed ssb
channels... or as many as 16 x mark/space combo's... sometimes
interleaved.

You will read the arguments of referencing IMD to one tone of
a 2 x tone sig instead of PEP. For several multiplexed ssb
channels or many data tones... this is valid. For a single
voice channel on ssb, like we use.... it's not needed.

The ARRL USED to ref IMD to one tone.... now they ref to
PEP. S-meter's on xcvr's are all PEAK reading devices. We all
hear.... "your signal is 10 over S-9.... but ur splatter is S-
6.... 4 khz away" The ref here is IMD to PEP. We don't
hear...." gee, I gotta ref off freq splatter to on freq signal
strength MINUS 6db".

Here's a quote from "SSB systems and circuits"

"ANOTHER deficiency of the 2 x tone test is that the "3rd order"
products observed on a spectrum analyzer are actually the sum of
the 3rd and ALL higher ODD order components. Typ, the 5th order
component is OUT of phase with the 3rd, which tends to PRODUCE
distortion CANCELLATION. This leaves the FALSE impression that the
IMD is better than it really is."

They go on to say a better method for single channel ssb voice
is to look at plane voice on a digital storage spectrum
analyzer... over a long time period... whereby all the out of
band IMD products are held in a "peak hold" mode.... the
concept being to look at long term spectral power densisty.

A 2 x tone test imo... is pretty lame duck... it won't dynamically
exercise HV and bias + fil supplies either.... since the 2 x
tone puts everything in a .."static state".

I tried the white noise test... and it def produces more IMD than
plane voice ever will.... since the white noise looks like
thousands of tones... all beating against each other.

BTW... when running white noise into the xcvr.... the plate current
on the linear is EXACTLY 1/2 the key down value.... so u can
use white noise to tweak the tune/load caps to max pep output.

Even EESB comes out looking better than a white noise test... OR
using W8JI's convoluted 2 x tone test, where he uses 2 x
extremly wide spaced tones.... like 100 hz and 3100 hz.... then
sez the total IMD BW is 9 khz wide.

Try as hard as you want... you can't find ANY combo of words or
phrases that will produce SIMULTANEOUS highs and lows.

Has anybody tried adjusting the Zsac on these big tubes from one
extreme to the other.. and actually measured the imd ?? Kinda a
moot point... unless the xcvr is the same or better IMD wise,
nobody would ever hear any benefit.

Later... Jim VE7RF

--- In ham_amplifiers@..., "pentalab" <jim.thomson@...> wrote:

If u scroll through the messages... u will see that # 863 has been
blown out ! I responded to it last night... then it comes back
as "message 863 can't be retrieved" Did the fellow blow it out
himself... or was it censored... or what ?

Yahoogroups allows the originator of a posting to delete it. Or the
moderator can. I don't fundamentally like that - once posted, a
posting ought stay as a matter of record.

The 2 tone test is flawed, and isn't used anymore in the
commercial world. By juggling the spacing of the 2 x tones, you
can hit a .."sweet spot" and come up with really good IMD numbers.

That's usually with very wide spacing. At very narrow spacing, you
challenge the power supply bypassing, so the worst numbers often occur
at that test condition.

They all use the noise test these days... pump the xcvr with
bandwidth limited white noise.... that will drive the xcvr to full
pep output.... and simulate voice or many data tones. In the
commercial world, it's common to use 4 x multiplexed ssb
channels... or as many as 16 x mark/space combo's... sometimes
interleaved.

Noise Power Ratio puts band-limited white noise through the rig, with
a notch in the middle of it. IMD products will tend to fill in the
notch. Very harsh test.

You will read the arguments of referencing IMD to one tone of
a 2 x tone sig instead of PEP. For several multiplexed ssb
channels or many data tones... this is valid. For a single
voice channel on ssb, like we use.... it's not needed.

The ARRL USED to ref IMD to one tone.... now they ref to
PEP. S-meter's on xcvr's are all PEAK reading devices. We all
hear.... "your signal is 10 over S-9.... but ur splatter is S-
6.... 4 khz away" The ref here is IMD to PEP. We don't
hear...." gee, I gotta ref off freq splatter to on freq signal
strength MINUS 6db".

Here's a quote from "SSB systems and circuits"

"ANOTHER deficiency of the 2 x tone test is that the "3rd order"
products observed on a spectrum analyzer are actually the sum of
the 3rd and ALL higher ODD order components. Typ, the 5th order
component is OUT of phase with the 3rd, which tends to PRODUCE
distortion CANCELLATION. This leaves the FALSE impression that the
IMD is better than it really is."

Sad. It's in error. The 5th order component is at a different
frequency than the 3rd order component, therefore they are completely
distinguishable from each other.

Ex: 5MHz and 5.001MHz are the incident sigs. The 3rd ord will be
4.999 and 5.002 MHz. 5th order will be 4.998 and 5.003 MHz. They
don't sit on each other, and don't add to each other in any way.

They go on to say a better method for single channel ssb voice
is to look at plane voice on a digital storage spectrum
analyzer... over a long time period... whereby all the out of
band IMD products are held in a "peak hold" mode.... the
concept being to look at long term spectral power densisty.

A 2 x tone test imo... is pretty lame duck... it won't dynamically
exercise HV and bias + fil supplies either.... since the 2 x
tone puts everything in a .."static state".

Yes, quite. The difficult is in coming up with a repeatable test.
It's not scientific unless it's repeatable - two guys in two different
locations, using two sets of test gear should come up with the same
results. The BW-limited noise test is a good one in this regard.

I tried the white noise test... and it def produces more IMD than
plane voice ever will.... since the white noise looks like
thousands of tones... all beating against each other.

BTW... when running white noise into the xcvr.... the plate current
on the linear is EXACTLY 1/2 the key down value.... so u can
use white noise to tweak the tune/load caps to max pep output.

You're driving it too hard. Peak to average ratio of BW-limited white
noise (the voltage distribution of BW-limited white noise is closer to
a Rayleigh distribution) is approx 16:1. The word "approx" is
important beause in truth, there is some percentage probability of ANY
power level being present at some time. 16:1 is the diff between 50%
probabiliy and 1%. Adequate for communications-grade amps.

Even EESB comes out looking better than a white noise test... OR
using W8JI's convoluted 2 x tone test, where he uses 2 x
extremly wide spaced tones.... like 100 hz and 3100 hz.... then
sez the total IMD BW is 9 khz wide.

In U.S. dialects, a vocalized sibiliant contains both low and high.
E.G. "Z" or "J". However, the wide-spaced test is actually one of
those that does not stress the power supply much, therefore you tend
to get artificially good values.

Try as hard as you want... you can't find ANY combo of words or
phrases that will produce SIMULTANEOUS highs and lows.

Sure can...any vocalized sibilant. To be exact, "Z" is a "voiced
alveolar sibilant" and is often used as a "torture test" for system BW
commercially when test gear is unavailable.

Has anybody tried adjusting the Zsac on these big tubes from one
extreme to the other.. and actually measured the imd ?? Kinda a
moot point... unless the xcvr is the same or better IMD wise,
nobody would ever hear any benefit.

The tendency is for IMD to vary in only a small amount. You can
improve it at low levels by sending the ZSAC very high, but that does
not change IMD at high levels. When you get ZSAC to a too-low level,
IMD shoots up quite a bit. That's why even in commercial gear,
fixed-voltage bias is common, it just doesn't matter much as long as
you've got some ZSAC.

Later... Jim VE7RF

Z

--- In ham_amplifiers@..., "zerobeat40" <zerobeat40@...>
wrote:

--- In ham_amplifiers@..., "pentalab" <jim.thomson@>

wrote:

The 2 tone test is flawed, and isn't used anymore in the

commercial world. By juggling the spacing of the 2 x tones,

you can hit a .."sweet spot" and come up with really good IMD
numbers.

Z SEZ.... That's usually with very wide spacing. At very narrow

spacing, you challenge the power supply bypassing, so the worst
numbers often occur at that test condition.

### say what ??? What diff does the spacing on a 2 tone test
have to do with challenging the HV supply bypassing... or any other
supply ? What am I missing here ?? The HV supply is just
pumping out DC current... nothing else. A 2 x tone test should
be in a steady state... ur not modulating it at an audio rate or
anything else ?

They all use the noise test these days... pump the xcvr with
bandwidth limited white noise.... that will drive the xcvr to

full pep output.... and simulate voice or many data tones. In
the commercial world, it's common to use 4 x multiplexed ssb

channels... or as many as 16 x mark/space combo's...

sometimes interleaved.

Z SEZ... Power Ratio puts band-limited white noise through the

rig, with a notch in the middle of it. IMD products will tend to
fill in the notch. Very harsh test.

### I tried it last night. Easy to do. The TX filters in my
xcvr are 6 khz wide. I notched out the portion from 2-4 kz.... and
passed 0-2 khz.... and 4-6 khz. You can hear the 2-4 notched
out portion.... being partially filled in.... on a 2nd Rx...3'
away. IMO... this just shows one INBAND IMD. Still... it
also shows OUT of band IMD.... a good test...and easy to do with a
Behringer DEQ-2496 master processor.

Here's a quote from "SSB systems and circuits"

"ANOTHER deficiency of the 2 x tone test is that the "3rd

order"

products observed on a spectrum analyzer are actually the sum

of

the 3rd and ALL higher ODD order components. Typ, the 5th

order

component is OUT of phase with the 3rd, which tends to PRODUCE
distortion CANCELLATION. This leaves the FALSE impression that

the

IMD is better than it really is."

Z SEZ...Sad It's in error. The 5th order component is at a

different frequency than the 3rd order component, therefore they
are completely distinguishable from each other.

Ex: 5MHz and 5.001MHz are the incident sigs. The 3rd ord will be
4.999 and 5.002 MHz. 5th order will be 4.998 and 5.003 MHz. They
don't sit on each other, and don't add to each other in any way.

### I don't think that's their point. Usual deal is to feed two
transmitter's, each with a dead cxr... into a combiner... then the
combined output feeds a Class A amp.. like a 4x5.... then into
linear amp under test. [both Eimac/Rauch and ARRL lab use the same
method] There is nothing to stop the PHASE of the IMD
products from being out of phase with each other... which could
easily skew the results.

BTW... when running white noise into the xcvr.... the plate

current on the linear is EXACTLY 1/2 the key down value.... so
u can use white noise to tweak the tune/load caps to max pep
output.

Z SEZ... You're driving it too hard. Peak to average ratio of BW-
limited white noise (the voltage distribution of BW-limited white
noise is closer to a Rayleigh distribution) is approx 16:1. The
word "approx" is important beause in truth, there is some
percentage probability of ANY power level being present at some
time. 16:1 is the diff between 50% probabiliy and 1%. Adequate
for communications-grade amps.

### I put some pure NON notched, full 0-20 khz white noise from
external audio rack gear directly into analog BM of xcvr. No ALC
showing... nothing over driven either. Then watched the RF on the
RF monitor scope... plus has 2 x PEP wattmeter's running... plus
2 x more wattmeter's.. switched to 'AVERAGE' Plate current on
linear is exactly one half the key down value. AVERAGE RF output
is only 1/5 the PEP output... or 14 db down from PEAK... or
7db down from PEP.

In U.S. dialects, a vocalized sibiliant contains both low and

high. E.G. "Z" or "J". However, the wide-spaced test is actually
one of those that does not stress the power supply much, therefore
you tend to get artificially good values.

Try as hard as you want... you can't find ANY combo of words or
phrases that will produce SIMULTANEOUS highs and lows.

Sure can...any vocalized sibilant. To be exact, "Z" is a "voiced
alveolar sibilant" and is often used as a "torture test" for

system BW commercially when test gear is unavailable.

### are u talking about "ZEE" or a "ZED" Not much of a torture
test at all. ZEE or ZED has not much low content in it at
all. Now words like Boom... Four... Ola... etc... will really
enhance low freq stuff... and the peak to average ratio really
drops. The point here is that ESSB doesn't splatter all over the
band.

Has anybody tried adjusting the Zsac on these big tubes from

one

extreme to the other.. and actually measured the imd ??

Kinda a

moot point... unless the xcvr is the same or better IMD wise,
nobody would ever hear any benefit.

The tendency is for IMD to vary in only a small amount. You can
improve it at low levels by sending the ZSAC very high, but that

does not change IMD at high levels. When you get ZSAC to a too-low
level, IMD shoots up quite a bit. That's why even in commercial
gear, fixed-voltage bias is common, it just doesn't matter much as
long as you've got some ZSAC.

### This is what I suspected. I also heard... if u bias a GG amp
like a SB-220 into zero zsac [class b] or into class C... on
CW, u will get key clicks ???

### I'm gonna try it anyway. I don't like this fixed bias idea..
never did. I see too many differences in zsac... between 4 x
diff tubes... all new... same maker... change maker's... diff
results. I have seen flat tubes with more zsac than a good
one.... [this is for a fixed bias V]

### On multiple tube GG amps... I used 2 x fil xfmrs [or 0ne
fil xfmr.. with 2 x sec] with 3 x separate plate curent
shunts.... one for tube 1 one for tube 2.. and 3rd for tubes
1+2. Plus independent adjustable bias for EACH tube.

## Now I just mess with one tube linears. Being able to vary the
bias from A-Z is a huge advantage. The constant current graphs
for most tubes... esp big ones... sorta are ballpark zsac
values... for say zero bias... and a fixed plate V..... could be
anywhere between 2 x extremes. A 3x 3... per the graphs could
idle at anywhere from 250-600 ma with zero bias at say 5 kv.
I want it to idle at 150 ma.... so just installed a sting of
6 A diodes... and a rotary switch... plus a huge lytic across the
entire string... works slick. Those zeners are a pain... and
failure prone... and none adjustable. Back in the mid-late
70's... 50 watt zener's were a dime a doz.. and cheap....but they
had to be heat sinked too... and insulated from chassis. Zener's
are ancient history now.

### This should be fun running the MK-V in Class A... then
tweaking the bias on the GG amp from Class A to AB.... then see
what happens. The amp will probably need it's tuned input
tweaked a tiny bit... diito with PI out put.... each time bias is
changed radically. Of course the anode diss will go UP...
since the eff in class A is going down. I'm guessing 25%
eff in Class A.

later... Jim VE7RF

Z

开云体育

Message 863 is not there as you stated...
I have no clue where it went..
And there is NO censoreing on this list.

Just play nice.

pentalab wrote:

If u scroll through the messages... u will see that # 863 has been
blown out ! I responded to it last night... then it comes back
as "message 863 can't be retrieved" Did the fellow blow it out
himself... or was it censored... or what ?

-- 
Bob
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