Re: [AMRadio] Mod Transformer

[D. Chester]

> From: "John Coleman" 

> The output voltage of a modulator is determined by its plate supply 
> voltage
> and the modulation XFMR turns ratio.

> You need to think in terms of voltage transformation.  If you are using a
> common power supply on the final and modulators, or more exact, the
> modulator plate supply and the final plate supply have the same voltage,
> then the ratio that you use is what determines the maximum modulation.

That is true irrespective of the nominal impedance of the transformer, the 
p-p load impedance of the modulator tubes or the modulating impedance of the 
final.  Of course, the tubes have an optimum p-p load impedance at any given 
plate voltage, and a transformer has an optimum primary and secondary 
impedance at which it works best.  But the actual transformation is based on 
turns ratio.  The impedance ratio stamped on the nameplate of the 
transformer is a nominal value, and a good transformer should be able to 
work at up to twice the nominal value and as low as half the nominal value 
with little degradation in performance.  The impedance transformation ratio 
is the square of the turns ratio.  For example, a transformer with a 2:1 
turns ratio has a 4:1 impedance ratio.


> 100% modulation occurs when the audio voltage from the modulation XFMR is 
> 2
> X the plate supply.

Actually it's when the peak output voltage, the combined audio and DC 
voltage from the winding adds up to 2 X the plate supply voltage.  The peak 
a.c. output voltage from the transformer is equal to 1 X the DC plate supply 
voltage.  When it is in the same polarity as the DC voltage, the two 
voltages add together to produce a sum that is 2 X the plate voltage at the 
positive modulation peak.  At the opposite peak of the audio cycle the 
polarity is reversed and the two voltages cancel, leaving zero volts on the 
plate of the final.  This is the negative modulation peak.

>
> At maximum drive the modulator tubes conduction (assuming they or big
> enough) takes the plate voltage close to 0 Volts at the peak of the audio
> for that conduction cycle.  Nothing you can do will take the voltage lower
> than zero.  As one tube hits the Zero volt peak then the other tube will 
> hit
> the 2 X plate voltage point.

That is theoretical.  In actual practice, there is nothing you can do to 
pull the instantaneous plate voltage below about 20% of the power supply 
voltage.  In the case of screen grid modulators, the plate voltage can never 
be pulled to a lower voltage than the DC screen voltage.  As one tube 
reaches maximum conduction, the instantaneous voltage on the plate of the 
other tube will reach about 1.8 X the DC plate supply voltage.

> Something between 2:1 and 1:1 is what is needed.  You need a little extra 
> to
> make up for the fact that the modulators will use some power in plate
> dissipation and you will want a little head room for voice lopsidedness
> (everything is not a perfect sine wave).
>
> Experience information from Don, K4KYV, indicates that between 1.2:1 and
> 1:4:1 is generally a good choice.  1.2:1 will give you more head room but
> will require more modulator current perhaps larger tubes.  1:4:1 will
> probably just be enough audio with very little head room, but will require
> less modulator current and lighter demand on the modulator tubes.  If you
> chose 1.2:1 for plenty of head room then choose modulators with a little
> more current capability or double up (push pull parallel).

Using a higher step-down ratio of 1.6:1 will just barely allow you to reach 
close to 100% modulation with no headroom whatever, but the modulator tubes 
will run more efficiently.  Somewhere between 1.2 and 1.4 will allow more 
headroom at the expense of efficiency.  But that extra headroom is needed 
for minimum distortion and splatter, since driving a modulator or linear 
amplifier (exactly the same thing except the modulator amplifies audio while 
the linear amplifies rf) right to the saturation point results in more 
distortion.  But watch the modulator plate current and make sure you don't 
exceed the tube ratings.  If so, double up to use a pushpull parallel 
modulator.  However, this may increase the audio driver requirements.

>You may want to
> consider a modulation reactor even if your XFMR says it can handle the
> secondary current.  Keeping the current out of the secondary will greatly
> improve the low frequency capability of the XFMR.  You want regret it.

Taking the DC off the secondary greatly reduced the talk-back when I was 
using a UTC VM-5 modulation transformer.  With the DC going through the 
secondary, the thing sounded like a small speaker inside the transmitter 
cabinet.  With the reactor, it was totally quiet.  This will also reduce the 
distortion from the modulator, since it will reduce the magnetic saturation 
of the core over the audio cycle.

A modulation transformer designed to run DC through the secondary will 
usually have a gap in the core, filled with paper 

[AMRadio] Madness at the Rochester

[CL in NC]

One guy gets really mad, and throws a monkey wrench in the works, but what 
happened to make him that upset?  Its hard to imagine him getting upset just 
over the new hamfest date.   Whenever this sort or battle rages online, it's 
always best to get both sides of the story.  Wonder what his is?

Charlie in NC


  
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Re: [AMRadio] 10 Meter AM Lives!

[Jim Miller WB5OXQ in Waco]

I just got home and tried 29 but I figured it is way too late at night.  I 
called CQ a few times at 25 watts and did not raise anyone.  I was not in 
the mood to wait for the 3CX800s to warm up and retune the amp for 10M so I 
returned to 160.
WB5OXQ

- Original Message - 
From: "Mark K3MSB" 
To: "Mike Duke, K5XU" ; "Discussion of AM Radio in the 
Amateur Service" 
Sent: Monday, January 26, 2009 7:42 PM
Subject: Re: [AMRadio] 10 Meter AM Lives!


> Just went to 29.0;  nothing heard, and no replies to my CQ (tried NW
> and SW) I'll keep the radio on fer a while...
>
> Mark K3MSB
>
> On Mon, Jan 26, 2009 at 8:29 PM, Mike Duke, K5XU  wrote:
>> I just completed a 10 minute QSO with Harry, W0LS, north of Minneapolis, 
>> on
>> 29.0.
>>
>> He was running a Flex Radio into an Alpha, and was pounding into 
>> Mississippi
>> despite the ever-present QSB that happens during Sporadic E.
>>
>> He told me that he had been calling CQ for a half hour before I answered
>> him, and that I was the first AM signal he had heard on 10 this evening.
>>
>> So, if you don't want to crank up the boat anchors, then dust off the
>> transistors, punch the AM button, and make some noise on or near 29.0.
>>
>>
>>
>>
>> Mike Duke, K5XU
>> American Council of Blind Radio Amateurs
>>
>>
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> 

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Re: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

[bob mccully]

Mark, Orlando is just too far to drive the green A.M. station. Or is it?  Bob  
AB8OP


  
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Re: [AMRadio] 10 Meter AM Lives!

[Mark K3MSB]

Just went to 29.0;  nothing heard, and no replies to my CQ (tried NW
and SW) I'll keep the radio on fer a while...

Mark K3MSB

On Mon, Jan 26, 2009 at 8:29 PM, Mike Duke, K5XU  wrote:
> I just completed a 10 minute QSO with Harry, W0LS, north of Minneapolis, on
> 29.0.
>
> He was running a Flex Radio into an Alpha, and was pounding into Mississippi
> despite the ever-present QSB that happens during Sporadic E.
>
> He told me that he had been calling CQ for a half hour before I answered
> him, and that I was the first AM signal he had heard on 10 this evening.
>
> So, if you don't want to crank up the boat anchors, then dust off the
> transistors, punch the AM button, and make some noise on or near 29.0.
>
>
>
>
> Mike Duke, K5XU
> American Council of Blind Radio Amateurs
>
>
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[AMRadio] 10 Meter AM Lives!

[Mike Duke, K5XU]

I just completed a 10 minute QSO with Harry, W0LS, north of Minneapolis, on 
29.0.

He was running a Flex Radio into an Alpha, and was pounding into Mississippi 
despite the ever-present QSB that happens during Sporadic E.

He told me that he had been calling CQ for a half hour before I answered 
him, and that I was the first AM signal he had heard on 10 this evening.

So, if you don't want to crank up the boat anchors, then dust off the 
transistors, punch the AM button, and make some noise on or near 29.0.




Mike Duke, K5XU
American Council of Blind Radio Amateurs


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Re: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

[Mark Foltarz]

Come to Orlando !  
http://www.hamcation.com/
We have a great group of AMers and a great selection of restaurants.
There is also Skycraft surplus.
And I can almost guarantee it will not rain!


de  KA4JVY

Mark

 


- Original Message 
From: Joseph Bento 
To: Discussion of AM Radio in the Amateur Service 
Cc: wb2...@dns-ny.com
Sent: Monday, January 26, 2009 7:36:08 PM
Subject: Re: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

And I wonder why I find amateur radio less and less enjoyable as time  
goes on.  I make the trek from Salt Lake to Dayton annually, but no  
longer find the enjoyment I once did with on-the-air activities.


73,
Joe, N6DGY
Pleasant Grove, UT

On Jan 26, 2009, at 3:22 PM, John Dilks K2TQN wrote:

>
> Forwarded without comment
> -John Dilks, K2TQN
>
>
>> Reply-To: 
>> From: "WB2PYD - Frank Schramm" 
>> Subject: RE: Madness at the Rochester (NY) hamfests
>> Date: Mon, 26 Jan 2009 09:19:47 -0500
>>
>> K2JD
>> Rochester Amateur Radio Assn
>> POB 9
>> Rochester NY 14692
>>
>> January, 2009
>> Re: Help spread the TRUTH about the Rochester Hamfest.
>>
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Re: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

[Joseph Bento]

And I wonder why I find amateur radio less and less enjoyable as time  
goes on.  I make the trek from Salt Lake to Dayton annually, but no  
longer find the enjoyment I once did with on-the-air activities.


73,
Joe, N6DGY
Pleasant Grove, UT

On Jan 26, 2009, at 3:22 PM, John Dilks K2TQN wrote:

>
> Forwarded without comment
> -John Dilks, K2TQN
>
>
>> Reply-To: 
>> From: "WB2PYD - Frank Schramm" 
>> Subject: RE: Madness at the Rochester (NY) hamfests
>> Date: Mon, 26 Jan 2009 09:19:47 -0500
>>
>> K2JD
>> Rochester Amateur Radio Assn
>> POB 9
>> Rochester NY 14692
>>
>> January, 2009
>> Re: Help spread the TRUTH about the Rochester Hamfest.
>>
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Re: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

[Don Merz]

A local ham club here had this exact same thing happen about 5 years ago. The 
club name, hamfest and web site were all in one guy's name and he wouldn't give 
them up whenever the club members made some decisions that he didn't like. So 
the members formed a new club, set up a new site and hamfest with newsletter, 
and the club went on as before--it is doing fine today.  That guy was left with 
nothing but the bitter memory of dead friendships. 

73, Don Merz, n3RHT

 


- Original Message 
From: John Dilks K2TQN 
To: amradio@mailman.qth.net
Cc: wb2...@dns-ny.com
Sent: Monday, January 26, 2009 5:22:08 PM
Subject: [AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests


Forwarded without comment
-John Dilks, K2TQN


>Reply-To: 
>From: "WB2PYD - Frank Schramm" 
>Subject: RE: Madness at the Rochester (NY) hamfests
>Date: Mon, 26 Jan 2009 09:19:47 -0500
>
>K2JD
>Rochester Amateur Radio Assn
>POB 9
>Rochester NY 14692
>
>January, 2009
>Re: Help spread the TRUTH about the Rochester Hamfest.
>
>We need your help to clear the air. The Rochester Amateur Radio 
>Association, Inc. (RARA) has been producing the Rochester Hamfest 
>for the last 74 years.  For many years the Hamfest Committee 
>Chairman was Harold Smith, K2HC.  At the November meeting of the 
>RaRa BoD it was voted to change the venue and the time frame for the 
>Hamfest.  Harold refused to comply and was relieved of his 
>duties.  In defiance he refuses to cooperate and because Harold's 
>name is associated with the original Hamfest web site, the BoD at 
>this time does not have control of what is displayed there.  Since 
>RARA is the parent organization of the current, and past, Hamfest 
>Committee you can be assured that what RARA says in print and on the 
>web site " www.rochesterham.org" is the TRUTH.  The ARRL has already 
>recognized the change in venue and time frame and the "New Rochester 
>Hamfest" is the location of the Atlantic Division Convention for 
>2009. This can be verified at: 
>"http://www.arrl.org/sections/WNY.html";.
>
>We realize how confusing this can be if people see Harold's postings 
>on the internet. We have requested he remove the confusing content 
>numerous times, each met with flat out refusal. It's disappointing 
>that someone who has put a great deal of effort into the event in 
>the past has taken up the position to confuse the public. This 
>certainly demonstrates his disloyalty to the club, the event, and 
>his fellow HAMS.
>
>We at RaRa would greatly appreciate it if you and could use your 
>channels of communications to inform other area HAMS of the TRUTH: 
>There will only be one Hamfest, not two, and The Rochester Hamfest 
>will be held Saturday May 30th, at the Barnard Carnival Grounds. 
>Further details are available at 
>"www.rochesterham.org".  Warn them 
>that K2HC no longer has anything to do with the Rochester Hamfest 
>and people should disregard his solicitations for ticket 
>sales.  Admission tickets are now only $5.00 and being sold 
>exclusively at the gate. If anyone is still in disbelief, encourage 
>them to contact their ARRL representative for clarification.
>The 2009 Rochester Hamfest flyer can be downloaded here: 
>http://www.rochesterham.org/Documents/2009_Rochester_Hamfest-Flyer.pdf
>
>There will only be one Hamfest in Rochester.
>
>Thank you VERY much!
>Sincerely,
>WB2PYD
>Frank Schramm
>President, Rochester Amateur Radio Assn Inc.

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[AMRadio] Fwd: RE: Madness at the Rochester (NY) hamfests

[John Dilks K2TQN]

Forwarded without comment
-John Dilks, K2TQN


>Reply-To: 
>From: "WB2PYD - Frank Schramm" 
>Subject: RE: Madness at the Rochester (NY) hamfests
>Date: Mon, 26 Jan 2009 09:19:47 -0500
>
>K2JD
>Rochester Amateur Radio Assn
>POB 9
>Rochester NY 14692
>
>January, 2009
>Re: Help spread the TRUTH about the Rochester Hamfest.
>
>We need your help to clear the air. The Rochester Amateur Radio 
>Association, Inc. (RARA) has been producing the Rochester Hamfest 
>for the last 74 years.  For many years the Hamfest Committee 
>Chairman was Harold Smith, K2HC.  At the November meeting of the 
>RaRa BoD it was voted to change the venue and the time frame for the 
>Hamfest.  Harold refused to comply and was relieved of his 
>duties.  In defiance he refuses to cooperate and because Harold's 
>name is associated with the original Hamfest web site, the BoD at 
>this time does not have control of what is displayed there.  Since 
>RARA is the parent organization of the current, and past, Hamfest 
>Committee you can be assured that what RARA says in print and on the 
>web site " www.rochesterham.org" is the TRUTH.  The ARRL has already 
>recognized the change in venue and time frame and the "New Rochester 
>Hamfest" is the location of the Atlantic Division Convention for 
>2009. This can be verified at: 
>"http://www.arrl.org/sections/WNY.html";.
>
>We realize how confusing this can be if people see Harold's postings 
>on the internet. We have requested he remove the confusing content 
>numerous times, each met with flat out refusal. It's disappointing 
>that someone who has put a great deal of effort into the event in 
>the past has taken up the position to confuse the public. This 
>certainly demonstrates his disloyalty to the club, the event, and 
>his fellow HAMS.
>
>We at RaRa would greatly appreciate it if you and could use your 
>channels of communications to inform other area HAMS of the TRUTH: 
>There will only be one Hamfest, not two, and The Rochester Hamfest 
>will be held Saturday May 30th, at the Barnard Carnival Grounds. 
>Further details are available at 
>"www.rochesterham.org".   Warn them 
>that K2HC no longer has anything to do with the Rochester Hamfest 
>and people should disregard his solicitations for ticket 
>sales.  Admission tickets are now only $5.00 and being sold 
>exclusively at the gate. If anyone is still in disbelief, encourage 
>them to contact their ARRL representative for clarification.
>The 2009 Rochester Hamfest flyer can be downloaded here: 
>http://www.rochesterham.org/Documents/2009_Rochester_Hamfest-Flyer.pdf
>
>There will only be one Hamfest in Rochester.
>
>Thank you VERY much!
>Sincerely,
>WB2PYD
>Frank Schramm
>President, Rochester Amateur Radio Assn Inc.

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Re: [AMRadio] Comments on the Multi-Elmac A-54H

[Larry Szendrei]

Bob wrote: 
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[AMRadio] Comments on the Multi-Elmac A-54H

[Bob Bruno - K2KI]

Hi all,

I have been watching a *Multi-Elmac A-54H on that auction site. The 
auction ends in 4 hrs. Looks a little rough and no PS but I have one 
that should work.

Anyone have any experiences with these beasties? Drop me a line pls.

73, cul...
Bob de k2ki
*
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Re: [AMRadio] Mod Transformer

[John Coleman]

Opps, I should have said

100% modulation occurs when the peak to peak audio voltage from the
modulation XFMR secondary is twice the plate supply to the final amplifier.



Not:
>100% modulation occurs when the audio voltage from the modulation XFMR is 2
>X the plate supply.


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Re: [AMRadio] Mod Transformer

[Paul Baldock]

Thanks John, good info

- Paul


At 10:07 AM 1/26/2009, you wrote:
>Paul:
> Modulation XFMRs have a lot of different ratings.
>
>1. Insulation breakdown voltage ratings.
>
>2. Audio wattage (can be misleading as this rating is often at 1000hz and it
>may not hold true for 100hz).
>
>3. Max secondary current if any.  Some XFMRs assume that you will be using a
>modulation reactor as well.
>
>4. Turns ratio of course.  (A confusing issue to a lot of people).
>
>The output voltage of a modulator is determined by it's plate supply voltage
>and the modulation XFMR turns ratio.
>
>100% modulation occurs when the audio voltage from the modulation XFMR is 2
>X the plate supply.
>
>You need to think in terms of voltage transformation.  If you are using a
>common power supply on the final and modulators, or more exact, the
>modulator plate supply and the final plate supply have the same voltage,
>then the ratio that you use is what determines the maximum modulation.
>
>At maximum drive the modulator tubes conduction (assuming they or big
>enough) takes the plate voltage close to 0 Volts at the peak of the audio
>for that conduction cycle.  Nothing you can do will take the voltage lower
>than zero.  As one tube hits the Zero volt peak then the other tube will hit
>the 2 X plate voltage point.
>
>The peak to peak plate voltage max is 2 X the plate supply on one modulator
>tube.  If plate supply is about 600 volts then the modulation max is 1200V
>PTP.  In push-pull circuits the output voltage would be 2 this or 2400 volts
>Peak to Peak.  Since the power supply voltage is the same on the final this
>would be twice the amount of audio voltage required to modulate it. This is
>too much of an over kill on a 1:1 XFMR.
>
>Taking a step down, and using a 2:1 turns ratio XFMR and the audio drops to
>1200 Volts.  This is the exact amount of voltage required with no head room
>for error or loss in the XFMR.  You will not be able to actually hit 100%
>and distortion will be fairly high.
>
>Something between 2:1 and 1:1 is what is needed.  You need a little extra to
>make up for the fact that the modulators will use some power in plate
>dissipation and you will want a little head room for voice lopsidedness
>(everything is not a perfect sine wave).
>
>Experience information from Don, K4KYV, indicates that between 1.2:1 and
>1:4:1 is generally a good choice.  1.2:1 will give you more head room but
>will require more modulator current perhaps larger tubes.  1:4:1 will
>probably just be enough audio with very little head room, but will require
>less modulator current and lighter demand on the modulator tubes.  If you
>chose 1.2:1 for plenty of head room then choose modulators with a little
>more current capability or double up (push pull parallel).  You may want to
>consider a modulation reactor even if your XFMR says it can handle the
>secondary current.  Keeping the current out of the secondary will greatly
>improve the low frequency capability of the XFMR.  You want regret it.
>
>This may be more info than you needed.
>Good Luck
>John Coleman, WA5BXO
>
>
>
>
>
>
>-Original Message-
>From: amradio-boun...@mailman.qth.net
>[mailto:amradio-boun...@mailman.qth.net] On Behalf Of Paul Baldock
>Sent: Saturday, January 24, 2009 6:36 PM
>To: amradio@mailman.qth.net
>Subject: [AMRadio] Mod Transformer
>
>Does anybody have a good reference as to how to calculate modulation
>transformer requirements?
>
>Thanks
>
>- Paul
>
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Re: [AMRadio] Mod Transformer

[John Coleman]

Paul:
Modulation XFMRs have a lot of different ratings.  

1. Insulation breakdown voltage ratings.

2. Audio wattage (can be misleading as this rating is often at 1000hz and it
may not hold true for 100hz).

3. Max secondary current if any.  Some XFMRs assume that you will be using a
modulation reactor as well. 

4. Turns ratio of course.  (A confusing issue to a lot of people).  

The output voltage of a modulator is determined by it's plate supply voltage
and the modulation XFMR turns ratio.

100% modulation occurs when the audio voltage from the modulation XFMR is 2
X the plate supply.

You need to think in terms of voltage transformation.  If you are using a
common power supply on the final and modulators, or more exact, the
modulator plate supply and the final plate supply have the same voltage,
then the ratio that you use is what determines the maximum modulation.  

At maximum drive the modulator tubes conduction (assuming they or big
enough) takes the plate voltage close to 0 Volts at the peak of the audio
for that conduction cycle.  Nothing you can do will take the voltage lower
than zero.  As one tube hits the Zero volt peak then the other tube will hit
the 2 X plate voltage point.  

The peak to peak plate voltage max is 2 X the plate supply on one modulator
tube.  If plate supply is about 600 volts then the modulation max is 1200V
PTP.  In push-pull circuits the output voltage would be 2 this or 2400 volts
Peak to Peak.  Since the power supply voltage is the same on the final this
would be twice the amount of audio voltage required to modulate it. This is
too much of an over kill on a 1:1 XFMR.  

Taking a step down, and using a 2:1 turns ratio XFMR and the audio drops to
1200 Volts.  This is the exact amount of voltage required with no head room
for error or loss in the XFMR.  You will not be able to actually hit 100%
and distortion will be fairly high.  

Something between 2:1 and 1:1 is what is needed.  You need a little extra to
make up for the fact that the modulators will use some power in plate
dissipation and you will want a little head room for voice lopsidedness
(everything is not a perfect sine wave).

Experience information from Don, K4KYV, indicates that between 1.2:1 and
1:4:1 is generally a good choice.  1.2:1 will give you more head room but
will require more modulator current perhaps larger tubes.  1:4:1 will
probably just be enough audio with very little head room, but will require
less modulator current and lighter demand on the modulator tubes.  If you
chose 1.2:1 for plenty of head room then choose modulators with a little
more current capability or double up (push pull parallel).  You may want to
consider a modulation reactor even if your XFMR says it can handle the
secondary current.  Keeping the current out of the secondary will greatly
improve the low frequency capability of the XFMR.  You want regret it.

This may be more info than you needed.
Good Luck
John Coleman, WA5BXO






-Original Message-
From: amradio-boun...@mailman.qth.net
[mailto:amradio-boun...@mailman.qth.net] On Behalf Of Paul Baldock
Sent: Saturday, January 24, 2009 6:36 PM
To: amradio@mailman.qth.net
Subject: [AMRadio] Mod Transformer

Does anybody have a good reference as to how to calculate modulation 
transformer requirements?

Thanks

- Paul

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Re: [AMRadio] New QTH for the Rochester NY hamfest

[VJB]

To minimize any confusion over the location of the Rochester (NY) hamfest May 
30, it will be at Barnard Carnival Grounds 380 Maiden Lane, Greece, NY.

This is according to a recording at the phone number 585-671-2424, the 
forwarding number from the old 585-424-7184, which was the business number for 
the old location that has since been disconnected.

Follow through is important on a story like this, and I hope the additional 
information is helpful.

One of the ARRL speakers at the new site will be the Atlantic Division 
Director, Bill Edgar N3LLR. Some will remember his visit to the AM Festival 
station at the old Gaithersburg (MD) hamfest when he was initially running for 
office.  He has indicated his receptiveness to improved inclusion of the AM 
community, and endorsed a survey in 2007 that showed nearly 20 percent of 
respondents include AM in their HF operating activity.

Even though the results of that survey have never been formally included in the 
ARRL's political, publishing and regulatory activities, the three Divisions 
that took part in that poll have established, for us, a presence that can be 
cited in our dealings with the League.


  
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