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eHam Forums => Boat Anchors => Topic started by: KD0ILS on February 26, 2013, 05:33:44 PM



Title: HF AM???
Post by: KD0ILS on February 26, 2013, 05:33:44 PM
I'll be the first to admit I'm rather new to HF i've had my ticket for 6 years and thought its time to venture away from 2m/440.  I know I'm only a technician and currently my bands are limited to 6 m and 10m ssb but the real question is concerning the two radios I have that could get me going into HF.  I have a hallicrafters HT-40 and a drake tr-4c and rv-4c that was given to me from a silent key and these radios havnt been touched since the early 80s.  I also have 2 astatic d-104 microphones to be paired with these radios but they just need to be rewired for the proper plugs.  The status of the HT-40 is unknown because i have no crystals and the drake doesnt seem to be transmitting on 10m ssb or measuring into a dummy load.  It could just be my lack of knowledge of boat anchors.  What this comes boiled down to is the question whether or not its worth to get the radios checked and re - tuned/aligned and when I do get the fixed does anyone work HF on AM anymore?  Which brings me to another question if anyone knows of a good place to take these radios to get a thorough once-over.  Cosmetically these radios look great and I'd really like to use them but i was just curious about other peoples opinions.  I know i could just buy a yaesu 857d and all my problems would be solved but i decided to go back to school and paying my way through college doesnt leave $900 in the budget.  thanks for the help
-73's
PETE


Title: RE: HF AM???
Post by: N4NYY on February 26, 2013, 05:47:32 PM
There is a group on 80M that does AM, and most use homebrew tube or boatanchor gear. Nice bunch of guys. I was once having a rag chew on their SSB side of their freq before their net started. When they informed me of it, we told them we would move and they said do not bother, and to just flip the switch to AM, and join them. But we did not, as I have a FT-950.


Title: RE: HF AM???
Post by: WA2CWA on February 27, 2013, 12:43:21 AM
You'll find AM operating on just about every major band (160, 80, 40, 20, 15, 10, 6, and even 2 meters). If you check the ARRL band plan you'll even find AM calling frequencies listed. And, since AM is "phone" you can find AM operating anywhere phone operation is authorized. Not only is homebrew and vintage equipment used,  you'll also find many AM operators using current state of the art rigs (Yaesu, Kenwood, Icom, Flex, Elecraft, Ten-Tec). Even the FT-950 can operate on AM. I've worked a number of stations using them on AM. The popularity of AM operating has been growing for years. There's even an AM page on the ARRL web site: http://www.arrl.org/am-phone-operating-and-activities

Pete, wa2cwa


Title: RE: HF AM???
Post by: KB4QAA on February 27, 2013, 06:58:25 AM
Here are some starting points....

http://amfone.net/Amforum/index.php
http://amfone.net/ECSound/
http://www.amwindow.org/index.htm
http://www.ami-west.com/

Gratuitous radio porn:
http://www.radioblvd.com/


Title: RE: HF AM???
Post by: KB5ZSM on February 27, 2013, 10:23:43 PM
Hey Pete,
         Your question about AM on HF is one you can answer yourself with a decent Short Wave radio. You'll find quite a bit of AM activity, especially on the lower bands. I recommend a lot of listening to the HF bands while you study for your General ticket. It will help you find your niche and learn more about how it all works before you ever pick up that microphone and when you do get to operate in those regions you'll be able to attack them with more confidence.
         As for your Drake equipment, Your radio setup is the same as the first one I ever got to play with many years ago back in high school. It was our school station so I have vary fond memories of that radio I may even buy one someday just for the fun and memories it will bring back. As far as fixing yours up, I think the first thing I would do is buddy up with a local ham who has some boat anchor experience and let him look at it. See what he thinks of its condition. Do NOT just plug it in to see if it works. If it has set for many years with out power, you could do damage to it if you don't bring it up slowly.

Hope this helps & 73s,
Win (KB5ZSM)


Title: RE: HF AM???
Post by: W2WDX on April 18, 2013, 09:18:44 PM
Two things about AM operation and why it is still popular. Higher fidelity audio and less critical frequency tuning. The latter being less important, the former being the primary reason people still operate on the mode.

The normal operating practice on AM in Amateur Radio is a frequency response in the audio pass-band of about 6-7kHz, compared to about 2.7 kHz (sometimes slightly higher) for SSB operation. This gives a very pleasing sound for normal ragchewing. However AM is very inefficient because of this, which is why SSB is so prevalent especially for DX work. But AM is unbeatable for the local ragchew operation. The extra bandwidth allowed makes for very natural sounding speech and reduces listening fatigue.

The advantage of using older boatanchors is that you can get close to this bandwidth, sometimes, depending on the transmitter. A Yaesu like the 857 still uses its filters so your audio bandwidth is usually limited to under 4kHz, and most times to 3kHz. AM is an afterthought on most modern Japanese/Chinese radios. SDR's like FlexRadio can give significant audio bandwidth approaching that of broadcast standards, albeit this may be a bit broad for amateur use, but not uncommon nor in violation of FCC A3E mode specification.

Actually the designator used in FCC regulations is 8K00A3E which is an 8kHz audio bandwidth. The designator describes the first four characters as "necessary bandwidth required to transmit the desired information". So this is the bandwidth of the information being sent. Most Amateur operators do not use this full bandwidth however even though they can if they wished. BTW, broadcast AM is designated (8K00A3E or even as wide as 20K0A3E (with limits on higher modulated audio frequencies), for reference.

Incidentally, the SSB designator is 3K00J3E. The "J" determines it is a single sideband mode with a 3kHz information bandwidth. Since it is single sideband the radio signal is limited to 3Khz. J3E was brought into Amateur since it reduces congestion within the Amateur bands. The most common in Amateur use is 2K70J3E at 2.7kHz. However this does not preclude that A3E at full bandwidth is not allowed. It should be noted that while these designator appear nowhere in Part 97, they are only referenced there and actually appear in Part 2 Subpart C.

Another fact is there is no mention about "communications quality" for using A3E in Part 97, as is commonly argued. That term is only used in describing certain single sideband emissions "... shall not exceed that of a communications quality A3E emission". In fact, in Part 97 there is no limit mentioned specifically about A3E other than it adhering to emission type standards outlined in other Parts (Part 2 specifically). So in theory one could technically operate at a 20kHz bandwidth as long as you adhere to the standard for that emission type, specifically 20K0A3E, However, in Amateur practice while technically allowable it would simply be rude. So most AM operators have settled into operating using the 8K00A3E emission type on HF bands as good amateur practice.

So as far as "High Fidelity" audio is concerned AM is the way to go in Amateur Radio. Achieving that "Hi-Fi sound and experimentation and developing a station for this goal is what AM operation is all about. Of course, with the virtually "unlimited" bandwidth of the A3E emission type make this possible. If one tries operating true "Hi-Fi" on SSB you may find yourself operating an emission mode not allowable by either the FCC or the ITU. Of course, the true purpose and reasoning for SSB is not fidelity, but instead the goal is efficiency.

John, W2WDX


Title: RE: HF AM???
Post by: K4KYV on April 26, 2013, 09:07:00 PM
No specific bandwidth limitation is mentioned in the Part 97 rules. The rules vaguely prescribe "good engineering and amateur practice". The FCC intended it that way, in order to allow the amateur the maximum flexibility for experimentation and self-instruction in the radio art.

Therefore, if you decide, for example, to transmit on 160m in the middle of the day, or 75m in the wee hours of the morning when there are likely to be few if any other stations using the band, good amateur and engineering practice might not preclude running hi-fi audio with frequency response up to 10 kHz or more.  No harm done transmitting a "wide" signal when there is no-one else on the band to interfere with.  OTOH, under congested band conditions during prime operating hours, good engineering and amateur practice would suggest limiting the frequency response of the audio modulating the transmitter to 3500 Hz or less.

The same standards would apply equally to AM or SSB. Why would it be less permissible to transmit an audio frequency response up to 5 kHz on SSB, resulting in a total bandwidth of 5 kHz, than to transmit with the same modulation on AM, resulting in a total bandwidth of 10 kHz?

There is an important distinction between the bandwidth of the sidebands resulting from the frequency response of the audio used for modulation, and spurious sideband products resulting from distortion or non-linearity in the transmitter.  Excessive bandwidth due to overmodulation or spurious distortion products is poor amateur and engineering practice, regardless of the actual bandwith of the transmitted signal or the level of band congestion.

The best operating practice would be to use a receiver with variable selectivity or several filters with a variety of bandwidths, and to adjust the audio response of the modulation so that the bandwidth of the transmitted signal is the same as the optimum receiving bandwidth under the given set of band conditions.


Title: RE: HF AM???
Post by: W2WDX on September 23, 2013, 03:24:41 PM
Just to be clear and this is often misunderstood by Hams, Part 97 should never be taken in isolation.

It is not the only Part of the FCC regs that apply to Amateur radio. When a specific emission type is mentioned in Part 97 it refers directly to other Parts, specifically Part 2. Amateur operators are bound to apply those other parts as well, since it deals with the specific emission types allowed for Amateur use as prescribed by Part 97.

A 5kHz SSB signal is not allowed according to specific emission type allowed for use on the Ham Bands (specifically 3K00J3E) as outlined in Part 97. However, an 8khz AM is allowed (8K00A3E), though I agree not a good idea or good practice in peak band use periods.

These detailed designators are specifically referenced in Part 2 for the Amateur bands. So Amateur use regulations appear in other Parts, not just in Part 97. Licensed US Amateurs are required to adhere to " ... all FCC regulations for Amateur use". Not just Part 97 in isolation.


Title: RE: HF AM???
Post by: AC5UP on September 23, 2013, 04:13:41 PM
...just flip the switch to AM, and join them. But we did not, as I have a FT-950.

And your ALC diode was clipped.

 :D


Title: RE: HF AM???
Post by: G3RZP on September 24, 2013, 12:43:08 AM
8K3 means 8kHz overall bandwidth. As 'necessary bandwidth' is so ill defined in the ITU Radio Regulations, common practice is to use the occupied bandwidth, which is the bandwidth containing 99% of the energy - usually, but not necessarily, the bandwidth at 20dB down from the maximum.

As it is AM with two sidebands, the audio bandwidth is limited to 4kHz, not 8kHz.


Title: RE: HF AM???
Post by: VE3FMC on September 24, 2013, 12:14:43 PM
There is a group on 80M that does AM, and most use homebrew tube or boatanchor gear. Nice bunch of guys. I was once having a rag chew on their SSB side of their freq before their net started. When they informed me of it, we told them we would move and they said do not bother, and to just flip the switch to AM, and join them. But we did not, as I have a FT-950.

You should have switched to AM because that FT-950 sounds very good on AM if you set the mic gain properly. Any of the new rigs should sound good on AM if they are operated properly.

I have run my FT-950 on AM while driving an AL-80A and was told the audio sounded very good, after I did some tweaking.

Get it set up properly and don't tell them what you are operating unless they ask!  ;D


Title: RE: HF AM???
Post by: W2WDX on September 27, 2013, 08:33:19 PM
Some folks are intimidated by the way many of the guys sound, (particularly on the East coast of the US). Many guys on AM are running QRO level using sophisticated homegrown ClassE technology, which is very high fidelity. Many run retired and converted Broadcast AM transmitters.

However this should never discourage anyone from operating AM. Due to the high quality audio and ease of tuning it is pleasing to the ear for ragchew, with little fatigue. Most of the folks running AM are either ol' timers with a vast amount of knowledge or younger folks with an understanding of newer AM technologies. Mostly all are very technically accomplished. The conversations can be very educational, interesting, sometimes a little crude maybe, but always different.

Most of the AM operators can very easily discern a radio like the FT-950 from a higher-end AM transmitter. Anyone using one may get a little friendly "ribbing". However if operated properly they do sound quite good on AM. Apparently, Yaesu decided to make some changes and realized AM is certainly not dead and that the modes main attraction is the higher fidelity audio. Yaesu realized AM should not be an afterthought mode.

And Peter, you are correct about the audio bandwidth at 4kHz on AM of course. I was refuting the assumption by others that one could operate a wider SSB signal, which is not correct. Many US hams misinterpret the vague "good engineering and amateur practice' clause that exists in Part 97 of the FCC regulation here in the States. There is a reason why manufacturers use 2.7kHz filters in SSB transmit modes. This is to gain type acceptance certification for amateur use. Any wider, taking into consideration the slope of these filters, and the transmitted signal would be beyond the specification of 3K00J3E limits set forth for Amateur use in Part 2. Many Hams do not understand this "practice" clause as meaning adhering to standards set forth in other sections, outside of Part 97, which define in detail the specifications of what is good engineering practice.

As I said earlier, SSB was a mode adopted by the amateur service to help alleviate the very congested Ham bands as they were in the 1950's. It is a power efficient narrow bandwidth mode with the smallest possible band "footprint" yet still allow for intelligible phone operation. However, this does not mean this can be changed during low activity periods. The limits set out by the specification of 3K00J3E for amateur use are clear, and short of an experimental exemption, are not open to interpretation; this would be seen as a misinterpretation of the "good practice" clause. However, it should be stated the FCC has little interest in enforcement of such things, unless of course a formal complaint is made.

In informal conversations with people such as Riley Hollingsworth, former FCC enforcement head, and Laura Smith the current FCC enforcement chief, the development and operation of newer types of AM transmitters for personal use, such as ClassE rigs and its derivatives and variants (and other types of transmitters), comes under the special exemption for experimental transmitters. Therefore the view is the emission limits are exempted, within reason. However simply modifying a type accepted commercially produced radio to allow it to operate outside its normal 3K00J3E emission limits is not generally considered experimental nor good engineering practice.

I find it fascinating how the oldest mode AM is the one where more sanctioned Amateur experimentation is going on then in any other mode, short of digital modes. In fact, newer Broadcast AM transmitters are using the technologies developed in Amateur radio since these developments have lead to smaller size, higher power, easier control and maintenance, and lower operating costs for Broadcasters. This is a revitalization of one of the primary functions of Amateur radio and why it exists.

AM is a wonderful mode. And some of the newest and most effective technologies also happens to be one of the easiest to experiment with. That being solid-state FET based AM transmitters like ClassE rigs and others. This of course should not discourage anyone from using commercially produced transceivers on AM. Just read the manual and understand how to operate the radio in this mode, and I guarantee you will have a great time.

This is a recording of two AM stations, on 160m I believe, of two well known East coast stations. The one station in the distance is using a Collins Broadcast transmitter converted to Amateur use. The loudest of the two is using a older boatanchor (I believe it may be a Hallicrafters HT-37 but I may be wrong). However, he is using only a 20 watt carrier. The recording was made off a Hammarlund SP-600 boatanchor receiver. These two fellows are typical of the types of technically accomplished (One is a Technical Director of a major broadcast national news program). They also exemplify the type of gentlemen you will find operating on AM. And yes indeed, it is an AM QSO between New Jersey and Virginia near D.C.

http://www.vikingvintage.com/NBC-K2DK.mp3 (http://www.vikingvintage.com/NBC-K2DK.mp3)

John, W2WDX


Title: RE: HF AM???
Post by: W8AAZ on September 28, 2013, 11:54:11 AM
I suppose some AM on the bands is beneficial as casual SWLs can tune you in easily.  Maybe good PR.  It does have a pretty wide footprint on 75 and 40, which are crowded bands to begin with.  And it seems to be the mode to be if you are a gear freak, as someone is always trying to out hi fi everyone else with vintage transmitters, studio mics, and audio processors galore.  I guess sounding like a broadcast would attract more SWLs than some of those noxious SSB roundtables on 75.  I would prefer to work AM on 160 if I could.  Activity is spread out alot up there and not so much chance of having someone right up against your freq.  I have heard that there are AMers on 10 and 6, using old rigs or converted CBs.  Especially 10 would be fine as there is alot of elbow room like on 160.  Except I have not heard them on 10.  Being that propagation is scarce these days, and a local net would be cool but none around here. My SSB rig can AM, but pretty low power, like 25 watts max carrier.  What is the point of being hi fi if your weak and in the noise?   


Title: RE: HF AM???
Post by: WA2OLZ on September 28, 2013, 04:53:00 PM
C'mon on down to 7285 or thereabouts. All of the regulation QRM and broadcast type audio requirements go away - fast! It's great to get into a QSO 1:1 or roundtable with a bunch of guys (and gals) that like to ragchew about every subject under the sun. You won't find contesters or "5X9, 73" contacts here, however. Pull up an armchair, sit down and relax with friends. That's what it's all about.


Title: RE: HF AM???
Post by: GW3OQK on September 29, 2013, 02:31:56 AM
There's an AM net in UK on 3615 many mornings. Talk about being relaxed, I heard one guy speaking for more than 15 minutes on his over.
73, Andrew


Title: RE: HF AM???
Post by: W2WDX on September 29, 2013, 07:11:18 AM
My SSB rig can AM, but pretty low power, like 25 watts max carrier.  What is the point of being hi fi if your weak and in the noise?   

You do understand of course that 25 watts of carrier on AM also has a PEP component? So the actual output of you radio is the same or similar. In the recording I posted the louder station, W2NBC, is using only 20w of carrier and he is in New Jersey and the station that recorded this was about 400 miles away. Like anything in Ham radio it's not about power, its about radiation efficiency. NBC was using a long and high random length dipole using ladder-line and a link coupled tuner. A very efficient antenna system.

Here in New York City there is even an open 2m AM repeater. There are numerous people who use AM regularly on VHF, 10m 6m & 2m. I am fortunate that I live here since there is a great deal of AM activity on most bands in this area. My Clegg Zeus gets a work-out regularly here. I also used some retired and converted ITT FAA AM transmitters on 2m.

AM operation has evolved into a very relaxed mode and is about casual conversation and discussion. It is one of the few modes where you will find all types of Hams; collectors, gear heads, restorers, audio aficionados, people from the broadcast industry and most importantly experimenters.

If any of you have seen many of my posts, you can tell I operate AM. I am not known for brevity, on the air nor in writing.


Title: RE: HF AM???
Post by: G3RZP on September 29, 2013, 07:31:30 AM
John,

I suspect that a lot of amateurs have forgotten that the PEP of a 100% modulated DSB AM signal is four times the carrier power. So a pair of plate and screen modulated 6146Bs running an output of 100 watts of carrier would be 400 watts PEP.


Title: RE: HF AM???
Post by: WA2OLZ on September 29, 2013, 03:57:52 PM
Back in the days before SSB, many of us worked the world with low powered AM transmitters. It took patience, technique and was a whole lot of fun.  Nobody was running lists to hand out contacts, no Internet based callouts of who was where, just listen and QSY.

My best DX on AM was 5A2TC on 10 meter AM. The transmitter was a WRL Globe Scout 40A feeding an indoor 10M dipole.  It took several tries before I realized his call wasn't WA2TC???. Oh, well! It would be a tough QSO to get today, I imagine. 5A2TC was at Wheelus AB, Tripoli, Lybia! I sure wish I still had that QSL card.


Title: RE: HF AM???
Post by: KA5N on September 29, 2013, 05:59:47 PM
John you say you are going back to school, I can't help thinking about the six years you
have had a ham ticket and how much you could have learned in those years about all phases
of amateur radio and care and feeding of older ham gear.  The gear you have is certainly
not in the "boat anchor" category.  Find a local elmer and get some advice and help and
you will soon close the knowledge gap about your equipment and what wonders await.

Good Luck and 73
Allen KA5N


Title: RE: HF AM???
Post by: W2WDX on October 01, 2013, 07:28:06 AM
John,

I suspect that a lot of amateurs have forgotten that the PEP of a 100% modulated DSB AM signal is four times the carrier power. So a pair of plate and screen modulated 6146Bs running an output of 100 watts of carrier would be 400 watts PEP.

Actually you're half right. A pair of 6146b's will run a 25w carrier with 100W PEP when modulated, either screen or plate.


Title: RE: HF AM???
Post by: G3RZP on October 01, 2013, 08:11:27 AM
RCA rate a pair in plate modulation ( which must mean screen as well) at 120 watts of carrier output - which would be  480 watts PEP.

With just screen grid modulation, you would want to keep to about 25 watts of carrier, though. The disadvantage of efficiency modulation.



Title: RE: HF AM???
Post by: KC4MOP on October 01, 2013, 05:22:19 PM
The real boatanchor transmitter Heathkit DX100 uses a pair of 6146B for a 100 watt carrier.
http://heathkit-museum.com/ham/hvmdx-100.shtml

Fred
Modern SDR's can make some nice audio on AM. Feed that 25 watt (or whatever drive the linear needs) carrier into a big linear and you have legal limit 375 watts of carrier which equals 1500W PEP
Fred


Title: RE: HF AM???
Post by: W2WDX on October 01, 2013, 05:38:03 PM
No ... on the DX-100 that's 100w input, not carrier.

At a 23w max plate dissipation at 750v max plate voltage in Class C the maximum power output is 62W for a single 6146b. That's it. You could not get 450W out of a pair of 6146's. That's 4 times higher than its maximum output capability in Class C. A pair of 572b's would be needed to get that kind of power, at 1800Vdc plate voltage at 300ma.

Let's do the math:

W = V x I

Watts = Volts x Amperage (in amps)

750Vdc x 112ma = 84w x .74 (~efficiency of Class C) = 61.16W

For two 6146B:

750Vdc x 224ma = 168w x .74 = 124.32w

And that efficiency is an estimate on the high side; 65% to 70% is more typical for real world Class C circuits. And this does not take into account real world things like voltage sag in the power supplies at peaks and tank circuit losses.

So a 25W carrier is typical with a modulation factor of 1 producing peaks up to around 110W to 120W with most Class C transmitters using a pair of 6146B's.

By your thinking my Johnson Valiant would be able to produce 675W peak!!! Holy shnikees!!!

John, W2WDX


Title: RE: HF AM???
Post by: K1ZJH on October 01, 2013, 10:02:18 PM
A pair of 6146B tubes should easily provide 120 watts carrier power. At 100% modulation the plate voltage doubles, which is a 4 times increase in power. Even at 100 watts output, the PEP would be 400 watts for 100% modulation. For example, a B&W 5100 is rated for 135 watts input on phone. with a 70% efficiency that is still 95 watts output; or 380 watts PEP output power. Only a true Class C stage will provide 4X pep power when the plate voltage is doubled.

http://faculty.frostburg.edu/phys/latta/ee/6146amp/6146b/6146b_big.pdf

Even my  two B&W 5100 AM transmiiters have 150 watt modulator sections...  that would be rather silly to modulate a 50 watt carrier, per your estimation :)

Now, a 6146 running as a linear might be limited to 25 watts carrier, in order to provide PEP headroom... but in high level plate modulated Class C the tube is run at CCS or ICAS ratings. PEP is always 4 times carrier power for 100% modulation and a symmetrical modulation waveform for Class C.

G3RZP is absolutely correct in his analysis.

Pete k1zjh


Title: RE: HF AM???
Post by: W2WDX on October 02, 2013, 03:26:09 AM
I think I had a complete DOH! moment there.  :-[

Looking at this this morning, I ran the calculation for carrier power, didn't I? Of all people, I know better.

Remind me not to post anything after a day out with the guys. Gotta love Tequila! Hey, I got the math right regardless! Go figure.

Never mind, I'll shut up now.



Title: RE: HF AM???
Post by: KC4MOP on October 02, 2013, 03:32:38 AM
No ... on the DX-100 that's 100w input, not carrier.

At a 23w max plate dissipation at 750v max plate voltage in Class C the maximum power output is 62W for a single 6146b. That's it. You could not get 450W out of a pair of 6146's. That's 4 times higher than its maximum output capability in Class C. A pair of 572b's would be needed to get that kind of power, at 1800Vdc plate voltage at 300ma.

Let's do the math:

W = V x I

Watts = Volts x Amperage (in amps)

750Vdc x 112ma = 84w x .74 (~efficiency of Class C) = 61.16W

For two 6146B:

750Vdc x 224ma = 168w x .74 = 124.32w

And that efficiency is an estimate on the high side; 65% to 70% is more typical for real world Class C circuits. And this does not take into account real world things like voltage sag in the power supplies at peaks and tank circuit losses.

So a 25W carrier is typical with a modulation factor of 1 producing peaks up to around 110W to 120W with most Class C transmitters using a pair of 6146B's.

By your thinking my Johnson Valiant would be able to produce 675W peak!!! Holy shnikees!!!

John, W2WDX

No................I owned a couple of DX 100's and even the scratchy the Apache.  They made 120 watts carrier. I saw it over and over on a Bird watt meter. 10M they would be sweating a little but, 100 watts out to the antenna.
Fred


Title: RE: HF AM???
Post by: W2WDX on October 02, 2013, 03:37:35 AM
I got caught up in the moment. I normally run my boatanchors rolled back, to reduce plate dissipation and drive amplifiers. Somehow in my Tequila driven mindset at the time, I translated that into ...

Well anyway ...

There are times I wish one could just remove a post from a message board. DOH! Now people are gonna be clicking "reply" on my bogus post without scrolling down to read this retraction and the thread is gonna be filled with now pointless flames.

John

(http://www.beeskneesdance.com/bees_knees/wp-content/uploads/2011/01/homer-simpson-doh.gif)


Title: RE: HF AM???
Post by: KC4MOP on October 02, 2013, 07:17:56 AM
I got caught up in the moment. I normally run my boatanchors rolled back, to reduce plate dissipation and drive amplifiers. Somehow in my Tequila driven mindset at the time, I translated that into ...

Well anyway ...

There are times I wish one could just remove a post from a message board. DOH! Now people are gonna be clicking "reply" on my bogus post without scrolling down to read this retraction and the thread is gonna be filled with now pointless flames.

John

(http://www.beeskneesdance.com/bees_knees/wp-content/uploads/2011/01/homer-simpson-doh.gif)

That is no problem........It is really being able to shift gears. Today's Amateur is not familiar with a plate modulated tube transmitter. The solid state stuff and class D E F whatever, and linear devices gets into that carrier mode and Peak Envelope Power mindset.
A class C power amplifier will output a lot more RF watts because of the bias setting on the tubes. To make AM we need one half of the input/output power of audio to PLATE modulate the transmitter. Hence a 100 W class C transmitter will need a 50 watt audio amplifier with the proper transformer matching to modulate the Class C transmitter.
Most people today are equating the use of linear amplifier with its Peak Envelope Power limitations.
To make what we call legal limit AM we need a linear to output easily 1500 W PEP or there will be flat topping and distortion of the RF output. Linear amps that claim 2500W are the ones that have the necessary headroom.
375 watts carrier fully modulated will make 1500 W PEP.
There are readers and nay sayers who will say phooey to me, and claim that they can make a 700 watt carrier, and with some inaccurate peak reading watt meter, claim that they will adjust the modulation to only produce 1500w PEP.
A.M operation is a lot of fun and a challenge to get that nice audio. Better antennas and keeping close to legal limit is necessary to calm down MaNature. A.M. reception will be lot noisier with the wider bandwidth.
I have used old broadcast transmitters outputting 250 Watts of carrier and did just fine on 160M. Very little difference in signal level from 250W and 375. Antenna Antenna Antenna is the key.
Fred


Title: RE: HF AM???
Post by: G3RZP on October 02, 2013, 01:48:11 PM
Fred,

Of course you can have a 750 watt carrier and not exceed 1500 watts PEP. But you mustn't exceed on peaks, something around 50% - or maybe less, I haven't done the sums - modulation depth.

My suspicion, again without having done the sums, is that you are better off with a higher percentage modulation and lower  i.e. 375 watt carrier.


Title: RE: HF AM???
Post by: W2WDX on October 03, 2013, 10:54:09 PM
And let's not forget about asymmetrical peak limiting! Negative peaks ... baaad, positive peaks ... gooood.

I'm still hurting from my Homer moment! I've owned about 30 or so boatanchors, many using 6146's, restored professionally literally hundreds, owned and converted two BC transmitters (one Gates and one RCA).

I have even designed and built a commercial design for a new AM plate modulated boatanchor type, using 6146's in high level Class C plate modulation with two EL-34's (AB1) using a toroidal modulation transformer and a DDS based VFO. It even had front panel switchable carrier output (20w to 100W). The fully analog audio section even had built in variable compressor with variable asymmetrical peak limiting, and a five band fully parametric EQ with high and low pass filters, and both standard communications mic input (hi-lo imp) & XLR balanced low impedance mic input (with phantom power) and a balanced line level input. It operated at full 8K00A3E bandwidth (or less by using the filters in the audio section). I would have been manufacturing now if the financing world hadn't gone belly up. Funny thing, as a result I am still sitting on about 300 new 6146's purchased for that project.

So for me, going Homer was really embarrassing!

John, W2WDX


Title: RE: HF AM???
Post by: G3RZP on October 04, 2013, 03:35:44 AM
John,

6146, 6146A, or 6146B? I suspect that if they are the B's, you got something that is appreciating in worth faster than a CD....probably even if they are 6146A, since the Collins rigs prefer those.


Title: RE: HF AM???
Post by: W2WDX on October 05, 2013, 07:51:34 AM
They are B's. I chose them because they still are being commercially produced, albeit by our "friends" in China. However I have discovered over time they are well made, have consistent performance from tube to tube, and relatively inexpensive.

I do not see them appreciating anytime soon, at least not from scarcity. My supplier in Chongqing tells me he can fill an order of 10,000+ if need be. The prices I see them sold in the West is ludicrous considering the cost at wholesale. The fact that they are in current production, and are in no way scarce, tells me retailers here are taking advantage of people who think no tubes are being manufactured anymore or just satisfying the audiophile fools who think if its expensive it must be better.

Still with my project on hold (most likely until the recession effects slackens) I have all these tubes. Grrr ... I hate bankers; especially, when they take on high risks for personal profit that put us all in financial jeopardy.


Title: RE: HF AM???
Post by: AC5UP on October 05, 2013, 08:01:13 AM

But, but, but... Without the wealthy many of us would be poor, financially insecure, afraid of illness, and living from paycheck to paycheck......................

Uhhhhhhhhhhhhhh.  I suppose.   :P


Title: RE: HF AM???
Post by: K6RMR on October 14, 2013, 08:32:40 PM
AM is not in the Privileges, of the Tech Class. Upper SSB 28.3 to 28.5Mhz. CW and Digital
 modes 28.0 to 28.5 Mhz. 200 Watts of power.On 10 meters you are granted the Novice Class
 Privileges. If you want to Operate  10 meter AM get your General.
                        Stan K6RMR


Title: RE: HF AM???
Post by: W2WDX on October 19, 2013, 07:06:40 PM
Strictly speaking in regard to privileges set forth in Part 97, in addition to J3E - amplitude modulation telephony, single sideband, with suppressed carrier, Technician, Technician Plus and Novice can use R3E -amplitude modulation telephony, single sideband, with vestigial carrier within 28.300 to 28.500. Which is basically AM with carrier but only one sideband. The 200W PEP power limit still applies, which with R3E would be 50W carrier (as a vestigial carrier) with only LSB being suppressed.

Also RTTY and Data are limited to 28.000 to 28.300 and CW is 28.000 to 28.500 for Technician, Plus and Novice.

See FCC Rules Part 97.307 paragraph 10

The ARRL Band Plan does not reflect this; however, that is not the where the privileges are defined. That's done in the FCC Part 97.

And just to be clear, technically SSB (J3E) is AM. However, in J3E the carrier and one sideband is suppressed. So Stan, if you are upset by heterodyne on 10m between 28.300 to 28.500, go to another part of the band.  :)

John, W2WDX


Title: RE: HF AM???
Post by: W2WDX on October 19, 2013, 09:24:48 PM
A bit more specific information about R3E emission type...

§ 97.307(a) states, No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice.

Good amateur practice is considered by the FCC as adhering to, as a minimum, the emission and bandwidth specifications outlined in the FCC rules (Part 2.201 & Part 2.202). Experimentation can be an exception to this in the Amateur Service. In the FCC rules, emission type specifications for all services (including the Amateur Service) are defined in Title 47, Chapter I, Subpart C, Part 2.201.

In it it states that R3E is defined as R -Single-sideband, reduced or variable level carrier 3- single channel E - Telephony

In § 2.202(b) they go on to define necessary bandwidth.

(b) Necessary bandwidth. For a given class of emission, the minimum value of the occupied bandwidth sufficient to ensure the transmission of information at the rate and with the quality required for the system employed, under specified conditions. Emissions useful for the good functioning of the receiving equipment as, for example, the emission corresponding to the carrier of reduced carrier systems, shall be included in the necessary bandwidth.

In later subsequent sections they go on to state. "... for all services the term Communications Quality is used as reference to Commercial Quality as outlined in the table in § 2.202(g)"

This means that in the Amateur Service R3E is defined in the rules as Single-sideband, reduced or variable level carrier, single analog channel telephony using a bandwidth of Bn=M or 2.99kHz. Furthermore, the carrier is determined such as to be useful for the good functioning of the receiving equipment.

As a general rule the R3E carrier reduction is at least 16dB below the maximum peak-envelope-power as corresponding to 100% modulation. Where with J3E it is at least 40dB below the maximum peak-envelope-power at 100% modulation.

John, W2WDX