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What rigs do you use for AM operation and why do you like using AM?

Sep 1st 2011, 00:42

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
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Okay, we aren't lively enougn on this forum, so let me start a topic. Hopefully, we can get a lot of good pointers and URLs that I can use to update one of ARRL's technical information pages.

In one of the other forum areas, there was a brief discussion of AM operation, with a poll. The poll did show that a number of hams are interested in AM operation, so let's start a thread that is focused more on getting people who use the mode to share more information with those that might be interested in trying it.

Now, I'm a CW op, so phone of all sorts is rare for me. But in the AM circles, I've noted that some are focused on using older equipment, using converted broadcast transmitters and homebrew designs, while others simply take their modern transceiver and try its AM mode. (Occasionally, the some of the first group have been a bit less than supportive of those using commercial SSB/CW/digital equipment in the AM mode, but that's what I have used the times I've operated AM.)

So, if the proponents of AM can explain what they like about the mode, and offer some encouragement and advice to those who haven't yet tried it, we may be able to get a few more folks trying something new for them, even if it's the oldest phone mode we have.

Those interested in learning can ask a few questions, and hopefully, one of the experienced AM folks will be willing to serve as an Elmer.

And let's avoid the terms "slopbucket, ancient modulation and ricebox." I'd think that those that like AM will do better at getting others interested if they use kinder terms for the non-AM phone modes and the non-tube rigs than some like to use. In my world of QRP, we are usually delighted when a QRO op cranks down the 100 watt rig and gives QRP a try. "Real" QRPers usually are into homebrewing and "real" QRP rigs, but being a QRPer, or AMer, or anything else in ham radio, does not necessarily mean that one is interested ONLY in that mode or operating convention.

73,
Ed Hare, W1RFI
ARRL Lab
Technical forums moderator
Sep 1st 2011, 06:01

KM3F

Joined: Mar 6th 2008, 13:50
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Here is an example of something a bit rare for AM.
On 2 meters I normally run SSB using a transverter 28 to 144 conversion driving a solid state amplifier 30 watts in 160 watts out.
However, wanting to be all mode, I modified the transverter input for adjustable RF drive so the output could be controlled downward for AM mode operation.
Sometimes we use this mode for the evening just to be different and for the audio.
Point is, there are some things to know about setting up for AM using equipment meant for either SSB or FM.
Basicly for my equipment, the transverter output full on is about 28 watts + driving an amplifier that is matched to that power level for peak envelope power without over driving either unit.
Going to AM mode and staying within the equipment linear operation, required the transverter drive to be lowered to about 7 watts carrier output into the amplifier who's max drive is 30 watts.
What all this means is 7 watt carrier x 4 = 28 watts peak envolope modulation AM power drive to the same amplifier without over driving either unit and causing distortion and splatter.
These are the types of operating parameters not often known to many hams for setting up to use the AM mode cleanly with the equipment at hand and why it needs to be considered.
How neat is it to have a 150 watts clean peak envolope power on 2 meters AM and still be able to use "clean" speech processing and outboard/inboard audio EQ when needed for the long haul contacts in either mode.
Works really nice for me.
Sep 19th 2011, 16:39

K8WHB

Joined: Jan 11th 2011, 19:02
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Ed, it has been many many moons since I've operated 2M AM - back when I was first licensed (1962) 2M AM was the only phone a Novice could do. With the help of my uncle I constructed a 2M AM transmitter from an article in the Handbook and had a ball with it.

Presently I'm just running FM & packet on 2M, but I have plans to build a plate-modulated AM amp for 2M using my FM rig as the oscillator/multiplier chain (and tapping the audio circuitry to drive the modulator). Not sure if I'll do it solid state or tube, though I'm tending toward using a 4X150 or a 4CX250 (my Kenwood TM-D710 should be able to drive either tube just fine).
Sep 21st 2011, 01:59

W8JI

Joined: Nov 28th 2000, 00:00
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Some modern SSB rigs are much cleaner than old "plate" modulated rigs. This is because of nonlinearity when a beam power tetrode is modulated.

As a matter of fact, it is impossible to plate modulate a tetrode properly. It has to be modulated on a grid as well as the plate, or in an earlier stage along with the plate, or have a complex form of envelope correction.

The only PA stage that can be directly plate modulated with low distortion is a triode hard-switched with RF drive.

Pro-iron folks are not necessarily correct. A typical FT1000D, properly adjusted, produces much better AM than almost any older plate modulated rig. Most other solid state SSB radios will too, with fixed external ALC bias applied.

http://www.w8ji.com/amplitude_modulation.htm

73 Tom
Sep 24th 2011, 00:58

WA2CWA

Joined: Apr 4th 1998, 00:00
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I presently spend most of my AM operating using a Flex 5000 driving an old Heath SB-200. Although the rig doesn't glow as pretty as my tube receivers and transmitters, my screen has lots of pretty colors. The quality of the AM reception and the great quality of the transmitted audio, are hard to beat. After using one of these rigs, it's hard to go back to some old tube rig other then for nostalgic or sentimental reasons. Probably why I keep my Heatkit Apache around. It's the first transmitter I built after I passed my General Class license.

Pete, wa2cwa
Oct 6th 2011, 16:24

KF0XO

Joined: Apr 4th 1998, 00:00
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I have an old DX-100 and an SP-600 that I use on HF for AM and I
always get good reports. However it is s myth that you need to use
old boat anchors to have a good time on HF AM. I have also used an Icon 756 Pro and the audio was very good. I just didn't mention my rig unless I was asked. I have always liked AM and tubes. I believe that tubes give a richer warmer sound. If you want to get on you can do it for less than 200 bucks. You don't need big amps or large antennas. All you need is a goot transmitter (DX-35) for example, reasonable receiver,( Halicrafters S-40) and a dipole. That will get you on 20 meters 14.286 or up on 10 meters 28.1 to 28.2 . There you can have a great time, meet alot of good people and hear great quality audio. All with stuff you can get at a ham fest at very reasonable prices.
73 Norb KF0XO
Oct 7th 2011, 00:54

WA2CWA

Joined: Apr 4th 1998, 00:00
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Quote by KF0XO
...That will get you on 20 meters 14.286 or up on 10 meters 28.1 to 28.2 . There you can have a great time, meet alot of good people and hear great quality audio. All with stuff you can get at a ham fest at very reasonable prices.
73 Norb KF0XO


I suspect you really meant to say 29.0 to 29.2 MHz. Phone band starts at 28.3 MHz.

Pete, wa2cwa
Oct 11th 2011, 02:19

K4TOJ

Joined: May 17th 2010, 00:56
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Here's a question about something I've noticed while looking at transceivers. I have a Kenwood TS-930S which will transmit 100W in all modes including AM. Most of the current rigs may transmit 100W in all modes but AM. For some reason, they limit AM to 25W, 40W or 50W max. So the question I have is why is this? Do they limit AM because they don't make the finals like they used to?
Oct 12th 2011, 18:56

W1VT

Joined: Apr 4th 1998, 00:00
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Yes, things are much different these days. Today, the final does all the work. Thus, the final not only produces the 25 watts of carrier power, but the sidebands as well. This requires a linear amplifier, which has less efficiency than class C amplifiers used in the old days. More heat produced for the same amount of power.

In the old days, the final produced just the RF carrier--there was a separate high power audio amplifier and modulation transformer to produce the high level audio for plate modulation. This worked well, but you added additional size and weight—those rigs are big and heavy!

Zack Lau W1VT
ARRL Senior Lab Engineer

Oct 12th 2011, 22:05

W8JI

Joined: Nov 28th 2000, 00:00
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Quote by K4TOJ
Here's a question about something I've noticed while looking at transceivers. I have a Kenwood TS-930S which will transmit 100W in all modes including AM. Most of the current rigs may transmit 100W in all modes but AM. For some reason, they limit AM to 25W, 40W or 50W max. So the question I have is why is this? Do they limit AM because they don't make the finals like they used to?


Your TS930 will not run 100 watts of AM.

If you read the manual, the carrier power is supposed to be adjusted to 15-20 watts carrier OUTPUT power.

Older rigs were rated in input power. Your Kenwood is rated 80 watts AM input power, and 15-20 watts carrier output power.

Nearly all AM rigs, at least for Ham use, were a combination of screen and plate modulation. About 60-80% of the modulation power came from the modulator stage, with the remainder of modulation power from the screen of the PA tube. It was a combination of efficiency and plate modulation.

http://www.w8ji.com/amplitude_modulation.htm


Older rigs like my Ranger were 65 watts AM input power. That was about 30 watts carrier power. Remember everything prior to 1982-83 was rated in plate input power. A 2KW Heathkit SB-220 amplifier is rated at about 600 watts CW output, and around 1100 watts SSB PEP output.

Those old rigs were not as big as the advertised power makes them appear because of the change from inoput power to output power in the early 1980's.

73 Tom
Oct 13th 2011, 05:18

KE8DO

Joined: Apr 4th 1998, 00:00
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The 25 watts AM carrier power will be 100 watts PEP when modulated 100%. Also, on AM the heating effect of the full time carrier on the amplifier must be accounted for in the duty cycle.
73 Don KE8DO 35+ years FCC First Class Radio Telephone License
Feb 3rd 2012, 00:04

VE5RB

Joined: Jan 11th 2008, 13:00
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I have sucessfully used my Yaesu FT 857 on AM. I got compliments on my audio too. I haven't been on the air much latelt but I really enjoyed AM.
Feb 3rd 2012, 19:22

W1RFIAdmin

Joined: Jul 25th 2011, 14:25
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Quote by W8JI
Your TS930 will not run 100 watts of AM.

At 100 watts of carrier power, the rig would be flat-topping very badly, generating lots of splatter up and down the band. One needs to adjust the carrier power to 15-20 watts to keep the PEP at or below the rated PEP of the rig.

It's wonderful to use modern rigs on AM, but keep the power level as specified for AM, to keep the rig clean and operating below the point at which it may overheat.

If the rig manual doesn't specify an AM carrier level, adjust it to 25% of the PEP rating of the rig and modulate the rig accordingly. If you have an *accurate* PEP reading watt meter, adjusting the audio level until the rig achieves its PEP rating on voice peaks is as high as you want to go. Some "PEP" wattmeters significantly underestimate PEP for voice modes, so it's also a good idea to listen to your transmitted signal on a separate receiver and ensure that there is no significant splatter up and down the band.

73,
Ed Hare, W1RFI

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