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Author Topic: HF rigs that transmit well on A.M.  (Read 1296 times)
KB9WIS
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Posts: 180




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« on: November 16, 2003, 03:51:57 AM »

On occasion, I like to hear the old timers on 160 meters transmit on A.M.. From my experiences, only the "older" tube rigs transmit legible AM audio in this emission. I've tried my newer ICOM rig on A.M., however the results very quite disappointing.., in comparison to my older Yaesu 101. The ICOM's reports were very distorted audio with reverse linearity upon modulation.. (even when reducing the carrier). Perhaps it's just a Newer ICOM thing/glitch.


Has anyone ever attempted to utilize a newer HF solid-state rig on A.M. with satisfactory results? If so, which rig have you had success with?



73's,

Kb9wis
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K0RFD
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« Reply #1 on: November 16, 2003, 09:59:05 PM »

My TS-570 worked fine on AM the one time I used it...
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WB2WIK
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« Reply #2 on: November 17, 2003, 01:16:09 PM »

I've found most of the newer rigs sound *much* better on AM than the old FT-101 did.  Trick is to adjust power output and mike gain properly, and sometimes the SSB settings are very wrong.

It really pays to have a second receiver, with headphones, so you can listen to yourself and see what sounds good.

My Kenwood TS850S sounds so good on AM (when properly adjusted!) that if I don't tell people what I'm running, they just assume it's an old plate-modulated tube rig (boat anchor).  I did break into an AM net on 75m one time, ask how my Johnson Valiant sounded (boat anchor, plate modulated) and got an hour of compliments on how wonderful it sounded, just like a modified and well adjusted Valiant should.  Next opportunity, I said, "only kidding," and signed off.

I can get the TS850S up to almost 100% modulation, monitoring on an oscilloscope, if I adjust the carrier power down to 25W and adjust the mike gain appropriately.  With 25W carrier power, it achieves 100W PEP power (100% modulation), or very close to it.

WB2WIK/6

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WA2CWA
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« Reply #3 on: November 17, 2003, 07:22:46 PM »

See my response on the Boatanchor forum where you also post the same question.

Pete, WA2CWA
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KB9WIS
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« Reply #4 on: November 17, 2003, 11:54:11 PM »

WB2WIK,



Sounds like you've had much success with your TS850S..  Have you tried any other newer rigs on AM, other than the TS850?  I wander how the TS870 sounds..?  I've heard it has "low-level" modulation and is limited to 70% modulation (regardless of carrier and if an amplified mic is used).  Overall, I'm not sure how it affects its audio.  I know both the TS850 and TS870 have awesome SSB audio fidelity, however I'm assuming the TS870 is limited with its AM audio characteristics, whereas a TS850S is not..


Any thoughts,


Kb9wis

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WA2CWA
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« Reply #5 on: November 18, 2003, 04:43:00 AM »

Most AM operators want fidelity and not "talk-power". "Low-level" modulation provided in most of these rigs, can provide the AM fidelity. An amplified mike (D-104 type) on one of these modern rigs, will, in most cases, restrict your audio range, and provide a poor fidelity AM signal. There are other pieces of audio-type equipment (compressors, limiters, equalizers, etc.) that you can put between the mike and the rig to enhance your AM audio presence. 70% to 80% modulation is more than adequate to provide a very good AM quality signal plus it provides a margin of head-room especially if you plan on driving a linear.

You need to check the AM Forum http://amfone.net/phpBB2/ or the AMFone web site, http://www.amfone.net/

Pete, WA2CWA
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WB2WIK
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« Reply #6 on: November 18, 2003, 12:53:42 PM »

All the SSB rigs made in the past decades use "low level" modulation for AM.  That doesn't mean it's low quality, or low modulation percentage.  It means they are modulated before the power amplifier stage, and the power amplifier itself is not modulated as it is in "high level" modulated (real AM) transmitters.  The power amplifier in all SSB rigs is linear and only amplify whatever is applied to them.

I don't have a TS-870S, but I'd be surprised if its modulation system is any different (or substantially different) from the TS-850S.  I have no idea why its modulation percentage would be restricted to 70%, and suppose this is Kenwood's way of staying well within the bounds and avoiding complaints from potential users who cannot achieve 100.000% modulation.  In reality, if the carrier level is adjusted for 25W output, and the mike gain is adjusted for 100W PEP, the rig is achieving 100% modulation.

Viewing my TS-850S on a scope, just looking at the RF envelope, and modulating the rig, I can almost (not quite) get the negative peaks to close down to the zero line.  If they did, that would indicate 100.0% modulation.  In my rig, I achieve probably 98% modulation -- but again, this is dependent on carrier level, mike gain and even to some extent on the RF load (antenna system) because all of these influence operation of the ALC loop, in which the modulator operates.

As Pete said, good amplitude modulation is dependent more on quality sound than anything else.  And that has very little to do with the microphone, in the Kenwoods I've used.  In fact, my normal operating microphone for my Kenwood is a $1.99 Radio Shack computer mike -- the kind you'd plug into a PC sound card for voice over internet use -- which sounds better than my Kenwood desk mike (MC60) or Heil boom headset (HC-4).  It's with that microphone that I get reports of "excellent boat anchor modulation quality."

WB2WIK/6



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N8FVJ
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« Reply #7 on: November 19, 2003, 10:20:23 AM »

Most older tube sets like the Drake, Yaesu, Kenwood, Swan, etc with the featured single sideband capacity transmits a carrier with only one sideband. Quality AM is a carrier with both sidebands.
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N4HVW
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« Reply #8 on: December 20, 2003, 03:13:02 AM »

I have a Kenwood TS 870 That I use on AM often. I adjust the output and carrier to about 15 watts. along with a few other menu adjustments. I use a Drake L4 B amp in line with the 870, which gives me about 200 watts. I get nothing but rave reviews with this set up. I use a Kenwood MC 60 microphone.
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WB9YCJ
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« Reply #9 on: March 12, 2004, 06:44:39 AM »

TS-570 series - read the TS-570 reviews here on Eham re this (AM) topic. Yes - I know there are plenty of other rigs as well.
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