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Yaesu FT-102 Question




 
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Author Topic: Yaesu FT-102 Question  (Read 11787 times)
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WA4JK
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« on: January 14, 2011, 10:55:17 AM »

I've been reading Maclcom's web page and came across this comment by him.
"Because of the high voltage final stages and dynamic head room of the power supply, the AM transmit capability can easily exceed 100% modulation. Properly realigned 102s will do 110 to 120% on positive modulation peaks without cutoff at the negative or positive peaks . Therefore, when properly adjusted there is no splatter distortion. In addition it is capable of HI-FI AM transmit audio with a frequency response (at 100% modulation) from 45 to 20,000 cycles with no attenuation and exceedingly low distortion. And, that is in all 102s that are unmodified, just stock. "

Can one of you guys who has or had a 102 shed some light on the for me. Would this frequency response from 45 to 20,000 cycles be wide enough for HI-FI Am Audio?
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WD8BIL
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« Reply #1 on: January 14, 2011, 11:02:17 AM »

45 to 20,000 Hz?

Ummmm..... ya!
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WA4JK
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« Reply #2 on: January 14, 2011, 11:19:54 AM »

So if it will do 45-20k why would you do the perscribed audio mod from the window tech list?? Or am I just missing something here?
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n1eu
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« Reply #3 on: January 14, 2011, 11:48:50 AM »

So if it will do 45-20k why would you do the perscribed audio mod from the window tech list?? Or am I just missing something here?
What you might be missing is the optional 40KHz AM filter   ;-)
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WA4JK
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« Reply #4 on: January 14, 2011, 11:56:33 AM »

What?? the only one I know of the the 6Kz filter.
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Steve - K4HX
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« Reply #5 on: January 14, 2011, 12:20:38 PM »

It will not have a frequency response of 45 Hz - 20 kHz without some modifications of the audio stages.
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K1JJ
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« Reply #6 on: January 14, 2011, 03:30:39 PM »

See the NE-602 balanced modulator mod for the FT-102:

http://www.amwindow.org/tech/htm/602mod.htm


There's perhaps four issues to hi-fi AM use with the stock FT-102 that can be overcome by building the simple NE-602 mod in the link above.

Used as a stock FT-102:

1) As Steve said, the TX audio would have to be broadened out.

2) There are some cross-over waveform anomalies when running a tone thru on AM. I know Mal didn't agree when I told him, but I have four FT-102's here that showed it before adding the NE-602 balanced modulator modification.

3) There is a keying up "overshoot" that will automatically be corrected with the mod. There is a Mal-mod to handle this stock overshoot problem too.

4) If you do not have the "rare to find separate" AM board, you're out of luck. The NE-602 will take a non-AM board FT-102 and make it TX AM beautifully.

I have four FT-102's that have this NE-602 mod. They sweep 5hz-20khz ++ and are clean clean clean. Positive peaks are limited only by pep power since the DSB wavelets fill in using the balanced modulator.

BTW, I may be selling off three of my Ft-102's now that I will have the SDR rig and the FT-1000D to fall back on.

T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
Steve - K4HX
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« Reply #7 on: January 14, 2011, 03:35:38 PM »

Quote
2) There are some cross-over waveform anomalies when running a tone thru on AM. I know Mal didn't agree when I told him, but I have four FT-102's here that showed it before adding the NE-602 balanced modulator modification.



I had a similar discussion with him. He claimed there was some special property of the FT-102 that would produce more than 100% positive peak modulation, regardless of the phase/polarity of the input waveform, and even if the input was a sinewave. My reply was that this is the very definition of distortion.
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WQ9E
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« Reply #8 on: January 15, 2011, 09:11:35 AM »

45-20,000?Huh  Let's think about that a bit.  This extends well beyond what is produced by commercial broadcast rigs (or recorded on most supposed high fidelity music).  Truly reproducing clean bass down to 45 hz (doubling distortion from an over driven driver doesn't count) is very expensive and the number of adults who have hearing out to 20K is just about the null data set.

I am not a bandwidth Nazi but you will need a buddy with a very wideband receiver to talk with and 40 Khz. of available spectrum. 

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Rodger WQ9E
WA4JK
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« Reply #9 on: January 15, 2011, 09:15:51 AM »

If that frequency response is correct and if it's not distorted what are the benift differences between the NE602 mod and this mod.
AF Board  Part Number Original Value New Value
 C02   .1 mfd  33 mfd
 C03  .001 mfd  remove
 C04  10 mfd  33 mfd
 C06  .0022 mfd  remove
 C07  1 mfd  33 mfd
 C08  1 mfd  33 mfd
 C09  10 mfd  33 mfd
 C10  4.7 mfd  33 mfd
 C17  4.7 mfd  33 mfd
 C19  33 mfd  100 mfd
 C20  4.7 mfd  33 mfd
 C21  4.7 mfd  33 mfd
 C76  .0027 mfd  remove
 C79  .01 mfd  remove
 C116  10 mfd  33 mfd
 C124  33 mfd  100 mfd
 

Note: If you desire to use the phone patch input for external audio feed, put 220k in series with the center conductor going to the patch input jack and a 1k to ground from the input audio side of the phone patch jack.

Also remove C04 (10mfd) from the AF unit to reduce the overall audio gain. I also changed R11 from 2.2k to 15k to set the gain properly for vox operation.
 
AM/FM Board  Part Number Original Value New Value
 C12   10 mfd  33 mfd
 C70  .01 mfd  470 pf
 R03  4.7k Parallel with 180k to set carrier
level for extended positive peak modulation
 

Set both tone controls on the AF board to 50%. Frequency response is essentially flat from 40-6khz and down 3db at 16 khz. If you want it flat to 16 khz, just turn up the treble tone control a bit.

There is a problem with the alc kicking in too early on AM. To fix this, connect a 10k resistor between pins 2 and 3 of P22/J15 on the I-F board. This will raise the point at which the alc kicks in.
 

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W2VW
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« Reply #10 on: January 15, 2011, 10:52:29 AM »

It's common practice to sweep transmitters looking for much wider frequency response than what one will actually use on the air.
This will guarantee minimal phase distortion within the desired transmit passband.
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K1JJ
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« Reply #11 on: January 15, 2011, 11:33:51 AM »

The benefits of the NE-602 mod?

Well, first, if someone were a purist, they would not have to modify the FT-102 boards when adding the NE-602. In my rigs, I have the tiny NE-602 board floating and sealed in tape. To remove it is easy and the rig is back to stock. Plus, the FT-102 is not an easy rig to work on when it comes to the boards. One must be careful.

Another point is some 102's don't have the AM/FM board and sell a lot cheaper. Adding the NE-602 solves this problem.

And finally, I would need someone to run some tones thru a STOCK FT-102 to double check the following. (All of mine are modified with the NE-602 board)    But IIRC, when an audio tone is put thru on AM mode and the % of modulation is increased past 100% positive, the little "wavelets" at the crossover point are not a perfect minature images of the larger, main waves, as they shud be. I've seen this crossover distortion before in many other DSB riceboxes. It's in the balanced modulator. The stock bal mod gets bypassed when the NE-602 is added and this distortion is gone.  This point Mal and I debated, but I still maintain that's what I saw on mine. Again, it is a common problem on many ricebox ssb/AM rigs.

Maybe someone with a stock FT-102 understands what I mean here and can sweep their rig to verify. Be sure to push the audio ABOVE 100% positive to see the wavelets appear.

Hope this helps.


T
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
Steve - K4HX
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« Reply #12 on: January 15, 2011, 01:40:38 PM »

In short, the advantages of the NE602 are

1. Lower distortion
2. Impossible to over modulate in the negative direction
3. If you run external audio directly to the 602, you don't need to do any of the mods to the low level audio stages.

The N602 fed directly will give you frequency response out to the 100 kHz range (not that you need it).
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WA4JK
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« Reply #13 on: January 19, 2011, 12:10:06 PM »

Ok I understand the issue and the difference between the NE602 mod and the AM/FM board mod by the same ham. So here is another question. Can the IF2 output be used as an input to a SB-614 to monitor AF? Thanks Tom for the info.
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