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FT726.MOD
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1980-01-01
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Subject: FT-726 AUDIO MODIFICATIONS
Further improvement in FT-726 audio quality can be achieved by a simple
modification to the product detector. The product detector seems to be
overloaded by the input IF signal, the 6dB attennuator described here
will improve the RX-quality
The circuit is proposed by LA8AK, and tested by LA7BI (Egil);
----------------- 1K --------------- to pin 5, Q13;uPC1037
I I
I I
T11 I
output 1K
link I
I I
--------------------------
I
I
C67
47nF( .047)
I
I
--- pcb/ground
the two resistors (1000 ohms) are easily mounted below the PCB
Break the pcb between the coil and IC pin 5, mount the resistor, and
connect the other resistor from the capacitor to IC pin 5
The audio quality should be much improved, and you should at least be
capable of understanding somebody who does not exactly speak the same
language as you. Englishmen should now be able to read foreigners who
speak english, although it is well known that foreigners from different
countries who use english understand each other, but the englishmen
often do not understand them.
HI HI
73 de jan-martin
LA8AK @ LA5IV 89 01 21 - 1828ZSubject: FT-726 AUDIO MODIFICATIONS
Further improvement in FT-726 audio quality can be achieved by a simple
modification to the product detector. The product detector seems to be
overloaded by the input IF signal, the 6dB attennuator described here
will improve the RX-quality
The circuit is proposed by LA8AK, and tested by LA7BI (Egil);
----------------- 1K --------------- to pin 5, Q13;uPC1037
I I
I I
T11 I
output 1K
link I
I I
--------------------------
I
I
C67
47nF( .047)
I
I
--- pcb/ground
the two resistors (1000 ohms) are easily mounted below the PCB
Break the pcb between the coil and IC pin 5, mount the resistor, and
connect the other resistor from the capacitor to IC pin 5
The audio quality should be much improved, and you should at least be
capable of understanding somebody who does not exactly speak the same
language as you. Englishmen should now be able to read foreigners who
speak english, although it is well known that foreigners from different
countries who use english understand each other, but the englishmen
often do not understand them.
HI HI
73 de jan-martin
LA8AK @ LA5IV 89 01 21 - 1828ZFT726.1
de ON4KVI @ LX0PAC
To improve the Auto-doppler control on my 726R which has 20hz steps, I
installed a 555 multivibrator circuit across the tuning switch which shorts
the line 2 times a second.
It now pulls the circuit into tune from 300 hz either side.
W9ODI
FT726.2
From : W6SHP @ WD6CMU.#NOCAL.CA.USA.NA
To : ALL @ ALLUS
Date : 900526/0352
Msgid : BN 63093@WD6CMU, 2821@NM3G $63093_WD6CMU
Subject : TAPR PSK mods for the FT-726R
Path : KA3NVP!W3KDC!WB4D!KD3O!WB9TYT!W9IUP!WB9MJN!K6IYK!AA4RE!W8GEC!W6PW!WD6CMU
Throughput improvement for the FT726R - Tapr PSK modem
-------------------------------------------------------
On the Lo-19 and Ao-16 digipeaters I was only averaging 1 in 5 UI frames
returned. Viewing my PSK signal on a scope at the FM varactor driver (Q08)
on the Sat Unit revealed a very distorted and jittery audio waveform.
Replacing the Tapr's obsolete 4030 (U21) with a 4070 gave me a steady but
still distorted wave. My throughput was now 1 in 3; better but not good.
Modifying Tapr's low pass output filter (as suggested by G3RUH for his PSK
modem) and a change in the Tapr's attenuator and alignment has given me
almost 100% throughput.
TAPR Attenuator mod:
Remove R5 (22K) by putting a jumper on JP7. Replace R6 (5K trim pot) with
a 100K trim pot. Be careful when unsoldering as those small trace pads come
off very easily.
TAPR filter mod:
Replace R7 (22K) with a 47K resistor and C8 (.047 mf) with a .01 mf disk
capacitor.
FT726R mod:
Find plug J04 on the Satellite Unit (front left corner). Buy an equivalent
plug and header pins and solder them together with short bare wire,
attaching the center conductor of RG174U coax to pin 2 and the shield to pin
1 of the adapter. Then plug the Yaesu's plug onto the adaptor's header
pins, and the adaptor's plug onto the Sat Unit board's male header pins.
You could solder the cable directly to the board or connector, but this way
the board's original condition is retained.
Alignment:
The waveform out of the TAPR (ungrounded end of JP8) will now be a somewhat
rounded sawtooth. Adjust the 100K pot (R6) to mid range. Set the FT726R's
Mic Gain to the first "tick" (8 O'clock).
Attach your scope to the RG174U coax and slowly increase the Tapr's output
(R6). You will see the PSK's distorted waveform smooth out and grow to
become more like a sine wave. Around .6 v pp it will be at it's best. As
you continue to increase the PSK output distortions will reappear as the FT-
726R's FM limiter clips the signal. Back off the audio until you get the
least distorted wave shape. It will be almost a sine wave.
When you set your transmit power lever, back off so your ALC is not active.
Assuming you have all your software switches and parameters set properly you
should now have greatly improved throughput. Let me know how this works for
you or if you improved your throughput in other ways so we can write it up.
Good luck. 73,
Howard Sodja W6SHP @ wd6cmu