[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: Anyone FT-847 and 56002EVM/RI?



Mike

Here is how to fix at least part of the 847 problem.

I did as you suggested and found that with that 1K resistor still there and
set to max or 0 ohms, it still doesn't work right.

It has to do with impedance matching.

No matter if you set it to 0 ohms or not, you need to replace the 1k with a
10K.

I looked at pin 32 on the CODEC with a scope.  With a back to back cable
from the out to the in, the signal looks great.  It just happens that the
impedances match when doing that.  You can look at either the HPHONES or the
out and either will look great.  The HPHONES DOES have a 2.2V DC offset, so
I don't think I'd plug that into my varactor until I ac coupled it somehow.

I then hooked up the interface board and with a simple loop back connector
from pin 1 to pin 4 ran the same test.  The waveform looked like crap!!!
The impedance mismatch was acting like a filter and the top of the waveform
was bascially flat, but up from grd on my scope looking at it in AC mode.

I'm not going to play expert here, I faxed the schematics over to a friend
of mine and we talked for awhile.  He had me take a 10K. (btw, the 847 wants
10K ohm input impedance) and replace the 1K.  When I did that, the waveform
looked great and there was no more distortion.  Now I don't know if it's
clipping, that's next to check.

Now, the same signal at pin 32, same at p2 of p5 and the same at pin 1 on
the din 8 going to the radio.  I'm at 2.48V ptp and the radio wants 2.

Next will be to hook up the HP service monitor and see what kinda deviation
I get.

This little interface really calls out for an active interface and at some
point, maybe I'll think about laying it out to fit the same footprint and do
that.

We'll see.

Back to the scope and other assorted tests!

Alan

-----Original Message-----
From: Mike73@aol.com [mailto:Mike73@aol.com]
Sent: Tuesday, February 15, 2000 8:41 PM
To: ne1h@ne1h.dyndns.org; amsat-bb@amsat.org
Subject: Re: [amsat-bb] Anyone FT-847 and 56002EVM/RI?


In a message dated 2/14/00 8:53:58 PM Eastern Standard Time,
ne1h@ne1h.dyndns.org writes:

> I'm about ready to start hooking up data related stuff for my sat station.
>  Before I do, I figured I'd see if anyone is using this setup.
>  Yaesu 847 and the 56002EVM/RI?
>  Any hookup related issues, any tricks, etc?

Hi Alan,

Just a couple of tips...........

You'll find that the stock TAPR DSP56002EVM/RI doesn't quite have enough
output drive to get 3 KHz deviation at 9k6. 1k2 transmit is fine as is
receive at both speeds. On my EVM/RI I removed/jumpered the 1K output pot
for
radio #1. I'm using Doug Braun's 9k6 code and have set my 9k6 modem as
follows for transmit:
Under user controllable parameters in g3ruh.asm
OLevel  set 0.90        ; output signal level (in rms volts)
With this settings I'm getting ~2.8KHz transmit deviation. As you probably
know, 3 KHz is the recommended high limit.

For receive, I set it this way:
Under user controllable parameters in g3ruh.asm
RxGain  set     9.0        ; Codec input gain in dB, set to match radio.

Doug provided a neat piece of code called scope9600.lod Use this with Spy to
check input level. Scope9600 has the same gain structure as g3ruh.asm

I don't know if you'll be automating the tuning of the FT-847, but I've
found
my radio likes to see the frequency set slightly low. In other words if you
monitor the FT-847 DISC when in SAT mode (set menu #34 to DISC), the
indicator will be a little left of center. I see slightly better throughput
on receive when I set the receive frequency this way. FYI, I'm using
Uni_Trac
with WiSP for freq/tracking control.

Don't forget to set the radio data output speed via menu #23 Pkt Rate to
9600
when using the 9k6 birds. Good luck and hope to see you on the digital sats
soon.

73,
Mike, N1JEZ
AMSAT #29649
Local Area Coordinator
"A closed mouth gathers no feet."

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home