MASSACHUSETTS QSO PARTY 1994
The 1994 Mass QSO Party is organized by Framingham Amateur Radio Association.
Contest period: 1800Z Saturday, May 21 to 0400Z Sunday, May 22 and
1100Z to 2100Z Sunday, May 22
Classes: Outside MA; MA single, MA multi-single, MA multi-multi, MA portable
Exchange: RS(T) and QTH (state, province, DXCC country, or Mass county)
Points: 1 point per QSO on Phone and 2 points per QSO on CW/Digital/Video.
50 points for Massachusetts Club Bonus Stations.
Multipliers: For stations outside Massachusetts, the number of Massachusetts
counties worked per band (max 14 per band).
For Massachusetts stations, states + provinces + DXCC countries
per band.
Scoring: Final score equals total QSO points times total multipliers.
Frequencies: CW - 1810, 3550, 7050, 14050, 21050, and 28050 KHz
SSB - 1850, 3890, 7290, 14270, 21390, and 28390 KHz
Novices - 3705, 7130, 21130, 28130 KHz
Awards : Certificate for the highest score in each contest class and for the
highest score in each state, Canadian province, and DXCC country.
Send logs by June 21, 1994 to Framingham Amateur Radio Association
P.O. Box 3005
Framingham, MA 01701
For full rules, send an SASE to the above address, or send a request
by e-mail to dave_hoaglin@abtassoc.com .
(This announcement posted by Dave, K8JLF.)
>From John W. Brosnahan" <broz@csn.org Wed Apr 20 15:25:24 1994
From: John W. Brosnahan" <broz@csn.org (John W. Brosnahan)
Subject: FT-1000 audio corrections
Message-ID: <199404201425.AA13382@teal.csn.org>
Correction to Mario's posting on the FT-1000 audio problem.
>Hi Contesters,
>While reading recent discussions on Heil & CAT problems with YAESU,
>I got a feeling that nobody reads electrical diagrams any longer!
>FT-1000 dual audio output for headphones is generated by pair of transistors
>with 1 KOhm in emiter, supplied from +9V via 100 Ohm & 100 uF and biased by
>100 kOhm . Assuming optimal colector current of 4 mA, such a stage gives
>maximum of 16 mW output power in linear class A but to the 1 kOhm load.
>This is about 100 times less (- 20 dB) than available from final audio 2 W
>amplifiers. They use 1 uF coupling capacitors which makes nice 10 kHz
>high-pass filter with standard 16 Ohms headphones and greatly rejects hum!
(CAT part deleted)
>73 de Mario, S56A, S57MM, N1YU, ex YU3EA, YU1PCF.
>email: Marijan.Miletic@IJS.SI
This is not correct! But it is an easy mistake to make when reading the
FT-1000 schematic. I know because I first jumped to this same conclusion.
The audio signals that you are referring to are the higher impedance outputs
for a tape recorder, so the severe LPF problem and low level audio are
not problems for the much higher impedance of a tape recorder.
The headphone audio is amplified on the SHP Unit board by a dual headphone
amp designed for portable tape/CD players made by Mitsubishi (M5216L).
The M5216L will put out somewhere near 150 mW per channel when supplied by
+/- 9V and when used with typical headphones. There is a series 47 ohm
resistor in the output from each side of the stereo amp chip, limiting the
total current and reducing the audio. For maximum audio the load impedance
should equal the source impedance. With 47 ohms in series with the output,
any reduction of the headphone impedance below 47 ohms will actually reduce
the audio not increase it.
An increase in audio can be obtained by reducing the value of the series
resistors to as low as 10 ohms but the amplifiers are still inadequate
because their THD rises rapidly as the output is increased. I am currently
reviewing the data sheets to see just how much audio with reasonable THD can
be expected but the data sheets are inadequate.
In fact, I have two fundamental problems with the FT-1000 audio. Number one
is the inadequate power that is available, but number two is a little more
subtle. When I use good quality headphones (and most of them have similar
sensitivities) I would expect the gain distribution to be set up so that
the volume from the headphones is similar to the volume from the speaker
for a given volume control setting. But this is not the case with the
FT-1000. In order to get a volume similar to the speaker's volume from the
headphones requires that the volume control be advanced by about another
120 degrees! So the total power available is inadequate AND the gain of the
headphone amp is inadequate.
(For those without an FT-1000, you cannot just use the speaker output as
a source of high level audio, since the speaker output is mono and the
dual receivers drive headphones in stereo.)
The best solution is an external stereo amplifier for both headphones and
for two speakers. It would be nice to try the two receivers with
polarization diversity antennas and hear the effect either on headphones
or on two speakers.
I just received the data sheet on the M5216L yesterday (Thanks Jay, K0GU!)
and haven't had time to fully explore the implications. Was planning on
waiting to make a posting until I had a strategy formalized for repairing the
audio, but felt I needed to jump in and correct the misinformation before it
spread too widely.
Again, sorry, Mario, it is an easy mistake to make on the FT-1000 schematic.
73 John W0UN broz@csn.org
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