[CCF] VB: Topband: FT1000MP click reduction

Fri, 25 May 2001 08:50:12 +0200

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Since there are many many MP=B4s in Finland this can be
very useful.

Regards

SM2EKM

=2D----Ursprungligt meddelande-----
Fr=E5n:	w8ji@akorn.net [SMTP:w8ji@akorn.net]
Skickat:	 den 24 maj 2001 20:41
Till:	cq-contest@contesting.com; topband@contesting.com
Kopia:	160m@qth.net
=C4mne:	Topband: FT1000MP click reduction

The FT1000MP is entirely different than the 1000D or 1000. It keys=20
the carrier after the filters, not before them.

The problem with the MP is entirely due to the waveshape of the=20
envelope near the maximum amplitude spot. Yaesu uses a single=20
pole R/C filter, which does not provide an optimum-bandwidth=20
waveshape for a given rise and fall time. The rise and fall is too=20
fast,=20
besides having the poor one-pole R/C filter shape.

While there are much better methods, such as something=20
producing a raised sine waveform, adding one capacitor will help=20
until someone finds a better solution. Either a multi-pole filter or a=20
more complicated system that produces a raised sine waveshape=20
would be much better.

With a single pole filter we are limited in BW improvement, but it=20
can still be much better than stock.      =20

This mod should only take a couple of minutes.

Locate T2018 at the right front area of the IF Unit. Remove the IF=20
Unit by unplugging the ribbon cables in that area and flip it over.

C2128 is a .0047uF chip capacitor on the center pin of the=20
secondary of T2018. Either change C2148 to .15uF, or add a .1 uF=20
capacitor in parallel with C2148 (from the CT of T2018 to ground).=20

When I have more time I might try some form of active filtering, but=20
at least this is much better than stock!

I noticed the radio I looked at had the high power limiting pot set to=20
150 watts. 3rd order SSB IMD was only -21 dB with that power=20
setting. IMD improved about 11 dB by reducing the power limiting=20
control to 100 watts. (IMD referenced to one tone as in commercial=20
standards, not PEP like the ARRL uses.)

About 1-1/2 dB more power at a cost of 11 dB IMD is NOT a good=20
tradeoff.

73, Tom W8JI
W8JI@contesting.com=20

=2D-
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From: "Tom Rauch" <w8ji@akorn.net>
To: cq-contest@contesting.com, topband@contesting.com
Date: Thu, 24 May 2001 14:41:07 -0400
Subject: Topband: FT1000MP click reduction
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