Hi Rich,
I just did some calculations using the data I found for the MV2201 in an old
Motorola Semiconductor Data Book I have on the shelf. It looks like the
easiest way to increase your Offset Tuning range is to change C2 in the PTO
from 10pf to 1000pf. This will give you approximately +6/ - 9 KHz tuning
range. You would also have to retune the inductances per the manual to
reset the PTO frequency. The +6/-9 is on 20m. It would be double that for
80m and 15m, and triple that on 40m and 10m because of the multipliers used
in the 509. I haven't looked very far into changing the varactor diode yet,
but what I've seen so far is that the slope of the tuning curves look pretty
similar, so this may not be the best way after all. I'll keep digging, and
let you know what I find. In the meantime, if you come across any
information about increasing the tuning range, I'd be interested in what you
find.
73,
ed - k9ew
----- Original Message -----
From: "Richard Arland" <richard.arland@verizon.net>
To: "Ten-Tec" <tentec@contesting.com>; "QRP-L" <qrp-l@mailman.qth.net>;
<qrparci@qsl.net>
Sent: Thursday, February 24, 2005 23:04 PM
Subject: [TenTec] T-T Argonaut 509 Offset Tuning & IF Filter Mod
Has anyone ever tried increasing the RIT (offset tuning) on an Argo 509? If
so, what was your approach to the problem?
I'd l;ike to increase the OT to cover a minimum of +/- 5 kHz on each band so
I could have a better chance at working DXpeditions. Actually +/- 7 kHz
would be better, come to think of it. Anone done it?
My latest 509 has just undergone a mod to replace the stock 2.4kHz 4-pole
filter with an InRad #752 2.1 klHz 8-pole filter and the results are nothing
short of spectacular! Using Spectagram software and an Elecraft white noise
generator I graphed out the results and the difference in the stock filter
compared to the new InRad filter is amazing.
I am planning on writing all this up in the an upcoming issue of the
American QRP Club's newsletter "The Homebrewer". So, if anyone has a
worthwhile solution to the Offset Tuning problem or some other mods that you
have done that improve the T-T analog Argonaut series of rigs, please get
them to me ASAP. Credit will be given at time of publication.
73
Rich K7SZ
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