Definitely put a fan on the heatsink. It will moderate heat buildup
inside the unit and reduce any drift with digi modes. I use a small 12
volt muffin fan mounted about 1/2" above the heatsink fins. I also put
styrofoam baffles in around the crystal to delay any drift from
temperature extremes. My unit is now very stable on 222 for JT65 etc.
No real drift at all.
Dave K1WHS
On 1/5/2022 1:00 PM, Ethan Miller K8GU wrote:
Bill, et al,
Thanks! That is the right manual. Not sure how I missed it before. I
think I have everything I need...thanks to everyone who replied on the list
and direct.
See you on the bands (and 222 when I get there)...
73,
--Ethan, K8GU.
On Wed, Jan 5, 2022 at 12:57 PM Bill Olson <callbill@hotmail.com> wrote:
Ethan, the DEMI instruction manual for that transverter is online here it
is for the "kit" version: vhflna doc (netsolhost.com)
<http://01895fa.netsolhost.com/PDF/Manuals/222-28_677.PDF> This has all
the info on the high power and low power IF drive options..
The M67712 is pretty robust.. I suspect it will be just fine when run at
the output level you need for the Larcan..
bill, k1DY
------------------------------
*From:* VHFcontesting <vhfcontesting-bounces+callbill=
hotmail.com@contesting.com> on behalf of Ethan Miller K8GU <ethan@k8gu.com
*Sent:* Wednesday, January 5, 2022 3:11 AM
*To:* VHF Contesting <vhfcontesting@contesting.com>; Midwest VHF/UHF
Society Mailing List <mvus-list@lists.febo.com>
*Subject:* [VHFcontesting] DEMI 222 help
All,
I acquired an old DEMI 222-28 transverter from the K8CC estate last summer
and I'd like to get it rolling for the spring/summer contests (I have to
beam through "Mount Kettering" to get to the center of 222 Tuesday nights
from my home QTH and biggest amp I have for 222 is a 60-watt Larcan
pre-driver).
This unit has the M67712 hybrid as the PA and does not seem to match any of
the legacy schematics found on (the current) DEMI web site. It's wired for
common-IF with what looks like an attenuator for high drive power. Do I
need to know anything special about converting it to low-drive split-IF to
work with my K3 and K2 (and TS-930S)? Or can I just remove the
attenuator/switching board and run coax straight from the rear panel
connectors to the RXIF and TXIF pads on the board?
Also, any experience or opinions about using the M67712-based transverter
on digital modes? Muffin fan? Low power? Both? I've been off the bands
above 6m the past couple of years since I moved from FM19 to EM79; but, if
my experience on 6m and the kvetching on the reflectors are any indication,
I'll need to spend some time on FT8. I'm sure the Larcan pre-driver will
be fine at high duty cycle.
Thanks/73,
--Ethan, K8GU.
--
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