The symptoms of a bad oven are frequency change. It is normal for the radio
to change freq, typically about 100 Hz, from a cold start due to the oven
warming up to operating temperature. This can be eliminated if one allows
the 12 VDC to be applied to the radio at all times. In some cases, the
thermostat has been known to fail thus the oven does not heat and frequency
drift will be apparent with temperature change, either by nominal room
temperature, or by heat generated inside the radio by operation associated
with the transmit mode.
A second area of drift is due to the BFO crystals which are not oven
devices. Theses drift areas are usually very small and often not detected.
Most noted in PSK-31 operation or other very narrow band modes.
Filters in the N-1 and N-2 positions are located in the 9 MHz IF chain.
This is prior to the AGC system and these filters provide protection from
adjacent strong signals causing a pumping of the AGC system. The other 3
filter positions, 1.8KHz, 500 Hz, & 250 Hz, are the filters in the 6.3 MHz
IF. The PBT system affectivity is more noticed by the insertion of these
filters.
From my experience, installing 1.8 MHz and 500 Hz filters in the N-1 and N-2
positions and then the normal filters in the other three positions, 1.8 KHz,
500 Hz, 250 Hz, make for an ideal SSB and CW operating configuration.
73
Bob, K4TAX
----- Original Message -----
From: "John Cox" <jecox@tri-lakes.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Wednesday, November 07, 2007 7:48 AM
Subject: Re: [TenTec] Omni-VI plus question
John
What are the symptoms of a bad oven. I have an Omni VI with option 1 and
a
VI+. I am going to sell one of them. Yhe VI+ had low power when I
bought
it and went back last year to ten-tec to have one or more pin diodes
replaced. They did a operational check when the repair was completed so
its
oven should be ok. The VI has no frequency drift that I can detect. They
both operate exactly the same except for the extra filter in the VI+.
Maybe someone here on the list can explain the advantage of the extra
filter? I currently have 1.8 kc filter in N1 and a 500 cycle filter in N2
I just came back to the hobby last year after being away since 1955. I
find
that on CW with the passband tuning and the 500 cycle filter selected that
I
can get rid of almost all adjacent signals.
John Cox KC0YAI (prior K6HSG)
Bona, Missouri
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