In my SX-115, putting the selectivity switch to the widest position (5KHz):

- I see a two S-units drop in the S-meter reading
- selectivity is actually narrower than in the 3 kHz position.

I wonder whether SX-115 owners have same or similar experience.

Looking at the schematic diagram, there are five switch wafers that determine
selectivity, two of which switch capacitors and three switch resistors. I have
determined that the switch works fine, so I am wondering whether the problem
could be due to a mistuning of the 50 kHz IF coils.

Thanks for any advice.

73

Tony I0JX
Rome, Italy

On 3/25/2010 4:10 PM, Antonio Vernucci wrote:
In my SX-115, putting the selectivity switch to the widest position (5KHz):
- I see a two S-units drop in the S-meter reading
- selectivity is actually narrower than in the 3 kHz position.

I wonder whether SX-115 owners have same or similar experience.
snip

Hi, Tony

I also realigned my SX-115. Results were excellent on cw and SSB
bandwidths, but the a.m. wide response was disappointing.
There was some very noticeable sensitivity loss in a.m. wide,
but I don't remember it being so much (maybe 1 S/unit).
My receiver is in storage, so I can't check easily.
I thought my problem was the T-notch filter still being
within the a.m. bandwidth. There is no on/off switch for the T-notch,
you just shift it away from where you are listening when not in use.

73,
Ed Knobloch

Hi, Tony

I also realigned my SX-115. Results were excellent on cw and SSB
bandwidths, but the a.m. wide response was disappointing.
There was some very noticeable sensitivity loss in a.m. wide,
but I don't remember it being so much (maybe 1 S/unit).
My receiver is in storage, so I can't check easily.
I thought my problem was the T-notch filter still being
within the a.m. bandwidth. There is no on/off switch for the T-notch,
you just shift it away from where you are listening when not in use.

73,
Ed Knobloch

Ed,

yes, paying more attention I realized that, in the 5kHz position, bandwidth is
actually nearly twice the bandwidth in the 3 kHz position, but .... there is a
notch just in the middle, despite the notch knob is positioned at OFF (I know
that notch cannot be excluded, but just moved in frequency... ).

The consequence was that, at 5 kHz selectivity, I experienced the very strange
effect to hear the same AM station at two distinct frequencies, a few kHz apart
from each other.

But then, moving the notch knob, such "doubling" effect disappeared and I could
hear the AM station just at a single frequency, though with a much higher
bandwidth.

In conclusion, I had to put the notch knob at the other extreme with respect to
the OFF position, and the problem seems to no longer exist.

Thanks & 73

Tony I0JX

BTW: yes, the signal drop is closer to one S units than to two

On 3/25/2010 7:44 PM, Antonio Vernucci wrote:
snip
The consequence was that, at 5 kHz selectivity, I experienced the very
strange effect to hear the same AM station at two distinct frequencies,
a few kHz apart from each other.

But then, moving the notch knob, such "doubling" effect disappeared and
I could hear the AM station just at a single frequency, though with a
much higher bandwidth.
In conclusion, I had to put the notch knob at the other extreme with
respect to the OFF position, and the problem seems to no longer exist.


Ah, very good info, thanks, Tony.

I will try shifting the SX-115 notch to the other extreme
when in a.m.

73,
Ed Knobloch