Thanks vm again Bob.. All good stuff which I've carried out in more
salubrious times when younger but practically speaking if there is a
deterioration in receive signal path/sensitivity it basically comes down
to either a board change..
I recently with assistance renewed the T/R diodes on the receive path in
the LPF board and thought it may be down to that but there is no
significant change in signal strength when bypassing the LPF board and
injecting a sig directly (fm antenna) into PL17 o/p .
As my technical ability is no vm impaired I was hoping someone may have
experience and repaired a similar problem to facilitate an easy
troubleshoot.
73
Malcolm/F5VBU
On 11/14/2019 8:07 PM, Bob McGraw K4TAX wrote:
In order to determine if there is an issue with the Omni VI one needs a
calibrated signal generator. In general, connect the generator to the
receiver input, set the RF Gain a max, and any ATTN at off. Slowly
increase the signal generator level until the signal is heard just
coming out of the noise. This determines the MDS or Minimum
Detectable Signal. This should be about the sensitivity but slightly
above the noise floor of the receiver. Typical level is 0.10 uV or -127
dBm. This is also equal to a S-0 signal. A level of 0.2 uV or -121
dBm is equal to a S-1 signal.
I have seen hams crank the RF Gain and audio gain to max and compare the
noise, then declaring one is "hot" or really sensitive. Nope, not the
case. Usually one is just noisier than the other.
Also the receiver actual bandwidth has an effect in as much as a
receiver with a wider bandwidth, and not filter width, will "hear" more
noise. Again, this has little to do with sensitivity. As to filters,
the bandwidth of a filter in a Tentec radio will have a different shape
factor than that of a Yaesu radio, even though both may be 2.4 kHz
filters. The 2.4 kHz points are determined by some value between two
points on the upper and lower slope of the filter. Thus a filter which
has a BW of 2.4 kHz at the 3 dB points is a wider filter than a filter
which has the 2.4 kHz value at the 6 dB points.
Good luck with your measurements.
73
Bob, K4TAX
On 11/14/2019 11:21 AM, Malcolm McLeman wrote:
Thanks your reply Bob..
I did say purely under operational circumstances and by that I mean
simply comparing the two receivers with the same receive signal..
I'll take your word for the technical spec figures and also that
there's a possibility my O-6 is performing under par.
But where?
On 11/14/2019 1:46 PM, Bob McGraw K4TAX wrote:
And how did you determine the difference in receiver sensitivity?
The specified sensitivity for the FT-102 is 0.25 uV preamp on, 1.0 uV
preamp off. The Omni VI sensitivity is 0.16 uV. I would say if you
find the FT-102 better than the Omni VI then there is something wrong
with the Omni VI. Also the noise floor for the FT-102 is stated as
-103 dBm and for the Omni VI as -133 dBm. The Omni VI is considerably
quieter than the FT-102.
73
Bob, K4TAX
On 11/14/2019 6:16 AM, Malcolm McLeman wrote:
Have just demothballed my FT102 and speaking purely operational am
astonished at the superiority of the FT102 over the O-6 on receiver
sensitivity.
Grateful for any comments.
Malcolm/F5VBU
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