[TenTec] Omni VI v FT102 receive

[Malcolm McLeman]

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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