[App_rpt-users] Hamtronics receiver issue with AllStar RTCM

Skyler F electricity440 at gmail.com
Wed Mar 30 12:01:58 EDT 2016

I don't have the test equipment to go through all of the dirty Local
Oscilator, SINAD, etc., so I will have to wait on that a few weeks before
the president of the club gets back in town.

WHEN I bypassed the capacitor and resistor ( 1k and .03µ) , the RTCM was
able to calibrate squelch. The LED flashed several times and then was
steady. Maybe the capacitor is the wrong value. There was no code on it,
but based on the resistor code, the value was correct.


On Mon, Mar 28, 2016 at 4:08 PM, Joe Leikhim <rhyolite at leikhim.com> wrote:

> If you are using an external reference, you cannot make up for the 2nd LO
> error if it is wildly off. There is an easy SINAD related test in EIA-603
> that is called Offset Acceptance Bandwidth that would indicate if the IF
> were off center. Things that could go wrong apart from simple misalignment
> of the Quad Detector coil could include the LO crystal being way off
> frequency, the IF filters being wrong BW or off spec pass frequency.
> Given the symptoms, I am putting my money on a misadjusted quad coil.
> Joe
> On 3/28/2016 5:06 PM, Bryan Fields wrote:
>> On 3/28/16 2:51 PM, Joe Leikhim wrote:
>>> 1) Make sure the receiver First Local Oscillator is adjusted correctly
>>> on frequency. (Fo -10.700 MHz) Likewise the second LO should be at
>>> around 10.2450 MHz. The second LO is not adjustable, so any minor error
>>> would have to be made up with the TCXO U3. After this second step:
>>> Then :
>>> 2) Make sure the general alignment is set properly, especially the
>>> discriminator coil T2 which responds to 10.7000 MHz from a signal
>>> generator, has an S curve response.  In my experience with these sort of
>>> Quadrature  Detector chips, you can get a false sense of IF centering
>>> where the noise component is suppressed. You might try adjusting for
>>> maximum noise first without the 10.7000 MHz signal. Be careful you don't
>>> jam the coil slug.
>> These are both very good points i didn't consider.  I normally don't
>> check my
>> reference oscillators in the hamtronics as they are using an external
>> 10MHz
>> source.
>> You will want to check SINAD on it as well, if it's not making spec (and
>> those
>> hamtronics are very sensitive), something else is wrong with it.
> --
> Joe Leikhim
> Leikhim and Associates
> Communications Consultants
> Oviedo, Florida
> JLeikhim at Leikhim.com
> 407-982-0446
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Skyler Fennell
electricity440 at gmail.com
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