[App_rpt-users] Hamtronics receiver issue with AllStar RTCM

Joe Leikhim rhyolite at leikhim.com
Wed Mar 30 12:08:17 EDT 2016


Were these receivers factory built and tuned or did individual club 
members build them? Either way, you might try others from the lot. If 
you have only a rudimentary signal generator and / or frequency counter, 
perhaps I can walk you through some "field expedient" steps over the phone.

On 3/30/2016 12:01 PM, Skyler F wrote:
> 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.
>
> 73
> Skyler
>
> On Mon, Mar 28, 2016 at 4:08 PM, Joe Leikhim <rhyolite at leikhim.com 
> <mailto: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 <tel:407-982-0446>
>
>     WWW.LEIKHIM.COM <http://WWW.LEIKHIM.COM>
>
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>
>
> -- 
> Skyler Fennell
> amsatnet.info <http://amsatnet.info>
> KDØWHB
> electricity440 at gmail.com <mailto:electricity440 at gmail.com>

-- 
Joe Leikhim


Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com

407-982-0446

WWW.LEIKHIM.COM

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