[App_rpt-users] Hamtronics receiver issue with AllStar RTCM
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.
> 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.
> 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
> 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
> 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>
> electricity440 at gmail.com <mailto:electricity440 at gmail.com>
Leikhim and Associates
JLeikhim at Leikhim.com
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