[hpsdr] ANAN 10 28Mhz tx spectrum and generated birdie

[Helmut]

Hi,

I agree with John. Something seems not perfect in the test equipment. Even
PIM can cause that products.
Moreover I can't confirm the predication that the harmonic suppression of
Hermes would be bad and a LPF between the Exciter and the XVTR is
recommended. Don't forget that a bad matched XVTR produces a lot of
harmonics of the IF and LO frequency itself.
I measured with my HP analyzer several HPSDR boards (2 manufactured by
Apache Labs) at 28 MHz and max. power output (OPA 2674 tends to compress!)

Typical harmonic suppression:

f1 = + 27 dBm ; 2f1 = - 23 dBm ; 3f1 = -12 dBm 

SFDR of the TX path is better than 60 dB.

73, Helmut, DC6NY

 

-----Ursprüngliche Nachricht-----
Von: Hpsdr [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von John
Ackermann N8UR
Gesendet: Freitag, 5. August 2016 21:25
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] ANAN 10 28Mhz tx spectrum and generated birdie

***** High Performance Software Defined Radio Discussion List *****

Are you sure that you're not overloading the spectrum analyzer input and 
generating distortion in the front end?  One way to tell is to increase 
the input attenuation -- if you add 10dB and the spurs drop by more than 
10dB, that's a sign of front end overload.

I always try to keep input levels below 0dBm to minimize this problem 
(of course, the overload level is different for every analyzer model).

73,
John
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dr-openhpsdr.org/