Digital Up Conversion - low signal power and SNR

Hi,

Signal in digital domain: Centre at 10Mhz, with bandwidth of 10Mhz.

The signal is sampled by a DAC at the rate of 80Mhz. 

Analog output: Fundamental at 10Mhz and many images following that, one of
image is the signal of interest which is located at 90Mhz. The signal will
be preserved by applying a suitable band pass filter,

Problem: the power level of the signal is many magnitude lower than the
fundamental.  The SNR of the signal is therefore much less than that of the
fundamental.

I tried to use amplifier to increase the power level but find that SNR is
further degraded due to intermods.

Question:  what can I do to maximise/improve the power and SNR of the
signal? 

Much appreciate your advice.

Cheers,
Ben

B.chay wrote:
> Hi,
> 
> Signal in digital domain: Centre at 10Mhz, with bandwidth of 10Mhz.
> 
> The signal is sampled by a DAC at the rate of 80Mhz. 
> 
> Analog output: Fundamental at 10Mhz and many images following that, one of
> image is the signal of interest which is located at 90Mhz. The signal will
> be preserved by applying a suitable band pass filter,
> 
> Problem: the power level of the signal is many magnitude lower than the
> fundamental.  The SNR of the signal is therefore much less than that of the
> fundamental.
> 
> I tried to use amplifier to increase the power level but find that SNR is
> further degraded due to intermods.
> 
> Question:  what can I do to maximise/improve the power and SNR of the
> signal? 

Upconvert the signal to 30Mhz in the digital domain, then extract the 
desired alias at 90MHz with the analog filter?

> Much appreciate your advice.

How much exactly is the appreciation?


> 
> Cheers,
> Ben
> 
> 
> 

Vladimir Vassilevsky wrote:

> 
> 
> B.chay wrote:
> 
>> Hi,
>>
>> Signal in digital domain: Centre at 10Mhz, with bandwidth of 10Mhz.
>>
>> The signal is sampled by a DAC at the rate of 80Mhz.
>> Analog output: Fundamental at 10Mhz and many images following that, 
>> one of
>> image is the signal of interest which is located at 90Mhz. The signal 
>> will
>> be preserved by applying a suitable band pass filter,
>>
>> Problem: the power level of the signal is many magnitude lower than the
>> fundamental.  The SNR of the signal is therefore much less than that 
>> of the
>> fundamental.
>>
>> I tried to use amplifier to increase the power level but find that SNR is
>> further degraded due to intermods.
>>
>> Question:  what can I do to maximise/improve the power and SNR of the
>> signal? 
> 
> 
> Upconvert the signal to 30Mhz in the digital domain, then extract the 
> desired alias at 90MHz with the analog filter?

Oops. I meant harmonic, not alias.

VLV

>Oops. I meant harmonic, not alias.
>
>VLV
>

Thank you Vladimir.

I seem the same method can not be used on the following setup, due to 1,
interpolate samples 3x will breaching Nyquist rule, 2, no harmonic will
generate at 90Mhz.  Any suggestion?

- Centered at 18Mhz, bandwidth: 20Mhz. (Fundamental at 8-28Mhz)
- 11 Carriers within the band, frequency modulated.
- Desire band/image of interest 88Mhz - 108Mhz (FM), Fcenter = 90Mhz.
- DAC sample Rate: 80Mhz

Cheers,
Ben