FPGA Central

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 o
image is the signal of interest which is located at 90Mhz. The signal wil
be preserved by applying a suitable band pass filter,

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

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

Question: what can I do to maximise/improve the power and SNR of th
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 wil
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