[Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver

Fri Feb 16 16:39:39 EST 2007

You can't assume that just because it is direct sampling is has to be worse 
than a superhet. A current state of the art ($70) ADC like the Linear 
LTC2208 has 16 bits. It has a S/N ratio in a nyquist band of 78dB. This 
means that when sampling at 100 MHz and assuming a full scale level of 5 dBm 
after the transformers and matching, the noise floor is 
5dBm-78dB-10*log(50000000)=-150dBm. This is a 24dB NF. If you look at the 
plots on page 9 of the datasheet, you can see that with two signals at 
-7dBFS which is roughly -2dBm, the 3rd order products are about 93dB down. 
That is still an IP3 around 45dBm. The noise figure can be lowered to where 
it is more than ideal for HF and still keep an IP3 better than 35dBm at all 
frequency separations. Some modern radios get really good IP3 numbers by 
using such a narrow roofing filter that the IP3 numbers at wide spacings 
look incredible.

I think the direct sampling receivers are here to stay. Once the noise 
figure of the ADC is lowered to the point where the antenna can be connected 
directly to the ADC, they will offer NFs in the 10 dB range with IP3s 
approaching 45dBm at all frequency separations. The 10dB NF is roughly 
equivalent to an MDS of -137dBm in 500 Hz if I recall.

Pieter

DATASHEET:

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1155,C1001,C1150,P13693,D9659

>From: sig346 at netscape.net
>To: Premium-Rx at mailman.qth.net
>Subject: Re: [Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver
>Date: Fri, 16 Feb 2007 15:21:06 -0500
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>-----Original Message-----
>From: sig346 at netscape.net
>To: premium-rx at mailman.qth.net
>Sent: Thu, 15 Feb 2007 10:32 PM
>Subject: Re: [Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver
>
>
>
>
>
>-----Original Message-----
>From: sig346 at netscape.net
>To: farson at shaw.ca; Premium-Rx at mailman.qth.net
>Sent: Thu, 15 Feb 2007 10:01 PM
>Subject: Re: [Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver
>
>    The RS Datasheet reveals potentially weakness of all Direct Sampling HF 
>Receivers: their limited
>  dynamic range. To hide this RS tries stretching both German and English 
>languages . As a result,
>  a new wording has been invented: LOW DISTORTION MODE. In this mode, which 
>actually is nothing
>  more than an attenuator at the input, the receiver has IP3 of 30dBm, BUT 
>NOISE FIGURE OF 26dB!.
>
>  I will send email to Rhode und Schwarz suggesting one more mode: ULTRALOW 
>DISTORTION,
>  to obtain 50 dBm of IP3, but that would require 30dB attenuation, 
>bringing noise froor to
>  45 dB. It would be, nevertheless, sufficient to listening to Deutsche 
>Welle in the World Bavarian Capital of Munich.
>
>  Rockwell Collins describing their similar direct sampling receiver CX7800 
>simply "forgets" include some data
>  regarding dynamic range. That makes their life simpler: no need to hide 
>an army of technical linguists.....
>
>  On a serious note, I tried CX7800. It is a respectable receiver, but far 
>from being "Premium", not much
>  better than SDR14. So, you, gentlemen - owner of WJ, TCI, CUBIC, 
>Telefunken, etc - remain cool -
>your receivers are still "Premium" without stretching imagination.
>
>Regards,
>AW
>
>
>
>-----Original Message-----
>From: farson at shaw.ca
>To: Premium-Rx at mailman.qth.net
>Sent: Thu, 15 Feb 2007 2:31 AM
>Subject: [Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver
>
>  Rohde & Schwarz have announced their new EM510 direct-sampling HF
>
>
>intercept/surveillance receiver:
>
>
>
>
>
>http://tinyurl.com/2lan7h  (EM510 brochure in PDF format, in German)
>
>
>
>
>
>Cheers for now, 73,
>
>
>Adam VA7OJ/AB4OJ
>
>
>
>
>
>
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>
>
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>
>
>
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