LarryF

Lectro SRc front end

19 posts in this topic

Hi Larry,
Sorry to bug you with a private message. I have a quick question about the SRc which you can probably answer in just a line or two if you don't mind. I am thinking of upgrading/cross-grading to them from a mix of 411's and SRb's. What I wanted to know is if the tracking front end works on channels 1 & 2 independently? If I have ch1 tuned to block 21 (for example) and channel 2 tuned to block 23, do they each benefit from their own set of filters? I had a read of the user manual from your site but it didn't mention anything about that.  
Thanks

Hi,
There are two independent front ends. The tracking is done after the RF is split to the two receivers. Specifically, you can run different blocks with no loss of sensitivity. I'm going to post your redacted question on Equipment since I have been asked this before. We should put this in our manual.
Best Regards,
Larry Fisher

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Hello Larry,

Was curious, what is the width of the que for the tracking front end on the SRC?  Also is there any limitation on the SRC as far as should RX1 be lower in freq vs RX2?

Thanks

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Hi Nick,
I'm not as close to things as I was when I was working at Lectro. I can speak very well to the thermal dynamics of rope hammocks in the mid-afternoon of a New Mexico summer. Bring along lots of cold water.

I will have one of the crew jump in here with real numbers. I believe the high-lo frequency thing was resolved in later SRb's and should be resolved in the SRc. I also think the bandwidth is 22 MHz but again I'm not sure.

Best Regards,
Larry Fisher

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Hi Nick,

Larry asked me to jump in here. The front end bandwidth varies slightly with the frequency in use; however 15 MHz would be an accurate number.

In regards to frequency selection: One channel doesn't have to be higher. It is just that there are certain relationships between the channels which are problematic. The firmware will alert if you happen to hit on one. The formula for failure on an SRB (and SRC) is 4.2 <= (ch2 - ch1) <= 4.8. Notice that any time ch1 is higher, this relationship becomes impossible, but there are many, many combinations with ch1 lower that work, too.

On the SRB and SRC, if channel 1 is set exactly 4.5MHz lower than channel 2 then both the 1st conversion oscillators are set to the same frequency and an audible beat frequency can be heard. On the SR and SRA if channel 1 is set exactly 4.5MHz higher than channel 2 then both 1st conversion oscillators are set to the same frequency.

If you set the receiver to the "bad" combination you will see the message "FREQ WARNING" on the display.

 

Best regards,

Dean Slotness

 

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Thanks Dean,

Just to clarify: Don't worry about setting frequencies higher or lower; the receiver will warn you of any rare problems.

Best Regards,
Larry Fisher

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So the 411 is still King but not by much (15 vs 11 MHz filter).

Side question... Are the tracking modules for the Venue2 currently the best receiver Lectro makes? Since they have the smart Q fanciness?

 

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Hi Derek,
The IMD3 performance of the SRc is overall a little better than the 411. It depends a little on where you are in the passband but on average, it is higher. IMHO they are now equal performers front end wise.

Also in the IMHO category, the Venue2 is the best. There is more raw power for the RF sections and the smart Q really works.

Best, LEF

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Good to know. I was half anticipating the smart Q technology to be integrated into the SRc but that's a pretty small box. More limited processor I understand. 

Sounds like the end of the 411a sized format for portable receivers. 

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Hello,

 Are there any official specifications on how the SRc and 411s reject stray RFI?

 Anecdotes describing how the early SR series was more susceptible than a 411 to RFI have me wondering if the SRc is as good as the 411 in this regard.   

Thank you.

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Did you read this thread? That's what they were discussing.

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Yes I did read this thread, and then I asked my question. Perhaps I should have worded the question more specifically.

Reading here and elsewhere I have learned that:

UCR411a have a tracking filter 11MHz wide while the SRc have a tracking filter 15Mhz wide.

I have also considered that UCR411a have a IP3 of +8dBm, SRc have a IP3 of +0dBm, and UCR210d have a IP3 of +12dBm.

I have read quite a bit about how the original SR(a) evolved into the SRb and appreciate how developments in the pcb layout and construction resulted in remarkable improvements.

I am fascinated with the new broad band SRc but also scared off by a few reports that some users have had them swamped by interference.

I am wondering if the SRc may be such a new design that it will evolve in a manner and timeline similar to the SR(a) to SRb transition.

I am grateful that Lectrosonics is clear about the comparisons between the 411a and the SR series.

My specific question is asking if there are any issues with RF interference that may occur after the tracking filter. I am asking if any interference picked on the internal circuit but not necessarily via the antennas can be compared between two appliance designs. I am asking how the SRc compares to the 411a (with its enormous metal case/shield) and if there is any way to quantify the difference. 

I realize that tacking this question on the end of a thread about the "front end" may have been a poor decision.

I have been avidly reading everything I can find about the SRc.

 

Thank you.

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I think it's tremendously difficult for anyone, except perhaps Lectrosonics themselves, to say where the RFI is hitting thr receiver. How can you tell if it affects the antenna or the electronics inside? Does it even make a difference?

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I agree that the question is best answered by Lectrosonics. I suppose they must have some way of making distinctions and employed some method when developing the improvements in the earlier SR products. 

Thank you.

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Yes perhaps, but why does it matter to you? What matters is overall rf performance, right? Why does it matter where rfi hits occur? If it were after the filter, the receiver would probably behave poorly, and you'd know that by now.

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Well, I have seen a few claims that users have had their SRc swamped with RF despite clear scans and normal precautions.

These observations have caused me to go back and forth on choosing 411s or SRc on an impending purchase.

Why does it matter to me where the issue is? It seems as if the front end is using state of the art tech, so I am wondering if there is potential for improvement that has been identified elsewhere or if Lectrosonics feels that the SRc is on par with 411 with regards to the circuit layout, shielding etc.

I suppose some people upgraded from SR(a) to SRb simply because the performance was better but other people probably appreciated knowing why the performance was better. I think Lectrosonics did a great job of providing explanations.

Thank you.

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I don't work for Lectrosonics, but I can offer my own anecdote. I switched from 411a's to the SRC and got one of the first batch of SRCa's. There was a substantial problem with the first batch and I heard that some were recalled from dealers. They replaced one of the board's. I have since sent in my SRCa for a much needed firmware update and it appears that there has been another change in the board since the board was replaced again. I'm guessing (hoping) that Lectrosonics has all of the bugs worked out now. The previous anecdotes you heard about rf problems may have been people such as myself who had early builds.

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Thank you for the information.

 

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