[Elecraft] K3 RS323 and Data Modes {was YAQ - Yet Another (K3)Question}

[Bill Coleman]

On Jul 9, 2007, at 4:44 PM, Brian Lloyd wrote:
>
> Well, you have just described the product offerings from Flex Radio.

Not exactly what I had in mind -- there's way too much hardware  
involved.

> My concern over the Flex Radio SDR approach compared to Elecraft's  
> approach in the K3 is that, in order to be able to receive multiple  
> signals simultaneously, e.g. like we do in demodulating PK31, you  
> have to accept all the noise and cruft in the wider passband. If  
> there is a strong signal in there you have to pass it through to  
> the A:D and hope that the A:D has sufficient dynamic range to deal  
> with the difference between the desired signal and the undesired  
> signal.

No. You don't "hope" the A/D has enough dynamic range. You have to  
design in that kind of dynamic range. Which means you've got to use  
an A/D converter which has lots of bits -- very expensive today.

> Elecraft gets rid of the undesired signal by using tight roofing  
> filters.

Yup, that's one approach. It also is very cost-effective for a single- 
signal type receiver.

>> It's still possible to get good IMD characteristics with an up- 
>> conversion general-coverage receiver. There are some $10,000  
>> radios on the market that do exactly this.
>
> But all of them upconvert to something like a 70MHz 1st IF. You  
> aren't going to find a 200Hz roofing filter there. That means you  
> aren't going to get the good close-in (1KHz spacing) IMD and BDR  
> performance. So to get general coverage receiver performance you  
> give up close-in BDR and IMD performance. Again TANSTAAFL.

Consider the Yaesu FT DX 9000. This design has a 40 MHz first IF that  
has roofing filters of 3, 6 and 15 kHz.

Similarly, the Icom IC-7800. This design has a first IF of 64.455 MHz  
and roofing filters of 3, 6 and 15 kHz.

Both of these designs have competitive IMD and BDR characteristics.  
It is possible to do this with wider roofing filters in an up- 
conversion design. However, it isn't as cost-effective as the  
Elecraft design. (I can buy several fully-loaded K3s for the price of  
one FT DX 9000 or IC-7800)

> I agree. Elecraft should be receiving the order from the ARRL for  
> our school's K2. I plan to let the kids (4th-8th grades) build the  
> rig under my guidance. I think that the K2 will perform a lot  
> better than the other rigs that they were offering us, e.g. Icom  
> IC-706, and I think that the kids will understand and appreciate  
> the radio better if they have a hand in building, testing, and  
> calibrating it.

I totally agree. When I was first licensed, one of my dreams was to  
design and build a state of the art homebrew transceiver. For a  
number of reasons, I never quite did that, but with the Elecraft  
K2/100, I've come close. (I didn't design it, but I certainly built it)


Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901