[Elecraft] K1 # 690 receiver: more good news

[Bill Coleman]

On 3/14/02 2:27 PM, Ron D' Eau Claire at rondec@easystreet.com wrote:

>The 1960's and 70's saw a virtual stampede toward the high-performance
>single-conversion designs with careful attention being paid to dynamic range
>and signal levels throughout the receiver. I have a hunch that Goodman's
>article helped start that revolution. "Less" was better and produced
>superior results with far less complexity.

I thought that most rigs in the 60's and 70's were typically dual 
conversion, with the first mixer stage controlled by an HFO (usually 
crystal controlled) to a wide IF (usually 200-500 kHz wide), and then an 
LMO to a narrow IF (where the crystal filter was), then a product 
detector to audio. This is the basis for the Collins, Heath, and Drake 
units, I'm pretty sure. (Although the Drake was probably triple 
conversion, getting the narrow filtering from a low frequency IF)

These radios were somewhat limited by the noise in each stage, although 
for bands like 160m, an old Drake with the Sherwood mods is probably 
unsurpassed to this day.

>But we keep drifting back into the idea that more is better. More gadgets
>become essential -- just like the electric can opener is essential to keep
>us from starving because no one remembers how easy it is to pick up the
>hand-operated one and turn the crank.

The key revolution here was the introduction of general-coverage receive. 
To accomplish this, most radios had to go to up-conversion to an IF of 
about 40-70 MHz. At the same time, banks of HFO crystals gave way to 
digital PLLs, and some of the early ones were quite noisy. Taming the 
phase noise of those early PLLs was (and continues to be) a challenge. 

Ten-Tec got around this problem with the OMNI V and VI by going back to 
the old ways -- a bank of HFO crystals. In it's day, the OMNI V had much 
better receiver performance than anything else on the market -- but it 
wasn't general-coverage!

The K2 is even simpler in some ways than those old designs of the 60's 
and 70's. It just has one conversion mixer, not two. And the narrow 
filtering right after conversion helps to eliminate possible IMD products 
-- which is missing on general-coverage receivers with wideband 
up-conversion.







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