[Elecraft] KX3 Computer Interface for digital modes

[k3ndm at comcast.net]

Jim, 
Yeah, I knew that there was a problem with many of the amplifiers. I just don't know how pervasive the problem is. I know Tentec and a few others have a way to deal with the problem. And, I just haven't needed to deal with the issue since I was playing with 10KW amplifiers when I was working for TMC down in Virginia more than 40 years ago. I knew there was a reason I didn't want to go high power. ;-) 

I totally forgot about the preamp switching problem. That too is something that I haven't needed to deal with in a lot of years. Way back when, most of us used preamps just ahead of our downconverters. There were a few smarter hams around who figured out the the transmission line from the antenna to the preamp was adding dramatically to the noise figure. It was they who started to mast mount their preamps; it was the same crowd that used the noise figure equation and were smart enough to know that line loss = negative gain. It's terrible to get old and forget those early lessons. 

73, 
Barry 
K3NDM 


----- Original Message -----
From: "Jim Brown" <jim at audiosystemsgroup.com> 
To: elecraft at mailman.qth.net 
Sent: Sunday, July 29, 2012 3:56:28 AM 
Subject: Re: [Elecraft] KX3 Computer Interface for digital modes 

On 7/28/2012 9:36 AM, Barry LaZar wrote: 
> The real issue is amplifier turn on timing. 

And the switching of relays for mast-mounted preamps used in serious 
VHF/UHF stations. 

> As I don't use an 
> amplifier as QRO to me is a 100 Watts. I can't address the issue from 
> experience. However, I suspect that there is an easy fix since all high 
> power users face the same issue, particularly on CW. 

But it is NOT an issue for ALL those who use power amps, it is an issue 
for those who use badly engineered power amps with slow relays! It is 
NOT an issue for my me with my good quality Ten Tec amps, designed c.a. 
1980, which use good vacuum relays, nor with my Elecraft amp, nor, I 
suspect, is it an issue with most Alpha and ACOM products. 

The problem is with CHEAP amps -- ever look inside an Ameritron? -- and 
with home builders playing it CHEAP. Example: I recently posted asking 
about build quality of relay switching systems for antennas, and more 
than half of the replys included phrases like "you can use so and so's 
much CHEAPER relays" and "so and so's system is much cheaper." Mom and 
Dad were both accountants, but they also taught me the difference 
between quality and junk, and when it was worth spending ENOUGH to do it 
rignt. 

Now, the nature of some relays is such that fast switching is not 
consistent with good RF performance, and I suspect that the high quality 
coax relays that Lance and others are talking about to switch preamps 
and to switch 2M and higher power amps are inherently not that fast. 
But for conventional ham power amps at HF, decent relays ARE fast enough 
to switch with the delay times provided by rigs like the K3 and 
FT1000-series. 

73, Jim K9YC 


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