Re: {Collins} 30L-1 Input SWR High on 21/28 bands



Thanks Mike but, yes, even RG-58 (of which there are a lot of different types) would be typically 2 db loss at 30 mHz for 100 feet which would make the typical 20 foot length less than 0.5 db, or even two passes up and back of less than 1 db..  This is not going to help much with any stability problem.

 

I think we can most assuredly say, that based upon Warren Bruene’s article, discussions with Gene, Don Jackson’s analysis and common sense looking at the specified length of 20.5 feet, that the driving factor in the recommendation was not loss - but phase related.

 

One of the things we learn for sure is that you have to be careful what you read, where it comes from, and who you believe. This is a growing problem particularly now with the internet, unfiltered info, and the availability of blogs and self-publishing.  One has to be careful and get multiple inputs and then test the info carefully.

 

The CCA tries very hard to use known professional experts and do very careful research and analysis when issues like this come up. Our articles are professionally reviewed technically and factually in an attempt to publish only what we feel is factual info – like any good technical journal. We walk a difficult line where we solicit open opinions on subjects on our reflector and also try and assure that our users get good information and the real solutions get archived. Everything lives forever now and, while we try hard to not come right out and say someone is wrong, we also have a responsibility to leave the real solution somewhere visible in the trail without offending others. Even my email was reviewed.

 

Bill

 

From: Mike Waters [mailto:mikewate@xxxxxxxxx] 
Sent: Friday, May 29, 2015 4:45 PM
To: Bill Carns
Cc: collins@xxxxxxxxxxxxx
Subject: Re: {Collins} 30L-1 Input SWR High on 21/28 bands

 

I don't have time to read all this now, but so far, so good, and I've learned a few things. Thanks.

However, I did notice that you refer to RG-8; but Collins specified RG-58C/U with more loss. Just food for thought. I didn't calculate anything.

73, Mike

www.w0btu.com <http://www.w0btu.com> 

 

On Fri, May 29, 2015 at 4:24 PM, Bill Carns <wcarns@xxxxxxxxxxxxx <mailto:wcarns@xxxxxxxxxxxxx> > wrote:

 [snip] 

Re the loss of the longer cable helping with stability.  Hmmm..  The loss of a typical 9913 type (RG-8U) cable is less than one db total PER 100 FEET at 30 MHZ.  The amount of loss injected into the stability picture at the input by using a 20.5 foot cable instead of the typical 4 to 6 feet of cable is mice nuts – much less than one db.  I suspect strongly if loss was the motivation for the recommendation to use the longer cable, the length would not have been set at 20.5 feet. 

 

In fact, Warren Bruene wrote an article about the use of the 20.5 foot cable in the 30S-1. ... Gene Senti was the designer of that amp. This amp “inherited” the 30S-1 20.5 foot cable recommendation as far as we can tell. ... While there is a theoretical basis for using the 20.5 foot cable and Don did confirm the theory, he also concluded, as did Art, that it was unnecessary and lost in the “noise”.

[snip]




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