EMRFD Message Archive 9647

Message Date From Subject
9647 2014-01-09 16:30:35 boblarkin02 TRansmission lines in Radio Designer
Pardon me for being slightly off topic.  But, i bet somebody here can help me!

ARRL Radio Designer program is an offshoot of Compact, and is in the process of disappearing.  However, I still use it some as a linear circuit analyser.  I ran into a problem that needs a solution.

In its simplest form, you have a single element circuit consisting of a transmission line connected between a node and ground on one end, and shorted on the other, like
  CAB 1 3 0 3  Z=70.0 P=0.25m K=1.0
This one is 0.25 meters in length and should be open Z at 299.8 MHz, shorted at 599.6 and so forth with odd and even multiples.  If I check this out carefully by looking at the phase of S11 (PS!!) I find that the open is at 266 MHz, the short at 599.6MHz (that looks good), the next open at 889 MHz (not right, but not 3 x 266 either), and so forth.

You can get the same behavior with the TRL model as well.

Am I missing something?  Has anybody else seen this?  Is there a work around? 

Many thanks,
Bob  W7PUA
9648 2014-01-10 09:40:23 boblarkin02 Re: TRansmission lines in Radio Designer

I thought I had replied last night, but it apparently got lost in the Yahoo jungle. Or, I pushed the wrong button.  In any event...

I found out by experimenting with Radio Designer that the 4-terminal TRL model seems to be a 3-terminal model, and two of those need to be grounded.  This can be used for any place a 4-terminal model is needed by placing a 1:1 perfect TRF transformer on either or both ends.  It isn't pretty, but it seems to get the job done.

For instance, I am modelling comb line filters, and this needs a coupling transmission line that is not grounded anywhere, and has the "far" end shorted.

  TRL 5 0 0 0 Z=100 P=0.5 K=1

  TRF 1 5 2 0 N=1

will produce such a floating transmission line between 1 and 2, even though three of the terminals of the transmission line are grounded (zeros).


73, Bob  W7PUA