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?
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