AIM_840 Program Update - new TDR

[Bob]

This version features the new TDR function !

w5big.com/prog_update.htm

-- 73/Bob

[mac]

Dear Bob: Thank you! To have a TDR function is truly frosting on the cake. It is to late to try to use the new v. tonight, but it will be given a good go in the morning.
I have several 400 to 500 foot runs of coax and wire in need of evaluating. They get chewed on by something.
Thanks to all who crafted this major improvement.
73, Mac N8TT

[n9fyx]

I can't seem to run any of the 800 series of updates. The program hangs after it says com port 5 and has to be killed. Is there a way to pre-configure it to use a different com port?
I have a 4170 bnc type with XP.

Steve

[Bob]

Yes, you can use any comm port from 5 on up. Use the Windows Device Manager to set an appropriate comm port and then start the AIM program. Use the Setup->Set comm port dialog to enter the same value you entered with Device Manager. Then close the AIM program and restart it. You don't (usually) have to reboot the computer. Occassionally I've had to reboot.
Another thing that might help get the new version going is to delete the *.ini file that came with the zip package. Then when the program starts, it will say it didn't find the ini file. Manually load the cal file and config file using the File menu and set the comm port value. Close the program and restart it.

The program works with Win2K, XP, Vista and Win7.
I don't have a computer with Win 98 to test it now, but it used to work with Win98.

-73/Bob

[n9fyx]

Thanks Bob. I'm using comm port 1. It worked when I deleted the .ini file.

Steve

[mac]

It took a lot longer than expected to try v840 and TDR.
I get Error 278. One can guess that the custom calibration file needs to extend over the whole frequency range. (The one I use most of the time with antennas goes from 0.5 MHz to 65 MHz.)
I am in the process of having the 4170C calculate/craft a new calibration file from the lowest frequency (5 kHz) to 169.005 MHz in 25 kHz steps.
A full procedure for using TDR might include words about what the calibration file must cover.
I am keen on receiving advice. 73 Mac N8TT

[mac]

The use of a full span calibration got rid of the error message.
Changing from regular resolution to high resolution results in an unexpected very big change in results.
Results seem also to change with a change in "distance."
What is the frequency set used as input to transform? How does it change with settings? What I am seeing may be due to too few data points. How might one trade time to perform a scan (more frequency points) for reduced variability?
Shifting to and from time and frequency domain is a fundamental idea and well used here. 73, Mac N8TT

[Bob]

The TDR function needs to be run with Standard Cal.
Version 840 doesn't check this.

I have uploaded a new zip with version 840A which gives an alert message about the calibration. It also fixes some of the file naming issues that popped up in the TDR mode. Let me know if you notice any inconsistencies in file names when changing modes.
www.w5big.com/AIM_840A.zip

The difference between the low resolution and high resolution modes is illustrated by this screen shot:
www.w5big.com/CompareHiRes&LowResTDR.gif

--73/Bob

[mac]

Dear Bob: I would not have guessed that I needed to use an alternative calibration. I will need to re-read the manual to learn the difference.
The graphic you suggested showed slight (expected) differences. What I saw was large (random appearing factors of like two).

I will assume that 840A only differs by containing a warning and some file housecleaning.

Thanks for the help. . . . off to figure out how to perform a "Standard Cal." 73, Mac N8TT
P.S. Some questions remain.

[mac]

In re "calibration"
This is what I understand about the two schemes for calibration:
1. Standard Calibration: This appears to be intended for the calibration of the port on the instrument (or a short distance from the port as with an UHF to BNC adapter). The scheme is said to use one MHz steps, which would only allow accurate interpolation at (or very near to) the instrument's port.
2. Custom Calibration: This appears to be the more common scheme that is intended to allow the apparent port to be some distance from the instrument's port. Small frequency steps are possible and needed when the distances are significant.

Since Standard Calibration must be used with the TDR function, it follows that the display starts at the instrument's port.

Please correct my errors. 73, Mac N8TT

[Bob]

Hi Mac,
You are correct about Standard Cal. In the TDR mode, the data display starts where the standard cal loads were attached.

73/Bob

[mac]

Re: TDR and 840
I get reasonable results only for the near lengths of coax and shorter settings. For settings beyond 200 feet, the results can not be believed. I have runs of Heliax that are longer than 200 feet.
An additional issue is that changing the settings even for the shorter lengths results in noticeable changes in the Z.
It seems as if results depend in part on the display length.

It is possible that some of what I observe is due to too few Z samples. Might that be adjustable? How many samples are taken?

Again, transforming Z samples to the time domain is a great idea. 73, Mac N8TT

[Bob]

Hi Mac,

Please send me a screen shot of the tdr trace for your 200 foot cable.
Also a screen shot of the regular impedance scan from 0.1 to 5 MHz with steps of about 0.025.

How much does the cable impedance vary when you change scales when measuring a relatively short cable?

73/Bob

[mac]

Dear Bob: I think that I have files of the data requested. I will look for an E-mail address. 73, Mac N8TT 6:22 P.M. EDST

[g3txq]

Bob,

TDR is a great new feature - thank you! But I seem to be getting some strange impedance values reported:

If I take 3 coils of 50 Ohms coax - 20ft to 30ft each - and connect them in series like this: AIM/CoilA/CoilB/CoilC/Open-circuit, the impedances reported for the three sections are 50/57/54 Ohms. Now if I swap a couple of coils: AIM/CoilA/CoilC/CoilB/Open-circuit, I still get 50/57/54 for the impedances.

Also, when I measure my hexbeam, which is fed with a continous 150ft length of RG213, I see an impedance which starts at 50 Ohms and steadily falls to 30 Ohms before the antenna feedpoint discontinuity.

73,
Steve G3TXQ