At Diamond X-50N #2 at VK2OMD I reported some details of a new antenna at VK2OMD, including some baseline measurements using a Rigexpert AA-600.
This article expands that information with some measurements made using AIMuhf, and gives some contrasts between the two tools.
The AA-600 measurements were made 26/11/2014, and AIMuhf a couple of months later on 29/01/2015. The system measured should have been identical, the feed line is 9.83m of LDF4-50A with N-type connectors at both ends.
2m band
Above is the VSWR curve referred to the antenna feed point using Antscope’s subtract feed line feature.
Above, the details of the line subtraction.
Above is the R, X, |Z| curves referred to the antenna feed point using Antscope’s subtract feed line feature.
Above is a screenshot from AIM865 showing R, X, VSWR and Return Loss (albeit upside down). The AIMuhf was calibrated at the connector, so the reference plane for these displays is the input to the coax rather than the feed point.
Worth noting that at this point (input to the feed line), the frequency of minimum VSWR is not that where X passes through zero (resonance to some), though if you look at the Antscope chart, X crosses through zero at approximately the frequency of minimum VSWR and demonstrates that the antenna itself is resonant at the frequency of minimum VSWR.
70cm band
Above is the VSWR curve referred to the antenna feed point using Antscope’s subtract feed line feature.
Above is the R, X, |Z| curves referred to the antenna feed point using Antscope’s subtract feed line feature.
Above is a screenshot from AIM865 showing R, X, VSWR and Return Loss (albeit upside down). The AIMuhf was calibrated at the connector, so the reference plane for these displays is the input to the coax rather than the feed point.
Comments
A back level version of AIM was used because of a host of defects in the current version (AIMuhf – my strategy).
Both tools produced broadly consistent results, though the AIM displays are at the feed line input as it does not have a working facility to adjust out the feed line.
Both tools have the facility to be calibrated so that the reference plane is at the antenna end of the feed line, but the AA-600 with standard calibration and Antscope’s cable subtract facility is very convenient and sufficiently accurate for the purpose at hand.
Update 25/03/2015
Further work testing various versions of AIM software and the AIMuhf have cast serious doubt on the credibility of the AIM measurement system At his point I would disregard the measurements that were made with the AIM system. The Rigexpert measurement are unaffected.