This correlation activity was provided by Harold Johnson, W4ZCB, using his N2PK VNA and Boonton
250-A RX Meter. The Boonton 250-A is fitted with the 515-A coax "N" connector adapter kit.
A variety of common Devices Under Test (DUTs), mounted on "N" connectors, were tested at the same frequencies using both instruments. The VNA was calibrated using three male "N" connector calibration standards and the Rs and Xs values, stored in the VNA data file, were used in the table below. For the Boonton 250, the Rp and Cp values were read from its dials, as accurately as possible. The Rp, Cp, and frequency values were then supplied to a Quattro spreadsheet that converted them to Rs and Xs.
While there are generally offsets due the inclusion of the connectors in the DUT measurements only on the Boonton 250, no attempt was made to make any corrections to the measured data.
|Rs, ohms||Xs, ohms|
|DUT||Freq MHz||N2PK VNA||Boonton 250||Delta||N2PK VNA||Boonton 250||Delta|
|10 ft RG-213, 25 ohms @ far end||14.06||92.43||92.34||0.09||10.49||10.51||-0.02|
|10 pF silver Mica 0.125 leads||4.98||10.00||9.63||0.37||-3153.00||-2956.00||-197.00|
|5 turns #12 on T150-6 core||27.78||0.54||0.61||-0.07||94.50||99.00||-4.50|
|510 ohm, 1%, 1206, on "N" male||10.01||514.10||502.02||12.08||23.97||22.23||1.74|
|49.9 ohm 1206, soldered on "N" male||10.00||49.98||49.99||-0.01||0.09||0.72||-0.63|
|50 ohm male "N" VNA Cal std||10.00||50.00||0.63|
|Two 49.9 ohm 1206's on "N" male||1.00||25.02||25.05||-0.03||0.00||-0.09||0.09|
|Three 49.9 ohm 1206's on "N" Male||1.00||16.67||16.80||-0.13||-0.00||-0.08||0.08|
Generally the correlation in the Rs and Xs data between the two instruments is good. Harold notes "... any differences are probably due to my inability to interpolate the Boonton analog dials to 5 decimal places."
Some differences are also likely due to the inclusion of the "N" connectors, on which the DUTs are mounted, only for the Boonton and not the VNA data.
For example, the Xs=0.72 ohms for the '49.9 ohm 1206, soldered on "N" male' differs from its VNA measurement by 0.63 ohms. The following measurement of the '50 ohm male "N" VNA Cal std' on the Boonton 250 with Xs=0.63 ohms at the same frequency nicely accounts for the above discrepancy.
The difference in measured Xs for the '10 pF silver Mica 0.125 leads' is also likely due mostly to the "N" connnector on this DUT in the Boonton data. The equivalent capacitances for the VNA and the Boonton are 10.1 pF and 10.8 pF respectively. Most of the 0.7 pF higher capacitance on the Boonton is likely due to "N" connector.
Please feel free to contact me with any comments or questions at:
Paul Kiciak, N2PK