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LP-100 Screen Captures

Antenna Plots...

Here are some full size screen grabs from the LP-100 Plot program, versions 0.96 & 0.97 showing several of the screens displaying a sweep of an OCF dipole on 10m.










Non Antenna Loads...

Below are plots of a reactive load I use for LP-100 calibration. The load consists of a 50 ohm dummy load fed through a 6' length of RG-59U 75 ohm cable. This creates a complex but repeatable load. The LP-100 plot is a JPEG output from the program. The green plot is from my HP VNA, and represents the "correct" curve. The LP-100 values are very close to the VNA in this example. The little bumps in the LP-100 curve are caused by the fact that gain/phase correction is done band-by-band, and the bumps are at the band correction boundaries. I could interpolate between bands to eliminate this, and I may do this in the future. The LP-100 error compared to my VNA is generally within 1 ohm / 1 degree except above 25 MHz, where the phase error is ~2 degrees.
Transmission Mode Plots...

Below are some reduced size plots of a pi net low-pass filter, showing a reflection measurement of impedance and transmission measurement of power response, using the newly added power option of the Plot program. This test was done just to see how it would look. A practical application of this could be plotting bandpass filters for multi-multi contest stations. As above, the green plots are from my HP 87510A VNA. On the first pair, the HP plot starts at 1kHz, so that's why the curve looks expanded on the low end. Correlation between the two is within 2% for magnitude, and 2 degrees for phase in this case.



     

Correlation on the power response is within about 2 dB, but is affected by the SWR power reduction in the rig (TS-480S in this case). To minimize this I used a precision attenuator on the output of the rig, and the direct inputs of the LP-100 for more sensitivity. This is a really nice feature of the LP-100 Plot program combo. Antenna analyzers, being 1-port devices, only allow reflection measurements. This includes every antenna analyzer I know of, handheld or PC based. VNAs on the other hand, do allow this type of measurement. For many of the things you would measure with a VNA, the LP-100 / Plot program may be adequate. The main disadvantages vs. a HP or N2PK would be resolution, dynamic range and power accuracy, which is dependent on the rig being used as a source. Those devices are capable of producing results within 0.001 to 0.01 dB, and have dyamic range of 100 dB. The LP-100 has very good power accuracy, of course, but is limited to 50 dB dynamic range.

The accuracy of the LP-100 / Plot combo for transmission measurements is largely controlled by the transmitter. In my case, the TS-480S I use for measurements has an error of about 1 dB from 2-30 MHz, but it's proportional and easy to account for. In fact, a correction could be added in the Plot program to compensate for the transmitter response. For all practical purposes, this would not make much difference in its usability in this mode, which is mainly one of seeing response curve shape, mismatch problems with filters, etc.

         

Below are transmission measurements of a Coilcraft P3LP-156 low pass filter, including the published curve for this filter. The LP-100 does nicely here as well. Again, the only anomaly is the 1 dB power drop of the TS-480S from 2-30 MHz.


   


Here transmission plots of a coax stub tuned to 7 MHz...

 

...and here are plots of a 11.1125 MHz xtal. No attempt was made to resonate the xtal. I did add series resistors to approximate a match, however. These plots show the excellent correlation between my LP-100 and my HP VNA.

 

And here are plots of a KVG XF9B crystal filter. I matched the 500 ohm input and output Z for this test, but I did not add the required 30pF shunt caps to minimize the ripple. Since the LP-100 only has about 50 dB dynamic range, I made two passes at different levels and stitched the results together in Photoshop. The far left picture is the original LP-100 sweep, the righthand picture is the stitched sweeps, and the bottom picture is a sweep with my HP87510A VNA. The LP-100 sweep width is 6 kHz, and step size is 0.1 kHz.