Phil, All dummy loads are not created equal. Connect yours directly (no coax) to the LP-100 or an antenna analyzer to determine its characteristics with frequency (I assume Larry calibrated your LP-100 to NIST standards). A common ham dummy load is something to tune your amplifier into and use for general purposes. If you are going to do measurements, you will need something more like lab quality dummy loads.
Both your dummy load and the 6 feet of RG8X will show a frequency dependency since you do not have a precision 50 ohm dummy load. A transmission line that is not terminated in its characteristic impedance acts like an impedance transformer, and that transformation ratio is frequency dependent. If you want a dummy load that is flat WRT frequency and suitable for instrumentation use, take a look at the Caddock 50 ohm Thick Film Resistors - they are available up to 100 watt rating. You must use them on a heat sink, and keep the leads as short as possible, and you will have a precision dummy load. Caution - even with the heat sink, do not exceed their power ratings, they will go open circuit in an instant. I use several of those as instrumentation precision loads. Other sources of precision dummy loads is Ridge Equipment - https://www.ridgeequipment.com/store/dummyloads.html. They have one rated at 75 watts for $12 and one rated at 15 watts for $7.50 - those are quite good for instrumentation purposes. 73, Don W3FPR On 12/22/2011 11:37 AM, Phil Hystad wrote: > Is this normal or can someone explain? I was looking at the R+iX values > reported by the LP100A with my K3 feeding a dummy load. The SWR reported was > always small but never super close to 1:1. Most of the SWR in this setup was > 1.1:1 up to 1.5:1. The R values ranged from 34 ohms to up to 59 ohms and X > was ranging over a number of smallish values< 20 for all the bands. > > Is this what most of you would call normal? > > Does the K3 output R+iX vary from band to band (I assume so) and is that what > I am seeing? > > I had thought my dummy load was mostly frequency independent so I am not sure > if I am seeing mostly the K3 here or maybe the K3 plus the 6 feet of coax > (RG8X) + dummy load. > > 73, phil, K7PEH > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
