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I've just knocked together a 50 Ohm Dummy Load with 3 x 150 Ohm resistors in parallel as per my pic, it measures 49.8 Ohm so pretty much smack on tolerance. The patch lead that I used is about 12" long (30 cms), but when I key up the mic the SWR reads at about 1:7, does anyone have any suggestion where I can go from here to get it down please? Also tried and alternative patch lead to rule out that
Thanks in advance..
Dave
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Last edited by Dave C on 22 May 2020, 14:07, edited 1 time in total.
Life is like a box of chocolates.... Usually empty when I get there....
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as above, are they inductive wirewound resistors?, or is the patch lead 75ohm coax.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
The video is using dale none inductive resistors, they have two windings in opposite directions to cancel inductance, it sorta works at low frequencies,
your welwyns are single winding inductive resistors, neither type are suitable for rf dummyload at higher frequencies,
you may be able to cancell most of it out with a parallel capacitor but that aint a rf dummyload anymore, its a very lossy tuned circuit,
good loads have flat vswr over a very wide bandwidth, anything else can screw with your rf power measurements if the transmitter/amplifier is not as clean as a whistle on harmonics,
easy option that will work good enough is one of the flat pack DC-daylight resistors ch25 posted link to & stick it in an old cb amplifier heatsink,
don't use skinny wires, use flat wide strap or braid or copper clad board for wiring.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
