[NLRS] [10GHzContest] SBMS Project challenge

[Dr. Gerald N. Johnson]

As for a horn antenna for the counter, ideally one would wish for a 
double ridged waveguide coax adapter and horn made for wide band RFI 
measurements. It could have useful and predictable gain from 10 to 25 
GHz or an even wider band. The bandwidth of ridged waveguide increases 
as the ridges get wider and closer together. The impedance goes down and 
the loss increases.

As a practical antenna, WR62 waveguide passes 10.368 with more loss than 
WR90 but not enormous loss. Kent Britain claims to have heard his first 
10 GHz EME signals through RG62. RG62 waveguide switches have been used 
at 24 GHz, without any hard work at matching, just butting WR42 flanges 
to WR62 flanges and maybe a tuning screw or two. That makes me believe 
that a WR62 horn, like from a 14 GHz satellite uplink would work 
adequately for the counter at both 10 and 24 GHz. Further I believe that 
its very likely a WR90 horn will work at 24 GHz though there is the 
possibility of the WR90 passing higher order modes above 18 GHz, I don't 
believe they are automatically created when the coax probe is in the 
middle of the guide, where the fields of the next higher order modes are 
zero. And in the horn spreading the guide doesn't cause higher order 
modes, it stretches what was the fundamental mode in the feed guide. In 
the next higher order mode, the left half of the guide is out of phase 
with the right half of the guide so when it radiates, the two cancel out 
front of the guide but add off to the sides. But a horn peaks out front 
showing the field at the aperture is in the same phase all the way 
across the aperture.

WR62 hardware is fairly easy to find on epay, and horns aren't hard to 
construct using W1GHZ plans and software for making patterns for bending.

24 GHz is also above the frequency for the first waveguide mode of type 
N connectors and RG-8 sized coax. Since the fields in that waveguide 
mode are at right angles to the coax fields, I'm not convinced there 
will be any coupling to that waveguide mode in good coax and coax 
connectors. A coaxial right angle might cause lots of coupling. The next 
higher frequency waveguide mode has the same fields as coax so that one 
definitely will be coupled, but its cutoff frequency is about half again 
higher than the lowest cutoff mode. I plan to do experiments someday to 
prove my contentions.

73, Jerry, K0CQ

On 11/12/2015 7:31 AM, NLRS Regional 10GHz Contest mavens wrote:
> Let me try again with the counter info.
> Mel