[Lowfer] e-probe vs loop

[Bill Cromwell]

Hi Garry,

I wonder if you have accounted for a couple of variables that may be 
under your control. I believe that 'lobes' - directional characteristics 
- are a feature of loops. Do the e-probe antennas also have that 
'feature'? Even if they are not supposed to I doubt they are completely 
free of any directivity.

Two different receivers (SDRs) with two different computers could 
introduce some measurable and noticeable differences. Have you swapped 
the antennas between the two different receive systems to sort 
differences there?

The e-probe antennas I have seen have a physically smaller aperture so I 
would suspect they have have lower signal AND noise capture. Any 
associated amplifiers - even untuned amps - would discriminate against 
wideband noise. If they are essentially non directional then I would 
expect the loop of having a significant head start on performance.

I am currently working on a loop while putting the 'e-probe' on the back 
burner due to my suspicions. Your initial results are encouraging.

73,

Bill  KU8H


On 07/31/2013 09:04 AM, Garry Hess wrote:
> Spurred by Jim Davey, I've begun measuring simultaneous SNR 
> performance of my e-probe and 10' shielded loop for daytime, nearby 
> NDBs. There is a tremendous amount of experience out there so I'd like 
> to hear what others have to say about e-probe vs loop sensitivity.
>
> So far my procedure has been to tune in candidate NDB carriers with a 
> pair of SDR-IQ receivers, one for each antenna, feeding separate PCs 
> running SpectraVue and Spectrum Laboratory. The latter is programmed 
> to save text files of signal, noise, and signal/noise powers each 
> second. Data collection is ended after about 2 minutes (to match the 
> SNR window of WSPR). The text files are input into Open Office 
> spreadsheets for easy calculation of average and median values (the 
> latter is the preferred statistic because it is resistant to 
> outliers/errors).
>
> Based on 9 NDBs sampled thus far, the 10' loop has a median advantage 
> on the order of 5 to 6 dB. Variation is appreciable - the smallest 
> advantage is 2.6 dB, the largest is 11.5 dB. While the absolute 
> numbers change with time (as seen by measurements repeated a day 
> later), the SNR values are steadier.
>
> Future measurements (if they aren't reinventing the wheel) may examine 
> the impact of e-probe length and loop size. Both antennas seem to be 
> free of obvious, local man-made noise but it might be possible to 
> measure performance at different antenna locations too.
>