Nooelec H1 Dipole Feed Dimensions

[Alex P]

FYI 

looks like its cut for ~ 1.6GHz

[Miguel Ríos Martín]

I've done several tests with different dipoles and feed arm lengths for the Nooelec parabolic antenna. Here are some conclusions I've reached (I have more if anyone is interested):
- With the original dipole (9.3 cm end to end and a 4.5 cm balun) and the original 46 cm feed arm (end to end), the hydrogen line is visible.

- I modified the dipole to 9.9 cm end to end and the balun to 5.3 cm. I also shortened the feed arm to 33.5 cm (end to end), and the results are much better. I've attached a photo.

I also don't know why Nooelec changes the length depending on the frequency the antenna will be used for. The geometric focus is the same in all cases!

I've also experimented with different versions of the RTL-SDR driver, but that's a whole other story!

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Miguel Ríos Martín

[b alex pettit jr]

Hello Miguel,

Do you have a plot of the Stock Antenna for comparison ?

Thanks,

Alex

[Miguel Ríos Martín]

With the original antenna (9.3 cm dipole and original 46 cm arm) I obtained a graph like the following

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Miguel Ríos Martín

[b alex pettit jr]

The problem with using that software is that the vertical scales are not consistent.

The Y axis values on the stock is 2X higher amplitude than the modified  ???

                  Y range 0.8 - 1.6                                                                      Y range  0.3 - 0.8 

Could you use other software such as SDR# & IFavg ??

Alex

[b alex pettit jr]

Miguel,

Can you 'calibrate' the Software ?

Use a 50 Ohm terminated LNA as a constant signal source and impose several steps of known attenuation

in front of the SDR and record the values measured by the Software .

=  How do the signal levels displayed by the software correlate to the known atten steps ??

 

Alex Pettit

[Miguel Ríos Martín]

It's true that the graphs show different scales on the Y-axis, but I understand (perhaps I'm misunderstanding) that these are relative values, and that when the data is processed with ezCon.py or ezSky.py, you can see whether the hydrogen line is detected with greater or lesser clarity. In the cases I've shown, the version with the modified dipole and the shorter arm has improved compared to the original.

Regarding the use of SDR# and IFavg, I haven't used them yet, but I'll test them.

Furthermore, to complicate matters further, I've used different versions of the rt-sdr driver (on Linux), and this also causes the relative values (RMS power) to differ depending on the driver version.

The graphs obtained with the modified dipole were generated using the latest version of the RTL-SDR driver, v-2.0.3 (released this August).

The data with the original dipole was obtained using an earlier version, v-1.3.6.

My conclusion (based on the processed graphs) is that either setup works, but the results are better with the modified dipole and arm.

I will continue testing, further refining the options:
- Testing with SDR# and IFavg
- Performing the calibration suggested by Alex.

Suggestions are welcome.

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Miguel Ríos Martín

[Miguel Ríos Martín]

Two graphs generated to compare both cases

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Miguel Ríos Martín