log-periodic antenna for Solar observations

[Kimmo]

I am interested to make spectrographic observations of the Sun in the frequency range of 50-88 MHz.
The lower frequency limit is determined by the size of the antenna, and the upper frequency is limited by the start of the FM broadcast band.
Another possible frequency range is from 50 to about 200 MHz.
I am not sure which is more useful, fast scanning over a smaller frequency range, or a slower scanning over wider frequency range.
I will use the tinySA Ultra as the scanning receiver.

Anyway, I need a log-periodic antenna for that frequency range.
Anybody interested in helping to design and build such an antenna ?
There are on-line tools for designing, but building the antenna may be more demanding :-)  (I do not have special tools).

Cheers, Kimmo 

[Dave Typinski]

Hi Kimmo,

An LPDA is expensive, complex, heavy, and must be steered in azimuth and elevation.

A single terminated folded dipole (TFD) running north-south may be all you need
(or east-west if you live at really high latitude).

We have been using them for a while to observe Jovian and solar emission from 15
to 30 MHz. Scaling the TFD to 50 to 100 MHz would leave the antenna about 7 to
9 feet long and about 3 feet off the ground (or above the ground plane of your
choice).

A TFD is not nearly as efficient as an LPDA, but the 5 to 6 dB loss due to
inefficiency is immaterial if you're doing solar work because solar radio burst
emission is so strong.

On the other hand, a steerable LPDA would be the "righter" way to do it because
you could use it like a heliostat and keep the Sun right at the center of the
beam all the time.

A third option is a semi-bi-conical dipole antenna like the Air Force uses.
https://media.defense.gov/2010/Mar/02/2000389811/-1/-1/0/091118-F-2907C-0040.JPG

A fourth option is a low-band LOFAR style crossed dipole.

A fifth option is an LWA style crossed dipole.

It all comes down to how much time, effort, and money you want to spend.
--
Dave

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