# RF energy harvesting using UHF and HF from tv, radio and cell towers [duplicate]

I am busy with a project where I want to harvest energy from UHF and VHF such as tv broadcasts, radio and cell phone towers to charge a 100uf capacitor to be able to power a low power appliance such as a cell phone.

My plan is to use a polarized match linear antenna and using the theory and maths of friis equation I expect to get 10-100 mv.

How do I work out or know what the gain will be in dBs?

What should the antenna width be to give me a wavelength impendance of 50ohms to minimize reflection loss with a matched RF-DC charge pump circuit?

The incoming power transduced across the antenna is RF and would induce a very low voltage across the antenna terminal , so how would I rectify and step this voltage up to 3.5v-4v?

If you have any tips or advice please let me know, as well as if you think im on the wrong track. Your help is appreciated.

• Read this: electronics.stackexchange.com/questions/175121/… and decide if what you are doing makes any sense. Also a 100 uF capacitor might power a cell-phone for a second. – Andy aka Mar 23 '16 at 9:10
• ... if you charge that 100uF to more than a 1000 V or so. Oh, but I'll just use a step-up converter, feed that from a 100m antenna, wait 1 week for the 100 uF to charge to 1000 V. Hmm, is that in any way practical ? – Bimpelrekkie Mar 23 '16 at 9:19
• "polarized match linear antenna", "wavelength impendance of 50ohms"? these terms make no sense and I suggest you go through your RF class textbooks again.. Gain in dBs is calculated as 20log(Vout/Vin) – Roker Pivic Mar 23 '16 at 9:20
• Thanks guys. I have been curious about the subject for a while now. No better way to learn than from people that actually know what is going on :) – Armand Currie Mar 23 '16 at 9:35