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Project:Hackney Space Centre: Difference between revisions
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Project:Hackney Space Centre (view source)
Revision as of 13:26, 20 November 2011
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the sky. We don't officially have roof access. | the sky. We don't officially have roof access. | ||
I suspect the 10dBm EIRP figure is an optimistic best case. | I suspect the 10dBm [http://en.wikipedia.org/wiki/EIRP EIRP] figure is an optimistic best case. | ||
The KickSprites are going to tumble in space and the radiation will be mostly perpendicular to the wire antenna. | The KickSprites are going to tumble in space and the radiation will be mostly perpendicular to the wire antenna. | ||
The received signal is going to fade in and out as it tumbles, plus there may be polarisation loss. | The received signal is going to fade in and out as it tumbles, plus there may be [http://www.amsat.org/amsat/archive/amsat-bb/200101/msg01220.html polarisation loss]. | ||
I've put some numbers into a free space path loss calculator. | I've put some numbers into a [http://en.wikipedia.org/wiki/Free-space_path_loss free-space path loss] calculator. | ||
I suspect that a 10dB gain yagi is about the minimum for a chance of receiving a few beacons if you get it pointed in just the right direction at the right moment. | I suspect that a 10dB gain yagi is about the minimum for a chance of receiving a few beacons if you get it pointed in just the right direction at the right moment. | ||
Thats a three foot long antenna. | Thats a three foot long antenna. | ||
A bit more antenna gain would help a lot but a 15dB gain 70cms yagi is a fifteen foot long antenna and an engineering project to mount and motorise it so it can both be rotated and angled with computer controlled tracking. | A bit more antenna gain would help a lot but a 15dB gain 70cms yagi is a fifteen foot long antenna and an engineering project to mount and motorise it so it can both be rotated and angled with computer controlled tracking. | ||
Given the RF environment of the business center roof (a mobile phone base station right on top of the building plus various very strong UHF PMR signals from other London rooftops) it may be worth borrowing a breeze block size 70cms bandpass filter, we know a tall person who has one. | Given the RF environment of the business center roof (a mobile phone base station right on top of the building plus various very strong UHF [http://en.wikipedia.org/wiki/Professional_Mobile_Radio PMR] signals from other London rooftops) it may be worth borrowing a breeze block size 70cms bandpass filter, we know a tall person who has one. | ||
Software radios are limited in their ability to cope with strong signals near a weak signal that you want to hear. | Software radios are limited in their ability to cope with strong signals near a weak signal that you want to hear. | ||
There is a continuous trunked radio control channel on 440.0375 that is a huge signal on London rooftops. It's right on the edge of the ham band, the only way of keeping it out of a ham receiver is a cavity filter the size of a big propane cylinder. | There is a continuous [http://en.wikipedia.org/wiki/Trunked_radio_system trunked radio control channel] on 440.0375 that is a huge signal on London rooftops. It's right on the edge of the ham band, the only way of keeping it out of a ham receiver is a [http://en.wikipedia.org/wiki/RF_and_microwave_filter#Cavity_filters cavity filter] the size of a big propane cylinder. | ||
A high sensitivity receiver connected to the antenna with as short as possible a length of thick coax might work better than using an LNA, assuming that having it right next to the mobile phone base doesn't overload it anyway. The USRP might have to be in a big metal box with filtering on the power connections etc. to work up on the roof. | A high sensitivity receiver connected to the antenna with as short as possible a length of thick coax might work better than using an [http://en.wikipedia.org/wiki/Low-noise_amplifier LNA], assuming that having it right next to the mobile phone base doesn't overload it anyway. The USRP might have to be in a big metal box with filtering on the power connections etc. to work up on the roof. | ||
The primary purpose of a masthead LNA is to amplify the signal before some of it is lost in the antenna cable. Even thick expensive coax loses a few decibels at UHF over a sixty foot run. Probably worth borrowing an LNA anyway. | The primary purpose of a masthead LNA is to amplify the signal before some of it is lost in the antenna cable. Even thick expensive coax loses a few decibels at UHF over a sixty foot run. Probably worth borrowing an LNA anyway. | ||
