Antenna Planning Guide

NOTE: This is a work in progress and open for comments. The intent is to familiarize a user with the knobs available in the PAW. It is not intended to be RSS or RP-1 specific.

Before reading this guide, make sure you've read the quick start guide to RealAntennas. There are several important basics to understand about RealAntennas before you start using the planner.

First, lets go over the part action window (PAW) for RealAntennas. The RealAntennas tab controls the antenna parameters, and these are explained in the quick start guide. For this guide, we will focus on the features of the antenna planning tab.

1. Peer This line tells you what your antenna is trying to connect to. By default it will set the peer to the most sensitive ground station on your home body. The planning peer can be changed via the antenna planning GUI to a specific ground station, a particular antenna on a ProtoVessel, or an antenna on the current craft.
2. Planning Altitude (Mm) This is the distance between your antenna and the other antenna/ground station you are trying to connect to. It is in units of megameters (1000 km) and can be varied from 1 to 1000 Mm. If you would like to plan around interplanetary distances (> 1000 Mm) then you should change the peer to the relevant body using the antenna planning GUI.
3. Transmit The nominal data rate you will be able to send to your peer at the given settings. So long as this number and the next number are greater than zero you will have a connection.
4. Receive The rate at which you can receive data from your peer. As above, if this number and the previous number are greater than zero then you will have a connection.
5. Active Transmission Time This line will only appear if you have installed Kerbalism alongside RealAntennas. It is the percentage of time that you believe your craft will spend actively transmitting. The Kerbalism planner can then give the EC consumption rate of your antenna without assuming it will constantly be actively transmitting.
6. Antenna Planning GUI Will open a new window that allows selection of the peer antenna. It is explained further below.
7. Refresh Planner A button that will refresh the connection calculations if you have made changes to the peer. Particularly useful if you are planning a connection between two antennas in the VAB.

This window gives you the ability to select your antenna planning peer. The default behavior is to set the peer to the most sensitive ground station on the home body. However, there are plenty of situations where that connection is not the one you are concerned about. In those cases you will use the antenna planning GUI to select the peer.

1. Ground Station TechLevel Lets you adjust the level of your tracking station in the planner. Useful when designing a mission that will not work with existing ground stations, but may work with upgraded ground stations.
2. ProtoVessel Antennas Allows you to select any antenna which is on a craft in flight. Useful if you have existing relays that you want to plan around.
3. YOUR_CRAFT_NAME Gives you a selection of antennas on the current vessel. Useful if you are planning craft to craft communications without a relevant ProtoVessel antenna.
4. Celestial Bodies This functions differently from the other options. When you set your peer to another celestial body, the planner will calculate the link between your antenna and the most sensitive ground station on your home body at both the maximum and minimum separations between that celestial body and your home body. If you are planning interplanetary communications then you want to use this option.
5. Ground Stations Opens the list of all ground stations. Use this when you want to plan connections to the more common ground stations which are less sensitive.

Examples

In this first example, the antenna will be representative of an early lunar probe in Real Solar System. The planning peer is set to the default, so the calculations will be in reference to our most sensitive ground stations. The planning altitude is set to the approximate maximum separation between the Earth and the Moon (406,000 km). Looking at the rates for Transmit/Receive, we see there will not be a connection at this altitude. Remember that the rate for both transmit and receive must be greater than zero to establish a connection.

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In the next example, the situation will be more complicated. We'll look at craft to craft communications at relatively short distances. In this scenario, we're planning a relay network of four satellites to reduce communication drop outs with craft in low orbits. This network will consist of four evenly spaced satellites around the Earth in circular orbits about 3400 km above the surface. At the selected tech level, we have the option to use S-band, but opt to use UHF because there are more ground stations that can receive at that frequency.

We're using the built in antenna on the procedural avionics part as a stand in for the craft in LEO, and the Communotron 16 for the relay. Although not strictly necessary, we've set the planning peer for both antenna on the craft. This link should be identical either way, so it gives us a sanity check. Note that the built in antenna on the procedural avionics is slightly worse (1.5 dBi vs 3.0 dBi) than the extendable Communotron 16.

The planning altitude is set to a bit more than the distance from a given relay to a satellite in LEO on the limb of the Earth as seen from our relay. We see that with these settings, both transmit and receive are greater than zero. Therefore the relay can talk to craft in LEO with a built in omni and 30 dBm transmit power.

Note that we do not check if the relays can talk to the ground stations. Due to the considerable sensitivity of ground stations, this is a given. A more interesting question is whether relays can talk to relays. The distance between relays is more than 12,000 km but the link will have the higher gain Communotron 16 on both ends. In this case it works out that relays can talk to relays.

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Finally, here is an example of planning interplanetary communications. The planning peer has been set to Venus, so the calculations for transmit and receive will be at both minimum and maximum separation between the Earth and Venus. At minimum separation the antenna can establish a connection back to Earth because both transmit and receive are above zero (645 bps and 41.3 Kbps respectively). At maximum separation there will not be a connection because transmit and receive are not both greater than zero.