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howto:hambasics:stationassembly

Under Construction: VA7FI is editing this section, please do not edit it until this notice is taken down.

Station Assembly, Practice and Safety

Block Diagrams

The next few sections use block diagrams to illustrate the configuration of various pieces of equipment. Here's an excellent introduction that should help with what follows:

HF Station

Some of the components shown above may be integrated into one device, and others may be optional. But if all are included, this is how they should be connected.

  • The transceiver takes the audio from the microphone and creates a modulated radio signal. Typical HF radios can output about 100W of power. Hams with their advanced ticket can feed that into…
  • The amplifier takes the radio signal from the transceiver and amplifies its power to 1 kW or even 1.5 kW.
  • From there, the signal may contain higher frequencies (called harmonics) that are not desirable, so it goes through a Low Pass Filter, which passes low frequencies and filters out high ones.
  • After that, the SWR Bridge measures how much of the signal is reflected back toward the radio from the antenna system. We saw earlier that the length of the antenna needs to match the frequency we use. When the match isn't perfect, some of the radio signal “bounces” at the antenna back to the radio, which isn't good for the equipment. The SWR Bridge measures this.
  • A trick we use to protect the radio equipment is to add a Tuner. This device uses varying combinations of capacitors and inductors (more on this later) to match the impedance of the antenna system to the radio (more on that later). Although there is still reflection at the antenna back toward the radio system, the tuner will “protect” the radio from it.
  • An Antenna Switch is a handy piece of equipment to quickly switch between antennas without having to disconnect and connect coax connectors.
  • Because of their size difference, it's usual to have a multiband antenna that will work on 20m, 17m, 15m, 12m, and 10m (and maybe even 6m), and a second antenna for 40m, 80m (and maybe even 160m).
  • Where as a tuner for the upper band is optional if the antenna is well designed, the lower bands (specially 80m and 160m) are very wide compared to their frequencies so it's practically impossible to have an antenna that will work over the entire band. For that reason, a tuner for these bands is pretty much mandatory.
  • The Dummy Load is a 50Ω resistor that can dissipate all the power from the radio without converting any of it into a radio waves. It's useful for test purposes or to tune an amplifier.

All that being said, it's possible to go on HF with a transceiver that has an small integrated tuner in it, and a single antenna. It'll just be a matter of knowing which frequencies your system can transmit on, and stay within them.

Transmitters

Review the Wave Modulation page. You should:

  • understand the difference between the baseband signal and the carrier, and how they combine to form the modulated signal.
  • understand the difference between AM and FM.

CW Transmitter

  • The master oscillator generates a stable sine wave signal at the rest frequency.
  • The driver / buffer is the first stage in the amplification process.
  • The key is basically an on/off switch used to let the signal through to the amplifier or block it.
  • The power amplifier is the last stage of amplification before the signal is released to the antenna.

FM Transmitter

  • The microphone picks up the sound waves carried by the air and converts them into a weak electrical signal that becomes the baseband.
  • The speech amplifier increases the strength of the baseband signal before it can modulate the carrier.
  • The modulator uses the baseband signal to change the carrier oscillator frequency in the next stage.
  • The oscillator generates a stable sine wave signal at the rest frequency when no modulation is applied. Its frequency changes linearly when fully modulated with no measurable change in amplitude. Note that the oscillator frequency can be much lower than the final transmitted frequency.
  • The frequency multiplier increases the frequency of the modulated signal by a factor of 2, 3, or 4. This is so that the oscillator frequency can be lower than the frequency transmitted at the antenna.
  • The amplifier increases the power of the signal to be transmitted by the antenna.

SSB Transmitter

  • The microphone picks up the sound waves carried by the air and converts them into a weak electrical signal that becomes the baseband.
  • The speech amplifier increases the strength of the baseband signal before it can modulate the carrier.
  • The RF oscillator generates a stable sine wave signal at the rest frequency. Note that the oscillator frequency can be much lower than the final transmitted frequency.
  • The outputs of the speech amplifier and the RF oscillator are mixed together in the balanced modulator. This produces a signal with two side bands, only one of which we want to keep.
  • The filter only lets one sideband through.
  • The VFO creates a sine wave frequency that can be varied.
  • The mixer uses the output from the filter and the VFO to generate a higher frequency signal.
  • The linear amplifier increases the power of the signal to be transmitted by the antenna.

Note that a Frequency Mixer multiplies two signals together, which usually results in a total of four (or more) frequencies. This is not to be confused with an Audio Mixer, which adds different signals together. See the optional Wave Modulation Math page for more details.

Receivers

FM Receiver

Before we look at individual components, there's an important step we should highlight: The received radio frequency (RF) is converted down to a predetermined intermediate frequency (IF) before being processed further. This solves a lot of problems that plague simpler receivers. Now let's look at the details.

  • The RF amplifier increases the strength of the weak radio signal received by the antenna.
  • The local oscillator creates pure sine wave that can be tuned by the listener.
  • The mixer takes in the RF signal and mixes it with the pure sine wave from the local oscillator. This produces two frequencies: one is the sum of both input frequencies, the other is the difference. Only one of these is the IF that we want to keep.
  • The filter removes unwanted frequency created by the mixer and lets the IF pass through to the next stage.
  • The IF amplifier increases the strength of the IF signal.
  • At this point, the signal's amplitude may vary due to noise. The limiter removes these amplitude modulations before the next stage.
  • The frequency discriminator extracts the baseband signal.
  • The audio amplifier increases the strength of the baseband signal before passing it to the speaker.

SSB/CW Receiver

Digital System

Regulated Power Supply

Questions

  • B-003-001-001 → B-003-003-010

howto/hambasics/stationassembly.txt · Last modified: 2020/03/12 15:46 by va7fi