Chapter 25: UHV/VHF Operation

1. Chapter 25: UHV/VHF Operation

2. Introduction: First Contacts • For most amateurs, their first solo-contacts tend to be on 2m or 70cm (VHF/UHF respectively) • Recall: 2m = 144-148 MHz & 70cm = 430-450 MHz • Only basic qualifications required • Affordable equipment for under $100 • Relatively simple operating procedures • Offers best introduction to local (established) amateurs

3. VHF/UHF: Basic overview

4. Operating: Basic Guidelines • Listen, Listen, Listen! • No matter what the frequency, ensure that you will not interrupt a contact in-progress before transmitting • By listening first, you learn the established etiquette on-air • Use only the minimum power necessary to conduct a contact • When using a “calling frequency” be sure to QSY once established • Determine a mutually agreed frequency and move to it to continue chatting • Always comply with the Radiocommunication Act

5. QSO: Methods of making a contact • There are three possible schemes for making a contact: • Simplex • Half-Duplex • Full-Duplex • Each method has benefits and drawbacks • Ease of implementation • Cost of hardware associated • Etc..

6. Simplex: The most basic QSO • Any method of communication which uses the same frequency for transmission and reception • Only one person may transmit at a time, otherwise, you are “doubling” over each other • Simplest form of communication • Ex: Walkie-Talkies as a kid

7. Duplex: Using different TX/RX Freq. • Duplex (half and full) is any method of communication which uses different transmit and receive frequencies • Half-duplex: • As with simplex, only one person may transmit at a time for effective communication • Repeaters commonly operate as half-duplex • Full-duplex: • Seldom used due to the technical challenges • Common example is the cellular telephone

8. Repeaters: A Primer • Repeaters are a very popular resource in amateur radio • Frequently used by local residents to improve their “coverage area” • Many local “nets” are hosted on repeaters because of their enhanced coverage area • May be used to link distant geographic locations via • RF • Eg. VE2REH network in Quebec • Internet • IRLP, Echolink 147.3 MHz 147.9 MHz

9. Repeaters: Major Types • What: • Any radio station which automatically retransmits an input signal to increase the effective range of the original signal • Generally placed in a highly favourable location such as top of a tall building, mountain-top, etc.

10. Repeaters: Privileges • Basic licensee: • Use any open repeaters with operating frequencies which are within the permitted range of the user (ie. your privileges) • Basic (70% < 80%) can use only those repeaters which operate on: 6m, VHF, UHF • Basic+ (≥80%) may use any repeaters, even those which theoretically retransmit on HF • Own/operate a cross-band repeater • In addition to Basic privileges, an Advanced operator may • Own/operate a same-band repeater • Repeater is generally given its own callsign and the input/output frequency pairs are supposed to be managed by a repeater council • Must conform to all Radiocommunication Act requirements • Ie. station identification at least every 30 minutes

11. Repeaters: How It Works • Simply take an incoming signal and retransmit at higher power, generally in the same band but on a slightly different frequency (the offset) • Generally done with two commercial radios designed for this purpose (100% duty cycle) • Repeater is generally controlled via DTMF tones and a controller board • Handles on/off operation, CTCSS tones, identification • When operating in the same band, a cavity filter (very high Q) is frequently used so that the same antenna can be used for simultaneous TX/RX

12. Coded Squelch: Preventing Noise • Sub audible tones used in (RF) noisy environment to trigger a radio’s squelch only when a signal with the associated coded squelch is present • Two major code types: • CTCSS • Continuous Tone-Coded Squelch System • DCS/DTCS • Digitally (Tone) Coded Squelch

13. CTCSS: Most Common • As many as 50 sub-audible tones • Originally only 32 tones, but was adapted to incorporate PL tones (Motorola)

14. DCS: Seldom Used • DCS superimposes FSK data (134.4bps) onto the transmitted signal • Similar to CTCSS, the DCS data serves to prevent squelch opening unless the correct data is received • Has great potential, however, control boards are more cumbersome to implement

15. Repeaters: How to start • To use a repeater, you need some information: • Repeater’s TX & RX frequencies • Repeaters are listed by the frequency at which they transmit • You must determine the repeater’s receive (listening) frequency by using the offset for the band the repeater is operating on • Control tone(s) (if used) • Often used in radio-congested areas to reduce unwanted retransmission of garbage • Generally listed with the repeater’s TX frequency

16. Repeaters: Simple Example • Let’s use VE3TWO as an example. It is listed simply as: • This is the repeater’s transmit frequency • Following convention, we know that repeaters which operate on 2m use 0.6 MHz as the offset value (unless otherwise stated) • The (+) means a positive offset frequency for the repeater’s receive frequency so we add 0.6 MHz to determine the “listening” frequency 147.3 MHz + 0.6 MHz = 147.9 MHz

17. Repeaters: Advanced Example • Suppose a repeater is listed as: • To use the repeater, set your radio to: • RX on 147.65 MHz • using CTCSS tone 151.4 on receive • TX on 147.05 MHz • using CTCSS tone 110.9 on transmit *unless otherwise stated, assume that CTCSS tones are listed as (out/in)

18. Repeater Linking: RF • Repeaters may be linked to each other by an RF link to increase total coverage area • When you transmit on repeater A’s input (listen) frequency, all repeaters (including A) retransmit your signal “Hi Tom..” 147.4 MHz “Hi Tom..” A’s Incoming 70cm RF link locked out by 2m reception (in use) B Blue = 2m “open repeater” frequency Red = 70cm “rf link” frequency you distant station (Tom) PTT is pressed 147.05 MHz 434.86 MHz 434.80 MHz “Hi Tom..” 147.4 MHz(-) 434.80 MHz (+0.6) A C 146.3 MHz 147.65 MHz 434.86 MHz “Hi Tom..” 147.65 MHz(-) 434.86 MHz (-0.6) 146.3 MHz(+) 434.86 MHz (-0.6)

19. Repeater Linking: Internet • IRLP • Internet Radio Linking Project Radio↔ Repeater (A) Repeater (B) ↔ Radio 147.05 MHz(+) Node: 2001 146.7 MHz (-) Node: 2002 Internet • Using your radio which is set to: (TX 147.65MHz, RX 147.05MHz) you would link to the distant repeater by pressing: “2002” on the DTMF keypad while holding the PTT button • Once the IRLP link is established, you could then transmit to your local repeater and have the distant repeater (B) retransmit at 146.7MHz

20. Repeater Linking: Echolink • Echolink is similar to IRLP with the exception that you can link to distant repeaters directly from a computer, dropping the radio-to-repeater portion of the link • Theoretically possible to have straight echolink-to-echolink contacts without even using a radio • Not really radio any more, huh?