2 meter simplex

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N4LHY, Feb 26, 2017.

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  1. K9STH

    K9STH Ham Member QRZ Page

    Starting around 1965, through the 1970s, and into the early 1980s, there were a few of us who were really "selling" VHF / UHF FM and repeaters. Unfortunately, we "oversold" the mode and things got out of hand in a hurry!

    Glen, K9STH
  2. KN4BSH

    KN4BSH Ham Member QRZ Page

    Why has FM become the most used on handset and mobile units for cars? If I understand the technology correctly, FM gives you a better sound quality when the signal is strong but requires more power; however, when the single degrades - the quality suffers a great deal. Due to the latter, wouldn't it be better to use AM or SSB for HT? I do not know the technology very well, so I am just brainstorming and asking questions for my own enrichment.

    Thank you
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    FM for such work has a lot of advantages:

    -Tremendous noise cancelling. Even if you have terrible ignition noise, you normally won't hear it on an FM receiver.
    -Ability to be well understood even if tuned a bit off frequency. With standard NBFM as we use it today (5 kHz deviation, 15 kHz channel spacing) you can be 2-3 kHz off frequency and still be understood.
    -Easiest designs ever! It take "nothing" to make any transmitter into an FM transmitter.
    -Great transmitter power amplifier efficiency, as it can all be Class C without worries of distortion. Class C amplifiers are the highest efficiency (or at least "were" for decades). No linearity issues.
    -Also, no linearity issues in the receiver! You can "desensitize" any receiver including FM ones, but an FM receiver really can't be "overloaded," so signals from weak to extremely strong are all perfectly understood.
    W0GSQ likes this.
  4. K9STH

    K9STH Ham Member QRZ Page


    In addition to what WIK has posted, the cost factor plays an important role. An FM, or PM, transmitter requires substantially fewer parts than a comparable AM transmitter (let alone a transmitter for SSB operation). In addition, it is certainly possible to receive FM / PM on an AM receiver using "slope detection".

    Also, FM / PM have the "capture effect" wherein it takes a considerably stronger signal to override (interfere with) the signal being received at the time.

    Glen, K9STH
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Another advantage of FM that comes to mind is lack of "cross-modulation" which occurs on AM when a very strong modulated signal entering the receiver mixes with the desired weaker signal and creates detected modulation of the weaker signal that shouldn't be there. Doesn't happen with FM.

    FM has a lot of advantages for "hands-free, low-cost, very little operator knowledge required" type work.

    Then again, aircraft operations are AM for various reasons...but it's channelized and should be using very stable equipment so being "off frequency" isn't much of an issue like it might be with lower-cost amateur gear. It's also mostly "strong signal" work, which makes everything easier.
  6. KJ4RZZ

    KJ4RZZ Ham Member QRZ Page

    Isn't that MOST of the hobby? To talk to someone on the radio ??? Sure having a net to pass "messages" is nice, but isn't that just rag chewing where there are no messages to report? "Anything to report?" "Uhhh I just ate a bagel and I'm getting ready to take my meds. Otherwise no."
  7. AI3V

    AI3V Ham Member QRZ Page

    You got it.

    The single biggest reason?

    You can get a squelch circuit to actually work on FM.

    W0GSQ likes this.
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    And you miss the weaker exotic DX in the process. SquelchVHF/UHF = FM. Squelch HF (SSB/CW)= missed DX.
  9. WA9SVD

    WA9SVD Ham Member QRZ Page

    And you miss the weaker exotic DX in the process. Squelch VHF/UHF = FM. Squelch HF (SSB/CW)= missed DX.
  10. KK4YWN

    KK4YWN Ham Member QRZ Page

    times are a'changin.

    if radio makers would add attack/decay to the squelch circuit, it could work on ssb. especially on these new whiz-bang sdr jobbers. i use squelch on ssb and my only complaint is that is slams shut. if it would decay it would be brilliant.

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