History of VHF repeater splits

Discussion in 'General Technical Questions and Answers' started by Guest, Jun 14, 2003.

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  1. Guest

    Guest Guest

    I've always wondered where the standard 600KHz 2m repeater split came from. It sure seems like a odd choice for those that have to dig up huge duplexers to build repeaters. If the shift was 2MHz it sure would save money and repeater shack space. Does anyone know where this came from? And what about that 100KHz on 10m?

  2. KD5KUF

    KD5KUF Guest

    They had to learn all their mistakes somewhere. The 2 meter band just happened to be where. And you can use a wider split if you get coordination for it and if the hams can figure out how to program an odd split into their radios. Too late to change it all I guess. [​IMG]
  3. WA2ZDY

    WA2ZDY Guest

    There's another factor too. Before about 1978 (plus or minus a year or so) the repeater band was only 146-148. The addition of repeaters from 144.5-145.5 was a more recent development (as I said above, '78 or so. You newer hams do realise that repeater frequencies - input and output - are restricted to the "repeater subbands," right?) So the repeater pioneers of the day had less to work with than we do now. Of course I'm sure someone had a reason for picking 600 KHz, but . . . I don't know the reason. Picking a 1 MHz split wouldn't have resulted in fewer available pairs or anything, so who knows? I'm sure we'll see lots of suggestions here, and if anyone DOES know, I suspect it will be Glen or Steve (WIK.)
  4. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page

    One reason for the 600 KHz split on 2 meters was that intermod was worse with the 1 MHz split. For a while, in areas that had considerable 146.940 MHz simplex, 146.340 MHz was paired with 146.760 MHz instead of 146.160 MHz. This was especially true in the southeastern part of the US. For example, the original Stone Mountain repeater in the Atlanta, Georgia, area was on 146.340 / 146.760 MHz for a number of years before going to 146.160 MHz input and 146.340 / 146.940 MHz for another repeater.

    Now, as for the "inverted" above 147 MHz that came from pressure from the West Coast more than any other area. However, it was primarily due to the fact that in the older commercial FM equipment that the transmitter would spread farther than the receiver. Thus, by using "inverted" repeater outputs above 147 MHz this kept the receive frequencies more together while letting the transmitters that were more broad banded do all the work. This was the source of a lengthy argument at SAROC in Las Vegas in January, 1972, at the 3 hour FM forum that had several hundred amateurs from all over the country in attendance (over 700 if I remember correctly). The forum was headed by Wayne Green, W2NSD, from 73 Magazine and myself as the FM Editor of CQ.

    The 5 MHz split at 70 cm comes from the commercial standard of 5 MHz for the 450 - 470 MHz band. The split for the 470 - 512 MHz band is 3 MHz. Commercial standard calls for "high in, low out".

    Glen, K9STH
  5. N6HLE

    N6HLE Ham Member QRZ Page

    You learn something new everyday. And it's usually something that you didn't even know you wanted to know.


    Harry - KG6PTD
  6. Guest

    Guest Guest

    Thanks Glen, somehow I had a feeling that you would know (or, as was the case, been there.) Great information.


  7. Guest

    Guest Guest

    This is a BIT long.. but it gives a lot of  background and helps fill in (for new folks) a lot of the stuff that Glen either mentioned OR alluded to.

    REPEATER OFFSETS - Prior to the establishment of +/- 600 kHz. offset becoming the standard, repeaters were split in all sorts of interesting ways.  When I was introduced to 2M FM back in 1970 we had a VERY popular machine that had the operating frequencies of (in) 146.340 MHz and (out) 146.760 MHz.  Others were the standard 600 kHz offset. They eventually changed, but it took a while. :)

    As Glen pointed out, the originally authorized band of frequencies for FM were 146.000 MHz to 148.000 MHz.  When the bandplan was being hashed out, they started as low as they could go in frequency, keeping mind the necessary bandwidth and the frequency allocation for the FM mode.

    FREQUENCY SPACING OF PAIRS - Since (by the 70's) 30 kHz. frequency spacing was the accepted value AND allowing for needed space for 'guard bands' to minimize the adjacent channel QRM, they started at 146.010 MHz.  Then they went up 30 kHz to determine the next 'channel' frequency assignment.  Because most rigs were crystal controlled AND usually came from commercial service, they decided on discrete frequencies rather than a 'band' such as we have on HF. - Ergo, the 'channelization' of 6 meters and up for FM.

    (It should be noted that +/- 15 kHz. frequency deviation <known as wideband> was still used as that was the standard for the commerical gear we used at that time.  This set up the 30 kHz. channel frequency spacing. However, newer rigs used 15 kHz frequency spacing since the frequency deviation had been reduced from +/- 15 kHz. to +/- 5 kHz.

    ADDITION of 'SPLINTER' FREQUENCIES - When the 2M band became 'full and crowded' during the repeater 'boom' in the 70's.. they looked for ways to accomodate MORE repeaters.  'Splinter' channels (i.e. those channels between the accepted 30 kHz spaced channels) were designated as available since the accepted deviation standard was NOW +/- 5 kHz which meant you needed 10 kHz. bandwidth to accoodate the signal. They chose 15 kHz. as the spacing to allow for protection of adjacent channels from QRM. As many of the OT's will recall.. with the surplus rigs being in use and their filters STILL set for the 'old' 30 kHz. spacing, it led to QRM and problems. (It took a while for the manufacturers to catch up and narrow their filters to accomodate the narrower channel frequency spacing).

    Of course.. when the 144-146 range opened up, it set up a schism in the Country. Some wanted to go 15 kHz. totally to maintain the standard and others wanted to go to 20 kHz. to allow a bit more space to keep the adjacent channel QRM to a minimum.


    WHY did they choose 'in low, out high' from 146 - 147 MHz. and 'in high, out low' from 147 - 148 MHz?  'In-low' 'out-high' referred to the input frequency of the repeater/output frequency of the repeater. Since the repeater is a fixed frequency system it can be tuned for most effective operation on that specific frequency and need not worry about  covering a wide frequency span.

    As Glen noted it was due to the technical capabilities of the rigs currently available (most surplus commercial rigs) to hams back then.  Most were NOT designed to operate a wide split for either transmit or recieve. In other words, the hams wanted the transmitter/receiver to work from 146 - 148 MHz.

    The older surplus rigs would NOT shift the receivers that much without a great deal of degradation of sensitivity. Some transmitters would also maintain power output across 2 MHz of frequency spread although transmitters were MUCH more forgiving of wide frequency spread than receivers!  So the receiver technology drove the decision.

    SO.. they decided that since the receivers were the key determinent in maintaining the sensitivity, and it would accomodate a 1 MHz frequency excursion fairly well, they decided that they would center receiver tuning at 147.000 MHz and go out about 500 kHz either side of that value.

    (Beginning to see the picture as to WHY the input/output and SIMPLEX frequencies are as the are? ;-)

    That made the receiver range 146.500 MHz - 147.500 MHz. approximately.

    Transmitters would, as noted before, USUALLY tune 2 MHz without bitching too much or losing enough power to make a difference.

    Since 600 kHz was the standard offset, and knowing that they could not exceed the frequency limits AND knowing that they needed to keep channels far enough apart to minimize adjacent channel spillover and QRM (remember, 15 kHz was now the standard and most rigs were set for +/- 5 kHz. deviation as the standard)

    WHY SIMPLEX IN THE MIDDLE? These frequencies were the ones that would NOT accomodate the 'in-low' 'out-high' from 146.000 - 147.000 MHz range. Ditto for the 'in-high' 'out-low' range for 147.000 - 148.000 MHz.

    WHY 146.520 MHz. for simplex? 146.940 MHz. USED to be the accepted, standardized, 2M SIMPLEX frequency. (just as 52.525 MHz. was, and is, the 6M simplex frequency EVEN though it does not conform to the formal bandplan BUT it IS within the simplex frequencies in the bandplan.)

    Anway, there was a GREAT battle between those who wanted to maintain SIMPLEX frequencies and those who wanted to make the ENTIRE 146-148 MHz. range repeaters with one or two simplex frequencies.  When the bandplans were drawn up, 146.520 MHz. was the 'middle frequency' in the SIMPLEX range as that was what was chosen.


    FM band - 146.000 - 148.000 MHz. Allowing for deviation and bandwith limitations, they stayed 10 kHz up from the 146.000 and 10 kHz down from 148.000 MHz. (146.010 MHz and 147.990 MHz. respectively) Even with 15 kHz spacing, this is STILL the way it is.

    600 kHz is the standard split between TX/RX.

    Standard is 'in-low', 'out-high' for repeaters 146.000 - 147.000 MHz. since 147.000 was designated as the 'center reference frequency' based on the accepted 1 MHz receiver technical capability.  Between 147.000 - 148.000 MHz. it was 'in-high' 'out-low' so as to cluster the receiver tuning range within that 1 MHz. (approx) range.

    15 KHz. spacing, +/-5 kHz audio deviation.

    Bandplans came into play to accomodate repeaters, simplex users.

    Band plan pairs keeping to the 'in-low, out-high' plan in  146 -147 MHz. and 'in-high' 'out-low' in 147-148 MHz. all using 15 kHz channel spacing.

    They started at 146.010 and went up. When the upper frequency exceeded the upper range, they stopped and the middle frequencies were simplex. For 147.000 - 148.000 MHz. they did the same thing.

    144.000 - 146.000 MHz. REPEATER PAIRS - When the FCC opened up the lower 2 MHz. to FM, some of the country went to 20 kHz splits while the more entrenched, crowded parts of the USA (mostly EAST of the Mississippi and CA) did 15 kHz while other parts of the Country chose 20 kHz. to get more pairs AND eliminate a bit of QRM.  There wasa time when you had two separate standards and we all had to carry around lists if we traveled. However, over time, it was decided to go with 20 kHz. in the lower 2 MHz. range.

    OTHER BATTLES -  There were (and still are) ongoing battles between digital users, FM users, weak-signal users, and simplex  users.  While they have subsided quite a bit, they STILL flare up.

    I won't cover the GREAT REPEATER WARS OF THE 70's AND 80's. They would take multiple inputs to explain.

    Chuck K3FT
  8. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page

    A little more history:

    When the commercial deviation was +/- 15 KHz, the channel spacing was 60 KHz on the commercial highband and 40 KHz on lowband.  Since most of the high band FM equipment that came into the amateur ranks was commercial surplus like the Motorola FMTU30D transmitter / FMRU16V receiver, FMTRU-5V, FMTRU-41V, General Electric 8th MO series, etc., amateurs went to 60 KHz channels to start with.

    Prior to the Technician Class licensees getting 2 meter privileges (1960 or 1961 - don't remember exactly when) "the" 2 meter FM frequency was 147.300 MHz.  When the technician class licensees were given part of 2 meters to start with, they were given the same frequency range as the Novice Class licensees which was 145 - 147 MHz (it was a couple of years later that the Technicians were given the entire 2 meter band).  Since "the" FM frequency was 147.300 MHz, but the Technicians could not operate on that frequency, the first channel down from the high end of the Technician 2 meter band was chosen.  This, of course, was 146.940 MHz (147.000 MHz - 60 KHz = 146.940 MHz).  This allowed the equipment used on 147.300 MHz to also be used on 146.940 MHz.

    When the commercial equipment was narrowbanded in 1957, with an effective date of 1962 as the absolute end of type acceptance of +/- 15 KHz deviation (except for public safety which was given a total of 10 years to meet the new type acceptance), many of the older equipment could not meet the new standards.  Actually, the deviation had to be reduced by 1958, but the equipment was given various "grace periods" (depending on the service - public safety had the longest time period to be modified) to have the transmitters modified for the new deviation and tighter frequency requirements (went from +/- .002 to +/- .0005 percent which meant that at 150 MHz the transmitter could only move around in frequency 750 Hz instead of the old 3 KHz under the "wideband" standards").  Although the receivers did not have to be modified to meet type acceptance, they really did need to be modified with narrower filters and to have "audio recovery" modifications made (these increased the audio level due to the reduction in deviation).

    May of the older equipment was not type accepted under the new regulations even with modifications.  For example, the oldest Motorola equipment that could be modified was the FMTRU-41V with the older FMTRU-5V, FMTU-30D, etc., going by the "wayside" since they could not be modified to meet the new frequency standards.

    This produced a real "boon" for the amateur radio operators who found FM equipment for very low cost, if any cost.

    By the late 1960s, many of the "newer" tube-type radios became available.  These had come from the factory with +/- 5 KHz deviation.  This was due a lot to the fact that solid-state (at least solid-state receivers) had become the "norm".  For example, Motorola introduced the "A" model Motrac for low band and high band in 1957 and General Electric had introduced the MASTR PRO shortly thereafter.  RCA came out with the "Super Carfone" around 1958, and the race for solid-state was on.

    Radios like the Motorola T43GGV series became very common in 2 meter usage by the late 1960s.  Because the newer equipment could not receive the old "wideband" +/- 15 KHz deviation (the signals would "chop out"), the tendency was towards "pulling in" the amateur deviation to +/- 5 KHz.  But, the older equipment had very low receiver audio output because of the reduced deviation.  Therefore, in a few areas, a compromise of +/- 7.5 KHz deviation was used.  This was just under the deviation that would "chop out" on most of the narrowband receivers but produced enough audio that the wideband receivers could comfortably copy the signal.  Some amateurs referred to this as "bellyband" deviation rather than wideband or narrowband.

    Within a very short period of time, the +/- 7.5 KHz deviation went away and amateurs standardized on +/- 5 KHz.

    Now, the narrower deviation allowed the channel spacing to become the same as on the commercial frequencies which was 30 KHz.  Next, the commercial interests reduced the maximum audio frequency of the transmitted signal from 5 KHz to 3 KHz (the FCC at the time called the 5 KHz maximum frequency 20F3 and the 3 KHz maximum deviation 16F3).  The channel spacing on the commercial frequencies then became 15 KHz when 16F3 was used.  However, in some areas, amateurs did not want to go to the 15 KHz frequency channels because many of the i.f. filters used in the receivers were not that narrow.  Therefore, in some areas (and Texas is one of these) the coordination boards went to 20 KHz channels instead of 30 KHz or 15 KHz channels.  This does cause some problems  because coordinated repeaters can be 10 KHz or even 5 KHz away from one in another state.

    By 1968, 73 Magazine was really "pushing" FM operation on VHF for amteur radio operators.  There were also some specialized publications dealing with FM that were popular for a very few years until the major magazines got "on board".  CQ Magazine started "pushing" FM when I became the first FM Editor in 1971.  It wasn't until 1972 or 1973 that the ARRL "discovered" that FM had become very popular and QST started "pushing" the mode.  By the late 1970s or early 1980s, FM had become the most used mode in all of amateur radio.  Frankly, I sometimes think that those of us who were "pushing" the mode back in the late 1960s did too good a job!

    Today, with the no-code Technician being the entry level into amateur radio, I believe that FM, especially 2 meter FM, is still the most used mode.

    Anyway, there is a lot of history out there about amateur radio.

    Glen, K9STH
  9. Guest

    Guest Guest

    Again, great info Glen and Chuck! It would be nice to get this stuff in the handbook or maybe the tech license manual.With more and more people getting on 2m FM a little history of the band/mode may help newbies understand why this isn't CB. It's hard to respect tradition if you don't have the history to work from.

    Myself, I like playing with FM gear. I'm moving most of my equipment to commercial stuff so that I can get the best sound on the air. Larson and Batwing yank my crank, that's the part of the hobby I like. Building and operating repeaters is a blast for me. IRLP is great too. Now, I do need to upgrade to at least general so I can work some of the fine 10m FM repeaters around here.
  10. Guest

    Guest Guest

    Glen, EXCELLENT BACKGROUND! I had forgotten, honestly, about much of that info and your recollection of it brought it all back - and MORE! I played with the old 41V's, U43/44's, 'tracs, MASTRs, BRICK MOTO HT's..etc..

    Now.. for some 'old phart' fun.

    YOu know you're an OLD PHART HAM who has been around the VHF/UHF-FM worlda while when..

    You know what the term 'TOOTH BUSTER' means relative to operating mobile.

    When someone tells you that they have 'gold' or 'silver' strips in thier gear you know what that means AND you know which are the preferred ones to have!

    You have memorized, the ENTIRE set of frequency ranges that defined the low, medium, and high split commercial rigs.

    You can, at the mere mention of a partial rig ID (Such as U44) tell WHO made it, what band it was for, and give a fairly good concise description of it, its long/short suits, etc.

    YOu had (and probably STILL have a '2150 key' on your ring OR in your key box)

    You have no fear about opening up your HT220 and tweaking aroudn with it.

    When someone wants youto transmit for a deviation check you unconciously say a loud, drawn out, "FIVVVVVVVVVVVE!"

    Type 35 pads and schematics for hooks up are burned into your brain.

    You recall, with fondness, the sound of T-whine which would dip nicely when the TX was keyed.. IN FACT! YOU TUNED YOUR TRANSMITTER FOR THE DEEPEST LOWEST PITCH OF T-WHINE WHEN TUNING! (Wattmeters? We don't need no stinking wattmeters&#33[​IMG]

    You KNOW what T-whine is!

    The gentle humming whirring sound of a dynamotor coming up to speed isa sound that you recognize instantly!

    EP3/EP4/EP38 are NOT cryptic terms to you.

    International Crystal was THE only place to get crystals!

    Ovens were the standard.

    You kept spare channel elements in your junk box.
    You had EVERY PL tone code frequency memorized.

    If the radio case color wasn't Blue, dark Brown, or Putty White you didn't consider it a REAL radio!

    JAPTRACK, RICEBOX were all epithets.

    You became a pro at dissasembling your car to run HIGH CURRENT DC power cables, control head cables, and speaker wires in your car.

    You kept a spare HORN RELAY around to replace hte one the would pit whent he contacts arced.

    An HT without a speaker mic was just not complete.

    You had a supply of batteries for your HT stored in your car and at home in your MULTIUNIT charger.

    EVREYONE who saw your car and DIDN'T KNOW you were a ham.. ALWAYS asked 'Are you a (choose one) Cop, FBI AGENT, DEA, Undercover?' (Although I must admit, this helped because folks tended to think I WAS one of those and left my car alone! Especailly when the next one was noted)

    Your car had 'through hole' mounted antennas like the 'pro's andyou used Antenna Specialist, Motorola, or other commercial antennas.


    You weren't happy unless you had 6M, 2M, 440 MHz. ALL inthe car and were able to operate them all at once.

    YOu thought it was neat to be able to have the UHF rig on in th ebackground while talking to your buddies on 2M. That way.. when they wanted to zing you.. or harass you they would call you on 440 and hear themselves coming back over on to 2m.

    and the beat goes on!

    Chuck K3FT
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