The UARC 146.62 Synchronous/Voting Repeater System

Farnsworth Peak and Scott's Hill

The UARC 146.62 repeater system presently consists of two sites - the Farnsworth Peak and Scott's Hill repeaters.

These are linked together full-time and function as a single wide-coverage repeater - see the
Coverage Map to find out where!

Building on Scott's hill - looking toward the
                  north and east
The Scott's Hill site, looking toward the north and east with the lights of Park City visible in the background.  This site provides coverage east of the Wasatch into the Park City and Heber areas as well as into southwest Wyoming - not to mention helping to fill in "holes" of coverage elsewhere!
Click on the picture for a larger version.

What is a Synchronous/Voting repeater system?

Although used frequently in the commercial radio world, synchronous and/or voting repeaters aren't too common in Amateur Radio use.  Knowing that, however, you may still be wondering what, exactly, a "synchronous" (also called "simulcasting") or "voting" repeater system is?

Synchronous transmitters:

If you have used 2 meter or 70cm FM very much at all you'll already be familiar with what happens if two transmitters key up on the same frequency:  Often called "doubling", one typically hears a bit of a squeal and a mish-mash of noises as the signals from both stations obliterate each other, making both of them uncopyable if they are of similar signal strength.

You may have also noticed something else that occasionally happens:  One station will "win" the double by overriding the other.  In these situations you may not even have noticed that two people have keyed up at the same time until someone unkeys and you hear the "other" person that had been transmitting underneath.  In these cases you witnessed the "capture effect" - that is, the ability of a strong FM signal to override the other with little evidence of the weaker one.

In the first case where there was no clear winner - only a mish-mash of noises - the two signals were probably of roughly equal strength at the receiver (either yours, or the repeater's!) but if one signal is much stronger than the other, the strongest one comes through quite clearly with, perhaps, only a little bit of noise in the background being the only evidence that there was someone else transmitting at the same time.

Why, then, would one intentionally put two transmitters on the same frequency if they are going to clobber each other?

Again, it comes back down to that "capture effect" - but with a twist:  If the two transmitters are very close to the same frequency and they carry the same audio, it turns out that they do not obliterate each other as they would otherwise.  Having two transmitters on the same (or very close to the same) frequency is often referred to as having synchronous transmitters - and it is also called simulcasting.

In reality, the two transmitters do not need to be on exactly the same frequency,  but just "very close" (within a few 10's of Hertz) to each other  If this is the case then one will typically hear one transmitter OR the other at any given instant with "destructive interference" occurring only when the signals from both transmitters are of nearly identical signal strength - but even then, the two signals probably wouldn't obliterate each other, but more-likely cause a little bit of distortion - but not so much that intelligibility was compromised.

You may be familiar with the fact that in some cases you can move your Handie-Talkie's antenna just a few inches to find a "hot spot" and considering that, you can already appreciate how hard it might be to find a spot where two signals are of precisely the same strength and if you are in a moving vehicle, you probably won't notice that you are hearing two, identical transmitters at all!  If you are mobile in an area where the signals between the two transmitters are approximately equal overall, you probably won't notice any evidence of the two separate transmitters - aside from a bit of "picket fencing" as your receiver randomly hears one transmitter or the other.  In testing, we have found that offsetting the two transmitters by somewhere in the either 1-4 Hz or 35-60 Hz area provide the most aesthetically pleasing effect in those areas where the signal strengths of the two transmitters are precisely equal:  For this reason, the term "synchronous" may not be completely accurate.

Why have multiple transmitters?

So, what's the advantage of having two transmitters on the same frequency, then?  If you have these two transmitters at different sites - especially ones that have minimum to moderate overlapping coverage - you can then use just one frequency to cover a larger geographical area.  Not only does this conserve frequency spectrum by using just a single frequency, but it also makes using the system much easier as you don't have to keep switching from one repeater's frequency to another as you move through their coverage areas - as you would had you been trying to use different-frequency repeaters that were linked together!

There's another benefit of having two transmitters on the same frequency and that's the fact that the total coverage is greater than the sum of its parts!  In other words, in those "fringe" areas where you might get little bits of signals from either transmitter, having multiple transmitters at different sites on the same frequency helps "fill in" those tiny gaps in overage where one would otherwise have to constantly switch between different repeaters to find the best coverage as you would in a conventional linked system where the transmitters were on different frequencies!

For a set of maps showing the predicted coverage of the Farnsworth Peak, Scott's Hill and the combined transmitters, visit the 146.620 Coverage Map page.

Voting receivers:

                  receive site, showing the tower and two antennas
The receive site at Farnsworth Peak.  This site provides coverage along the west side of the Wasatch Front, to the west past the Nevada border, to the north into Idaho, and beyond Utah county to the south.
Click on the picture for a larger version.

If you have wide-area coverage with multiple transmitters, what good is it if the users can't get back into the system everywhere that it covers?  That's where having "diversity reception" - multiple receivers tuned to the same receive frequency - comes into play.

As you might imagine, two receivers located at two different sites won't hear the same mobile transmitter equally:  Usually, the one closest to the transmitting station will get the best signal while the more-distant one will be more-likely to have the worse signal.  Again, if you've used FM very much, you'll know that this isn't always the case as local obstructions (buildings, hills, mountains, etc.) will sometimes cause blockage of the more-local repeater while you can still get into the more-distant repeater that might lie in a direction with fewer obstructions.

In the case of a voting system, all the audio from the different receivers is sent to one place and there the voting controller analyzes all of the signals from every receiver in the system and then picks the best one to be transmitted by all of the sites.

How does it "know" which is the best signal?

Using FM, you may be aware of something else that happens as signals get weak:  The audio doesn't get softer as the signal gets weaker, rather it gets noisier until the audio is lost completely - in the noise:  It is this same "noise" that your receiver uses for the radio's squelch - and by the time it gets too noisy, your squelch has probably closed and you don't hear anything!  It makes sense, then, that if you have two signals from two different receivers that you see which of the two is noisiest:  Knowing that, you can decide not to use the noisiest signal(s) and pick the "cleanest" one instead!

Imagine, then, that you have several receivers listening to the same mobile signal as it drives around amongst buildings, trees, hills and mountains.  Sometimes it may be getting into one site better than the other, but other times it may be the other way around.  By having a voting system constantly looking at the signals from all of the receivers we can always take the best signal at any instant from the receiver that has it!

Just as with synchronous transmitters, the coverage of the entire receive system is greater than the sum of its parts!  If you are in a location that isn't covered well by either system alone, there's a better chance that with multiple receivers hearing you you'll have a good signal into at least one of them at any given instant, and with the system automatically looking for the "best" signal, it will be that one that will be heard by everyone listening.  Unlike a linked repeater system with different repeaters on different frequencies, you don't have to worry if you were lucky enough to happen to choose the "best" receiver for your location!

How can I tell what repeater site I'm hearing?

Because all receivers and transmitters in the 146.620 linked system are operating on the same frequency, you may wonder how you can tell what site you or someone else is getting into and/or which transmitter you are hearing.  In order to be able to tell which receiver is hearing you and which transmitter you are hearing, some "beeps" have been added.  If you listen carefully, you can determine both which transmitter you are hearing and where the last person that transmitted was being received.

Where the beeps come from:

Unless you have a trained ear, you may have a bit of difficulty trying to figure out exactly when each beep occurred, so here are some simple rules:

No beeps at all - audio clip:

                  tail of a signal going into Farnsworth as heard by a
                  user listening to Farnsworth
Squelch tail of a signal going into Scotts as
                  heard by a user listening to Farnsworth
Squelch tail of
                  a signal going into Farnsworth as heard by a user
                  listening to Scotts
Squelch tail of a signal going into Scotts as
                  heard by a user listening to Scotts
The different sounds and beeps heard on the 146.620 repeater system.
Top Left:
  Hearing someone getting into Farnsworth, via Farnsworth.  Notice that there are NO beeps.
Top Right:  Someone getting into Scotts, but YOU are listening to Farnsworth.  Notice the beep immediately after the first squelch burst.
Bottom Left:  A user getting into Farnsworth who is being heard via Scotts.  Notice that in this case the beep happens immediately before the second squelch burst.
Bottom Right:  The squelch tail from a user getting into Scotts who is also being heard via Scotts.  It is only in this case that you will hear two beeps - like a cuckoo-clock!

Left-click on an image to "hear" what that squelch tail sounds like, or right-click to view a larger version of each image.

You will likely hear NO beeps at all if you are along the Wasatch front (Salt Lake, Ogden or Provo) and talking to someone else who is also operating from a location along the Wasatch front.

You are hearing TWO beeps - audio clip:

You will likely hear two beeps if you are in a location east of the Wasatch and you unkey, or if you are talking to someone else who is also east of the Wasatch.

You will only hear two beeps if you are in a location where you can hear the Scott's Hill transmitter instead of Farnsworth, and this will probably happen only if you are somewhere to the east of the Wasatch front.

If you are hearing ONE beep:

Unfortunately, this can be confusing at first - at least until you know exactly what to listen for.

Different numbers of beeps:

As you might guess, if you are leaving an area that is covered by one transmitter and going into an area covered by another - or if you are listening to someone who is mobile and moving between coverage areas - you can expect to hear different numbers of beeps as you (or the person using the repeater) goes in and out of the various coverage areas.  This shouldn't be too surprising, however, as one area is covered better by one site than another!

Sometimes, a person is in a location where they can get into both Farnsworth and Scott's equally well.  In this case, the voter will randomly choose which receiver (the one from Scott's or the one from Farnsworth) to use.  Since both are equally good signals, there's no real way to tell which one is "better" so it's the luck of the draw!  It is often the case that people living on the west side of the Salt Lake valley with good antennas will randomly get into either Scott's or Farnsworth and no those people, you'll sometimes hear beep - but sometimes not!

Technical stuff:  How the system works

If you are are a technical person and are wondering how this system works, read on!  If you aren't technical - but are still interested - read on, anyway.

Synchronized Transmitters (a.k.a. "Simulcasting")

                  "guts" of the Disciplined Oscillator
The "guts" of the Disciplined Oscillator.  This unit locks a standard GE "EC" ICOM to a 10 MHz OCXO to provide precise frequency control.  There are two such units - one each at Scott's and Farnsworth.
Click on the picture for a larger version.

Technically, the transmitters aren't actually synchronized to each other, but are held to the intended transmit frequency with high accuracy - typically being within 1-2 Hz of  their intended frequency.  To do this, 10 MHz oven-controlled crystal oscillators (OCXO's) are used at each transmitter to provide a highly-accurate (approximately 10E-8) frequency reference.  In the years since the system was installed, the transmit frequencies of the two sites have been observed to stay within 2 Hz or so of where they were set:  We haven't checked to see if both sites are staying on their respective frequencies or if they just happen to be drifting together, in the same direction - but it doesn't matter, really!

Setting frequency offsets:

Even though the transmit frequencies can be set to within 1-2 Hz of each other, one may not wish to do this, particularly for those areas in which signals from both transmitters may be heard.

Soon after installation, we heard from Brett, W7DBA, who lives in Huntsville - a community east-ish of Ogden and behind the mountains and it turns out that he doesn't hear either
Scott's Hill or Farnsworth very well, but hears both equally poorly.  As luck would have it, propagation has often caused both signals to be of almost identical signal strength at his house when received on an omnidirectional antenna!  Needless to say, this particular situation is unlikely to occur, but Murphy's Law would seem to make it inevitable for someone!

As the opportunity arose, we worked with him to find a frequency offset that provided the "least annoying" effects, and here is what we found:
Based on these observations, we left the frequency offset in the 50-60 Hz range for a while before changing it back to something in the 2 Hz range after further field observations.

In addition to adjusting the frequency offset, it is important that the audio phase of the transmitters be set equally - that is, all transmitters' deviations should go up and down at the same time.  If this isn't done, addition distortion can occur on the overlap areas.

Another factor that can affect how overlapping transmitters affect each other is the time-of-flight delay.  Since light travels at a finite speed, the signal from the nearby transmitter will reach you before the signal from the more-distant one will.  More significant, however, is the fact that the "slave" transmitter not only has to send its audio to the master site (on Farnsworth) but then Farnsworth has to send it back again.  Not only is this extra "round trip" adding a bit of extra delay, but also do the transmitters, receivers in the link to and from the master site.  As it turns out, matching this delay is less-important than many make it out to be - particularly if only radio links are used.  It is far more important to make sure that the phases of the audio match overall (particularly in the low-to-mid speech range) and that the frequency offsets are adjusted to reasonable values.

How it works:

For transmitting, GE Mastr II exciters are used at each site, but instead of using standard channel elements (called "ICOM"s by GE) there are modified channel elements that plug into the standard, unmodified GE exciter that accept oscillator-frequency inputs from an external source - a device called a "Disciplined Oscillator."  This Disciplined Oscillator module uses a PIC-based synthesizer to precisely lock a standard, unmodified GE "EC" type channel element to the crystal frequency - which is, in this case, 1/12th of the transmit frequency, or 12.218333 MHz.  Using DDS techniques, the crystal frequency can be adjusted and the ultimate transmit frequency can be tweaked in steps of approximately 2 mHz (yes, that's millihertz and NOT Megahertz!) at the VHF transmit frequency, so the ultimate accuracy of the transmit frequency is essentially that of the 10 MHz OCXO.  The output of the "EC" ICOM in the Disciplined Oscillator is then buffered and fed to the exciter via coaxial cable to the modified channel element.

Why use the GE Mastr II exciters?  For one thing, they are readily available on the surplus market.  Another important point is that the GE radios are phase-modulated instead of being frequency-modulated.  Why is this important?  With phase-modulated transmitters, the actual frequency source of the transmitter (in this case, that being produced by the transmitter's channel element) is un-modulated and simply needs to be held to the correct frequency.

Practically speaking, one could use a frequency-modulated, synthesized transmitter and simply make sure that the reference frequency of each transmitter is held to very tight standards, but those who have carefully observed such transmitters have noted that the actual frequency tends to wander around the intended frequency and only on "average" does it tend to stay close to intended frequency.  It is these low-frequency variations that are most-critical in a synchronized-transmitter system:  Modulated PLL (Phase-Locked Loop) transmitters tend to wander around 10's of Hz (or more!) with modulation as the PLL tries to keep the oscillator on frequency - despite the modulation put on it for the express purpose of knocking it off-frequency!  It is these slight differences (10's of Hz to 100's of Hz) in transmit frequency that tend to be most-noticed in the overlap areas between transmitter sites.

A phase-modulated transmitter, on the other hand, has a rock-solid oscillator frequency that never changes.  It is also the intrinsic nature of the phase modulator to resist low-frequency modulation as it is, in fact, rather difficult to achieve much modulation at low audio frequencies (such as those used for subaudible tone encoding) with a phase modulator.  By virtue of this fact, the phase-modulated transmitters are arguably rather better-suited for synchronous operation in a communications radio system such as an amateur repeater!

For Scott's Hill a minimally-modified GE radio is used for transmitting:  The only modification required is that to bring in the signal from the Disciplined Oscillator from the outside requiring the installation of a connector on the transmitter's case.  The actual transmitter itself is stock, with the modified "EC" channel element being plugged in where a standard channel element would go!  In fact, should the Disciplined Oscillator fail, one could simply unplug the "EC" element from it, put it in the exciter, and then set it to frequency as one would on a "normal" repeater as it would still get its compensation voltage from the receiver's channel element:  In this configuration the transmit frequency would not be held to such great accuracy, but it would still be perfectly functional.

For Farnsworth Peak, the original, circa 1978 2-watt exciter was replaced with new exciter based on an unmodified GE Mastr II exciter.  The exciter board was mounted in a shielded enclosure along with a regulated 10 volt supply, a simple transmitter keying circuit and a voltage reference for the temperature compensation line to allow possible emergency use with the un-locked "EC" element.  As with the Scott's Hill transmitter, the signal from the Disciplined Oscillator is brought in via a modified "EC' channel element but it, too, could also operate at reduced frequency accuracy by installing the channel element from the Disciplined Oscillator.  The output of the exciter is boosted to the 2-3 watt level using an external amplifier and that is used to drive the same 100 watt external power amplifier that had originally been driven by the old exciter.

The Disciplined Oscillator module has another function:  To control the local VHF transmitter and the UHF link transmitter.   Since the Scott's Hill site is normally functioning as a dual cross-band repeater, there needs to be a means to provide transmitter control, provide a legal ID on the UHF link transmitter, and to insert the 3.2 kHz "squelch tone" on the UHF link to Farnsworth as noted below.  For the VHF transmitter, the Disciplined Oscillator inserts a "transmit beep" to identify to the users that they are hearing the Scott's transmitter and not Farnsworth (see above.)

The Disciplined Oscillator (as well as the Voting Controller) have RS-485 multi-drop interfaces that allow them to be connected on a common bus, providing a means of remotely controlling and configuring them.

Voting receivers:

Getting the received signals from Scott's Hill to Farnsworth:

The front panel of the
                  Voting controller.
The front panel of the 8-channel voting controller.  Status LEDs indicate current and past receiver/voting activity.  The UHF link radio (to/from Scott's) is partly visible above.
Click on the picture for a larger version.

To allow the use of multiple receivers for "diversity reception", the audio and COS (Carrier Operated Squelch) information from the Scott's Hill receiver is shipped to Farnsworth Peak via a 70cm link.  At Scott's, the audio from the 2 meter receiver is placed on the 70cm link transmitter along with a 3.2 kHz "squelch tone" that is used to indicate the COS state of the Scott's receiver:  When the 2 meter squelch is open on Scott's, the UHF transmitter is keyed up and the audio from the VHF receiver is relayed on the link, but the instant the 2 meter squelch on Scott's closes the receiver's audio is muted and the 3.2 kHz tone is activated and transmitted for the duration of the "hang time" of the UHF link transmitter.

At Farnsworth the COS signal from the UHF link receiver and the presence of the 3.2 kHz tone together form the COS signal used to feed the voting controller:  If the COS drops or if a 3.2 kHz tone is detected, the voting controller gets a "squelch closed" indication from Scott's, but if the UHF receiver's COS is active without a 3.2 kHz tone being present, the signal is considered valid.

Why is there a 3.2 kHz tone at all?  In theory, the VHF receiver's COS could have been used to key the UHF link transmitter and the UHF link receiver's COS could have thus signaled the VHF COS state at Scott's, but this scheme would inevitably introduce an extra burst of squelch noise as the UHF receiver's squelch opened and closed on "fluttery" signals.  By having the 3.2 kHz squelch tone signaling the closing the the squelch at Scott's these extra "squelch noise" bursts are eliminated.  At Farnsworth there is a detector specifically for the 3.2 kHz tone, but it does not respond instantly so a 3.2 kHz notch filter in the voted audio prevents users from ever hearing that tone at all.

The 3.2 kHz tone also serves another purpose.  The voter itself determines the signal quality by comparing the amount of energy of each receiver channel after it passes through a 3 kHz, 3-pole Butterworth high-pass filter.  Actually, this 3 kHz filter doesn't resemble much of a "brick wall" as it still allows quite a bit of audio energy through down to 2 kHz or so, but it is these "higher" audio frequencies that tend to "noise up" first as signals get weaker and it is this "noise plus audio" that is actually measured:  By seeing which of the channels has the most "noise plus audio" one can determine which signal is, in fact, the noisiest overall.  Since the 3.2 kHz squelch tone is quite strong, it will be "seen" by the voter as "noise" and since that tone only appears at the instant that the squelch from Scott's closes, it further reinforces the fact that the signal from Scott's at that moment is "bad" and should not "win" the vote.

Using the "local" receiver at Farnsworth:

For the "local" signal from Farnsworth - that is, the "original" receiver - we had the luxury of having direct access to the COS and audio lines after modifying the existing controller.  Almost from the beginning, the Farnsworth Peak repeater has had a remote-controlled squelch to allow adjustments without having to visit the the mountaintop - a near-impossibility in the dead of winter!  Because the repeater uses a receiver located at a remote site several hundred feet away -  and the tendency of a high mountain to accumulate lighting, all signals had to be transformer-coupled - including a PWM-encoded squelch signal.

With the squelch circuity entangled within the original controller, modifications were made to break out the receiver audio and the decoded COS line.  In addition to these two lines, this modification also made available a "COS Input" and "Receive Audio Input" line by the simple expedient of interrupting those lines internally and routing them externally, allowing us to insert the Voting controller into the circuit:  This had the effect of allowing the Voting controller to be "seen" by the original repeater controller as just a single receiver.  For diagnostic and "backup" purposes there's even a "voter bypass" switch that returns the controller to its original configuration, allowing it to look at the Farnsworth receiver only.

The Voting controller, like the Disciplined Oscillator, is custom-made and it has provisions to allow up to 8 different receivers to be used.  To accommodate varying levels of audio and the expected different amounts of audio "coloration" - both of which could affect the ability of the controller to vote equitably - a number of different parameters are provided to adjust channel gain as well as the "noise detector" gain.  With the proper adjustments the voter can be "tweaked" so that equally-noisy signals from the two different receivers - the one from Scott's via the UHF link and the one from the local Farnsworth VHF receiver - can be also voted equally, or even adjusted to slightly favor one site over another.

Even with the adjustments available on the voter, a 3.5 kHz lowpass filter was added at the input of the local receiver audio at Farnsworth.  This was done because, unlike the audio from Scott's, this is "local" audio, fed by copper wire from the receiver and as such it contains more high-frequency energy in its audio than does the audio from Scott's, which loses some of its high-frequency content because of its passing through the link transmitter and receiver.  With that "extra" high frequency energy present from the Farnsworth "local" receiver the voter would tend to see more of what it considered "noise" on the audio of those signals being received at Farnsworth than it would on a signal of equal-quieting being received at Scott's and passed over the link and therefore, it would tend to deem signals received at Farnsworth to be "worse" than those received from Scott's even if they were equal.  The addition of this lowpass filter is generally "invisible" to the user, but not to the voter!

An additional feature provided by the voting controller is the ability to insert a "Squelch Beep" on a received signal after its COS drops.  At the moment this feature is used only to indicate signals that originate from Scott's Hill.

The link back to Scott's:

The output of the original Farnsworth controller feeds into the Disciplined Oscillator module which, in addition to frequency control, has another function:  To provide direct control of the local VHF transmitter and the UHF link transmitter.  In the case of Farnsworth, the Disciplined Oscillator uses the PTT signal from the old controller to "know" when to key both the VHF and UHF transmitters.  Additionally, the two audio inputs of the Disciplined Oscillator are fed from one source - the output of the original repeater controller.

The "guts" of the Disciplined
                  view of Scott's Hill, as seen from Farnsworth Peak.
Wider-angle (top) and a zoomed-in view of Scott's Hill, as seen from Farnsworth Peak.  Both of these pictures have been "adjusted" to compensate for some of the haze in the air at the time the picture was taken.
Click here for an annotated version of the lower picture that points to the precise location of Scott's Hill.
Click on the picture for a larger version.

While the Disciplined Oscillator inserts a "transmitter beep" on the VHF transmissions from Scott's, this feature is not used on Farnsworth as no beeps were required and the audio is passed straight through the the VHF exciter with this unit adding some extra hang-time.  For the UHF transmissions to Scott's, however, as soon as the PTT signal from old controller drops, a 3.2 kHz "squelch tone" is activated, signaling to Scott's Hill that its hang time is to begin.  In this way, the extra burst of noise from the UHF link's squelch tail is suppressed and the hang-time of both the Scott's Hill and Farnsworth Peak VHF transmitters may be precisely synchronized to "drop" at the same time.

"YAFB" (or, "Yet Another Fine Box"):

Because the new devices have RS-485 interfaces, it is possible to interconnect them and provide control via one interface.  One option of this "command and control" is to have a device controllable via the receiver using DTMF, returning information to the control operator.

These boxes are present at both Farnsworth and Scotts and allow the control operator to remotely read and modify parameters as well as reporting the status of various devices, and it can do so in either Morse or ASCII AFSK (e.g. RTTY) allowing either "human" interfacing or a computer running an RTTY program.

Scott's Hill remote squelch:

While we were working frantically to complete the installation of the gear on Farnsworth before winter weather moved in, we became painfully aware of a problem that we were expecting to happen - but hoped would not:  Scott's Hill's 2-meter receiver started to blow squelch noise.

The reason for this wasn't clear, but it was probably due to a transmitter from another service radiating some garbage under certain conditions, but regardless of the cause, the result was the same:  The '62 repeater became unlistenable and we had to shut off the Scott's link.

Earlier in its history this lesson had been learn on Farnsworth, necessitating the use of a remotely-controlled squelch control which has been occasionally invaluable over the years as it saved having to take a trip to the mountaintop (or attempting to convince one of the people that work up there) just to turn a knob.  In addition to having remote-control capability, it also allowed one to precisely set the squelch to the same setting repeatedly - something not easy to do with a squelch knob!

Finishing our installation work at Farnsworth we dashed over to Scott's in the early hours of the morning - chaining up the tires and braving the hazardous road, just hours before a large storm front moved in - just to turn a squelch control a fraction of a turn!  Making a guess, we turned it a bit farther than we really wanted to - but we decided that we'd rather have a somewhat "deaf" receiver than one that kept blowing noise!

In 2010 - during the same trip as the installation of the "YAFB" (see above) we finally installed a remotely-controlled squelch on the 2-meter Scott's receiver.  This is essentially a computer-controlled adjustable-gain amplifier that is connected inline with the original squelch control.  The modification to the GE Mastr II receiver was simple:  The addition of a 1/4" switching-type audio plug.  When the remote squelch was unplugged, the receiver's original squelch control functioned exactly as originally designed!

With this new box we can now set and read the 2-meter squelch on Scott's remotely - and this box also provides a few additional useful functions:  It can read the power supply voltage - which gives us one way of telling if the Scott's site is on AC power or battery backup - as well as the temperature inside the building on Scott's Hill and recording the minimum and maximum of each since the last "Min/Max reset."

The "Scott's Hill" controller:

There is yet another box at Scott's Hill - a repeater controller.  This is a modified NHRC-4 controller and its function is simple:  To make the system legal.

Normally, Scott's Hill operates as a dual cross-band repeater:  2-meter signals received at Scott's are relayed to Farnsworth on UHF and the UHF signals from Farnsworth are retransmitted from Scott's on 2 meters.  The Disciplined Oscillator provides an ID for the UHF link to Farnsworth while the normal repeater ID from Farnsworth on the UHF link and is thus repeated, identifying both it and the VHF transmissions from Scott's.  In this mode the NHRC-4 controller does absolutely nothing other than "listen" for commands.

What if we needed to turn Scott's off for some reason?  To do this the NHRC-4 controller can disable the transmitter control provided by the Disciplined Oscillator and put the repeater in "Standalone" mode.  In this mode the Scott's Hill site can function as an independent repeater, apart from Farnsworth Peak and once so-configured, one may disable the on-site transmitters completely!

Comment:  At the moment the controller at Scott's Hill is running the original NHRC-4 software.  Eventually, this software will be replaced with a custom-written version as there are a number of things that we would like to have the controller do, but it can't, owing to the fact that we are using the controller in a way that the original designers didn't envision.  For the time-being, however, it serves its main purpose of being able to remotely turn the Scott's repeater on and off!

Q&A about the system:

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This page last updated on 20111W107