The UARC 146.76 Repeater Lake Mountain

Panoramic view of Utah Valley from atop Lake Mountain, looking toward the east - click on the image for a larger version of this same view!
For a very large (41 megapixel, 4.3MB) image  full-sized 360 degree view, click here.
(Warning:  Image is 17735x2333 - your browswer may not display the image properly!)

This map shows the transmit coverage of the '76 repeater. - Red areas are likely to provide good HT coverage - even with a rubber duck antenna. - Yellow areas are likely to provide solid mobile coverage and good HT coverage in a good location (e.g. not indoors, or with an outside antenna) - Green and Cyan areas should be easily accessible using mobile or home stations with modest outdoor antennas. - In Light Blue and Dark Blue areas coverage will be spotty and require a good outside mobile or home antenna - even a beam.. - Coverage in un-colored areas is likely to be spotty or nonexistent. Click on the image for large 2000x2000 pixel (1.3 Megabyte) version

Repeater coverage and operation:

Repeater coverage:

• Via mobile (50 watts, 1/4 wave or better): This repeater covers the Utah and Salt Lake Valleys, south along I-15 as far south as Filmore (spotty coverage,) portions of the west desert, and points north to the Idaho border. Very spotty coverage eastwards into the Wasatch.
• Via handie-talkie: Coverage is good in Utah county, marginal in many parts of Salt Lake county, particularly in the southern part of the valley.
• A map showing approximate transmit coverage of the '76 repeater may be seen to the right.  Note that for the transmitted signal, there is a "null" to the north making signals in parts of the Salt Lake valley and into Davis and Weber counties weaker than they should be.  This null does not affect the receiver, though, so you may be able to get into the repeater better than you can hear it.  For more info on the transmit antenna's pattern, see the article at the bottom of this page.
  

Keep in mind that while the repeater itself is an open repeater, use of the autopatches and IRLP node is reserved for UARC members (who pay the bills!) and out-of-town guests for whom club members may bring up the patch. Remember:  It is UARC policy that the IRLP and autopatch access codes are not to be given out over the air or to non-UARC members!.

Because of past abuse, users will likely find that the 911 emergency service is locked-out. If you have an emergency, it would be better to have someone on-frequency make the telephone call for you. Also, keep in mind that the duration of the call is limited to 3 minutes - not likely to be enough time to effectively pass on necessary emergency information.

Notes on repeater and autopatch operation:

• The Timeout timer: After a continuous transmission of approximately 3 minutes, the repeater will become disabled until the uplinking transmitter unkeys. This is done partly to encourage users to leave breaks in their conversations, as well as to protect the repeater should some signal appear continuously on the input. Upon cessation of the input signal, the repeater will transmit a special ID with the tone starting out low, swooping up to its normal pitch, somewhat reminiscent of a record player spinning up. This sound lets the user know he/she has transmitted too long and lets others know the repeater is again available for use.
• The "tone." Every once-in-a-while one may hear a brief DTMF (e.g. "touch-tone" [tm]) tone in the background. This is normal, indicating that the control link is functioning.
• There are currently no autopatches on the '76 repeater.  With the proliferation of cell phones - plus the fact that, due to abuse, direct dialing of emergency services was blocked - there has been less emphasis on returning the autopatch to operation.  If you feel that you have a compelling argument in favor of returning the autopatch to service, please feel free to present it to the UARC board.
  

View of the UARC 146.76 repeater site atop Lake Mountain.  The '76 receive antenna is the left-most vertical on the very top.
Click on the image for a larger picture.

A brief history of the '76 repeater

Quoting Gordon Smith, K7HFV, who has been involved with repeater from the beginning:

"In the early 1970's, when the Salt Lake City area had only two repeaters, Erv Greene, W7EU, proposed that UARC should put up a repeater and go beyond its traditional role as a club emphasizing HF activities. He procured equipment at practically no cost and made arrangements for use of some space on Lake Mountain in a building owned by the State of Utah. The club voted to support him in this effort, and in a few years, the '16/76' repeater was born.

"The road was a bit rocky during 76's first months of operation. The Motorola transmitter was designed for intermittent mobile use, and in repeater service its driver tube had a life expectancy of about two weeks. Pat Buller, W7RQT, came to the rescue. Using his considerable RF expertise, he made large modifications to Motorola's design in the last few stages of the transmitter. At last, the transmitter was clean and reliable.

"Many changes and upgrades have been made since the original repeater was tested at Erv's house. (It is now on its fifth transmitter.) In fact only one module - the ID and timeout unit - remains as a connection to the original '76."

The cluster of antennas near the midpoint of the tower.  The '76 repeater's transmit antenna is the left-most white vertical.  The link/autopatch antennas are the two yagis that are just visible near the bottom.
Click on the image for a larger picture.

As is true of most repeaters, '76 must share its site with installations of many other users.  Many repeaters use a single antenna to conserve tower space and to require only a single feedline. This, however, requires that the filtering (i.e. the Duplexer) be of very good quality and precisely adjusted. Using separate antennas allows slightly less filtering and fewer cavities, often resulting in increased repeater sensitivity and less probability of desense.

The transmit antenna is at the 40 foot level and the receive antenna is at the top of the tower - at the 120 foot level (see the picture at the top of the page.)  These antennas are approximately 22 feet long (each) and have about 6.1dBd gain - about 2 db better than the old ones (which were replaced in 1996.)  The receive antenna seems to perform about 4db better than the old antenna in response to stations in the Salt Lake area, owing to its greater height and better tower location. The new transmit antenna, however, performs, on average, 3db worse than the old antenna - probably because of its proximity to other antennas, the tower itself, and few large microwave dishes.

Nestled among the upper antennas are the 70cm link antennas for autopatch and control purposes. One antenna points toward Orem (for the Utah County patch) and the other points toward Salt Lake for that patch. Beams are used to receive the best possible signal from the autopatches.  70cm is used for several reasons: It is less crowded than 2 meters, it requires physically smaller antennas, and it is far-enough removed in frequency from the 2 meters that filtering is not much of an issue. (It is illegal to use bands below 1.25 meters for primary repeater control or other auxiliary functions - like the return autopatch audio - anyway...)

Bandpass cavities for the '76 repeater

As is typical in a repeater, cavities (left) are used to keep the transmitter's energy and other unwanted signals from getting into the receiver. The transmit cavities allow the transmitter's signal to pass through and block (i.e. "notch out") any low-level noise generated by the transmitter on the receive frequency, while the receiver's cavities allow the the receive signal to pass, and block (notch out) the transmit frequency. If too much energy from the transmitter entered the receiver, it would overload it causing a reduction in sensitivity, and possibly even intermodulation distortion.

The 2 meter receiver (146.160 MHz)

The 2 meter receiver (right) receives the signals on the 146.160 MHz repeater input frequency.  Since the user of the repeater may not be radiating a strong signal (because he/she is using an HT or is in a bad location) it is particularly important for the repeater to have the best possible sensitivity. For this reason, this receiver has a GaAsFET (low-noise, high-sensitivity) preamplifier.

This receiver also has metering to monitor various points within the receiver to facilitate testing, servicing, and adjustment.

The repeater controller chassis

Constructing a good repeater takes more than simply connecting a receiver to a transmitter. The controller chassis (left) along with a companion unit is responsible for things like IDing, hang-time, timeout timer, controlling the autopatch, and controlling the repeater in general.

"Behind the panel" of the repeater controller chassis.  Left to right:  The DTMF decoder;  Audio Equalizer, Switching, and PL generator board;  Controller/ID board

The transmiter for the '76 repeater:  A Yaesu FT-2500.

Since it was first installed this repeater has used a number of transmitters. Originally, they were tube-type. However, as technology progressed (and as the old transmitters died...) new transmitters were installed.

The radio being currently used for a transmitter (left) is a Yaesu FT-2500 Mobile rig. One of the best-known features of the radio is the extremely tight front end of the receiver, highly resistant to intermod! However, that isn't important in this case since the receiver isn't even being used!

What is important is that this radio as a clean transmitter, spectrally speaking, and that it has a nice, big heat sink capable of handling even the most long-winded of conversations without a fan. Of course, to keep it happiest, there is a fan suspended just above the transmitter (not shown) circulating air over the radio and amongst the other components in the repeater.

The transmit antenna being installed at the 60 foot level.

On November 8, 1997, an intrepid group of amateurs braved the elements and make a pilgrimage to the top of Lake Mountain - the site of the 146.76 repeater. Their purpose: To risk life and limb climbing about on a wet (and possibly icy) tower, to trust life and limb to safety belts, harnesses, and ropes, and to blindly go where no-one had gone before - at least for a week or so...

Why?

To replace antennas, of course!

It seems that the State of Utah (who is our landlord on Lake Mountain) had decided to take down the old guyed tower at the Lake Mountain site. While this tower has served well for the past 30-40 years, it was just too small for current and future needs. The antennas on the old tower had to be re(moved) to the new, 120 foot self-supporting tower that was next to it prior to the removal of the old tower (which happened in '98.)  Since the antennas were already 20 years old (see below) it was decided to install new antennas.

The day started out cold and clear. Lake Mountain, however, was shrouded by clouds - thick enough that we could not (usually) see the ground- this would account for the wet, cold, icy tower (and the 'blindly' part...) It took several hours just to get the antennas hoisted to their mounts and secured (as seen in the picture to the left and up.)
 
 

The receive antenna being installed at the 120 foot level (the top of the tower) by Garth, then KA7MHN.

Once the antennas were mounted, the heliax had to be run. Heliax is like coax, but this is bigger than standard RG-8, and heavier. Not only that, it isn't very flexible and great care needs to be taken to avoid kinking (and ruining) it! The coaxial cable needs to be attached carefully to the antenna, secured carefully (to keep it from moving in wind) and carefully waterproofed. The picture to the right shows Garth, KA7MHN, at the top of the tower (at the 120 foot level) where he attached had just completed this task - hanging in free space by his safety belt - unable to see the ground most of the time.

The original antennas were still there (for the moment) as were the control antennas. While the new antennas on the new tower were being used, the control antennas were still on the old tower, waiting to be moved the following spring. Although they were over 20 years old they still appeared to perform as well as their specifications would indicate. Also, a new television station - Channel 16 - was going on-air from an adjacent site: This would put the '76 site in an extremely strong RF field and make any metal-to-metal connections potential interference sources. New antenna (and tower) hardware was installed reduce the possibility of this becoming a problem now, and in the future.

Performance of the current antenna system:

The measured transmit antenna pattern of the '76 repeater.  "0" degrees corresponds with true North.  Although not clear from the chart, the null was at least 30 dB below the the "average" gain of the antenna denoted at the -6 dB ring. Click on image for a larger version.

As mentioned above, the Receive antenna is at the 120 foot level and has a clear view in all directions. This relocation, along with the fact that the new antenna has higher gain than the old, has caused the receive gain of the repeater system to be improved by about 4db (about 120%) in the Salt Lake Valley. The transmit antenna, although higher in gain and farther from the ground than the old transmit antenna, has shown a marked decrease in effectiveness in the Salt Lake area - typically a reduction of 6db in signal strength.

Further investigation has revealed that the blockage of the transmit signal to the north is far more severe than expected!  In March of 2001 Gordon, K7HFV and Clint, KA7OEI "circumnavigated" Lake Mountain, taking continuous readings (read more about that effort here.)  Analysis of the data revealed that there was, in fact a null toward the Salt Lake valley.  What was a surprise to us, however, was the fact that at a bearing of approximately 359 (True North) from the repeater, the null is approximately 30 dD in depth!  This very narrow null causes the signals in the west portion of the Salt Lake valley to be much weaker than expected.  There are several plans under consideration to mitigate this problem.  A plot of the signal based on the calculated antenna pattern is available on the web page mentioned above.
 

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This page last updated 20120426