John Martins'
Amateur Radio from near Empire Michigan USA

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VHF Propagation


The wI0OK Glen Arbor - Empire repeater provides both 70cm, 6m, coverage to southwest Leelanau, northern Benzie and much of Grand Traverse counties. The repeaters even provide some coverage to Kalkaska, Antrim and Manistee counties.

The 444.725 repeater, with an input on 449.725 (114.8hz or 146.2hz PL) is functionally tied together with the 52.92 repeater.  The 52.92 repeater has an input on 52.42 and requires a PL tone of 146.2hz for access.  The wI0OK 442.200 Harrietta-Cadillac and the 145.27 Traverse City repeaters are also linked to this system.

The 70cm and 6m pair of 'conjoined repeaters' has two remote base transceivers which can operate on a selection of two meter ham frequencies or on 224.56 MHz .  When the remote base is in the 224.56 MHz mode, the repeaters are effectively tied to the WB8DEL 224.56 repeater in Stutsmanville MI (near Petoskey). The two meter remote base is typically used to link with the 147.04 Benzonia MI repeater.

The summer of 2005 saw the repeater antennas moved up the tower t the 330' level, with a corresponding improvement to the coverage.  During 2004, the addition of satellite  voting receivers for both 6m and 440,  a new control system which gives the machine much greater functionality and flexibility, along with battery backup on 440 and a synthesized 2 meter remote base transceiver.   These improvements have provided a reasonable improvement in coverage .   I've got a system block diagram showing what's in place.

A blog has been created to keep those of us interested in the repeater up to date on technical issues related to the system.  You can view the wI0OK Blog at: http://wi0ok.blogspot.com . Sadly, it has not been updated in a while-- and will soon be moved here to kf8kk.com/blog.

This is the view of the 400' tower that primarily holds the antennas for the 95.5 and 98.1 'Real Rock' and 'The Bear' FM stations (WJZJ, WGFN) licensed to Glen Arbor.   The site is south of Glen Lake and east of Empire and just north of M-72 atop a good sized hill.

Also on the tower are two 'cellphone' companies, and a local gas company.

This photo was taken before the 'new' repeater antenna was placed at the 330' level on the tower.  

You can see the remote-base and secondary receiver antennas in this photo, as they are at the 100' level.  There is also shown a 220mhz AEA Isopole at the 60' level, that has since been removed and replaced with a 7 element 220mhz M2 yagi.

This photo shows our antennas on the left, just above the side marker lights, and below the sidearm for one of the cellphone antennas.

While it might have been nice to put the antenna at the very top, this location is 'just ducky' as it's not going to be the first thing a lightning strike will want to hit-- and it's at least a few feet away from all that FM broadcast energy.

This image is looking west.

From this view you can only make out the single element DB products vhf-low (6m) folded dipole. Intermixed with the 6m antenna on the mastpipe is a DB products four bay UHF antenna for the 444mhz repeater.

That VHF-lo/6m antenna is also used by the 145.36 DStar repeater. While the SWR on 2m is far from ideal, the radiated and received signals using this antenna are far greater than my next best alternatives-- so the SWR is tolerated in exchange for better coverage (that makes good logical sense to anyone but an asshole-- you could call it an AH test of sorts).

Below on the left you can see the 450 Mhz Cellwave Super Stationmaster antenna at the outer end of the mount.  This is presently hooked up to 449.725 receiver #3 and also is used to receive the Traverse City link signal, and is also connected to the UHF control receiver.   What is particularly good about this antenna, even though it's only at 100' on the tower, is that it's orientation is somewhat different giving it the ability to fill in for a bad UHF tower shadow in nearby downtown Glen Arbor.  HT coverage at the local watering holes is still possible.

On the left, just inside the UHF Super Stationmaster, is a dualband Diamond X50A modified for inverted mounting and connected to the 2meter and UHF packet systems.

On the right side of the mount is an element from a 2mtr dipole array.  This is a vestige from a former packet node and is mostly used for feeding RF through the system from my signal generator when I am tweaking things.

Below on the right you can see another six meter DB products folded dipole, also at the 100' level.  This antenna sometimes feeds a third 52.42 receiver. Temporarily this 6mtr antenna is being used by the 2mtr remote base transceiver via a diplexer. Next time up the tower it should be swapped out for a 2mtr antenna.

To the left is the M2 Antennas 7 element 220 yagi aimed at the WB8DEL repeater in Stutsmanville.  This is at approximately the 60' level on the tower.

These photos show the tower base and the concrete block building that houses the radio equipment.  The cellular phone operators have their own 'prefab' buildings to house their equipment.

The wI0OK repeater rack sits quietly in the corner of the building and is watched over by the careful eye of a guard ducky-- our local control operator.

This rack has removable side panels and doors and was previously used for the 147.30 repeater, many years ago.  Sadly, the doors spent some time outside and need to be repainted. The little handles on the front of the DStar gear prevents the front door (now removed) from closing. Sometime I'll have the ambition to remove the DStar handles, but for now it's working fine.

Regretfully, the rack is just so big and some of the gear is finding itself relegated to the top of the rack. Behind the rack are presently two six meter bandpass cavities which add some extra isolation from the strong nearby broadcast transmitters (the heliax duplexer is notch-only!).

Bolted to the rear is yet another 440 bandpass cavity for the primary 449.725 receiver.  Another bandpass cavity atop the rack is for one of the other UHF receivers.

Atop the rack is a stack of radios which comprise the packet system. Mounted above the rack, to the roof trusses, is the heliax six meter duplexer. Overhead as this photo was taken is where the DStar duplexers are positioned.

This photo shows the overall view of the front upper portion of the repeater rack before the DStar gear was added.

Thankfully, the rack has both front and back 'rack rails' so equipment can be mounted on either side of the rack.

At the top of the rack is an old Motorola 'M' series Motrac base receiver which is used for the 'FCC-legal' control system. 

Behind this receiver is a Micor 100w power amplifier for the 52.92 repeater.

Visible below the Motrac receiver is a panel where a Kenwood TK860 is mounted. This receiver is used to pick up the signal from the W8TVC repeater site that carries both 449.725 and 52.42 remote receiver signals along with signals from the 145.27 repeater.  The black box just below on the rear rails is a Cellwave six cavity UHF duplexer for the 444.725 machine.

At the middle of this view, on the rear rack rails is a  Motorola Micor 75w base UHF power amplifier for the 444.725mhz transmitter.  

Below the brown cardboard box containing 'spare parts' is the main unit of the 444.725 Motorola Mitrek used as the UHF repeater.

That empty space below the Mitrek shelf is now filled (see below). Below that are four rack boxes that comprise the repeater control system.

This is the view of the top of the rack showing the DStar RP2C controller in place above the UHF control link receiver. This unit has since been moved to the Traverse City tower along M72.

While it would have been nice and pretty to mount the DStar components all together in the rack, there were issues with other items mounted to the rear rack rails that preculded that.

Yes, both the front and rear rails are used in this setup-- and it can be an interesting juggling act to change things. Thankfully, with the side panels removed, it's possible to get to the rear panel connectors without having to remove things.

In this mid rack photo,  you  see the Motorola Mitrek 444.725MHz and 449.725MHz main repeater transmitter and receiver sitting on a rack shelf at the top.  This Mitrek has been modified for 'exciter output' as you can see the RG400 coax coming out just above the normal antenna connection.  This feeds the Micor PA quite nicely and keeps the Mitrek from heating up during long QSO's.  Out of view is the Advanced Receiver Research GasFET preamplifier.

Below the shelf with the Mitrek is four black rack mount boxes which comprise the repeater control system.  Those boxes are stuffed full of all sorts of electronics and provide a great many 'bells and whistles'.

The top box holds the Arcom RC210, the second is the LDG RVS-8 voting comparator used for the 52.92 repeater.  The third contains the Doug Hall Electronics voting comparator used for the 444.725 repeater, along with some ancillary controls. Finally, the fourth black box contains the seperate 'FCC Legal' control system.

Under all the black boxes is a Motorola SyntorX formerly used for the synthesized 2mtr remote base.  Sadly, after years of great service the SyntorX developed a temperature dependent squelch problem and was replaced by a Kenwood TM-271. I just plain did not have the time to devote to recreating the intermittant problem (which conveniently occurs only while I am wintering in Arizona!). That SyntorX has been repurposed and rides along in my old green van as my APRS node kf8kk-9.

This updated photo shows the DStar RP2000V 2mtr RF deck squeezed in below the 444.725mHz Mitrek and above the Arcom RC210 controller.

Moving the DStar repeater out of this rack gave me back some working room for tweaking the controller! yee haa!


Below the SyntorX is a rack shelf with the weather receiver in a grey box on the left.  This little weather receiver also has the ability to decode the S.A.M.E. weather alerts and feed them onto the controller to signal that threatening weather is approaching.

To the right of the weather receiver is a Motorola Mitrek that comprises the 52.92MHz transmitter and 52.42MHz receiver.   This Mitrek has had it's PA section removed and it feeds it's Micor 100w power amplifier directly (PA at top of rack in rear).

Atop the 6mtr Mitrek is an Icom IC37A 220MHz transceiver which is the 220 link rig.   This transceiver is set to 10w output power, which provides plenty of signal to access the WB8DEL Stutsmanville repeater.  The IC37 sits at an odd angle for better cooling, at the expense of cosmetics.

The two Astron RM70 power supplies provide the 12v for the system.  The top supply powers the devices NOT on the backup battery, while the lower supply feeds a power isolator and all the items receiving emergency power.

To the left of the lower Astron is an MFJ1270 TNC formerly used for the wI0OK-8 'BENQMN' TheNet X1J packet node on 145.76.

At the very bottom, on the left is the home built power isolator.  On the right is a 500 amphour deep cycle battery used to supply the repeater with emergency power.

The complete 444.725 repeater, 220 remote base and packet gear is equipped with emergency power and should have enough 'juice' to go for a few days (perhaps a week) without problem.  The six meter side and DStar will go 'dark' without commercial power.

This photo shows the side of the rack with the 52.92MHz Motorola Micor 100w power amplifier at the very top on the rear (left) side.

Below the six meter amp is the six cavity UHF duplexer and below that is the 444.725MHz 75w Micor power amp.

There is a pair of 'muffin fans' which keep the air circulating over the UHF Mitrek and the power amps.

As you can see, there are many wires connecting the various items.

On the lower left is a bandpass cavity for the 145.07 packet node.

Next to the bandpass cavity is yet another 52.42 receiver for the six meter repeater, this one (from an RCA700 system) is connected to the lower 6mtr antenna (though it is unused at the moment).

Atop the rack is where I used to have a three port X1J4 TheNet packet node. This has since been taken out of service.

I've put online a few notes on how I convert Motorola Mitrek's for repeater use, along with how I built that battery combiner

Starting at the bottom, there is a Motorola SyntorX transceiver which was the wI0OK-7 145.07 TheNet node. This has the 'hi sens' option and is tuned back to 60w. The TNC connected to this transceiver is the very top TNC, the MFJ1270 just below the Control Operator Ducky.

Above the SyntorX is a UHF Motorola Mitrek ('rx-2') which is used as the #2 449.725 receiver, and could be placed into service as a backup for the main 444.725 repeater should the other Mitrek fail. This receiver is crucial for HT coverage at Arts Tavern in downtown Glen Arbor-- it's fed with that lower antenna that does not have a nasty tower shadow to the downtown area as the higher antenna has.

Atop the 449.725 'rx-2' Mitrek is a six cavity mobile duplexer.  This is used to feed RF to both the alternate 449.725 receiver and the 440.05 link receiver and provide adequate isolation from the other UHF transmitters on site.

Atop the mobile duplexer duplexer is yet another Motorola Mitrek.  This Mitrek was the 433.125/438.125MHz bit regenerative 1200 baud packet repeater.  This is the wI0OK-2 TheNet port.  Atop this Mitrek are the TNCs associated with this packet node, two MFJ1270's.

Behind the rack, atop the block wall is a lime green six cavity Celwave UHF duplexer which was used for the 433mHz packet repeater (and is now part of the 442.2 Harrietta rptr)-- even atop the rack I ran out of space!

I have a special packet page with information on the local packet systems and how to get the most out of TheNet and Jnos from a users perspective.

Above the racks, in the roof truss system is where I've managed to place the two meter and six meter duplexers.

Shown here is a really swell 2m six cavity duplexer that is used for the 145.36 DStar repeater.

If you stand in front of the repeater rack and look up you can see the eight stub heliax six meter duplexer.

This was the first of these that I've built using the WB5WPA design.

This duplexer works great and has been trouble free. Thanks to Del WB8DEL for donating the heliax (amongst other things).

The duplexer fits nicely on a 4' x 2' piece of OSB and mounted to the bottom chord of the roof trusses.  It was tough to get it up there, but it's out of the way.

I plan to build another of these duplexers, with more 'beefy' interconnecting cables, and then crank the power on 52.92MHz up to the full 100w the system is capable of.  I hesitate running the system at full power as I used RG58 in the interconnecting cables and wish for more 'reserve' power handling capacity.

I have a page with more info on building one of these 6mtr duplexers.

ver 4/11