Here's something that's not too common anymore (unless you're the CHP). I am interested in building a 33 MHz repeater using a Maxtrac for receive and Desktrac for transmit. Two seperate antennas will be used. Input is 33.020. Output is 33.880.
My questions is....does the Maxtrac have enough rejection where this will work on lowband and not require any tuning networks?
The antennas will be 30 feet apart. We currently use carrier squelch, but the input will require a DPL to activate the link. Do I expect to see any problems with this?
question for a lowband repeater expert!
Moderator: Queue Moderator
At that frequency spacing ther will be some desense to the receiver and antenna spacing.
It would be better to try for way more seperation in frequency, like a couple of mhz or more.
You will need lots and lots of vert spacing on the antennas and at least a cavity filter on the receiver. I would also remove the diode antenna switch in the receiver radio to help the receiver intermod and the problems diodes cause in high rf inviorments.
If you could find a Micor mobile or base/repeater receiver, they mite be better at the closer spacing. They are fairly simple to interface to my custom built RICK module to make repeaters WORK.
It would be better to try for way more seperation in frequency, like a couple of mhz or more.
You will need lots and lots of vert spacing on the antennas and at least a cavity filter on the receiver. I would also remove the diode antenna switch in the receiver radio to help the receiver intermod and the problems diodes cause in high rf inviorments.
If you could find a Micor mobile or base/repeater receiver, they mite be better at the closer spacing. They are fairly simple to interface to my custom built RICK module to make repeaters WORK.
Unfortunately, those are the frequencies that our FD is licensed for. I'd love to be able to go down to about 31 MHz for the input, but it ain't happenin'. I think we MAY have an old Micor laying around that could be used for the receiver, if it would be better suited for the job. Any suggestions or recommendations on the input filter?
You will need a cavity filter, looks like a fourty gallon water heater. Thats what we called them, water heaters.
There are some used radio dealers that have used cavities and duplexers available. A lot of low band systems were replaced by trunking ect; and they are available on the used market.
What about more physical seperation, we used to have all the receivers in one building on the west end of the mountain and the transmitters on the east side in the old days. 500 feet at least, and oh all the problems with ESD on the buried phone lines going from the rx to tx buildings.
They don't call me "Will from the hill" for nothing!
<font size=-1>[ This Message was edited by: Will on 2002-01-01 16:05 ]</font>
There are some used radio dealers that have used cavities and duplexers available. A lot of low band systems were replaced by trunking ect; and they are available on the used market.
What about more physical seperation, we used to have all the receivers in one building on the west end of the mountain and the transmitters on the east side in the old days. 500 feet at least, and oh all the problems with ESD on the buried phone lines going from the rx to tx buildings.
They don't call me "Will from the hill" for nothing!
<font size=-1>[ This Message was edited by: Will on 2002-01-01 16:05 ]</font>
Jim,
With the frequency small frequency seperation you have, you will need a lot of seperation. Vertical seperation is about all thats practical. Horizontal takes much more distance. I would say that you should purchase a good duplexer (like Wacom), but that will be about $1k. You could look for some surplus cavities, and use them with 2 antennas seperated vertically. Use identical antennas for best results, and cable with very good shielding. Also, keeping the power low will help the desense issue, but hinder coverage.
Remember....There's no band like low band!
Josh
With the frequency small frequency seperation you have, you will need a lot of seperation. Vertical seperation is about all thats practical. Horizontal takes much more distance. I would say that you should purchase a good duplexer (like Wacom), but that will be about $1k. You could look for some surplus cavities, and use them with 2 antennas seperated vertically. Use identical antennas for best results, and cable with very good shielding. Also, keeping the power low will help the desense issue, but hinder coverage.
Remember....There's no band like low band!
Josh
We use several Maxtracs as receivers in the 44.XX Range for our Channel 2 Repeater, even at a 4 MHz spacing from our Transmit Frequency the Maxtrac Sufferd From Some Really Bad Desense. Our Solution Was Separation by about a Mile and Linking via an Existing Microwave Link. Many Folks also use UHF links as we do on another site.
Our Main repeater is a Mastr II Station with a water heater and it has been on the air for many years without a hitch.
Good Luck
Vince
Our Main repeater is a Mastr II Station with a water heater and it has been on the air for many years without a hitch.
Good Luck
Vince
That's one of the things that I was thinking about- to place the receiver at the other end of town and connect via phone or twisted pair. This would elliminate all of the problems above and probably even work better, as our station is on the edge of town.
We've been on lowband for years around here. Everyone wants to go to UHF or 800, but I still think lowband is the best and most reliable. All of the local "installers" think that you can throw an antenna on a car without tuning it and it's gonna work like it would with UHF. I can reliably talk at great distance with any base or mobile that I set up or installed. The big problem here is the hills- they play hell with a 4 watt HT. Once I get the link up, we'll be on a 110 watt rebroadcast.
I never realized a cavity for lowband was this size, as I've never done anything with a repeater in this band. Whew! If I keep everything at one location, I'm going to have to find somewhere to put that thing- I'm lucky to have room for the "Desktrac/PA in a box" cabinet.
We've been on lowband for years around here. Everyone wants to go to UHF or 800, but I still think lowband is the best and most reliable. All of the local "installers" think that you can throw an antenna on a car without tuning it and it's gonna work like it would with UHF. I can reliably talk at great distance with any base or mobile that I set up or installed. The big problem here is the hills- they play hell with a 4 watt HT. Once I get the link up, we'll be on a 110 watt rebroadcast.
I never realized a cavity for lowband was this size, as I've never done anything with a repeater in this band. Whew! If I keep everything at one location, I'm going to have to find somewhere to put that thing- I'm lucky to have room for the "Desktrac/PA in a box" cabinet.
If you are looking to improve your HT coverage, by repeating dont bother, it will probably still suck. You may have to add a bunch of remote receivers, & a voter setup.
If your current Mobile to Mobile, Mobile to Dispatch coverage is acceptable now perhaps you should consider crossband repeaters (PAC*RT)in your rigs & UHF or VHF High Portables.
If your current Mobile to Mobile, Mobile to Dispatch coverage is acceptable now perhaps you should consider crossband repeaters (PAC*RT)in your rigs & UHF or VHF High Portables.
Hi:
After reviewing most of the comments, which
I might add is pretty good, there were a few
things that I can add.
When dealing with " Close Spaced " Frequencies, one really can get some
ideal performance by lowering the Transmitt
Power....This will reduce the Desense in the
receiver.
Another way of improving the Tx-Rx performance is by finding a GOOD Notch
Filter....That way you can Notch" out
the Transmitt elements on the Receive
line....In other words, if you can find
a good Band-Pass / Band-Reject Cavity for
the Frequency range you are operating in, you wil be ahead of the game there......There are plans where one
can " build your own " or if you can get
a hold of a Low band RX-TX Brand Cavity, those will work very well....
As others have stated, good Vertical seperation is ideal too !!, To make it
better, use good 1/2" Hard-Line and make
sure you use RG-124B/U or better cable ( Minimum ) for all the interconnect cables
Keeping a VERY LOW vswr well help as well.
Please note, although Micors are still good
radios, they do NOT have the Selectivity of
a good Maxtrac, and if you can find a later
model radio with the Narrow Band spacing capabilities ( 12.5Hz ), you can lower the Tx Dev of your exsisting radios, and let the receiver improve the audio to your transmitter.
Running " just enough power" to suit your needs is a " Real Key " in making your system work properly while minimizing Desense
to the Receiver.
If you are a Die hard and wish to run 60 to
100 Watts, be prepared to pull out your pocket book, as a Suitable Duplexer for that
Close Range will be Expensive, and also
will be several times larger than your
Radio set up.
I too like Low Band, but that range has special needs ( and technical needs ) to make it work well...
One system I support here in Ca down here due to the ( High-Power )
has the Receiver Linked to the Transmitter via UHF and is spaced 40 Miles apart.
Receiver on ( 1 ) Mountain Top, Transmitter
on another. Linked together with a HT90/Factory Link made by Motorola
Works Great, no desense at all !!
Monty
After reviewing most of the comments, which
I might add is pretty good, there were a few
things that I can add.
When dealing with " Close Spaced " Frequencies, one really can get some
ideal performance by lowering the Transmitt
Power....This will reduce the Desense in the
receiver.
Another way of improving the Tx-Rx performance is by finding a GOOD Notch
Filter....That way you can Notch" out
the Transmitt elements on the Receive
line....In other words, if you can find
a good Band-Pass / Band-Reject Cavity for
the Frequency range you are operating in, you wil be ahead of the game there......There are plans where one
can " build your own " or if you can get
a hold of a Low band RX-TX Brand Cavity, those will work very well....
As others have stated, good Vertical seperation is ideal too !!, To make it
better, use good 1/2" Hard-Line and make
sure you use RG-124B/U or better cable ( Minimum ) for all the interconnect cables
Keeping a VERY LOW vswr well help as well.
Please note, although Micors are still good
radios, they do NOT have the Selectivity of
a good Maxtrac, and if you can find a later
model radio with the Narrow Band spacing capabilities ( 12.5Hz ), you can lower the Tx Dev of your exsisting radios, and let the receiver improve the audio to your transmitter.
Running " just enough power" to suit your needs is a " Real Key " in making your system work properly while minimizing Desense
to the Receiver.
If you are a Die hard and wish to run 60 to
100 Watts, be prepared to pull out your pocket book, as a Suitable Duplexer for that
Close Range will be Expensive, and also
will be several times larger than your
Radio set up.
I too like Low Band, but that range has special needs ( and technical needs ) to make it work well...
One system I support here in Ca down here due to the ( High-Power )
has the Receiver Linked to the Transmitter via UHF and is spaced 40 Miles apart.
Receiver on ( 1 ) Mountain Top, Transmitter
on another. Linked together with a HT90/Factory Link made by Motorola
Works Great, no desense at all !!
Monty
We're not looking to increase coverage. We can talk to each other in town just fine. Our dispatch center is three municipalities away and can't hear our portables. If we repeat with our base, the dispatch center along with our other station will hear us fine (with our base as the transmitter).
The dispatch center will not foot the bill for a remote receiver to be placed in town and our dept. will not pay for the phone line or a UHF/microwave link.
Doing the lowband repeater will accomplish what we need with only another radio, antenna and cavity. We already have a Desktrac and 110 Watt P.A. in place and I already have the few necessary materials to connect the Desktrac with another radio.
There are better ways we can do this, but $$$ is the object and the department bean counters don't want to spend it.
The dispatch center will not foot the bill for a remote receiver to be placed in town and our dept. will not pay for the phone line or a UHF/microwave link.
Doing the lowband repeater will accomplish what we need with only another radio, antenna and cavity. We already have a Desktrac and 110 Watt P.A. in place and I already have the few necessary materials to connect the Desktrac with another radio.
There are better ways we can do this, but $$$ is the object and the department bean counters don't want to spend it.
We're not looking to increase coverage. We can talk to each other in town just fine. Our dispatch center is three municipalities away and can't hear our portables. If we repeat with our base, the dispatch center along with our other station will hear us fine (with our base as the transmitter).
The dispatch center will not foot the bill for a remote receiver to be placed in town and our dept. will not pay for the phone line or a UHF/microwave link.
Doing the lowband repeater will accomplish what we need with only another radio, antenna and cavity. We already have a Desktrac and 110 Watt P.A. in place and I already have the few necessary materials to connect the Desktrac with another radio.
There are better ways we can do this, but $$$ is the object and the department bean counters don't want to spend it.
The dispatch center will not foot the bill for a remote receiver to be placed in town and our dept. will not pay for the phone line or a UHF/microwave link.
Doing the lowband repeater will accomplish what we need with only another radio, antenna and cavity. We already have a Desktrac and 110 Watt P.A. in place and I already have the few necessary materials to connect the Desktrac with another radio.
There are better ways we can do this, but $$$ is the object and the department bean counters don't want to spend it.
Jim,
You might create a huge nightmare by repeating, thats why I suggest crossband repeaters instead. Chances are more than not that the portable coverage will not be improved by much.
e-mail me direct.
[email protected]
Vince
You might create a huge nightmare by repeating, thats why I suggest crossband repeaters instead. Chances are more than not that the portable coverage will not be improved by much.
e-mail me direct.
[email protected]
Vince
-
Batman
- Posts: 973
- Joined: Sun Sep 09, 2001 4:00 pm
- What radios do you own?: JT1000, Spectras, CB-555, 540
Hey Jim
I have a couple of Mastr II L-Band Base Stations For sale also have a bunch of Mastr II mobiles. the base stations are 250w & 500w and the mobiles are 110w. i have all the cables and control heads make your best offer and bring a pickup truck!!!
Batman
ps: I live in Hunterdon County,NJ.
Lambertville,NJ.
Email: [email protected]
<font size=-1>[ This Message was edited by: Batman on 2002-01-02 13:07 ]</font>
I have a couple of Mastr II L-Band Base Stations For sale also have a bunch of Mastr II mobiles. the base stations are 250w & 500w and the mobiles are 110w. i have all the cables and control heads make your best offer and bring a pickup truck!!!
Batman
ps: I live in Hunterdon County,NJ.
Lambertville,NJ.
Email: [email protected]
<font size=-1>[ This Message was edited by: Batman on 2002-01-02 13:07 ]</font>
Last edited by Nand on Sun Jan 18, 2004 6:17 am, edited 1 time in total.
You would be better off trying to build several VHF (for the portables) to low band vehicle repeaters. They would cost much less. You get the use of the portables and still have the contact on low band to the dispatch.
I have had about 30 years with low band repeaters. As all have said above, the desence from the transmitters will be a problem. The noise floor of the receiver site is also a concern. You have to make sure that both your antennas are exactly above each other to get max isolation.
You need to use the best shielded coax you can afford. RG-214 or 1/2 heliax style cable is probable a good choice. Make sure you use type N connectors. These will give you the best connection and provide the max isolation.
You would be wise to find a receiver already set up with the RF isolation kit installed. The old Motrac and Micor base station repeater chassis have this option. If you use an old Maxtrac, you need to change the mixer transistor and change the bias. This makes a much better receiver than before the modification.
The filter cavities may be available from one of the old paging companies. Try to find one that use to maintain some of the lower frequencies. The cavities will be about 6 feet long and about 18 inches in across. Will take 2 people to move them. Not so much from the weight, but rather hard to move by yourself. Most of the ones I have seen in the past, were straped to the ceiling. That way, they didn't take up valuable floor space.
Jim
I have had about 30 years with low band repeaters. As all have said above, the desence from the transmitters will be a problem. The noise floor of the receiver site is also a concern. You have to make sure that both your antennas are exactly above each other to get max isolation.
You need to use the best shielded coax you can afford. RG-214 or 1/2 heliax style cable is probable a good choice. Make sure you use type N connectors. These will give you the best connection and provide the max isolation.
You would be wise to find a receiver already set up with the RF isolation kit installed. The old Motrac and Micor base station repeater chassis have this option. If you use an old Maxtrac, you need to change the mixer transistor and change the bias. This makes a much better receiver than before the modification.
The filter cavities may be available from one of the old paging companies. Try to find one that use to maintain some of the lower frequencies. The cavities will be about 6 feet long and about 18 inches in across. Will take 2 people to move them. Not so much from the weight, but rather hard to move by yourself. Most of the ones I have seen in the past, were straped to the ceiling. That way, they didn't take up valuable floor space.
Jim
Well.....we applied for three UHF frequencies 1-1/2 years ago and are still waiting.
I was hoping the lowband repeater would be an easy route to go, but it looks like there's a little more to repeating this band than what I thought. I'll have to run all of this info past the treasurer and see what is gonna happen. If they're willing to spend some $$$ for the phone link, the receiver will go at the other end of town and be hard wired to the xmtr. about 3/4 of a mile away.
I was hoping the lowband repeater would be an easy route to go, but it looks like there's a little more to repeating this band than what I thought. I'll have to run all of this info past the treasurer and see what is gonna happen. If they're willing to spend some $$$ for the phone link, the receiver will go at the other end of town and be hard wired to the xmtr. about 3/4 of a mile away.
Jim202, I noticed you reply a staement about a mod to the Maxtrac receiver. Do you have more info on this?
And I would agree on the mobile extender or a xband repeater on the other agencies frequency. Several fire departments who have centralized their dispatch are using simmular radio set ups.
Fire dept one has lowbwnd simplex with a local base and a cross band "link" on low power UHF to reach the dispatch center.
Also the Verdugo Dispatch center in Glendale Ca handels some nine cities fire departments including a volenteer department, using UHF linked into the exzisting VHF cahnnels.
And I would agree on the mobile extender or a xband repeater on the other agencies frequency. Several fire departments who have centralized their dispatch are using simmular radio set ups.
Fire dept one has lowbwnd simplex with a local base and a cross band "link" on low power UHF to reach the dispatch center.
Also the Verdugo Dispatch center in Glendale Ca handels some nine cities fire departments including a volenteer department, using UHF linked into the exzisting VHF cahnnels.
Another important factor to remember.
Check your license to ensure that your class of station permits repeater operation.
I am not sure what class shoud appear but most lowband firebases in my area were originally coordinated as a fixed base that did not permit repeating.
If after 1 1/2 years of waiting for the UHF license it still hasn't showed up, the freq coordinator needs called as the app probably fell through the cracks.
Check your license to ensure that your class of station permits repeater operation.
I am not sure what class shoud appear but most lowband firebases in my area were originally coordinated as a fixed base that did not permit repeating.
If after 1 1/2 years of waiting for the UHF license it still hasn't showed up, the freq coordinator needs called as the app probably fell through the cracks.
Jim,
My fire department had the same problem. We tried a micor repeater system with duplexers and had a lot of skip problems. We ended up placing a 100 watt micor base in a building below our city water tower, the antenna on top (125') and using a phone link into our dispatch center. The phone line is resonable, and we've found this to be the most stable option, in our case. Our handhelds can reach dispatch within a 10 mile radius (4 watts) and I've been able to talk to dispatch from 50-60 miles away with a little static, using a 60 watt maxtrac. Hope this helps.
Bundy
<font size=-1>[ This Message was edited by: bundy125 on 2002-01-03 11:58 ]</font>
My fire department had the same problem. We tried a micor repeater system with duplexers and had a lot of skip problems. We ended up placing a 100 watt micor base in a building below our city water tower, the antenna on top (125') and using a phone link into our dispatch center. The phone line is resonable, and we've found this to be the most stable option, in our case. Our handhelds can reach dispatch within a 10 mile radius (4 watts) and I've been able to talk to dispatch from 50-60 miles away with a little static, using a 60 watt maxtrac. Hope this helps.
Bundy
<font size=-1>[ This Message was edited by: bundy125 on 2002-01-03 11:58 ]</font>
[quote]
On 2002-01-03 03:12, Will wrote:
Jim202, I noticed you reply a staement about a mod to the Maxtrac receiver. Do you have more info on this?
Sorry Will, must have been almost asleep. I meant to say Motrac not Maxtrac to do the receiver mod to. Motorola has managed to provide us radio tweeks with too many trac type names in the last 30 years or so. Have to almost stop and think twice which word to use with the radio your talking about.
Jim
On 2002-01-03 03:12, Will wrote:
Jim202, I noticed you reply a staement about a mod to the Maxtrac receiver. Do you have more info on this?
Sorry Will, must have been almost asleep. I meant to say Motrac not Maxtrac to do the receiver mod to. Motorola has managed to provide us radio tweeks with too many trac type names in the last 30 years or so. Have to almost stop and think twice which word to use with the radio your talking about.
Jim
Thank you, Jim.
I am in the process of building some mobile extenders for a fire department. These little modules work on any Radius or Maxtrac mobile radios, and are small enough to put on the side of the radio in your car. I also make modules to add an rf link/repeater for cross band repeat/link to the dispatcher.
I am in the process of building some mobile extenders for a fire department. These little modules work on any Radius or Maxtrac mobile radios, and are small enough to put on the side of the radio in your car. I also make modules to add an rf link/repeater for cross band repeat/link to the dispatcher.