2 Meter Portable Repeater

[rescuecomm]

I have a 2 meter wide split repeater for portable use only. The present input frequency is 147.600 mhz which is unused in our area because the 147.000 mhz repeater uses the low input (146.400 mhz). The output frequency is 145.110 mhz which is not used in our area. The problem during the last communications test was getting Yaesu radios to program the 2.490 mhz offset. It appears that the VX-170 and other units can easily do a 2.500 mhz offset, but requires a rather lengthy keystroke sequence to do the 2.490 split. No one was able to do it on the fly without their software. To remedy the situation, I have a choice of buying a new crystal for the transmitter to move it lower in frequency (145.100 mhz is easiest, but not really a bandplan frequency). The other choice is to recrystal the receiver to 147.610 mhz. Any changes need to be multiples of 50 khz which is the odd split step in the Yaseu radios. The repeater is an old Micor trunk mount conversion. Changing the transmit is easy and the repeater will see very limited on air time. Any suggestions? I am in the SERA coordination area.

Bob

 

[gewecke]

What's wrong with a standard split for your portable repeater? Kiss principle might apply here?:lol:
N9ZAS

 

[zz0468]

Consider who's going to use this thing, what they're going to use it for, and what they're going to talk to it with. If it's to have any utility at all, it needs to be reasonably easy for the users, and that may well include sticking to a standard 600 KHz frequency split.

It's customary for repeater owners to put the repeater on the frequency it needs to be, rather than trying to get the rest of the world to conform. That seldom works out as well as you'd think it would.

What does the bandplan have to say about temporary repeaters? Why are you restricting yourself to an odd split? What's limiting you from applying for coordination for a temporary pair to be used only on whatever special occasion causes you to pull this thing out?

 

[mancow]

How are you going to make a 600 kHz split capable duplexer portable, or reasonably portable? I'm staring at one in the room here and it's about 2.5 ft x 2.5 ft x 2 ft.

 

[zz0468]

How are you going to make a 600 kHz split capable duplexer portable, or reasonably portable? I'm staring at one in the room here and it's about 2.5 ft x 2.5 ft x 2 ft.

Good question, but running the repeater at low power can reduce the isolation requirements to the point that a compact duplexer can work just fine. Remember the old MTS and IMTS phones, and the compact duplexers they used?

Then again, there is the old WWII era definition of "portable" - anything that can be loaded on to a truck.

 

[gewecke]

How are you going to make a 600 kHz split capable duplexer portable, or reasonably portable? I'm staring at one in the room here and it's about 2.5 ft x 2.5 ft x 2 ft.

There ARE Phelps-Dodge mobile vhf mobile duplexers that will do this.
N9ZAS

 

[kayn1n32008]

I have a 2 meter wide split repeater for portable use only. The present input frequency is 147.600 mhz which is unused in our area because the 147.000 mhz repeater uses the low input (146.400 mhz). The output frequency is 145.110 mhz which is not used in our area. The problem during the last communications test was getting Yaesu radios to program the 2.490 mhz offset. It appears that the VX-170 and other units can easily do a 2.500 mhz offset, but requires a rather lengthy keystroke sequence to do the 2.490 split. No one was able to do it on the fly without their software.

The VX-170 will store independant transmit and recieve frequiencies. no software needed and it is easy to do on the fly. all the non-ham memories in mine have a 146.440Mhz transmit.

i donot know about all ham stuff but i can think of a couple other radios that would do it too

in the first picture you will see that both the +and - signs are on. this is a memory that has independent transmit and recieve frequencies. In the second picture, just the - sign (oddsplit repeaater) is showing. this is a standard 600Khz offset, down, not up from the 147.060 recieve in the sorry for the lousy pictures but it is my camera phone and bad light.

If you have questions on how to do it PM me and i will step you through it

 

[kayn1n32008]

Good question, but running the repeater at low power can reduce the isolation requirements to the point that a compact duplexer can work just fine. Remember the old MTS and IMTS phones, and the compact duplexers they used?

Then again, there is the old WWII era definition of "portable" - anything that can be loaded on to a truck.

Not sure what the offset the equipment you are thinking of but in BC/Yukon the MTS mobiles transmitted 5.26Mhz higher than the base.

 

[prcguy]

Not really, they are rated for a 5 to 6MHz split, not 600KHz. I have a rather small VHF duplexer that will do a 1MHz split and its a 4 cavity pass/notch thats about 2 1/2ft X 1 1/2ft X 4in. I also had a pile of VHF mobile duplexers but they are 5MHz minimum split for 70dB isolation and about 1.2dB through loss.
prcguy

There ARE Phelps-Dodge mobile vhf mobile duplexers that will do this.
N9ZAS

 

[zz0468]

Not sure what the offset the equipment you are thinking of but in BC/Yukon the MTS mobiles transmitted 5.26Mhz higher than the base.

Yes, and the duplexers were tiny. The point being, a reasonably small duplexer for a portable repeater can be made to work if transmitter power is low enough.

 

[kayn1n32008]

Yes, and the duplexers were tiny. The point being, a reasonably small duplexer for a portable repeater can be made to work if transmitter power is low enough.

well as prcguy stated after me:

...They are rated for a 5 to 6MHz split, not 600KHz... I also had a pile of VHF mobile duplexers but they are 5MHz MINIMUM split for 70dB isolation and about 1.2dB through loss.
prcguy

it may 'work' but how well? what kind of isolation at 600Khz split? its trying to make a repeater out of components that are not designed to work how you are wanting them to work. yes they maybe tiny but not made for a 600Khz split

 

[mancow]

It's too bad we don't have a bit of spectrum at least 5 megs away in the Vhf band. It would be nice to be able to throw together a small repeater out of those little mobile duplexers like you can do with Uhf.

 

[zz0468]

well as prcguy stated after me:



it may 'work' but how well? what kind of isolation at 600Khz split? its trying to make a repeater out of components that are not designed to work how you are wanting them to work. yes they maybe tiny but not made for a 600Khz split

Perhaps I need to make myself a bit more clear. I'm certainly NOT advocating using a 5 MHz split mobile duplexer for a 600 KHz split repeater. The point I'm trying to make, in response to mancows comment about a 2.5 ft x 2.5 ft x 2 ft contraption, is that if REASONABLE design limitations and performance objectives are observed, a 600 KHz spaced duplexer for a portable repeater application need not be nearly that large.

 

[zz0468]

It's too bad we don't have a bit of spectrum at least 5 megs away in the Vhf band. It would be nice to be able to throw together a small repeater out of those little mobile duplexers like you can do with Uhf.

I've seen some helical resonator type duplexers for VHF, they're rated for a couple of MHz and 100 watts. I suspect that they could be made to work with 600 KHz spacing, and maybe 10 watts or so.

Perhaps I should get my hands on one and make some measurements.

 

[N1BHH]

The problem with most people is that they want to program with the dang software. Learn your radio and how to program it an all the features before you get the software. That way you'll be able to do it on the fly.

As far as setting up a portable repeater, your local repeater coordinators may have a problem with some of the frequencies you have in mind. The rule of thumb is to have your input and output fall within the standard band plan, just having it on 2 meters just won't do. An input or output at 145.1 would encroach upon packet users on 145.09 and would also not be in the recommended repeater input/output band plan. the 145.11-145.49 section is generally 20 kilohertz spacing, while the 146.01-147.99 section is generally 15 kilohertz, although some areas of the country are all 20 kilohertz there. Why not get a dedicated coordinated pair so that you can set up when needed and everyone can know the proper frequencies. And of course use PL so that you avoid unwanted signals.

Separate antennas will work. Many repeaters have split antennas. It's been common for years. One thing about duplexers, they need to be kept in a clean controlled environment, as changes in temperature can also change the tuning. Every time you move them, you need to tune them.

 

[rescuecomm]

1. Mancow has it correct. The Sinclair Helical Filter duplexer is barely usable at about 2.5 mhz split with the excellent Micor front end. Anything more is too bulky and delicate for the proscribed usage.
2. SERA has no portable wide spaced 2 meter repeater pairs to apply for. Why tie up a regular freq pair for something that may be used a couple of weeks out of the year?
3. In its present configuration, the repeater is small, compact, can be hidden in the woods easily and I am not out of any real money if someone steals it. Adding multiple antennas and things that have to be adjusted defeats the purpose.

The problem with most people is that they want to program with the dang software. Learn your radio and how to program it an all the features before you get the software. That way you'll be able to do it on the fly.

Exactly why we had to use a crossband repeater during the last test. People simply don't bother. My Icom radios were very straightforward to keypad the odd split. Unfortunately, most of the ops doing backcountry work were using Yaseu stuff.


Bob

 

[prcguy]

Yes it does unless you can change physics.
The problem is the Q of a helical resonator is not high enough to give a narrow enough band pass for the less than .4% bandwidth needed for 600KHz spacing, even with multiple stages. If you had enough of them it could work but you would probably be looking at 10dB insertion loss.

It takes six full size 1/4 wave band pass cavities with notch filters to give high performance (120dB rejection and .75dB through loss) at 600KHz. With 4 full size cavities the notch is so wide they cut into the band pass of the other side and loss goes through the roof at 600KHz.

It would be much easier to separate antennas and run low power with a high quality receiver, and then you may have close spaced transmitter noise that wipes out weak signals.
prcguy

Perhaps I need to make myself a bit more clear. I'm certainly NOT advocating using a 5 MHz split mobile duplexer for a 600 KHz split repeater. The point I'm trying to make, in response to mancows comment about a 2.5 ft x 2.5 ft x 2 ft contraption, is that if REASONABLE design limitations and performance objectives are observed, a 600 KHz spaced duplexer for a portable repeater application need not be nearly that large.

 

[zz0468]

Yes it does unless you can change physics.
The problem is the Q of a helical resonator is not high enough to give a narrow enough band pass for the less than .4% bandwidth needed for 600KHz spacing, even with multiple stages. If you had enough of them it could work but you would probably be looking at 10dB insertion loss.

It takes six full size 1/4 wave band pass cavities with notch filters to give high performance (120dB rejection and .75dB through loss) at 600KHz. With 4 full size cavities the notch is so wide they cut into the band pass of the other side and loss goes through the roof at 600KHz.

It would be much easier to separate antennas and run low power with a high quality receiver, and then you may have close spaced transmitter noise that wipes out weak signals.
prcguy

You're absolutely correct - but... you missed my comment about reasonable design limitations and performance objectives. It's a portable repeater we're talking about. Why use a duplexer with 120 db isolation if the requirement is 70 db isolation? What's still unclear is the OP's transmitter power requiremensts. If he needs 100 watts, the conversation is moot - and you're dead nuts right on. If the requirement is for 5 watts, a whole lot of possibilities open up. That's all I'm trying to say.

 

[prcguy]

When I mentioned the .4% bandwidth problem in making a filter, that would be like a 3dB down spec. In reality for marginal duplex performance at low power you might need at least 25dB down per duplexer leg @ 600KHz for a maximum rejection of 50dB. With a 5w transmitter that would leave a signal around -43dBm or about 1,500uv of signal 600KHz away in your receiver, not counting transmitter dirt thats nowonly 25dB down. Couple that with lots of insertion loss because its small and compromised and you have a repeater that might work a very small area if it doesn't lock itself up.
prcguy

You're absolutely correct - but... you missed my comment about reasonable design limitations and performance objectives. It's a portable repeater we're talking about. Why use a duplexer with 120 db isolation if the requirement is 70 db isolation? What's still unclear is the OP's transmitter power requiremensts. If he needs 100 watts, the conversation is moot - and you're dead nuts right on. If the requirement is for 5 watts, a whole lot of possibilities open up. That's all I'm trying to say.

 

[prcguy]

And another thing, the 6 cavitie small mobile VHF duplexers are rated around 70dB isolation at 5MHz. How are you gonna keep that spec and narrow the BW by over 10X?
prcguy

You're absolutely correct - but... you missed my comment about reasonable design limitations and performance objectives. It's a portable repeater we're talking about. Why use a duplexer with 120 db isolation if the requirement is 70 db isolation? What's still unclear is the OP's transmitter power requiremensts. If he needs 100 watts, the conversation is moot - and you're dead nuts right on. If the requirement is for 5 watts, a whole lot of possibilities open up. That's all I'm trying to say.