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Author Topic: Using a jetstream 220 mobile?  (Read 13247 times)
KE6JZ
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Posts: 13




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« on: April 14, 2012, 08:58:52 AM »

Hello,

Has anyone tried or considered trying a Jetstream mobile back to back as a repeater? 50 watts out could be reduced to 25 to lessen strain on the PA. Any ideas?
Shane
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N5VTU
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Posts: 349




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« Reply #1 on: April 14, 2012, 04:45:32 PM »

I use a Jetstream 2200 for a base rig and it gets pretty warm at the mid power setting.  I guess making a repeater out of a pair of them could be done, but even 25 watts of continuous duty would probably kill it.  A local ham has a repeater made out of back to back Alinco 220 mobiles and is required to use supplemental cooling even at the lowest power setting, which I believe is either 5w or 10w for that particular radio.

You might consider using the back to back Jetstreams set at the lowest power setting, and then using a continuous duty external amplifier if you need higher output.

Take a look at http://www.repeater-builder.com/rbtip/ for more information.

Stephen
N5VTU
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K1CJS
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Posts: 5885




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« Reply #2 on: May 03, 2012, 08:53:43 AM »

One of the things that repeater builders do for best results is use commercial gear.  That gear has a higher duty cycle rating than almost all ham gear--but for the 220 band, that kind of gear is almost non-existant.  One local repeater in my area also has two Alinco 220 machines back to back in use for an area repeater, but the output power of the transmitter rig has been turned down to less than twenty watts from its maximum.  That repeater has also been located in the license trustees shack--where he can check it and disable it at any time.

Bottom line?  Yes, it can be done, but it isn't really good to do if the repeater will be at an unattended site.  The 220 mhz rigs just aren't as robust or reliable as the commercial gear that makes up the greater part of the 2 meter and 70 cm repeaters in use.
« Last Edit: May 05, 2012, 07:11:37 AM by K1CJS » Logged
WB2WIK
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Posts: 20547




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« Reply #3 on: June 11, 2012, 02:27:18 PM »

One of the things that repeater builders do for best results is use commercial gear.  That gear has a higher duty cycle rating than almost all ham gear--but for the 220 band, that kind of gear is almost non-existant.  One local repeater in my area also has two Alinco 220 machines back to back in use for an area repeater, but the output power of the transmitter rig has been turned down to less than twenty watts from its maximum.  That repeater has also been located in the license trustees shack--where he can check it and disable it at any time.

Bottom line?  Yes, it can be done, but it isn't really good to do if the repeater will be at an unattended site.  The 220 mhz rigs just aren't as robust or reliable as the commercial gear that makes up the greater part of the 2 meter and 70 cm repeaters in use.

I might also add that two mobile radios co-located (same physical location) normally wouldn't make any sort of repeater worth a darn due to the RECEIVER, which can be desensitized by the local transmitter even with a very good cavity duplexer, and also the TRANSMITTER off-channel noise, which usually isn't reduced even if you turn the power down.  The transmitter wasn't designed to be down 100 dB at 1.6 MHz offset, since in normal operation that doesn't matter at all.  In repeater operation, it matters.

These rigs don't have any real shielding to speak of and the only thing decoupling them from their DC power source is bypass capacitors.  Normally, that isn't nearly enough to keep the TX from getting back into the RX of the other rig.

Transmitter duty cycle would be almost the very last of my worries, as a combination of turning the power down and adding cooling fans could probably keep it reasonably cool.  I wouldn't use it without fans.

Then, if it's at a remote hilltop site without heating, the rigs could easily get too cold to even function.  A lot of amateur and consumer electronic gear isn't rated for operation below 0C (32F) and a hilltop repeater site in most places can get much colder than that.

This is why "real repeater gear" costs more.  It's designed for greater thermal extremes, is adequately heatsinked and cooled to permit continuous operation; the TX and RX and in very well shielded, separate compartments with DC feedthrough LC networks to isolate them both from the power source; the RX usually has a helical resonator in the first RF stage to start rolling off anything outside the band (high or low side); and the transmitters are designed for a reduced off channel noise spectrum.  They're also usually more frequency stable over temp extremes.  Amateur synthesized gear can drift in frequency quite a lot between 0 and 100 degrees F, while repeaters shouldn't and usually don't.
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KB9BPF
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Posts: 22




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« Reply #4 on: June 12, 2012, 06:53:15 AM »

All the things the other posters have said is true. For optimum performance there is no good substitute for commercial gear. I've been longing to convert a couple Micors to 220 using instructions on the Repeater Builder site in order to have Micor quaity on 220.

HOWEVER...

This is a hobby, after all. Hams in the St. Louis area may remember Bill Preiss K9KE, SK (ex- K9DZY) who had several high-profile repeaters that served the region extremely well for many years. Bill was a successful businessman, had money for toys, and given the nature of his repeater 'toys', shared them with the amateur community generously.

Maintaining commercial standards is essential if you're piggybacking at a 'big boys' site where it's important not to do anything that disrupts operations of the paying tenants. Bill's repeaters tended to be located at sites which weren't shared with non-hams. Indeed, they were usually his own sites. (At one time the 145.13 repeater was on a 1200-ft commercial tower Bill had purchased! After a few years he sold the tower to commecial interests and '13 moved back to it's old home on one of Bill's 200-footers located at one of his apartment complexes.) When Western Union went bankrupt they sold their infrastructure at ridiculously low prices (relative to their contruction cost) and for a time he had a couple 400-ft. H-frame towers all to himself.

Bill owned some commercial gear - Kenwood repeaters come to mind - but most of his repeaters were strung-together ham gear, often lying on an old desk or card table with the cases open and unshielded wires tack-soldered to the PC board for access to audio and PTT lines, which went to the controller. No disrespect intended to Bill, but the ones I saw were pretty haywire. I honestly don't know how it all worked as well as it did, but work, they did! And were some great assets which are sorely missed now that they're gone.

Moral of the story: If you've got control of your site and can afford to experiment, don't be shy! You will have to work harder in the long run, pay more in the long run, and will be forced to accept performance compromises, but it will be a labor of love and I suspect you'll wind up learning a lot more about RF, too!
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KG4BEK
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Posts: 2




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« Reply #5 on: December 15, 2012, 06:05:04 AM »

I have tried using the Jetstream 220 Mobile as a repeater transmitter.  Unfortunately it gets way to hot and shuts down, even at lower power settings.  I did run a fan to keep it cool but that was not enough.  The Jetstream radio is fine as a mobile or base radio but it is not built well enough to be a full duty cycle repeater transmitter. 
The Alinco Dr-235 works great at it's full power settings.  If you check the power output after it comes out of the duplexers you loose about 5 watts.  The transmit power is only about 20 watts once it reaches the antenna.  If you have the antenna at a good height it will work well.  I do wish Alinco would make a 50 Watt 220 MHz radio. 

If you are interested in a 220 repeater you might want to check out the 220 MHz facebook page:
http://www.facebook.com/pages/The-Charleston-SC-220-MHz-Repeater-Club/133149446773560?ref=hl

You can also email me at KG4BEK@aol.com if you have any questions.  The repeater is also connected to Echolink if you would like to talk to contact me.
Chris
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WB5ITT
Member

Posts: 100




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« Reply #6 on: May 10, 2013, 05:31:47 PM »

All the things the other posters have said is true. For optimum performance there is no good substitute for commercial gear. I've been longing to convert a couple Micors to 220 using instructions on the Repeater Builder site in order to have Micor quaity on 220.


Go with a GE MII/Exec II or MVP.....better performance than a MICOR on 220....and better audio.
BTW KW did make a 220 repeater. The TKR-720 was available on the 216-225MHz range...but not sure how many were sold and they are rare to find in that range. Most 720 models are 144-174.
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KB9BPF
Member

Posts: 22




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« Reply #7 on: May 18, 2013, 09:49:02 PM »

All the things the other posters have said is true. For optimum performance there is no good substitute for commercial gear. I've been longing to convert a couple Micors to 220 using instructions on the Repeater Builder site in order to have Micor quaity on 220.


Go with a GE MII/Exec II or MVP.....better performance than a MICOR on 220....and better audio.
BTW KW did make a 220 repeater. The TKR-720 was available on the 216-225MHz range...but not sure how many were sold and they are rare to find in that range. Most 720 models are 144-174.

Perhaps, but I have several Micors in the garage already.

73,
Brad
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