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10 MHz Split vs. Filter Technology


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Poll: Which approach do you prefer? (2 member(s) have cast votes)

Finding more spectrum, or making cheaper, better solid-state filters?

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#21 WPXM352

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Posted 07 February 2019 - 09:31 PM

Transportable != mobile.  Compliance could be achieved by, for example, powering it from an external 120v circuit via extension cord, or a double-pole double-throw switch that disconnects the battery from the vehicle and prevents vehicle operation while the repeater is in operation.  Tapping the signal line to the "BRAKE (!)" light on the dash to enable the repeater controller is yet a third option.  This is an engineering problem, and it is fairly tractable.  I may not have the patience to hack together the fanciest options, but running the gear off an extension cord should be quite simple, and would in fact allow me to locate the whole kit 'n caboodle in a truck tool box that can be moved, removed, or carried up a freight elevator if a rooftop is available and convenient.

 

:lol:

 

Exactly the edge-case I have in mind.  Besides that, the balloon-lofted antenna in my hobby project simply cannot be deployed in motion, or you won't have a balloon-lofted antenna - or any antenna - very long.  I was planning on something to support a local festival like the Highland games, and people enjoying themselves there.  (PS, really don't use that thing around power lines, and especially high-tension lines.   ;) )

 

I'm working on it.  But mostly this stuff is already available to amateurs, and does me absolutely zero good 'cause nobody else I know has, or is willing to, get an amateur license.  If they give me a justification, it's either due to not being arsed to study, too much hassle, or perceived toxicity in the culture surrounding amateur radio.  "Pushing forward the state of the art" as used here is really about improving the products available to customers via retail channels.  Finding new handies that are repeater-capable is an exercise in scouring eBay for new old stock.  I think the only products available are the TERA TR-505 and the BTECH GMRS-V1; the former requires PC programming and won't cover all the channels in the service, the latter requires … actually the BaoFeng meets spec IMHO.

 

I mean, if nobody makes it yet, there's always Kickstarter…

 

Not that I'll be ready for that until I have a few more years' experience under my belt, but I still really like the idea of a combination satnav and 50 watt GMRS radio.

 I don't think you have to go to fancy extremes to be compliant. Just don't operate with a balloon tailing behind you on the 417!.

 

"perceived toxicity in the culture surrounding amateur radio"

 

I am a ham and have seen this time and again. Folks ask on the board how they can get reliable two way communications for family and the answer right away is to get a ham license for every member of the family. I know of a few families where that is the case, but they are unicorns. Then there are the FCC "Nazi's" who look for an infraction in every sort of activity not positively supported by the rules, or twist wording to favor their prohibition de jour. Fact is If it is not specifically prohibited it is probably OK, The FCC's GMRS infraction filing cabinet buried deep in warehouse 13 in Gettysburg is mostly an empty drawer. The few NAL's they write are commercial users on GMRS channels. Or GMRS operators that are jamming part 90, well one guy from California basically. The filing cabinet for Ham radio infractions takes up three floors.


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#22 Ian

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Posted 09 February 2019 - 06:46 AM

 I don't think you have to go to fancy extremes to be compliant. Just don't operate with a balloon tailing behind you on the 417!.

 

"perceived toxicity in the culture surrounding amateur radio"

 

I am a ham and have seen this time and again. Folks ask on the board how they can get reliable two way communications for family and the answer right away is to get a ham license for every member of the family. I know of a few families where that is the case, but they are unicorns. Then there are the FCC "Nazi's" who look for an infraction in every sort of activity not positively supported by the rules, or twist wording to favor their prohibition de jour. Fact is If it is not specifically prohibited it is probably OK, The FCC's GMRS infraction filing cabinet buried deep in warehouse 13 in Gettysburg is mostly an empty drawer. The few NAL's they write are commercial users on GMRS channels. Or GMRS operators that are jamming part 90, well one guy from California basically. The filing cabinet for Ham radio infractions takes up three floors.

:D

 

I'm reminded of this Reddit thread.

 

Also, regarding balloons tailing behind me on the 417…

missile-balloons-for-your-car-xl.jpg

 

Edited to add:  Thank you for building a repeater that can be used by your neighbors in a pinch!  Especially in a hurricane area, that's a potential lifeline.


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#23 RCM

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Posted 09 February 2019 - 11:04 AM

:lol: :lol: :lol:



#24 n4gix

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Posted 09 February 2019 - 02:26 PM

At my club's board meeting last evening, I made a motion that we as a club make it known that GMRS licensees are welcome to become auxiliary members. Discussions will be ongoing for the next few monthly BoD meetings. Hopefully my motion will be passed and then we can present the proposal to the general membership.


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#25 Ian

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Posted 22 March 2019 - 12:54 AM

Well, I can help answer some of your questions....

 

The 452 MHz band is fully used by broadcasting, public safety, and general business radio service. (as is the entire 450-470 MHz band, except for our very generous slice)

The 472 MHz band is right in the middle of over-the-air television channel 14, which uses up everything between 470-476 MHz. 476-482 is channel 15, and it goes up every 6 MHz from there until you hit cellular telephone, which is currently 614-890 MHz, and expanding.

 

There is no such thing as an "underutilized slice of spectrum" in the UHF band, or anywhere else for that matter.

 

There is no problem with our current 5 MHz split.  It has been working just fine for decades.  There is already a filtering solution for this.  It is known as cavity filtering.  A set of UHF cavities made to handle 50 watts is about the same size as that little toy shoe-box repeater you linked to in your post, and the tuning on most are loose enough to be used on any 2 adjacent channels.  You seem to want an 8 channel repeater - I still don't know why you need this.  This thing you linked to is only 10 Watts anyway.  Just use Simplex.

 

Interesting note: That Retivis repeater seems to be built into a re-purposed cable TV line amp box.

 

Lastly, please refrain from using non-appropriate language on this site.

 

Fridge logic has struck me.  In how much of the country is channel 14 being used?

 

Microsoft is pursuing whitespace broadband designed to use under-utilized TV channels.  I can't help but wonder if that will herald a loosening up of these allocations -- or a clamping down on our guard bands.



#26 Jones

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Posted 23 March 2019 - 11:35 AM

...  In how much of the country is channel 14 being used?

 

 

A few hundred stations are currently on Channel 14, and will be more after the re-pack of TV channels is completed in a few more years.

Two different lists (with some overlap):

 

https://en.wikipedia...e_United_States

 

https://en.wikipedia...e_United_States



#27 berkinet

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Posted 23 March 2019 - 12:42 PM

...  In how much of the country is channel 14 being used?

 

In addition to @Jones comments. If the channel 14 frequency spectrum was used in even just one area of the country, the FCC would, with good reason, never allow the spectrum to be used for another service that did not have geographic restrictions in its licensing. Eg. GMRS.


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#28 WRAF213

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Posted 25 March 2019 - 03:08 AM

Adding T-Band spectrum to Part 90 use comes at a huge cost to broadcast services, which is why T-Band is only available where necessary. Broadcast spectrum won't be released unless the buyer can afford to give the FCC the money that spectrum's worth.

Whitespace devices are Part 15 and have several restrictions on their operation to reduce broadcast interference; they aren't high-power, fixed-frequency narrowband voice solutions. Lately the telecom industry has been leading a crusade against 'underutilized spectrum', eyeballing 9cm, 6cm, and 3cm Amateur bands along with the bottom of 70cm in hopes of getting free 'whitespace' spectrum (which is subject to the fundamental flaw of the hidden-node problem, particularly on duplex links). In October, 462.5375 and 462.7375 became available for allocation with a 4K00 mask or narrower per FCC-18-143.

Those licensees are paying far, far more money for that spectrum than we are, and our use case barely justifies what we have now (see FRS 22-channel expansion). We aren't going to get more than we already have.
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#29 Ian

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Posted 17 May 2019 - 03:18 AM

Okay, so it's time for some necromancy...  

 

The Retevis RT-97 that's motivated this thread is available now in eight different versions, and two of them are tuned to your spec (UHF and VHF versions)!

 

The boneheaded thing is that the split is backwards.  This thing can only be programmed with the Tx above the Rx.  So progress, perhaps, but the lunchbox repeater isn't ready for us yet.  Personally, it looks kinda nice, given that Kenwood 820s on eBay lately have all been broken, were missing buttons, or have occasionally had their controller boards removed and replaced with plugs for an external controller.  The GR1225s are routinely in better shape, but none of this has been in the budget for me lately, alas.  (I keep hoping I'll get lucky at an estate sale or something.)



#30 berkinet

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Posted 17 May 2019 - 06:44 AM

...The GR1225s are routinely in better shape, but none of this has been in the budget for me lately, alas.  (I keep hoping I'll get lucky at an estate sale or something.)

 

Well, from what I see on ebay for GR1225 UHF repeaters, there are several at or below the $399 price tag for the Retevis RT97. On a good (I.e. lucky) day you could even get an MTR2000 under $400.

 

BTW, should you decide to go for the GR1225, make sure you get a guarantee that the final PA is good. These radios have a nasty habit of either blowing or desoldering the final if run at too high a duty cycle, or too high power output. You should also ask to have the duplexer tuned for you.

 

However, if you run a GR1225 at 50% duty cycle and 1/2 power, it will give you excellent service and is small enough to be portable.


Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.

-- Marcus Aurelius


#31 Corey

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Posted 17 May 2019 - 11:28 AM

Well, from what I see on ebay for GR1225 UHF repeaters, there are several at or below the $399 price tag for the Retevis RT97. On a good (I.e. lucky) day you could even get an MTR2000 under $400.

 

BTW, should you decide to go for the GR1225, make sure you get a guarantee that the final PA is good. These radios have a nasty habit of either blowing or desoldering the final if run at too high a duty cycle, or too high power output. You should also ask to have the duplexer tuned for you.

 

However, if you run a GR1225 at 50% duty cycle and 1/2 power, it will give you excellent service and is small enough to be portable.

 

You cant go wrong with an MRT2000, this lunchbox repeater idea has been beat to death and tried with mostly poor results by many. I have not seen a single lunchbox or ammo can repeater outperform simplex. I currently own many MTR2000's with 5 of them in GMRS service at this time. I have also built and sold several others as turn key repeaters for people without a single complaint. I looked into this retevis RT97 and it has no FCC certification, its intended market is HAM or out of the country use.


Just My $.02

 

Corey

 

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https://mwgmrs.com


#32 Ian

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Posted Today, 06:30 PM

Oh, I'm well aware it's a ham repeater at the moment.  I'm just pleased that someone's working on something that could be adapted to legal, off-the-shelf GMRS use for under a grand, new.

 

Emphasis new.

 

Sooner or later, the surplus will either run out, or get priced out of affordability as it gets scarce.

 

Hopefully this sort of thing will be available before that happens.






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