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Motorola DTR and DLR series 900MHz FHSS digital radios

n1das

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in 900 MHz License-Free Radios (ISM)

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n1das Apprentice

n1das

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Below is general information on the Motorola DTR and DLR series 900MHz FHSS digital radios.  I am a user of the DTRs and the DLRs and have become a serious fan of them because they are professional quality and work amazingly well.  I own a small fleet of legacy DTR650 radios and a small fleet of DTR700 radios.  I have also previously owned a small fleet of DLR1060 radios.

 

DTR600/700:


 

DLR1020/DLR1060:


 

CPS download:


The Motorola Business Radio CPS is a free download from Motorola and programs all of their Business Radio models.

 

CPS cable on Amazon:


The same CPS cable is used for programming all of Motorola's business radios.  The one exception is the legacy DTR410/550/650 models because they use a different CPS cable.

 

No programming is needed to use these radios out of the box at the factory default settings.  The DTRs and DLRs work with each other right out of the box at the factory default settings.  Customization of settings and features requires the CPS.  Some settings can be changed without the CPS.  The fastest way to get some DTR and DLR radios talking to each other if they don't already do so is to reset all of them to the factory default settings and then go from there.  You don't need the CPS or the cable to get started with the DTRs and DLRs.  Motorola has made it insanely easy to get started with them.

 

Motorola DTR550 case study:


 

The Rutland Healthcare case study is a bit dated as the DTR550 was used.  The legacy DTR410/550/650 models have been on the market since 2006 and were discontinued in November 2018, marking the end of a 12 year production run.  Support for the DTR410/550/650 models end on November 30, 2023.  The DTR600 and DTR700 are the replacement models for the legacy DTR410/550/650 models.

 

DTR history:


 

The DTRs and DLRs are a spinoff from Motorola's MOTOTALK feature in several NEXTEL iDEN phones years ago.  NEXTEL called this feature Direct Talk and is not to be confused with the DirectConnect PTT feature which worked through NEXTEL's iDEN network.  The DirectTalk feature works PTT simplex phone to phone on 900MHz and uses FHSS.  The killer app for this feature is for PTT use between phones when network service is spotty or unavailable and phones are close enough to each other to communicate.  NEXTEL phones were popular with contractors and other professionals at jobsites and there was nothing more frustrating than the DirectConnect PTT feature would not work because one or more phones had no network service and phones were still relatively close to each other.  The off-network DirectTalk feature provided a solution.

 

The DTRs and DLRs use the same FHSS system but were coded differently from the phones to be incompatible and supposedly was done on purpose.  The DTRs and the DLRs are the modern day implementation of the MOTOTALK platform.  The legacy DTR410/550/650 models shared a common design with a NEXTEL phone during development and were originally part of the same design project until they spit apart to become separate products.  Users of the legacy DTR410/550/650 models will notice that they are very NEXTEL-like in their behavior.

 

The DTRs are commercial radios and loaded with features for business radio users.  However, they often are too much "radio" for the average retail business user.  Retail users just want a small radio with no keypad and display and minimal features to keep it simple.  The DLRs are Motorola's answer to that.  DLR = Digital Lightweight Radio, according to Motorola.  The DLRs have the features of the DTRs, minus a display and keypad and channel capacity but are compatible with the DTRs.  The DLRs were released in the summer of 2015.

 

The DLRs are incredibly easy to use.  The DLRs appear to be marketed toward users of the UHF analog CLS series analog business radios that are very popular for retail use.  The DLRs seem to make sense for the target market.  Some people don't like the large round PTT button on the front of the radio because they are so accustomed to PTT being on the left side of the radio.  The DLRs are smaller than most FRS bubble packs and the front button makes sense for the very small size and thin form factor.  A DLR radio is comfortable to hold in either hand and a thumb press activates PTT.  I found the round front PTT button makes perfect sense for such a small radio.

 

Old retired NEXTEL phones with the off-network DirectTalk feature can be found very cheaply on eBay.  The i355 is a good model to look for.  There are several videos on YT demoing their use.  Factory fresh new batteries are still available for them.  I know that because the legacy DTRs use the same battery and I recently re-batteried my DTR650 fleet.  The one gotcha with old NEXTEL phones is they need to have a SIM card in them that was previously activated on an iDEN network to activate the DirectTalk feature.  The MOTOTALK platform is an ID-based system and each phone or DTR/DLR radio has its own unique 11-digit Private ID, sort of like an Electronic Serial Number (ESN).  In the DTRs and DLRs, this is ID loaded by Motorola at the factory and is not changeable by the end user or with the CPS.  For private talkgroups and private 1 to 1 calling, individual radios only know each other by their 11 digit Private ID.  NEXTEL phones with the DirectTalk feature form the 11-digit Private ID from 1 plus the area code and phone number that was assigned to the phone when it was activated on the network.  This is why an old NEXTEL phone must have a previously activated SIM card in it to enable the DirectTalk feature.

 

DTR/DLR FHSS on 900MHz:


The DTRs and DLRs use a hopset of 50 frequencies spread across the entire 902-928MHz band and spend no more than 90ms on any given freq in the hopset.  The DTRs make about 11 hops per second.  The digital modulation on a given freq in the hopset is according to an 8-level modulation scheme.  The occupied BW on a given freq in the hopset is around 26 kHz.  Motorola's VSELP vocoder is used.  VSELP is what NEXTEL phones used.

 

Per FCC 15.247, an FHSS device operating in the 902-928MHz band must use a minimum of 50 frequencies in the hopset and output power is limited to 1W (+30dBm).  The legacy DTRs were FCC certified at 890mW (+29.5dBm).  The DTR600/700 models were FCC certified at 830 mW (+29.2 dBm).  The DLRs were FCC certified at 880mW (+29.4 dBm).  The few tenths of a dB under the +30dBm legal limit is to account for measurement uncertainty and slight variation in power output from unit to unit and not exceed the 1W (+30dBm) legal limit.  The power numbers in the FCC certs reflect what was measured from the individual sample submitted to the accredited test lab for cert testing.


 

My DTRs:

I own a small fleet of legacy DTR650 radios and a small fleet of DTR700 radios.  The DTR650 has been around since 2006 and was discontinued in November 2018 when the DTR600/700 models were released.  The DTR600 and DTR700 models are the replacement for the legacy DTR 410/550/650 models.  The DTR600/700 programs a little differently from the legacy DTRs but are fully backward compatible.  I have also owned a small fleet of DLR1060 radios which also work with the DTRs.  I later sold my DLRs to a friend for his business as I traded up to the DTR700 and kept my DTR650 fleet.  At first he wasn't sure what he was going to use them for except maybe as rental radios for his customers but now he and his employees use them all the time around the office and at jobsites.

 

The DTRs are my professional quality digital replacement for GMRS/FRS for local on-site simplex type use with family and friends.  I never got them to set any range records but they work amazingly well and are capable of outperforming conventional Part 90/95 UHF portables on simplex.  They totally blow FRS away.  Where they beat other radios is when working inside buildings.  Where they blow all others away is when aboard cruise ships.  People who have used them on cruise ships report having full ship coverage on all decks compared to a pair of 4W UHF commercial portables on GMRS simplex which had trouble penetrating more than about 2 decks.  Like when inside buildings, the ship is much more open at 900MHz compared to 462/467MHz (GMRS/FRS) and VHF MURS.  The ship represents a compartmentalized metal enclosure with many reflections created.  The many reflections inside the ship actually helps at 900MHz and the FHSS operation causes the individual hot spots and dead spots to hop around as the frequency hops.  The FHSS operation effectively stirs the modes so to speak as the frequency hops.

 

A coworker once asked me why not just use FRS?  My answer was that I have already been doing that since FRS was created in 1996 and longer than that as a GMRS licensee (KAE9013) since 1992 and using good quality commercial gear.  I want an all digital solution that is higher quality and more professional than FRS.  The fact that they are completely scanner proof and can be made very secure via private talkgroups and private 1 to 1 calling comes as a bonus.  While technically not encrypted, they can be made very secure.  They are not monitorable on any consumer grade receiver (i.e., scanner) so don't even bother trying.  I have also been bit by the digital radio bug as a ham (N1DAS) and want to use digital radios.  I still have GMRS/FRS and MURS as a backup and for interoperability with non-DTR/DLR users but they are no longer my default go-to modes local on-site simplex use with family and friends.  Aside from occasional light use of FRS with my young nephews when they come to visit, I hardly use GMRS/FRS at all anymore.

 

I love these radios for local on-site simplex type use.  My wife loves using them too when we are out shopping or doing whatever.  She is not a ham but totally gets it when it comes to having radios to stay in touch.  She has told me that she specifically DOES NOT want to use an FRS bubble pack radio.  She much prefers using the DTR radios and wants to use only the good stuff (LOL) when we chitchat on the radio.

n1das Apprentice

n1das

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Yep. n1das summed it up pretty much how it is. Nice write up.

 

G.

Thanks.  I just made a few minor edits.  Maybe the next thing for me to do is write up a DTR/DLR programming overview and explain a lot of the workings.

 

Programming the DTRs and DLRs is often cryptic and befuddling to new users.  No programming is needed to use DTRs and DLRs right out of the box at the factory default settings.  Customization of features and settings requires the CPS.  Some settings can be changed without requiring the CPS.  Programming the legacy DTR410/550/650 is cryptic and the DLR programming cleaned up a lot of things and made it a little less cryptic.  The DTR600/700 models program like the DLRs.  I suspect the DTR600/700 models use the DLR's code base.  I am not surprised Motorola adopted the DLR way of programming going forward.

 

The DTR600/700 models are backward compatible with the legacy DTRs but it requires some understanding of the differences.  When I owned DTR650s, DLR1060s, and DTR700s, I had them all working with each other on public and private talkgroups.  The DLRs and DTR700s added a 4 digit Profile ID Number (PIN) feature which the legacy DTRs don't have.  I had my DLRs and DTR700s working with each other on Profile ID mode channels.  The PIN feature allows you to take DLRs right out the box and set a 4 digit PIN to secure all channels in them without requiring the CPS.  With the legacy DTRs, the only way to secure them was to use the CPS to program private talkgroups into them.  Motorola made it insanely easy for DLR users and DTR600/700 users to secure their channels in radios right out of the box without needing the CPS.

 

A lot can be learned about them by downloading and installing the CPS and exploring the DTR and DLR programming.  The CPS has default DTR and DLR templates to work from so you don't need to read a radio first to use the CPS and play around with the programming.  The latest CPS version is R08.02 and programs all of the older models too.  You don't need an older version of the CPS to program an older radio.  Just use the latest version of the CPS.

axorlov Proficient

axorlov

Posted
Posted

I actually bought a pair of DLR1060 on ebay today. Going to compare performance with GMRS handhelds and mobiles. The usage mode is outdoors: camping, hikes, mountains, woods. It is not very clear to me how 900MHz at 1W with spread-spectrum and error correction would perform against ole wide-band FM at 4W (and at 40W). Of course, the moment I bought DLRs, the cheap chargers disappeared from ebay. But I'm not in rush, will wait for something below $30.

 

So, what you, David, are saying, is that the older DTRs do not have this 4-digit ID, mentioned in DLR manual. And to make the old DTR work with new DLR is to program talk groups into DLR. The programming the 4-digit ID into old DTR will not work because there is no 4-digit ID. Right? Wrong? I order to introduce the older DTR into the network of DLRs I will need to delete the 4-digit ID in DLRs and program the talkgroups, is this correct?

At this moment of time my interest is purely academical because I do not have old DTR, and DLRs are not here with me yet.

n1das Apprentice

n1das

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So, what you, David, are saying, is that the older DTRs do not have this 4-digit ID, mentioned in DLR manual. And to make the old DTR work with new DLR is to program talk groups into DLR. The programming the 4-digit ID into old DTR will not work because there is no 4-digit ID. Right? Wrong? I order to introduce the older DTR into the network of DLRs I will need to delete the 4-digit ID in DLRs and program the talkgroups, is this correct?

At this moment of time my interest is purely academical because I do not have old DTR, and DLRs are not here with me yet.

 

The 4 digit Profile ID Number (PIN) feature is a new feature which started with the DLRs when they came out in 2015 and was continued with the new DTR600/700 models.  The legacy DTRs don't have the PIN feature.  The PIN modifies the talkgroup ID for the first 20 public groups so they no longer are public groups when the PIN is a nonzero value.  The PIN feature also added Call All Available and Page All Available which are new features related to the PIN feature.  The legacy DTRs don't have the PIN features.  The 4 digit PIN provided a new way to easily secure your channels without needing the CPS.

 

The default PIN is 0000 (off).  The default channels in the DLRs are compatible with the default public groups in the legacy DTRs when the PIN is at the 0000 default.  If you are using the PIN feature, you will have to set it back to 0000 to work with the legacy DTRs if all other settings are at their defaults.  If you use the CPS, you can set up a mix of channels which use the PIN feature on some channels to secure them and have public groups on other channels identical to the legacy DTRs.  Setting up a mix of channel types requires the CPS.

 

The legacy DTR410/550/650 has public groups and private groups.  The legacy DTRs call them talkgroups instead of channels.   Channels in the legacy DTRs refers to the 10 frequency hopsets available to use.  Hopset #1 (channel 1 in legacy DTR-speak) is the default.  The DLRs and DTR600/700 refers to channels instead of talkgroups because that's what people are more familiar with (i.e., WTH is a talkgroup?).  The end user sees them as channelized radios anyway.  I tend to interchange the use of talkgroups and channels.

 

Available channel types in the DLRs and DTR600/700 are Profile ID mode (PIN required), public group (no PIN), private group (no PIN), and 1 to 1 private call (no PIN).  The default channel type is Profile ID mode. Available talkgroup types in the legacy DTRs are public group (no PIN), private group (no PIN), and 1 to 1 private call (no PIN).  The default in the legacy DTRs is public group.

 

DLRs are capable of private 1 to 1 calling like the DTRs but requires the CPS to set up and a channel has to be dedicated to it.  Private 1 to 1 calling wastes a channel in the DLRs and is a PITA to set up.  The DLRs have a 1 button Private Reply feature to enter a private 1 to 1 call after hearing a call from another radio.  Private Reply is the default for the top button on the DLRs.  The legacy DTRs and the DTR600/700 have a display and can dial up an individual radio to initiate a private 1 to 1 call and also have the 1 button Private Reply feature.

 

The MOTOTALK platform that the DTRs and DLRs use is an ID based system where each radio has its own 11 digit private ID in hardware, similar to an electronic serial number (ESN).  A radio in a public group will respond to any incoming private ID on that public group ID.  With a private group, a radio only responds to incoming Private IDs that are members of the private group.  This means that the private ID of every radio in a private group has to be programmed into every radio in the private group.  With a private group, a radio only hears and talks to members of the private group.  All other DTRs and DLRs in range and using the same frequency hopset are locked out of the group.  The PITA with private groups is when adding or replacing radios in a private group, ALL radios in the group have to get reprogrammed to add the new private IDs.  The DTRs have Over the Air (OTA) cloning ability to update a fleet of radios with new private IDs.  The OTA cloning capability is useful for updating large fleets consisting of hundreds of radios.  Private groups make the DTRs and DLRs very secure but they are a PITA from a programming and maintenance standpoint.  Programming private groups into the DTRs and DLRs requires the CPS.  With the legacy DTRs, programming private groups was the only way to secure them except for 1 to 1 private calling.  The PIN feature addressed this issue in the DLRs and DTR600/700.

 

The PIN feature in the DLRs and DTR600/700 made it easy to take DLRs and DTR600/700s at their factory default settings and set the PIN to secure them.  The default channel type on all channels is Profile ID mode.  When adding or replacing radios in a fleet, just set the PIN in the new radios to match what the fleet uses and you are done.  Choose a favorite 4 digit PIN that's easy to remember and hard for others to guess.  Don't using anything obvious like 1111 or 1234, etc.  This is the easiest way to secure them if all radios are at the factory default settings except for setting the 4 digit PIN.  The DLRs have OTA cloning capability to clone the PIN to a fleet of DLRs to secure them instead of having to manually set the PIN in each radio.

 

The DLRs speak the channel name given that the radio doesn't have a channel knob or a display.  You can customize the channel names with the CPS to make your own channel names if you want.  "Channel One", "Channel Two" etc. are the default channel names.  You can set up custom names like "Security", "Maintenance", "Loading Dock", etc.  The name of individual radios can also be customized.  You can create custom names like "Dave's DLR radio", "Lisa's DLR radio" etc.  The custom radio name plays when the radio first powers up.

 

The DLR quick reference guide is a worthwhile read.

https://www.motorolasolutions.com/content/dam/msi/docs/products/two-way-radios/on-site-business-radios/dlr-application-briefs/DLR-Quick-Reference-Guide.pdf

n1das Apprentice

n1das

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I actually bought a pair of DLR1060 on ebay today. Going to compare performance with GMRS handhelds and mobiles. The usage mode is outdoors: camping, hikes, mountains, woods. It is not very clear to me how 900MHz at 1W with spread-spectrum and error correction would perform against ole wide-band FM at 4W (and at 40W). Of course, the moment I bought DLRs, the cheap chargers disappeared from ebay. But I'm not in rush, will wait for something below $30.

 

They won't beat range with a 40W mobile and external mobile antenna but they will work surprisingly well.

 

While I never got my DTR/DLR radios to set any range records, my range record stands at 12 miles, from Cocoa Beach Pier in Cocoa Beach FL to the steps leading down to Hightower Beach in Satellite Beach FL.  A friend helped me test this.  We also had our 4W Part 90 UHF portables on GMRS to compare to. (We are both GMRS licensed.)  The 12 mile trip is along the FL coast and there is a bit of coastline in the way so it's not entirely line of sight.  It worked on the DTRs and on GMRS.  With GMRS, the received signal was noisy and we each had to find a hot spot and stay there in order to communicate.  On the DTRs it was clear audio all the time, right up to the limit of coverage.  The DTRs occasionally required moving around to find a better spot but this was less critical than on GMRS.  We have done this test with DLR radios and results were the same.  We also found that when the DTR/DLRs went away when finally out of coverage, GMRS portable coverage was already gone too.  Overall the DTRs and DLRs worked a little better.

n1das Apprentice

n1das

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The deep dive is hard to avoid because there is so much information to unpack.  :)

 

The DLR quick ref guide is a good read.  I also recommend downloading the CPS and exploring the the programming there to learn your way around the radio.  Pull up a default DLR radio template in the CPS and go from there. The CPS has help available for each feature.

n1das Apprentice

n1das

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David, thank you very much for the very comprehensive deep dive into DTR-DLR world. I will wait for my newly bought DLRs to come before asking more questions.

 

I am curious if your newly bought DLRs are new enough to be expandable to 10 channels with the CPS.  The DLR1060 has 6 channels by default but this can be expanded to 10 channels with the CPS as an unadvertised feature.  I stumbled upon this like a few other people have when I was tinkering with my DLR programming.  Then I checked the model information at the top of the main screen in the CPS and it said 10 channels supported.  Duh. Should have checked that first.  The 2 channel DLR1020 is not upgradeable.  The 1020 and 1060 are identical radios except for the number of channels supported.  The 1020 is the entry level DLR model.  For anybody in the market for DLR radios, the DLR1060 is the DLR model to get.

 

Early DLR1060s were not expandable to 10 channels and were stuck at 6 channels.  Motorola later updated the firmware to add 10 channel capability but still markets the DLR1060 as a 6 channel radio.  I'm not sure when the firmware change was made but I recall it was around 2017.  The last 2 digits in the firmware version is .01 in the newer DLRs.  The firmware in early DLR1060s that were limited to 6 channels ends in .00.  10 channel capability in the DLR1060 is supported in CPS versions R05.01 and newer.  The latest CPS version is R08.02.

  • 2 weeks later...
axorlov Proficient

axorlov

Posted
Posted

The pair of DLR 1060 is here, and I had a chance to play with them in suburban environment. The setting was simple: Operator1 is riding bicycle around, Operator2 is stationary at the BBQ table at public park. Communications were happening via a pair of TK-3170 and a pair of DLRs. TK-3170 were configured at wide-band full power (4W) with DPL. DLRs are on default setting: Channel 1, no PIN. So, the DLRs did not outshoot Kenwoods, but were not than much far behind. When we lost comms on DLRs, Kenwoods demonstrated a lot of white noise, and while squelch broke reliably and spoken words were 100% discernible, my experience tells me that we would lost comms via Kenwoods in about quarter of mile. Two experiments were performed.

Experiment 1: Across the park, quarries and along the river bank with minimal obstacles. Trees are rare and foliage is not dense. Not exactly open field, but close. Comms failed when our line of sight started to go through the suburban subdivision. Distance was 1.75 miles.

Experiment 2: Through dense suburban subdivision with 1- and 2-story homes on small lots. Comms failed at approx 0.75 miles.

Unfortunately, I was not able to borrow better FRS radios like GXT1000 to make a direct comparison. But DLRs were not much worse than full-power TK-3170s, so they will leave FRS in the dust, especially crappier ones. DLR is seriously smaller and lighter  than old brick TK-3170. It can sit in the front pocket of shorts and does not impede bicycle riding, while there is no way I can stuff 3170 into the pocket, it must be on the belt.

Next test is in the mountains, but it's not going to happen soon because of some time constrains in the coming month. Besides, Operator2, colleague and friend,  borrowed DLRs for their family outing over the weekend.

  • 1 year later...
WRQX963 Explorer

WRQX963

Posted
Posted

THANKS...I found the ten-channel expandability in the software too, though I have no radios yet, so I was not aware that it would actually work. I suspect that Motorola will change that "flaw" eventually, either for all existing units, for newer ones, or will update that software with some extra bells and whistles but only six channels. Sounds like FHSS is the way to go, but will we be saying the same thing in a few years about 2.4GHz or 5GHZ compared to 900MHz? Whoever suspected that we would be walking around with phones on those bands with hidden antennæ?

WRQX963 Explorer

WRQX963

Posted
Posted
21 hours ago, tweiss3 said:

Considering how empty the 902 ham band is, run P25 and nobody will hear you anyways. 

If I had a good rooftop or tower and $$$ were no option,
I personally like D-star on 23cm, 1.2GHz...de Always Itching 4 It.

tweiss3 Mentor

tweiss3

Posted
Posted
13 hours ago, WRQX963 said:

If I had a good rooftop or tower and $$$ were no option,
I personally like D-star on 23cm, 1.2GHz...de Always Itching 4 It.

I have 1.2, the base has D-Star, the HT does not. 900 is less expensive to get into.

Lscott Grand Master

Lscott

Posted
Posted
On 6/29/2022 at 5:20 PM, gman1971 said:

Agreed, FHSS makes so much sense, IMO, makes you hope they'll do the same for other crowded bands... it will make sharing the airwaves a lot easier too...

G.

Here is a real question. Who makes a practical and affordable FHSS repeater? I did a search and didn't really find much of anything. If the radios are only usable for short range communications because there is no infrastructure to expand the range sort of takes the shine off the attraction to FHSS radios as a general communication tool.  

tweiss3 Mentor

tweiss3

Posted
Posted
52 minutes ago, Lscott said:

Here is a real question. Who makes a practical and affordable FHSS repeater? I did a search and didn't really find much of anything. If the radios are only usable for short range communications because there is no infrastructure to expand the range sort of takes the shine off the attraction to FHSS radios as a general communication tool.  

I just tried to read through the rules (15C), and I don't see this being permitted. They even went as far as limiting the power, antennas and the gain on any antenna in an attempt to limit range. Also, I don't see how this would even work, its not operating on a frequency split, so it would have to be a store and forward type repeater, which might make the receiving stations hear the transmitted message twice.

Lscott Grand Master

Lscott

Posted
Posted
10 minutes ago, tweiss3 said:

I just tried to read through the rules (15C), and I don't see this being permitted. They even went as far as limiting the power, antennas and the gain on any antenna in an attempt to limit range. Also, I don't see how this would even work, its not operating on a frequency split, so it would have to be a store and forward type repeater, which might make the receiving stations hear the transmitted message twice.

That was exactly why I asked the question. I've read some archived posts talking about various digital modes where people are singing about how great they are, except they forget about the practical aspects. So if FHSS radios are so great what if one wanted to expand the range beyond a mile or so they would need a repeater. Oops, not going to happen. Looks like they might not be a great recommendation after all. I just wish people would think a little bit more about the practical ramifications and implementation requirements more. When that's done you just might discover the digital mode you thought was the greatest thing since sliced bread, and better than anything else out there, just isn't a good fit while another mode would be better suited for the application. 

WRQX963 Explorer

WRQX963

Posted
Posted
1 hour ago, Lscott said:

Here is a real question. Who makes a practical and affordable FHSS repeater? I did a search and didn't really find much of anything. If the radios are only usable for short range communications because there is no infrastructure to expand the range sort of takes the shine off the attraction to FHSS radios as a general communication tool.  

Trunking systems require multiple repeaters and associated hardware with master controllers, not single trunking repeaters.
Large hypothetical trunking systems with several hundred clients could only be installed by the Motorolas and GEs of the world,
but I think that both GSM and CDMA (or an even newer system) are more efficient..

Lscott Grand Master

Lscott

Posted
Posted
1 minute ago, WRQX963 said:

Trunking systems require multiple repeaters and associated hardware with master controllers, not single trunking repeaters.
Large hypothetical trunking systems with several hundred clients could only be installed by the Motorolas and GEs of the world,
but I think that both GSM and CDMA (or an even newer system) are more efficient..

The goal of trunking systems is far different than for a FHSS radio. Trunking systems are used to increase the utilization of very limited spectrum, frequencies, while FHSS radios consume a lot of spectrum while minimizing interference. 

tweiss3 Mentor

tweiss3

Posted
Posted
40 minutes ago, Lscott said:

That was exactly why I asked the question. I've read some archived posts talking about various digital modes where people are singing about how great they are, except they forget about the practical aspects. So if FHSS radios are so great what if one wanted to expand the range beyond a mile or so they would need a repeater. Oops, not going to happen. Looks like they might not be a great recommendation after all. I just wish people would think a little bit more about the practical ramifications and implementation requirements more. When that's done you just might discover the digital mode you thought was the greatest thing since sliced bread, and better than anything else out there, just isn't a good fit while another mode would be better suited for the application. 

I think any implementation would have to come from Motorola directly, or whichever FHSS radio manufacture you are using. That being said, lets talk about a theory that might work as a repeater.

My understanding is the radios utilize at least 50 frequencies, and hop about 50 times a second. The privacy is caused by changing up the hop set (order and number of frequencies), which means any repeater would have to be programed identically to the radios, but that's not a problem, that's typical of repeaters. Two problems exist, which we have to overcome:

1) At any given time (snapshot), the radios are using a single frequency for both receive and transmit. This could potentially be overcome by having a small delay in the re-transmission, say 2 hops behind the transmitting radio. Any radio in range of the transmitting station would continue to sync and receive from that station, stations outside that range would instead be synchronized and receive from the "repeater" station. Problem solved?

2) Second problem is, a traditional repeater usually has a fixed frequency set, and uses a duplexer to separate receive from transmit to eliminate desense in the receiver. The alternative is two antennas. Since 902MHz is such a high frequency, vertical separation can be relatively small and provide good isolation. 1 foot vertical provides 27dB isolation, and 2 feet increases that to 39dB, more than enough decent selectivity can overcome.

Make sense? I think the theory would work, practice might be a bit harder to accomplish. There there is getting 15C certification for the "repeater".

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