SL7550e 450-512 band split mod for 430-450 MHz?

[jeremym70]

I have an SL7550e that I obtained a while ago and never use it, I was going to post it for sale on a local DMR ham group list but just noticed it has the 450-512 split. Any mods available to make it work on the ham band? Been searching around but haven't found out yet? Maybe a hex edit of the band limits of the CPS, like I did once for an XTS300 or 5000?
Thanks

 

[Astro Spectra]

I can't talk to the UHF limits but I can say that the 800/900MHz e version can't be easily hacked. I doubt it can be hacked at all.

 

[gMan1971]

@mitaux8030

This member has done some investigation on the limits of the SL7550, might be worth asking him.

Hope this helps.

G.

 

[mitaux8030]

The 403-470 bandsplit would cover down to 382 MHz without any hardware hacking. I reckon the 450-512 model (fun fact: in other countries of the world it covers up to 527 MHz - same hardware) would also be able to bend down 10-20 MHz, by purely software out-of-band frequency entry methods. It involves using something like HxD or CheatEngine to edit RAM live while running CPS to open up the allowable software frequency limits of CPS. The technique is fairly simple, just search for TRBO out of band frequency entry and you should find how it is all done.

 

[Mars]

There are two issues which should be addressed here:

1. How to modify for out-of-band operation;
2. Will the 450-512(527) radio operate properly below 450 MHz? (tuning issues)


Modifying for out-of-band

I continue to use the utility I had from back in the day of manually modifying codeplugs to correct the audio AGC issues. This was applicable <2015, after which time Moto came out with new firmware/codelug templates, inclusive of those changes. The utility allows manual editing of the CTB file (which is encrypted XML data).

The bandsplit can be extended and CPS will recognize the extended limits. That said, we have noticed the XPR7580e -- of interest because of its applicability to 900 MHz ham operation, does not function on out-of-band channels. They can be entered into the codeplug and programmed into the radio but the radio does not unmute to inbound transmissions or transmit any RF. It will work fine at 935.0000, but has zero RX/output at 934.9875. It's clearly not a hardware issue, but rather some type of soft/firmware restriction. So will this oddity be replicated in a SL7550e UHF 2 where operating below 450?


The T-split tuning issue

There are numerous UHF2 repeaters and subscribers being used on the amateur radio service. The issue, which I posted about last year, seems to have fallen on deaf ears. It is a fact, these radios/repeaters are all foxtrotted up and DO NOT work properly when operating below <450 MHz.

A member of our local club recently picked up a XPR5550 450-512 25W for use with our UHF network. He didn't know any better; someone had told him to "Get a UHF XPR5550". I tried converting it for him, and did the codeplug mod, but I found it had major issues with getting channel grants (Capacity Plus Multi Site), even with strong inbound/outbound signals. I had freshly aligned the radio, too. Performance on the rated bandsplit was fine. To recap, here's what happens when a person uses a 450-512 radio/repeater, below 450.000000 MHz:

- The digital tuning values are not referenced any longer. There is a soft-limit in the radio firmware (or hidden elsewhere in the tuning file) which tells the radio to disregard those values, if below the soft "frequency limit". This is not new; the VHF (146-174) and UHF (450-482) ASTRO Digital Spectra and ASTRO Digital Spectra Plus behaved the same way. Fortunately on that platform, I was able to identify the soft-limit location and modify it. After modification, performance on ham was 100%.

- The oscillator warp adjustment is not referenced. This means whatever default value is used/referenced will be used. Your transmitter and receiver wil be "off frequency". On digital, this matters quite a bit (no pun intended) as signals which fall outside of the IF passband filter windows will manifest as packet loss;

- The RX front-end filter and gain control settings will be defaulted. This means degraded RX sensitivity and adjacent signal rejection;

- The PA Bias Adjustment will be off. This means too little (or usually, too much) current will be applied to the RF power amplification circuit to achieve the desired gain. The PA will run hot and draw too much (or too little) current. This could also cause distortion on the output.

- The deviation balance compensation is defaulted. This is by far, the most potent variable affecting TX operation on digital. During normal alignment, an RF carrier is modulated with something like a 80-100 Hz tone. You measure and record the deviation value. The radio then gets keyed with a 3 kHz tone. You adjust the slider to achieve the same recorded deviation as the low-tone value. The purpose is to achieve uniform deviation, regardless of audio frequency. On digital, this alignment affects the modulation fidelity of the C4FM-modulated signal. On analog, it controls low-level signalling, such as PL/DPL and of course the voice signal equalization. When this alignment is not referenced, digital signals have poor transmit fidelity. There are pictures in the thread I linked to above.

Long story short: Until such time as a method is figured out that restores reference to digital pot values when operating out-of-band, and a method to defeat the "soft" frequency limit of "e" (or "i" in AS region) firmware, using that radio on the amateur service is not recommended. There are plenty of people who will say "but my radio works fine". They have no idea what they're talking about. One can drive a car on rims and wipe their butt with sandpaper, too. Not recommended.

 

[Astro Spectra]

I know this thread is about the UHF version not 800/900MHz but to echo Mars comments I have also spent a ton of time on the XPR7580e and it was no go.

Recently a ham and helicopter EMS guy asked me to look at his auction site XPR6550 and of course it was UHF R2, sigh. It programmed out-of-band easily enough but when I went to tune it the TX modulation fidelity was bad. I did try a few tweaks of the soft pots in Tuner but it was not a happening thing.

Since I like to help out worthy causes, I ended up just dropping a R1 chassis into the fellow's case to get the radio done.

OK so the '6550 is not a SL7550e but it goes to the point Mars made on ham use of T band 'TRBO. My advice is get a XPR7550 and enjoy the factory 403-512 MHz goodness.

 

[gMan1971]

Wonder if the radio could be "convinced" to work with the one tool to rule them all, a craft of unspeakable power which's name we shall not utter here.

 

[mitaux8030]

Something interesting I found with the 403-470 MHz version of SL7550 was that even though you could enter wildly out of band frequencies - in this example, lets say 520 MHz, the radio would quit doing anything at exactly 475 MHz. The VCO was being commanded to shut down. Obviously there's a soft limit that kills the party at that threshold.
Two thoughts:
1) The presence of that VCO shutdown soft limit at 475 MHz (not coinciding with the CPS limit of 470 MHz), almost feels like they designed the system that way, begrudgingly letting you go up 5 MHz out of band, but no more.
2) There was no such limit going down in frequency. Wondering why only the upper limit was imposed... oversight? Lack of attention to detail? Intentional?

Might run my experimental SL7550 through some tests at some beyond-soft-limit-shutdown OOB freqs and see what is going on with respect to reference tuning and how it impacts operation. Maybe the subscriber units have been set up to be more forgiving in that regard? Obviously those tests will only be directly applicable to the 403-470 MHz version, but it may hint at what might happen to a 450-512 (527) unit.

 

[gMan1971]

A SL7550 with some limited VHF capabilities might be a handy thing to have... even if its just to listen to the NOAA weather radio... and not much else...

Thanks @mitaux8030

 

[com501]

Is there even any such thing as an SL7550 in VHF?

 

[Mars]

And the SL7550 will not allow analog frequencies. But it supports them, as I can put the radio into service mode via Tuner, and then key up on the test frequencies (after disconnecting from USB cable) and talk analog voice. It does work. I get that Motorola limited the SL from doing analog because the battery life would be shit, but I have a need for analog RX receive -- especially with QCII signalling. Would make an excellent little pager for fire/ems ops. Oh well. This is the suck that is Moto these days.

 

[mitaux8030]

Is there even any such thing as an SL7550 in VHF?

Doesn't appear so, though there's no technical reason why there couldn't be... Rodinia will support VHF, as indeed it does in the rest of the Gen2 portables.

 

[phonebuff]

-- especially with QCII signalling. Would make an excellent little pager for fire/ems ops. Oh well. This is the suck that is Moto these days.

@Mars you are correct it does. But we had to build an Option Board solution to really make it work well have about 500 Sl's on a Cap Max system and the QCII is driven from the Avtec Console deployment -

 

[gMan1971]

@phonebuff
Very nice!! I have 10 of them in service, for a simple floor intercom, no repeater. And yes, FM analogue on those would be beyond great, having the option to do NOAA weather I think it would've been a huge plus, even if it was hardcoded on the firmware... A lot of the other low-tier UHF radios can hear the NOAA frequencies.... so

I've read somewhere the AZ firmware supports this... but... what do I know...

And going off topic a bit, IMHO, these are the kind of radios Motorola should be making (instead of the over-engineered ION, which is probably riddled with bugs and all kids of other hidden "gems" that only the end users will get to discover as they beta-test (after paying) the latest MotoToy LOL... ),

In my little experience, the consensus here is that SL7550 appeals to the image-conscious eyes, and pleasing enough that very image-conscious female users won't be put off by it; or, as someone told me once: keying the XPR7550e feels like you're about radio in for an airstrike... ( which I, myself, find rather tacti-cool... )

G.

 

[jeremym70]

Thanks for all the info, guess the best solution is to find someone in commercial world that has interest in. Has connect plus option as well.

 

[mitaux8030]

Took some time to more closely examine the SL7550 R2 going down to 430/440 MHz. It is possible with the usual OOB frequency entry method.
The reference oscillator tuning remains valid below 450 MHz, no problem. That's where things start to go sideways a little.
Any frequency below the original 450 MHz soft limit will use the lowest tuning frequency value (eg: 450 MHz!) for things like modulation balance, RF power etc.
This results in increased BER on frequencies below 450 MHz. It's not entirely unusable, but the further down in frequency, the worse the impact becomes. If you have the gear, the modulation balance tuning value for 450 MHz can be adjusted to obtain better BER at 430/440 MHz... but at the expense of BER for any frequencies around 450 MHz.
I also observed around 6dB degradation in sensitivity down around 430 MHz. I couldn't test any lower, as the VCO becomes unlocked below 430 MHz.
So it's workable, but has drawbacks.

 

[N4KVE]

There are two issues which should be addressed here:

1. How to modify for out-of-band operation;
2. Will the 450-512(527) radio operate properly below 450 MHz? (tuning issues)


Modifying for out-of-band

I continue to use the utility I had from back in the day of manually modifying codeplugs to correct the audio AGC issues. This was applicable <2015, after which time Moto came out with new firmware/codelug templates, inclusive of those changes. The utility allows manual editing of the CTB file (which is encrypted XML data).

The bandsplit can be extended and CPS will recognize the extended limits. That said, we have noticed the XPR7580e -- of interest because of its applicability to 900 MHz ham operation, does not function on out-of-band channels. They can be entered into the codeplug and programmed into the radio but the radio does not unmute to inbound transmissions or transmit any RF. It will work fine at 935.0000, but has zero RX/output at 934.9875. It's clearly not a hardware issue, but rather some type of soft/firmware restriction. So will this oddity be replicated in a SL7550e UHF 2 where operating below 450?


The T-split tuning issue

There are numerous UHF2 repeaters and subscribers being used on the amateur radio service. The issue, which I posted about last year, seems to have fallen on deaf ears. It is a fact, these radios/repeaters are all foxtrotted up and DO NOT work properly when operating below <450 MHz.

A member of our local club recently picked up a XPR5550 450-512 25W for use with our UHF network. He didn't know any better; someone had told him to "Get a UHF XPR5550". I tried converting it for him, and did the codeplug mod, but I found it had major issues with getting channel grants (Capacity Plus Multi Site), even with strong inbound/outbound signals. I had freshly aligned the radio, too. Performance on the rated bandsplit was fine. To recap, here's what happens when a person uses a 450-512 radio/repeater, below 450.000000 MHz:

- The digital tuning values are not referenced any longer. There is a soft-limit in the radio firmware (or hidden elsewhere in the tuning file) which tells the radio to disregard those values, if below the soft "frequency limit". This is not new; the VHF (146-174) and UHF (450-482) ASTRO Digital Spectra and ASTRO Digital Spectra Plus behaved the same way. Fortunately on that platform, I was able to identify the soft-limit location and modify it. After modification, performance on ham was 100%.

- The oscillator warp adjustment is not referenced. This means whatever default value is used/referenced will be used. Your transmitter and receiver wil be "off frequency". On digital, this matters quite a bit (no pun intended) as signals which fall outside of the IF passband filter windows will manifest as packet loss;

- The RX front-end filter and gain control settings will be defaulted. This means degraded RX sensitivity and adjacent signal rejection;

- The PA Bias Adjustment will be off. This means too little (or usually, too much) current will be applied to the RF power amplification circuit to achieve the desired gain. The PA will run hot and draw too much (or too little) current. This could also cause distortion on the output.

- The deviation balance compensation is defaulted. This is by far, the most potent variable affecting TX operation on digital. During normal alignment, an RF carrier is modulated with something like a 80-100 Hz tone. You measure and record the deviation value. The radio then gets keyed with a 3 kHz tone. You adjust the slider to achieve the same recorded deviation as the low-tone value. The purpose is to achieve uniform deviation, regardless of audio frequency. On digital, this alignment affects the modulation fidelity of the C4FM-modulated signal. On analog, it controls low-level signalling, such as PL/DPL and of course the voice signal equalization. When this alignment is not referenced, digital signals have poor transmit fidelity. There are pictures in the thread I linked to above.

Long story short: Until such time as a method is figured out that restores reference to digital pot values when operating out-of-band, and a method to defeat the "soft" frequency limit of "e" (or "i" in AS region) firmware, using that radio on the amateur service is not recommended. There are plenty of people who will say "but my radio works fine". They have no idea what they're talking about. One can drive a car on rims and wipe their butt with sandpaper, too. Not recommended.

Could the same reasoning apply to using a 7580, or 6580 in the 902/927 band? Or even a XTL/XTS at 902/927? Just wondering since nobody offers an ISM band radio. GARY