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Thread: Turning Quantar into Quantro?

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    syntrx No Longer Registered

    Default Turning Quantar into Quantro?

    My local ham club has come into the possession of a bunch of Quantars. Unfortunately, a few of these have dead power supplies. What's involved in turning a Quantar into a Quantro, dispensing with the internal PSU completely and just running it from external power? Is it possible with a few parts changes, or is it a more involved operation than this?

    One workaround that's been suggested is depending on how the PSU failed, just hooking an external supply up to the battery revert terminals.


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    Do these quantars have ONAN power supplies? Those are junk and create fireworks when they fail. Use the quantars with decent power supplies and either scrap the rest or save them for parts. Honestly, how many repeaters does your club need? Are they planning on putting up a few SmartZone sites with them?

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    Quote Originally Posted by Pezking View Post
    Do these quantars have ONAN power supplies? Those are junk and create fireworks when they fail. Use the quantars with decent power supplies and either scrap the rest or save them for parts. Honestly, how many repeaters does your club need? Are they planning on putting up a few SmartZone sites with them?
    Well, by a "bunch" I mean 3, of which one supply works. Originally deployed around 1999-2000 if that helps in identifying them, but I haven't had a chance to see what supplies are in the quantars.

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    The best option would be to fix the supplies or get a replacement from eBay. Switching supplies are dangerous but not that hard to fix, but there is a risk of death. Anyone familiar with fixing the power supplies used in a desktop PC should be right at home in a Quantar power supply. Note that some units are pop riveted closed and you need to drill these out to get inside.

    The 25W low power station has a power supply rated at 14V at 12A, and 5V at 9A.

    The 100W high power station has a power supply rated at 28V at 24.5A, 14V at 9A, and 5V at 7A.

    I don't remember Quantars actually drawing anything like the full current, but obviously YMMV.

    One option would be to cable the backplane up for the three supplies (if you have a high power Quantar) using the pins on the back of the card edge connector for the power supply module - ugly but workable. The station will complain if there is no supply module fitted but it will still work. You'll need relativiely 'clean' supplies, not junker ex-computer units.

    Another option would be to see what parts of the supplies are actually 'dead'. The most common failure is the main supply caps which hold the rectified mains input. These blow on certain versions of supplies when running off 115VAC (doesn't seem to happen very often running off 230VAC). If it's just the main switcher it might be possible to feed in 24V and get the other rails but you'd need to have a look at the schematics.

    The 'bad' Onan units are the ones with holes drilled over most of the face plate and I think only the high power ones.

    You can never have too many Quantars ...
    Last edited by Astro Spectra; Dec 11, 2012 at 08:59 PM.

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    I've looked into this.. from what I can tell you would need the Quantro backplane and the IPA specific to your band range, with everything else coming form the Quantar donor. And a blank plate to fill the slot that would be occupied by the internal power supply, if you wanted to keep things tidy.

    Better still, I went over the IPA schematic and it looks like band-switching from 800 MHz to UHF R2 is possible with a handful of SMT components, a couple of jumpers, and the UHF power hybrid which was still available on MOL for a reasonable (less than $50US) price last time I checked. If I understand it correctly VHF stations don't use an IPA; the exciter drives the PA directly.

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    Confirmed - I have modified an 800 MHz Quantar with a 100W PA to a 20W UHF station by using a UHF receiver, putting an exciter PCB into the 800 MHz exciter can, and do a PA IPA module swap. The 100W hybrids and output circulator are just bypassed with a bit of coax. There are SMT resistor changes so the SCB sees the right PA version and the forward/reverse power detectors need a trim.

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    Quote Originally Posted by Astro Spectra View Post
    ...putting an exciter PCB into the 800 MHz exciter can
    Tell me more about this. How much is common between the UHF and 800 MHz exciters?

    Reason I ask is, 800 Quantros are getting very, very cheap these days, and if the IPA and exciter can be moved from 800 to UHF all you'd need to make a complete UHF station would be a UHF receiver and a PA scavenged from an old MSF.

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    The entire Exciter PCA (printed circuit assembly) must be replaced. However, the board from Motorola parts was quite affordable at the time like about $400 if I remember right. The exciter module consists of just the PCA and the metal case (can). The V/UHF and 800 MHz exciters all share the same metalwork. The receivers are different.

    I worked on Quantars years ago when they were start of the art and learnt a lot.

    Later I had the chance to acquire a bargain 'faulty' 800 MHz unit from Panik Electronics for myself, before P25 and Quantars became popular outside public safety. At the same time a bunch of UHF receivers came up on eBay which I grabbed, they went for $75 each. So it was easy to migrate the 800 MHz station with a new exciter PCA and the IPA hybrid (also cheap from Moto parts as you noted).

    You don't need the real PA to make a repeater, the real secret of the Quantar is the software will accept and try and operate even with missing modules. The station will try and operate with a missing PA, there will be lots of errors but yes you can run them with an external amp such as from the MSR2000. I have even used a Tait 100W T800 Series UHF PA.

    If you want to be really cheap another option is to leave the 800 MHz exciter inplace and pick out the high and low band two-point modulation signals from the backplane and use any other Motorola transmitter that supports two point mod such as a regular Spectra. The station will need serious transmit alignment as you now need to compensate for the modulation transfer functions of the Spectra rather than the Quantar exciter. There are a few pointers on this concept on the Repeater Builders web site in connection with a 900 MHz Nucleous conversion.

    Something I've not tried is to hack up an 800 MHz receiver module to bring the 1st IF out to the front to use an external converter.

    I've been thinking about these last two ideas in connection with building a 10m low band P25 Quantar using a low band Syntor X as the receiver 1st IF is compatible.

    This flexibility goes way beyond sane. You can for example take an Astro Tac Receiver aka Quantar Receiver and tell it that it is a Quantar. It won't transmit of course ... unless you solder on an extra connector and plug in an exciter! The connector you can unsolder from an old PC motherboard. The Quantar uses the same type of connector as the PCI bus (less pins so you need to saw the connector down to fit the exciter). Make your own PDR3500.

    Other Quantar hacks include sliding V/UHF modules up/down an adjacent range with a few SMT mods, moving the VCO hybrids using silver paint or dremel tool just like on the Spectra, etc. You absolutely need the full service manual for the schematics.

    It's a great platform and OK to discuss all this now as both the Quantar and PDR3500 are EOL. Yep I've noticed the bargain Quantro units on the 'bay and they're tempting.
    Last edited by Astro Spectra; Dec 19, 2012 at 06:40 PM. Reason: Add comments on a use of receiver as IF.

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    Does anyone have the part number for the PDR3500 service manual that is used in conjunction with the Quantar service manual?? Cant' find it on MOL.
    Regards,

    John