Anyone has seen a loadsharing schematic ?

[Radion©]

The modern A.M. transmitters nowadays use powermodules that can be pulled out when operating with no harm.
How are thes units connected with the output ? Just parallel to some LC circuitry ? Could someone upload some
schematics of such coupling stage ?
.

[RGORJANCE]

While a company might say their PA modules may be removed "hot", I personally don't feel that is a real good procedure. I ALWAYS POWER DOWN TO REMOVE BOARDS/MODULES in transmitters.

As for the schematic of the matching portion, Broadcast Electronics offers their instruction manuals for free download from their web site. I am assuming Harris also has that same availability. I do not know if Nautel has such an availability as I never needed one from them.

Fossil

[Muadeeb]

Nautel does have them on the website, and do require registration. They will email back your login info.

[Radion©]

While a company might say their PA modules may be removed "hot", I personally don't feel that is a real good procedure. I ALWAYS POWER DOWN TO REMOVE BOARDS/MODULES in transmitters.

As for the schematic of the matching portion, Broadcast Electronics offers their instruction manuals for free download from their web site. I am assuming Harris also has that same availability. I do not know if Nautel has such an availability as I never needed one from them.

Fossil

Power down ? Why ? If something goes wrong you can always blame the manufacturer
Thanks dear man for the fast info. And you call yourself fossil ? To bad.

[K4WRF]

Each manufacturer has their own method to accomplish this but it usually involves torroid wound inductances as complex as a transformer with a compensated summing buss as the secondary, all the way to a fairly simple loaded Wilkinson hybrid for summing the modules. As stated by earlier post, a hot extraction or insertion of a module can be detrimental. Those who do ‘tout the “hot swap” feature usually define a specific procedure to safely accomplish this. I know of one instance where a PA module was snatched from a Harris transmitter while it was running; about $9,000.00 later, the transmitter was working again and the engineer was working somewhere else.

[boiseengineer]

The DX series has the little door over the modules interlocked plus short the 240V when it's opened. Haven't had to disassemble the DX combiner yet.
Doesn't the Amphet have a switch on each module to short the torroid primary before pulling it "hot"?

[K4WRF]

The Harris 3DX50 modules are not secured behind a door and interlock like the DX50. They even have a convenient inviting handle on each PA and binary module as well as the modulation encoders. There is an extraction device that is used to disable the module and place a termination on the output torroid. I thought it was still a dicey proposition as you had to follow several steps. The extraction device also functioned as an extender card that would allow the convenient measurement of the PA drive levels and other related parameters. The BE 4MX50 had a process for disabling the specific module prior to removal. I haven’t worked on a Nautel but understand there is a process for those.

[RGORJANCE]

The older Nautel AMPFET 50 had some switching where you shut of one rack of modules, then throw a switch on the back of the rack to bypass the RF output of the large module. You could then pull that module out of the rack for service. It was nice and convenient. Don't know about the newer ones, although I had to pull a module out of an ND-5, but I can't recall the procedure. RF Warrier, where are you when we need you?????

Could he be out searching for lobsters???

Fossil

[BroadcastDoc]

The newer Nautel's have a bypass button on the front of the module. Pressing the button shuts down the module making it safe to remove. Pull it out, put another one in and hit "Reset" on the controller screen. The new module comes up and all is well!

[RFWarrior]

Sorry for the delay, I've been running at 150% mod trying to keep up with work and home, so lists got shunted to the sidelines for a bit!

As others have said, every manufacturer has a different approach and how the modules will react also varies. Ours work in this sequence...

Original AMPFET series:

1-10kW, modules are NOT hot pluggable. They are connected in series and pulling a module hot results in some pretty spectacular fireworks.

25 and 50kW modules are as Fossil indicated - there is a bank of toggle switches on the control panel that each power down a block of four modules, then on the rear of the transmitter you use another toggle switch to short the output of the module you wish to remove, so that the combiner coil for that module acts as a load to the rest of the transmitter. The shorted module can then be removed when the transmitter is running. The only catch to this is if somebody had previously powered up a module that had the switch in the SHORT position and blew the switch - in that case, you'll have a cool blue flame arcing out of the connector when you remove it from the module you thought you shorted. Always a fun time...

AMPFET ND series:

The original 5 and 10kW versions (have current meters on the power modules) had a similar configuration to the 25 and 50 above - an ON/OFF switch for the power supply to each module, then a SHORT/OPERATE switch on the combiner input for each module. Same possibility for blue flame if the SHORT switch was failed.

The ND series models from 2.5-10 kW that have no current meters, just alarm LED's, on the power modules, have only a simple ON/OFF switch for the power supply to each module - switching off the supply for the module engages a relay that shorts the module output. Again, if the relay or relay driver circuit is defective, you could have problems, but these have proven to be much more reliable than the original toggle switches, as user error caused more failures than component problems ever did.

The ND25 and ND50 transmitters had a bank of circuit breakers on the rear of each power supply cabinet so you could power down the module to be removed. Then on the module there is a CHARGE/DISCHARGE switch to enable you to do a fast discharge of the power supply caps on the module (these transmitters have 120,000 uF of capacitance on each module, so fast discharge is necessary!). This also drops in the relay to short the output, as with the smaller transmitters.

XL series:

The XL series had an inhibit switch on the front of the module which dropped the relay across the output, then when you disconnected the drive connector it broke an interlock circuit that operated the shorting relay on the module output - failure rate even lower now, as the switch is right above the connector so less chance of forgetting to press it.

XR series;

Operates the same as the XL series, but with failsafes installed to ensure that even if you forgot to push the inhibit switch, the module would be protected from catastrophic failure, although it might blow an amp or two when disconnected.

NX (current production model):

Drive is via RJ45 as digital data - unplugging the front panel RJ45 connector disables the module and shorts the output, there are no switches to remember - so far not a single failure as a result of module removal.

That's it in a nutshell, except for the J1000, which has a hybrid combined output and must be shut down for module removal, and the ND1, which only had one power module anyway, so also must be shut down. Hope it helps!

Best,

Jeff