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[Scott Holtzman]

Great story.   

One of my troubleshooting tips is "just look at the damn thing for a couple minutes". Finding a burnt component usually makes the rest of the search a lot shorter.

Agree completely and thanks. 

[Henry Cohen]

They used a R&S®ZVH Cable and Antenna Analyzer to visually see the null at a freq.  Put a T on it then a termination on one side and the cable on the other and left the end of the cable open.  Basically a distance to fault measurement, I think.

It's actually a 2 port VNA that can measure distance to the fault (the end of the cable) and then translate that length into frequency taking into account the type of cable. It can be calibrated to a reference length/frequency before each use so the measurements are consistently quite accurate. It can then measure VSWR of the tuned jumper connected to the next filter input, if they so desired.

[Henry Cohen]

In terms of overall number of interfaced radios, I think I saw that the system for the last winter games had quite a few more channels. Do you think that was a one-off rather than a trend in mega event comms system design? Would you like to have more radio channels on this show but limited by other factors such as budget or spectrum?

As Pete stated, budget and spectrum availability are always factors. On these large events, available spectrum, physical square footage and install time are generally the primary factors over budget. With a filter/isolator TX combine system, as opposed to hybrid coupler, adjacent TX channel spacing is greater (generally a minimum of 175-225KHz based on filter Q), a lot more floor space is required to accommodate significant numbers of relatively large filters, and (as Pete mentioned) a lot of time is required to build tuned interconnects.

On the flip side, a hybrid coupler system, requires lots of RF power to compensate for the insertion losses, and lots of AC power to run the RF amplifiers (and possibly air conditioning).

[Scott Holtzman]

It's actually a 2 port VNA that can measure distance to the fault (the end of the cable) and then translate that length into frequency taking into account the type of cable. It can be calibrated to a reference length/frequency before each use so the measurements are consistently quite accurate. It can then measure VSWR of the tuned jumper connected to the next filter input, if they so desired.

So it is not actually like a sweep generator/spectrum analyzer/S-axis test set that can show the response of a filter/network and be used to tune the filter in real time?  When tuning cavity filters as was just mentioned the same exact tradeoff occurs, the sharper the Q the greater the insertion loss.

While we are discussing combiners I am sure there are folks that have never seen one.  For the lurkers this is a 5 cavity hybrid combiner.  The things with the red caps and little dummy loads are where the transmitters are attached.  They are magnetic circulators that act as RF diode gates and shunt incidental energy returned from impedance mismatches to the dummy loads. 

The big cans are cavity filters.  The stick with the red cap is a rod that moves a plunger to alter the resonance of the cavity.  There are also matching loops that are on the input and output connectors that can be tuned for best match.

You can see the jumpers between the combiner network and the cavity are all of different lengths (count the dress loops) this is part of the tuning process and what was being discussed.

This looks to be about a 100w combiner to my eyes.

[Neil White]

Hi Pete,

Is the Rehearsal system tied to the main system using a trunk navigator for dynamic port usage or is it just conferences at each site I nterfaced over VoIP 4w? I take it there is a network data connection as well as voip between the two sites if Radouan is able to access both systems from his control poaition.

[Pete Erskine]

Hi Pete,

Is the Rehearsal system tied to the main system using a trunk navigator for dynamic port usage or is it just conferences at each site interfaced over VoIP 4w? I take it there is a network data connection as well as voip between the two sites if Radouan is able to access both systems from his control position.

Trunk Navigator.  2 VOIP cards in each system make 16 4-wire lines,  some are static for audio TC and showcall.  the rest are dynamic.   Audio playback and monitor routing are still at the stadium as are announcers.  We are on the same LAN as the venue.

[Henry Cohen]

So it is not actually like a sweep generator/spectrum analyzer/S-axis test set that can show the response of a filter/network and be used to tune the filter in real time?

Because it's a two port VNA, it does have a tracking (sweep) generator and can do S12 & S21 measurements. However, for the measuring VSWR, return loss or distance to fault, it's used as a one port device for S11 (or S22) measurements.

While we are discussing combiners I am sure there are folks that have never seen one.  For the lurkers this is a 5 cavity hybrid combiner.  The things with the red caps and little dummy loads are where the transmitters are attached.  They are magnetic circulators that act as RF diode gates and shunt incidental energy returned from impedance mismatches to the dummy loads.

This is not a hybrid combiner; there are no hybrid couplers. This is a star junction, filter-isolator configuration - the same as Pete is discussing. The isolators - circulators with port 3 (and port 4 if a dual stage) terminated - are connected between the final PA and the filter.

This looks to be about a 100w combiner to my eyes.

I'll agree with that.

[Scott Holtzman]

Because it's a two port VNA, it does have a tracking (sweep) generator and can do S12 & S21 measurements. However, for the measuring VSWR, return loss or distance to fault, it's used as a one port device for S11 (or S22) measurements.


This is not a hybrid combiner; there are no hybrid couplers. This is a star junction, filter-isolator configuration - the same as Pete is discussing. The isolators - circulators with port 3 (and port 4 if a dual stage) terminated - are connected between the final PA and the filter.


I'll agree with that.

I have been calling it the wrong thing for all these years.  So a combiner that uses a ferrite style coupler is properly referred to as a hybrid combiner?

Like this?

[Neil White]

Trunk Navigator.  2 VOIP cards in each system make 16 4-wire lines,  some are static for audio TC and showcall.  the rest are dynamic.   Audio playback and monitor routing are still at the stadium as are announcers.  We are on the same LAN as the venue.

Is comms responsible for all time code distribution to the users from audio playback? If so, how much redundancy has to be built in, as I'd expect timecode to be critical for most departments on this scale of show?

[Pete Erskine]

Is comms responsible for all time code distribution to the users from audio playback? If so, how much redundancy has to be built in, as I'd expect timecode to be critical for most departments on this scale of show?

You are right, it is the most important "audio" in the show.  It actually is a shared responsibility with audio where the TC originates.  Many of the Artist panels have TC displays and a lot are fed via the 2nd channel of the panels for users to see and take cues.  Audio distributes many of the displays too, and feeds key departments like automation, SFX, Lighting, video and Projection.  I don't know for sure but I think most have redundant feeds.  MediorNet transports TC to every department and to the Network as well.

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