[RVRC] W2QW 2 Meter system

[Craig W Saums via RVRC]

Thank you to all that have expressed concerns about the 2 Meter system problem.  
The Technical Committee is certainly aware and working on available options to resolve the problem with the least amount of impact.

There are 3 'best guess' explanations for the current problem - probably in this order.

Propagation changes
A reverse pair machine using our same PL (in combination with propagation changes)

Malicious deliberate interference.
Opinions vary on the cause but the solution options are the same

The problem is what I will call a 'ping-pong' loop where you can hear our courtesy tone repeated rapidly as the machines 'ping-pong' until there is a long enough break at some point for one side to drop the connection.  This is different than what we hear with the NY machine - you hear their tone and voice on the end of our squelch tail but it does not 'ping-pong' multiple times.  We have had malicious interference in the past but that was more like a 'key down' open carrier and not a 'ping-pong' loop.

Here is my viewpoint based on the recent email chains - - -

Changing the PL would, at best, be temporary for the purpose of diagnosing the problem further.  
A permanent change to the PL would have to be properly advertised and managed.

If the problem is due to a reverse pair machine (probably not coordinated) then changing our TX PL could break the ping-pong loop by making the other machine ignore our transmission.  Since we would still have our RX PL turned on - the foreign machine could still open our squelch if it initiates a transmission from the remote end but it would not be re-transmitting our signal (the ping-pong problem).  Since most club users are set up for TX encode on their radios - the W2QW machine would still hear the local call.  Anyone that uses RX decode would not hear a response although most users probably do not use decoding on the received signal.  The ARRL Repeater book does not indicate the need for decoding even though we transmit the PL on the output. Visitors would not be aware and would not be impacted by a TX PL change.  Our users could remove the decode option if they use it, assuming they read an email announcement.

If the problem is due to a malicious intruder - the PL change is even less effective since the PL can be scanned - at least for the repeater input (TX encode).

There have been a couple of other suggestions that would reduce our transmit power - not so good as this is part of our coordination spec and leaves us open to future issues.  The theory would be to keep our signal from getting to the other machine (ping but no pong).  This option would have a big user impact.

We cannot reasonably change the power output level unless we remove the 2M amplifier and run the repeater barefoot at 25 Watts.  Our 2M  Henry amp is a 200 to 1 amplifier.  The ICOM radio exciter normally runs at .5 watts with amplified power at 100 Watts out.  We ran the system barefoot at 25 Watts when the amp was out for repairs but the negatives above apply and it means the repeater duty cycle is at maximum - - not good especially for net usage. We had some overheating problems during nets with this configuration during the amp repair period.

Changing the antenna from the high gain dipole to the back up tri-band antenna would impact both the TX and the RX effectiveness so this is an option but still not so good.  Maybe this could be used for round 2 testing.

A software configuration change has been put in place as a first round of possible fixes (Sunday night 12/28).  
The change is on our RX side only. This change does not reduce our power output and still uses the primary high gain antenna.

The situation will continue to be monitored to see if there is improvement and to evaluate overall system performance.  
Please try to use the machine normally and report any problems to the system operators or technical committee

If this is atmospheric / weather / propagation related as it has been in the past - the situation may resolve naturally - hopefully soon.
If it is a reverse pair machine, then the software changes may be the best option at least for diagnostic purposes. 
If it is malicious, then we have more work to do.

If it is something else - we will keep working on it.

Thank you for your patience.

73

Craig AC2FE