May 30, 2006

Voting system adjustment


After a few days with the new Kenwood link receiver in place it appears to be functioning very well, but the audio output does not have the same 'composite equalization' as the former Motorola Motrac receiver had. The audio feed to the voting systems has more high-frequency noise energy in it than the previous receiver, thus causing the voting systems to mistake full quieting signals from the W8TVC site as being noisy.

With the assistance of Tom N8STZ on 52.42, I was able to adjust (via the placement of a .01mfd cap in the audio) the output of the link receiver to properly feed the voting receivers. The voters appear to be functioning properly now.

Additionally, this being the fourth 'hot' day in a row without any 6mtr intermod at the Empire site, it appears as though the intermod problem of last summer is gone. This is very good news. Apparently a potential source of the problem was discovered last January during a tower climb for the broadcast stations on site. I owe Glen Walker and Del Reynolds a few cold beers in thanks.

73 John KF8KK

May 28, 2006

TVC-Empire Link Operational

I'm very pleased to report that the problem with the 440.05 transmitter was conclusively found and has been repaired.

Apparently, the problem was with the Motorola Mitrek since it left the factory, but took all these years to manifest. A small ceramic bypass capacitor was mounted too close to the circuit board and the body of the capacitor would contact the exposed trace on the board beneath it (which happened to be the RF output of the exciter) and when the 'heat soak' of the unit reached that portion of the unit the expansion of the metal caused electrical contact to be made between the capacitor and the trace, thereby shorting out the exciter output and hence taking the transmitter down.

While the link was down, I proceeded to make the following improvements/updates:

1: A 146.2hz PL decoder was added to the 449.725 receiver at the W8TVC location (so mobile repeaters will have the voting system available to them).

2: The 440.05 link receiver in Empire was changed from the problematic Motorola Motrac 'L' to a Kenwood TK860. With luck, this should solve the problems the old receiver had with seasonal frequency drift and occasional interference on the IF frequency. The Kenwood is multichannel and includes scanning, which may prove useful for future linking configurations.

3: The PL decoders for the link receiver were changed from the former RCA700 series decoders to Motorola Maxar/Moxy decoders. This should solve some false-dropouts that have been noted on the 440 side.

4: The Kenwood receiver no longer requires the GasFet preamp in order to hear the link transmitter, so the Lunar GasFet preamp has been removed from the site and returned to workbench stock. It's a refreshing change to actually 'simplify' even a small portion of the system.

With luck, the linking setup will return to it's highly reliable nature.... or even better.

73 de KF8KK

May 26, 2006

TVC->Empire link Offline

Sadly, the 440.05 link transmitter at the W8TVC location is still failing.

At 8pm today (Friday) the transmitter was removed and the crosslink between the repeaters was disabled so the unit could be repaired on the workbench.

film at eleven.

73 KF8KK

May 25, 2006

Link transmitter maintenance


On Wednesday it was observed (for the second time) that the 440.05 link from W8TVC to Empire had failed intermittantly during a long conversation. On this day, the link transmitter was failing repeatedly and appeared to fail in a manner that would cause one to suspect it was heat related.

Normally, when the 440.05 link is transmitting, it is received at an S2-S5 level at the KF8KK TS2000 in the workshop. It can also be heard mobile on M72 in the area. It was not heard when failed, leading to the diagnosis that the problem was at the transmitter side.

On checking out the transmitter at 8:15p I found the unit transmitting a rather variable amount of power. The wattmeter reading fluctuated as if it was an SSB transmitter... everything from zero to 8 watts.

I did some tweaking and it stabilized and was set to 10.4w. An external blower fan was placed to add cooling to the unit (there had been no fan on the unit since original installation two years ago). It appears to be functional, but only time and long qso's will indicate whether this was an effective repair. What caused the detuning is unclear. It had been a couple of years since it was tweaked so there may be an ageing component to the 'tuning drift', though it equally could be some components in the process of failing.

Film at eleven after the late news....

John KF8KK

May 24, 2006

Packet repeater update

Both Monday 5/22 and Tuesday 5/23 saw maintenance and improvements added to the packet systems. Apparently during the previous week the 433.1 node (ben12) would not properly accept NetRom connections. Hard reset would only have the node functioning properly for a few minutes at best. The 'stats' page showed cpu loops in the 200 range-- not the 500-700 range as it should be. Something was amiss. Thankfully, this appears to have been corrected (bad trace was found on board).

New 3v lithium batteries were added to the 145.07 and 433.1 nodes. The 433.1 repeater was modified to improve transmit and receive performance with pre/de-emphasized packet stations. Additional work was done to eliminate some 'apparent jitter' in the repeated data and to eliminate the oddball 'data feedback' that would occasionally appear and lock up the system.

The Mitrek timout timer was also installed as a fail safe should the data feedback ever rear it's ugly head again.

A GasFet preamp was added to the 438.1 receiver for improved performance.

In other observations, the 440.05 link transmitter at W8TVC's appears to overheat and cease transmitting at times. Work on that will commence soon.

The backup battery charger at the 444.725 repeater appears to be working well.

John KF8KK

May 05, 2006

Link Antenna Upgrade


On Wednesday 5/3 the antenna for the 440.05 link at the W8TVC site was changed from a six element Cushcraft yagi to a M2 antennas 11 element yagi. It appears (so far- two days) that the fading problems on the link are history.

On Thursday 5/4 the Cushcraft yagi, formerly used for the link from W8TVC, was placed in service at the 'KKBBS' Jnos hamgateway to link it to the 433.1 packet repeater at the hilltop repeater site. After some tuning of the gamma match, the antenna appears to be performing well in this application.

73 John KF8KK

May 01, 2006

CTCSS addition


Today a CTCSS decoder for 146.2hz was added to the primary 449.725 receiver at the Empire site. This is to allow those with premium grade dualband mobiles to utilize the 'mobile repeat' function with the 444.725 repeater (the repeater transmits the 146.2hz tone with incoming signals-- mobile repeaters should operate in 'pl decode 146.2hz' in order to operate through the repeater without having to wait for the system to drop carrier before the mobile can transmit).

Additionally, work was done to the wI0OK-7 145.07 packet node to improve receiver performance. It was found that the addition of a GasFet preamp provided extremely minimal improvement in reception. This was NOT enough improvement to make it worth leaving the preamp in position-- the SyntorX already has the Motorola 'hi sensitivity' option installed (which appears to be working fine). It was determined that the packet TNC was seeing too much high frequency audio noise on the incoming audio line and a R/C circuit was added to reduce the hiss presented to the demodulator. This appears to have improved the packet decoding.

73 John KF8KK