Gates One / RF Spur

[RememberWHEN]

Has anyone had an issue with this transmitter and intermod issues with other local AMs?? Here are the basics: Gates One is on 1340kHz on a single stick. Other local station (roughly 2 miles away; 5kW DA 'towards' the Gates) at 1270kHz. 'Spur' shows up at 1410kHz with 1270 audio riding over 1340 audio. Our backup xmtr is an MW-1A with no such issue. Harris claims we need a filter between the Gates One and the ATU. Please contact me off-line.

Regards,

RememberWHEN

 

[ChiefEngineer]

You leave out some fundamentals here to check.

Local Fm had 101.5 and it's Am was on 1.010. Spur (with audio at 102.3). The math makes it 102.5. RF mixed in the rg 59 jumper.

1270 and 1340 have a difference of 70. 1340 and 1410 leave 70. Doesn't mean anytrhing until you find the mix.

The output network of any transmitter is dependent on it's impedance. When you proofed the transmitter did the impedance match on the MW-1 and the Gates One?

One possibility is : Something is different between the output network of the Gates One and the MW-1. neutralization? Grounding? make sure your ground on both transmitters is the same ground potential and not a make believe ground. Don't guess on this - have seen it happen.

Usually in any mix the audio of the highest rf station wins the battle and it's rf rides in on the mix. Where is the mix taking place that it is a problem?

The rf could be mixing elsewhere not related to your station and it is only noted as a result of the power level used on the MW 1 and Gates One.

Are power levels equal when the problem takes place? Using your Potomac field strength meter locate the strongest signal of the 1410 and see where this is. bet it isn't at your site?

The Gates One is identical in it's design to the SX Series. Not a big jump from MW-1.

Involve station B which is aprt of the mix. Just ask and see what response you get. Equipment you don't have might be available there.

 

[rew]

I had an issue with a Gates One a few years ago that wes throwing spurs + and - 70Khz (i think it was 70khz) of the main carrier. The PDM frequency of the Gates One is about 70 Khz. I found the filter capacitors in the PDM filter circuit bad. I dont have the book or access to the transmitter at this time but I think they were somewhere around 800uf at about 400 volts. I think it was the 2 big blue caps on the left side.(looking at it from the back). This may be a good place to start. Caps not real expensive and easy to change.
Good luck and when you fix it let us know what the problem was.

 

[boiseengineer]

Had to look at the book and the Gates series uses 60 kHz for the PDM. Think the DX series uses 70 kHz.

And there's this Service BULLETIN NO: AM-579-JKAs DATE: April 11, 2008

"...part of your normal periodic maintenance program, it is recommended that you check the
filter capacitors within your transmitter.
This can be easily done with an oscilloscope placed on the filtered DC supply lines. Ripple may
also be measured with good quality multi-meter on the AC millivolts scale.
Measure the amount of ripple present on the DC supply lines. In low voltage circuits, ripple of
300mV or more should be considered excessive as well as any observable noise. Capacitors
may also be checked with a capacitance checker or “Z” meter. A reliable method if no test
equipment is available is to visually inspect the caps for any leakage or bulging. Another
method is to remove them from circuit and give them a good shake. Any sound of sloshing,
clunking internally, or a cap that is extremely light in weight, should be considered bad.
Severely depleted or “dried out” capacitors can start to arc internally and in some cases arc
through the capacitor walls to the transmitter chassis shorting the supply line.
Our experience and history on the products show that electrolytic filter capacitors should
typically be refreshed every 7 to 8 years of service to prevent unwanted off air events.
Common Transmitter Symptoms:
Gates / SX Series
1. Low RF drive level – IPA supply filter capacitor.
2. Poor audio quality, noisy – H.V. Power Supply filter capacitors.
3. Does not meet NRSC mask / Spurs, 60kHz either side of carrier – PDM filter capacitors.
..."

bill