Dropping AM Power to 3 watts at night

[seacoastradio]

I'm in the process of buying an existing station that is 5kw Day and only 3 watts at night....been a while since I have operated an AM station and am somewhat lost on how to step down a transmitter from 5kw day, 2.5kw critical hours all the way down to just 3 watts for night power...any help would be much appreciated.

 

[RadioMan203]

The easiest way of accomplishing this is probably go get one of the Radio System's AM transmiiters - Radio Systems Low Power Transmitter

When I engineered my 1KW daytimer we had a pre-sunrise/post sunset power of 9 watts along with a 50 watt interim power from 4:30pm to 6pm in certain months. The late Art Silver from Harris added the third power position on our MW-1 and we had an LPB TX2-20 that was used for the 9 watts. Trying to dump any appreciable power into a dummy/waste load to achieve your desired power from a higher output box or otherwise trying to throttle down a higher power transmitter is only asking for problems . While the MW-1 worked well at 50 watts it was nothing short of a disaster at 9 watts.

 

[bossbill]

Depends on the transmitter. Some PDM transmitters can do it. While the Radio Systems approach would work well, it requires an antenna switch.

Is 3 watts worth it?

 

[BobOnTheJob]

At WIFE 1580 in Connersville, IN, we run with 4.6 watts night and YES, it's worth it...assuming your stick is in the city limits. If it's more than a mile out of town, save yourself the worry. WIFE reaches the entire city of 12000 people with a listenable signal...even penetrates the downtown business district pretty well. In their case, the BE AM500A transmitter (little rack mounted transmitter) handles 5 power levels. The lower couple of settings can go all the way to 0 watts. The 4.6 watts sounds just as clean as the daytime wattage.

At another station, I turned the BE down while the guy at the studio listened on a portable radio in the office at 2 miles. When it faded out, the meter on the transmitter was not even moving... You might be amazed at what 3 watts will do. As I tell people, the first 3 (or 4.6) watts are your most important 3 (or 4.6) watts.

 

[JB1011]

The low power transmitter idea works well. I had it at on of my former stations. Another option is a PCU, or power cutback unit, from Kintronic Labs. You can call Kintronics for more information.

There is one for sale online currently. Here's the link.

http://www.wlct.com/Kintronics/kintronic_power_reduction_unit_f.htm

If you need any technical assistance, you can send me a PM.

Good luck!

 

[rfry]

At WIFE 1580 in Connersville, IN, we run with 4.6 watts night and YES, it's worth it...assuming your stick is in the city limits.

Below per the FCC curves are the approx fields from a 1/4-wave stick using a 120-radial ground system in good condition. Even the 2.5 mV/m level would provide a good signal to a cheap indoor radio, without too much interference on the channel.

Input Data -

Frequency = 1580 kHz
Power = 4.6 watts
Radiation at 1 mile = 12.9 mV/m
Conductivity= 8.0 mS/m

Results -

Contour level : Distance to GW contour

10 mV/m : 1.05 miles
5 mV/m : 1.87 miles
2.5 mV/m : 3.15 miles

RF

 

[BobOnTheJob]

At WIFE 1580 in Connersville, IN, we run with 4.6 watts night and YES, it's worth it...assuming your stick is in the city limits.

Below per the FCC curves are the approx fields from a 1/4-wave stick using a 120-radial ground system in good condition. Even the 2.5 mV/m level would provide a good signal to a cheap indoor radio, without too much interference on the channel.

Input Data -

Frequency = 1580 kHz
Power = 4.6 watts
Radiation at 1 mile = 12.9 mV/m
Conductivity= 8.0 mS/m

Results -

Contour level : Distance to GW contour

10 mV/m : 1.05 miles
5 mV/m : 1.87 miles
2.5 mV/m : 3.15 miles

RF

Fortunately, 1580 is a fairly quiet channel at night. Everybody in this part of the world protects something in Canada at night, resulting in as good a place as any for 4.6 watts at the high end of the dial. Under the worst interference, you can tell what song is playing at 3 miles. In this case, flea power was worth the effort. Thanks for the analysis...appreciate it.

 

[Tom Wells]

You might be amazed at what 3 watts will do. As I tell people, the first 3 (or 4.6) watts are your most important 3 (or 4.6) watts.

Back when I was a pirate on 7.415 Mhz with 100 watts, people asked, "Only 100 watts?", I used to tell them if you can't get the job done with 100 watts on shortwave, you're doing something wrong...that first 10 watts is doing all the work.

I would love to go UP to 3 watts. Especially since WONX Evanston IL seems to have implemented their power increase, and the splatter
from their 1590 goes even wider than before.

 

[BobOnTheJob]

You might be amazed at what 3 watts will do. As I tell people, the first 3 (or 4.6) watts are your most important 3 (or 4.6) watts.

Back when I was a pirate on 7.415 Mhz with 100 watts, people asked, "Only 100 watts?", I used to tell them if you can't get the job done with 100 watts on shortwave, you're doing something wrong...that first 10 watts is doing all the work.

I would love to go UP to 3 watts. Especially since WONX Evanston IL seems to have implemented their power increase, and the splatter
from their 1590 goes even wider than before.

Are you also on 1580?

 

[Tom Wells]

No, I'm on 1620, but exactly due south of their array at about 2 miles.
I guess WONX has always been about as splattery as they are now, but the power increase just makes it more evident.
And I'm using radios with RF pre-amp selector sections, it's even worse for receivers with straight input to the converter.
100 milliwatts can't get too close to much of anything, lest it be stepped on.

I once heard WBEE Harvey IL 1570 in the Cinncinnati area clear as a bell.
Not a chance in a million of hearing WIFE 1580 here unless WONX is off for some reason.

There are no other really good options for a pt 15 here except maybe 1550, but I have a rock for 1620.

 

[OnTheAir123]

I engineer for a plant that has the exact parameters 5KW day and 3W night and it does a very fine job. The tower is 250' and the antenna is a folded unipole. The main transmitter is a Gates/Harris 5 and the night transmitter is an LPB 30W backed down to 3W. Antenna switch is a Harris 5KW unit.

http://www.radio-locator.com/cgi-bin/pat?call=WEBS&service=AM&status=L&hours=N

Randy Rhodes

CE: WTSH-FM, WQTU-FM, WSRM-FM, WRGA-AM, WEBS-AM, WGJK-AM, WJTH-AM/FM

 

[KyDXIn]

You might be amazed at what 3 watts will do. As I tell people, the first 3 (or 4.6) watts are your most important 3 (or 4.6) watts.

Back when I was a pirate on 7.415 Mhz with 100 watts, people asked, "Only 100 watts?", I used to tell them if you can't get the job done with 100 watts on shortwave, you're doing something wrong...that first 10 watts is doing all the work.

So you were one of these? http://www.youtube.com/watch?v=3AzpByR3MvI