Transmission Lines, in the dark here

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abwdvm
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Transmission Lines, in the dark here

Post by abwdvm »

We just purchased an FM station.
We need to move the Transmitter and Antenna to another tower.
The nitrogen bottle runs out in less than 30 days....
Should we replace the transmission line... If so with what?
The STL line seems to be in good shape, we are planning on cutting it down and reusing it.
line1.jpg
coupler.jpg
technician at an 1000w AM station in Texas
Nathaniel Steele
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Re: Transmission Lines, in the dark here

Post by Nathaniel Steele »

You should find your leak, it could be an O-ring, anywhere there is a coupling/connector, even at the antenna, or you could have a hole in the line itself. That said, Unless your tower crew is working for free, you might want to carefully weigh the cost of removing and refurbing the old transmission line, with the Cost of new, and the piece of mind of knowing that its all new, and if properly installed , should last many years to come. If you do re-use the old stuff you should inspect all your bullets, and replace if necessary, and I'd just go ahead and replace all the O-rings, same for the antenna. That looks like 3-18" line to me and it won't be the easiest to coil back up and move. you don't want to kink or deform the line in any way. I'v'e Pulled and re-used Half Inch line in the past, but I actually ran new line up the new tower and savd the old for emergencies (I was tending a lot of (previous to me) poorly maintained sites back then and it got used in short order). Not sure I'd try to re-use 3-1/8" line myself....I'm not telling you don't do it, But I am advising you to think about it. Someone with more experience than me ( I've only been doing RF about 8 years now, and am probably one of the younger guys here) may disagree, But I've not seen it done(With 3-1/8" before). I've seen people re-use old line that was abandoned(and I've done it myself), but never move a 3-1/8".

If this is a directional antenna, have you confirmed the pattern will be ok at the new location? have you talked to the tower crew about pulling the old line? of course if your paying theyll do anything you want as long as its safe.....

Just my thoughts, but I'd be good and sure the line was OK before taking it down If you absolutely must move the line....
ncradioeng
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Re: Transmission Lines, in the dark here

Post by ncradioeng »

Do you need a line that big? 1-5/8" would work for that transmitter TPO.
Nathaniel Steele
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Re: Transmission Lines, in the dark here

Post by Nathaniel Steele »

Possibly not. one would need to know the length of the line, antenna gain, ERP, and any additional losses such as filters and do the calculations. 3-1/8" will have less loss than 1-5/8" if most of that 10KW is needed at the end of a long line....
ncradioeng
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Re: Transmission Lines, in the dark here

Post by ncradioeng »

That all needs to be considered. Also, it's not recommended that an exhaust line be attached directly to the transmitter because it can diminish the air flow. It's better to have a hood over the exhaust with some space between it and the transmitter.
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abwdvm
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Re: Transmission Lines, in the dark here

Post by abwdvm »

Anyone have an 3 1/8 to 1 5/8 adapter?
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TPT
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Re: Transmission Lines, in the dark here

Post by TPT »

I would install a new 1 5/8th line, the output of that ECO-4's reflectometer is 1 5/8th. However--I do have a 1 5/8th to 3" adapter, if that is what you need to get into the antenna.

If you can swing it--buy an in-line Bird watt meter. RF Parts and RadioDan often have used ones. My TPO is 3900 watts out of an ECO-4--the Bird reads 3900 watts when the output meter on the Bernie Box shows 4500 watts.

Also--even if it is only a few feet, you will need to file a Form 302 for the new site. It's a minor change; provided that you meet the conditions set forth in Section 73.1690. If you new tower is some distance away, you need to apply for a construction permit.

Go to ECFR.Gov, find Title 47, and look for Section 73.1590.
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abwdvm
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Re: Transmission Lines, in the dark here

Post by abwdvm »

Bird 43 Thuline?

I think we can remove the 1 5/8 to 3 1/8 adapter after the sample ports tube, and simply install a 1 5/8 connector.

The 3 1/8 connector has the nitrogen port on it.
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Nathaniel Steele
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Re: Transmission Lines, in the dark here

Post by Nathaniel Steele »

ncradioeng wrote: Wed Jun 27, 2018 2:22 pm Also, it's not recommended that an exhaust line be attached directly to the transmitter because it can diminish the air flow. It's better to have a hood over the exhaust with some space between it and the transmitter.
Seconded.
Nathaniel Steele
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Re: Transmission Lines, in the dark here

Post by Nathaniel Steele »

abwdvm wrote: Wed Jun 27, 2018 3:48 pm Bird 43 Thuline?
Nah, you want to leave it inline permanently, get a line section:

https://www.birdrf.com/Products/Test%20 ... tion.aspx
And your meter set of choice, I like these:

https://www.birdrf.com/Products/Test%20 ... eter.aspx

I didn't see any decent looking 1-5/8" line sections on ebay.....but keep checking they come up.
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Re: Transmission Lines, in the dark here

Post by grich »

Nathaniel Steele wrote: Wed Jun 27, 2018 10:48 am You should find your leak...
Indeed. The line could be fine and the leak could be inside the TX room...one leaky system we had turned out to be a regulator that couldn't get a leak-free connection to the bottle.
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Re: Transmission Lines, in the dark here

Post by grich »

Nathaniel Steele wrote: Wed Jun 27, 2018 4:43 pm
ncradioeng wrote: Wed Jun 27, 2018 2:22 pm Also, it's not recommended that an exhaust line be attached directly to the transmitter because it can diminish the air flow. It's better to have a hood over the exhaust with some space between it and the transmitter.
Seconded.
Thirded.
TPT
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Re: Transmission Lines, in the dark here

Post by TPT »

Had local HVAC guys build the sheet metal hood for my ECO-4. Has "feet" that stand it off a few inches above the top of the transmitter, I have a 60X40 transmitter building (was a commercial garage), the transmitter room is 25X15, with a similar sized room behind it, the garage: 35X40. When we remodeled the building we put in HVAC for the two smaller rooms, but not in the garage. So I had the HVAC folks build me a sheet metal hood that is vented out into the garage--there are "feet" that keep the hood standing a couple of inches above the top of the transmitter. Cold air return from the garage behind the transmitter. Keeps the "damp" out of the garage in the winter, summertime we use an attic fan on the far wall to move air out of the building.

Seems to work well enough--have two extra kilowatt transmitters plus two small 500 and 300 watt units running along with the ECO-4: Another Class A and three translators at this site.
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abwdvm
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Re: Transmission Lines, in the dark here

Post by abwdvm »

So the hood draws hot air out, does it have a fan attached?
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Re: Transmission Lines, in the dark here

Post by ChuckG »

abwdvm wrote: Thu Jun 28, 2018 10:55 am So the hood draws hot air out, does it have a fan attached?
They way I build them, and TPT is likely similar, is to use a wide hood over the top of the transmitter, leaving a 10" or so gap between hood and transmitter. That gap is to keep downdrafts from air-starving the tube and from dumping the airflow switch. Heat will rise into the hood, helped by the transmitter blower.
That hood empties into a large duct (10" 12" etc) leading outdoors, through either the side or roof of the building with a weather hood to keep rain out and large gauge screen to keep critters out. No fan, as few restrictions along the way as possible.
The building will need to have positive air pressure, negative (like an exhaust fan) may pull air backwards through the ductwork causing issues.
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