Replacing sample lines

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W9PXZ
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Replacing sample lines

Post by W9PXZ » Mon Aug 26, 2019 11:08 am

I have a bad sample line to the reference tower on my 3 tower 5 kW DA. The existing line is Cablewave FCC38, no longer made and unobtanium. So what style of line would be best to replace it with considering cost, long term availability, and appropriateness to the use? I haven't been involved in a job like this before and haven't a clue of cable type. Would going to something common like LDF4-50 be appropriate? Or some LMR400?

Of course the bad one is the longest one and to put the cherry on top, runs about 50 yards through a swamp. If I have to dig up for new sample lines to all three towers, I might as well redo the control and power as well.

Mike Dinger
Wilmington, NC
Mike Dinger
Wilmington, NC

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RGORJANCE
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Re: Replacing sample lines

Post by RGORJANCE » Mon Aug 26, 2019 11:44 am

There are two different requirements as I recall.

1) equal electrical lengths - also called phase stabilized - again as I recall
2) unequal lengths for each tower, same type of line.

If you replace with a different type line, you will need to do a proof - two if it is D/N, and the tower is used in both patterns. I question the legality if you don't replace all with the same type.....mixing might not be permitted.

If the station is in Wilmington, the proofs aren't going to be lots pf fun. I did WDEL many years ago. Ran into many closed-"private roads to elite housing areas?????"

Also, for the exact requirements, Deep Thought is going to have current FCC standards/requirements. I am sure he will provide the details.

Fossil

dd92251
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Re: Replacing sample lines

Post by dd92251 » Mon Aug 26, 2019 12:10 pm

The Electrical Specs for FCC-38-50J -vs- LDF4-50 are nearly identical.

So from a performance standpoint it looks like an easy swap. Now from the FCC viewpoint, the waters are murky. I too would ask Deep Thought what the best approach would be for dealing with the FCC. It could be a simple Skeleton Proof is all that is required. Maybe a "Before/After" Skeleton comparison ??? However, I can't imagine a Full Proof would be required.

W9PXZ
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Re: Replacing sample lines

Post by W9PXZ » Mon Aug 26, 2019 1:03 pm

The station is WAAV licensed to Leland, NC. It is 5 kW Non-D day and 3 towers night at the full 5 kW. The night pattern is a parabola pointing straight at Wilmington and out to the ocean.

I am aware that all the sample lines must be the same electrical length, hence a buried vault at the rear of the hut with hundreds of feet of the current cabling coiled up inside it. Heck, the near tower is only about 30 feet away. So lots of "excess" cable.


I have engineered at directional AMs before, but never one in need of such intensive repair. It is a full mid-80's Harris package complete with the crappy motorized contactors that are all burnt to heck. I was able to get some used but good Kintronic contactors from the company stash, likely from the WMAL relocation in DC. Now need to plan to do this nearly full rebuild of the site.

Good to know about LDF4-50. That is one cable type that should have longevity for years to come. I was thinking that any LMR type cable might be too light weight, but cheaper. I'm looking at about a 1800 foot order for the cable. It is ~600 feet back to the far tower.
Mike Dinger
Wilmington, NC

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RGORJANCE
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Re: Replacing sample lines

Post by RGORJANCE » Mon Aug 26, 2019 2:44 pm

Wild crazy thought.......

Waaaayy back around 1982 or 1983, Cablewave had a bad batch of material. The cup inner connectors inside the connector that mated with the center conductor of the coax were failing due to metal fatigue/or just plain brittle material. The cup connection had a slotted section that broke off causing very poor to no contact at all with the inner. It might not be a bad idea to take the connector apart to see if this is what possibly happened to that sampling line.

I got really lucky and found the problem and saved my customer a lot of troubleshooting time. I think we found like three bad ones that afternoon.

Due to advanced old age and being from a galaxy far, far away, my memory is a bit foggy. Hope this works for you.

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Re: Replacing sample lines

Post by Deep Thought » Mon Aug 26, 2019 5:30 pm

Cablewave 3/8" FCC38-50J is 81% while Andrew LDF4-50 is 88% velocity. Bad things happen when you replace one with the other. Andrew FSJ4-50B is 81% but is really too fragile for long runs.

From an FCC standpoint, the lines must measure equal in electrical length within 1% and within 2 ohms characteristic impedance (§73.151(c)). WAAV appears to qualify for a Method of Moments re-proof and if you are going through the hassle of replacing the sample lines I would do it with 1/2" Heliax-type line and convert to TCT sample transformers if you currently have loops on the towers. The cost for doing the conversion is much less than you might think...I usually can knock this off in one night if everything is already on site. Last order of LDF4-50 I was involved with was around $1.70/foot. If you already sample using transformers it is definitely the way to go. This avoids having to do a partial proof and gets rid of the monitor points too.

Let me know if you want any other information about this.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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kkiddkkidd
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Re: Replacing sample lines

Post by kkiddkkidd » Mon Aug 26, 2019 6:28 pm

Deep Thought wrote:
Mon Aug 26, 2019 5:30 pm
Cablewave 3/8" FCC38-50J is 81% while Andrew LDF4-50 is 88% velocity. Bad things happen when you replace one with the other. Andrew FSJ4-50B is 81% but is really too fragile for long runs.

From an FCC standpoint, the lines must measure equal in electrical length within 1% and within 2 ohms characteristic impedance (§73.151(c)). WAAV appears to qualify for a Method of Moments re-proof and if you are going through the hassle of replacing the sample lines I would do it with 1/2" Heliax-type line and convert to TCT sample transformers if you currently have loops on the towers. The cost for doing the conversion is much less than you might think...I usually can knock this off in one night if everything is already on site. Last order of LDF4-50 I was involved with was around $1.70/foot. If you already sample using transformers it is definitely the way to go. This avoids having to do a partial proof and gets rid of the monitor points too.

Let me know if you want any other information about this.
What he said... I have been asked to do the physical work to replace a number of 3/8in sample lines with modern 1/2in and did so with great reservation and all the applicable warnings. Some were successful in getting the array back to normal MPs & monitor readings and a few found that no matter how long they beat their head against the proverbial wall, no amount of sample line trimming could get the MPs in with the original monitor readings.

Replacing all sample lines and converting to a MoM would be your best bet.

However be absolutely sure to eliminate ALL possible points of failure with the sample line. As Fossil related, I too have found what appeared to be a bad sample line to be a bad connector, bad sample loop, bad jumper, bad toroid, bad etc...
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

W9PXZ
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Re: Replacing sample lines

Post by W9PXZ » Mon Aug 26, 2019 7:04 pm

Thanks, folks. You gave me just what I needed. Sounds like LDF4 is the way to go if they need to be replaced. The TDR shows the bad spot in the cable is right about where it crosses the swamp, so I am betting on it being an actual bad cable, but it wouldn't hurt to swap the Delta TCT's and the short jumpers that come off the buried line around and see if the problem moves.

Now to figure out the retrofitting for the Kintronic contactors... I'll likely get some of their remote relay interfaces and use the ATU 120V power for them and only need the 24 V control lines to come back to the phasor controller. Rewiring the solenoids for the new voltage, of course. It is nice that the wire numbers on both Harris and Kintronic match. I wonder who copied who.

Writing capex proposals for 2020... Lots of money in this years list!
Mike Dinger
Wilmington, NC

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Re: Replacing sample lines

Post by Deep Thought » Mon Aug 26, 2019 8:00 pm

I've switched out those Harris motorized contactors with KTL units directly without needing to use slave relays. The Harris phasor controller shoots 240 VAC out to them through the control cable for (I think) a maximum of 5 seconds and the status returns should be compatible with the KTL microswitches.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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