My Ugliest ATU

Have a site with some cool media? Post the links here
Post Reply
User avatar
Dale H. Cook
Posts: 761
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

My Ugliest ATU

Post by Dale H. Cook » Fri May 22, 2015 6:20 pm

I've seen some ugly ATUs in my career, but the one at a new client's transmitter site is probably the ugliest I have seen:

Image

This box is inside the transmitter building with the tower on the other side of its wall. Note that the base ammeter is hanging from a wire draped over a J-plug and connected to the J-plug with a pair of flexible leads. Note also that the series output mica cap at left center is mounted on plywood, so the tower base is connected directly to that plywood. This weekend I will have a chance to take the station down, drive two hanger bolts into the plywood, and use the bolts to mount a pair of standoffs for the cap. I also have a spare J-plug jack to mount in parallel with the existing jack. I have no idea if the base ammeter works - I haven't yet mucked with it. I will do some other cleaning up, and then sweep the tower base and sweep and adjust the ATU match. I strongly suspect that no measurements have been made on the tower base or the ATU in decades, during which the ATU has been adjusted solely by using the transmitter reflectometer. I also have a refurbished old base current sampling unit to install.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

kcbooboo
Posts: 448
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: My Ugliest ATU

Post by kcbooboo » Sat May 23, 2015 12:17 pm

I've heard of breadboarding, but that's a fire just waiting to happen!

Bob M.

User avatar
Dale H. Cook
Posts: 761
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: My Ugliest ATU

Post by Dale H. Cook » Sun May 24, 2015 7:15 am

kcbooboo wrote:... that's a fire just waiting to happen!
I'm rather surprised that I haven't seen at least some signs of trauma where that cap is mounted. Of course, from internal evidence in equipment it seems likely that this station has not run at full licensed day power in at least 29 years. The ATU was modified at about the time that an improper parts sub was made in the transmitter that kept it from making full power.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

User avatar
RGORJANCE
Posts: 1382
Joined: Mon Dec 31, 2007 7:48 am
Location: RACINE, WI

Re: My Ugliest ATU

Post by RGORJANCE » Sun May 24, 2015 8:51 am

I thought I had seen some "winners" in my career, but that one tops them all. You indeed have a "first place" entry.

Golly, when I was a mere child of 13-14 years old, I scratch built a 1625 final ham xmttr that, by comparison, would have been considered museum quality. But, then, I tend to be somewhat partial. Actually, it was made up of a lot of used, re-purposed "war surplus" parts, placed in a paper sack, shaken, not stirred and didn't smoke the first time power was applied! As far as I could tell, it actually made power on at least one frequency.

Fossil

User avatar
Dale H. Cook
Posts: 761
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: My Ugliest ATU

Post by Dale H. Cook » Sun May 24, 2015 9:44 am

RGORJANCE wrote:You indeed have a "first place" entry.
Fossil -

I thought so too. Tonight I plan to sweep the ATU input before I start overhauling it, and will sweep it again after the overhaul. I will post Smith charts of the before and after sweeps here. I am willing to bet that the before sweep will be pretty nasty.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

w4cl
Posts: 479
Joined: Wed Apr 09, 2008 3:04 pm
Location: 1 3/4 meters

Re: My Ugliest ATU

Post by w4cl » Mon May 25, 2015 5:33 pm

Wow! Time for a complete rebuild! Would hate to see what the RF egress off that open circuit is in that building.

User avatar
Deep Thought
Posts: 3190
Joined: Thu Mar 20, 2008 9:23 am
Location: La Grange, IL
Contact:

Re: My Ugliest ATU

Post by Deep Thought » Mon May 25, 2015 11:27 pm

Where is the two feet of straw and miscellaneous trash from 20 years of mouse nests? 8) Not to play one-up, but I once opened a home-made plywood box ATU at a station I was doing engineering due diligence for a client and the 2' x 2' x 2' box was completely full of mouse condos. Completely. Unfortunately, I don't have a photo but you can imagine what it was like inside. The only thing that prevented the box from turning into a slow roaster is the station only ran 500 watts. Everything inside was coated in mouse pee.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

User avatar
Dale H. Cook
Posts: 761
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: My Ugliest ATU

Post by Dale H. Cook » Tue May 26, 2015 6:21 am

Deep Thought wrote:Where is the two feet of straw and miscellaneous trash from 20 years of mouse nests? 8)
I cleaned that out before taking the photo - much of it was in the cable trough in the slab. :-)
Deep Thought wrote:The only thing that prevented the box from turning into a slow roaster is the station only ran 500 watts. Everything inside was coated in mouse pee.
This one has been running 100 watts (licensed for 5 kW day) for more than a year. I went through lots of disposable gloves and disinfectant wipes while cleaning things up.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

BingNYEng
Posts: 90
Joined: Wed Jul 21, 2010 1:19 pm
Location: Binghamton, NY

Re: My Ugliest ATU

Post by BingNYEng » Tue May 26, 2015 7:21 am

I'm trying to wrap my head around what that contactor is there for. It looks like it is shorting the input to ground in one position.

User avatar
Dale H. Cook
Posts: 761
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: My Ugliest ATU

Post by Dale H. Cook » Tue May 26, 2015 8:45 am

BingNYEng wrote:I'm trying to wrap my head around what that contactor is there for.
The photo can be deceiving. The contactor switches between the Continental 315R-1 Power Rock used for day (5 kW) and PSRA (500 W) powers, and the LPB AM-100P used for PSSA (43/50 W) and night (20 W) powers.

I have not yet swept the base and the ATU input, but the latter may not be as bad as I had earlier expected. While searching for something else I found a 1999 redesign of the ATU as a -150 degree network. The most likely reason for the redesign would be cusp rotation for sideband symmetry. After I sweep the base I will rotate it on a Smith chart and see if that is the case. Of course, given the fact that the previous "engineer" did things including diddling the Power Rock PWM duty cycle without a 'scope, the ATU may no longer be set up properly.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

Post Reply