The AM Forum

Tonight we got some rain.  No lightning.  Storm was gone after an hour.  I flipped on the radio and heard South Africa 40 DB over on 20 meters,  Never worked SA before so here we go. Tune up radio and amp into Dummy.  1400 watts.  FT101EE and SB220.

Flip to Mosely beam 600 watts  1 watt reflefected.    Lost more then half my power.

Back to dummy load, 1400 watts on the nose.

Back to beam,  Retune amp.  Nothing helps.  600 watts max Flat match.

Retune radio and amp into beam.  600 watts max flat match. 

Plate current into dummy is 700 MA on tone.

Plate current into Beam is 350 to 400 max. 

I dont understand.  All I can think of is that the beam is wet.   The amp will not produce more then 600 watts into the beam while producing 1400 into the dummy.

Radio by itself makes 140 watts into the beam and dummy load.  Tried the contact with no amp, First call, Made contact and had a nice chat about my FT101EE and how good it sounded.  Said I was 40 DB over 9 into his 7600 icom with the mosely and FT101EE. That confirms the antenna is fine.

I dont understand what is happening here.. My only thought is that the water is lowering the impedance of the antenna to a point where the SB220 cannot load to full power?   If there was a problem the SWR would be high and its flat as can be.

Scratching head here.

Talked to Mosley.  They are suggesting one of the two driven elements is damaged.  This would explain the low SWR but odd load to amplifier.  They suggested it was struck by lightning.  I was away from house for hours during storm so maybe thats possible.   Looks like it has to come down off the tower..  :(

C

You said you tried the FT-101EE and it worked fine. I suspect that you may have other transmitters/transceivers/ amplifiers that you can also try with the antenna. If they all work and load fine into the antenna, I find it hard to believe that it's an antenna problem. What about 15 and 10 meters? How does the amplifier work on those bands. Does the antenna use any traps on 20 meters? Do you have an antenna analyzer like a MFJ-259 or 269?

You said: "Tonight we got some rain.  No lightning."
Mosley said: "They suggested it was struck by lightning."
 I say: ??? ???

I tried two amps, two radios. The antenna works fine until you cross over about 250 watts of RF power, Then the load goes way off.

I wanted to try the 259 last night but I left it on and the batts where dead.  I could not find my power adapater and it was 10 PM so I gave up. 

Mosely said I can confirm that one half of the two driven elements are dead if 15 meters works full power.  If it does and 20 does not, then the larger coil is damaged.

I am at work at all day on the dyno and cant do any tests until tonight.
C

It might also be a feed line problem. Water in the coax. Above a certain RF level of power, their might be an RF bridge through the water. Also check the coax connectors.

Thats a good point.  They are sealed with coax seal but very possible that could be the issue.   When I try 15 meters this evening we will know. Gary at Mosley was not sprised at all with this issue.  What I could not wrap my head around was how could the SWR still be low but only half power.

Did you try retuning the 220 into the yagi?

Yes.  Retuning SB220 does not help. 600 watts max.   Cant get enough load..  plate current is only 350 when on the beam

C

You didn't mention which Mosley it is and does it use a Balun (something in a box or container) to connect the coax to the driven element(s) or are you just using a coil of coax up there.

Check your balun if you have one.  One of the distressing things about Mosley is the coil forms in the traps can break because of lightning or extreme stress.  You may find one of them in the trap has broken causing the windings to move apart.  If that is the case you will see a dip in your analyzer below the band that is much better than the one in band.  That indicates one of the traps or maybe both have problems.

Mosley will sell you the individual ends for the traps by the way should it be just one end.

It was the water from the rain as I suspected.  My cure was to hold 500 watts AM carrier for 15 minutes on 20 meters. Just at the top of the band.  Now I can transmit full power on 20 again.  Forking Weird.   I hear our friend Steve Kl7of on 20 meters 40+ db right now.  1500 watts out.

I guess I cant use this thing in the rain.  I will have to inspect it when I lower the tower next.  We are getting more rain tonight, I bet the condition comes back.


Jim, I am using a palomar slip on balun over the RG213 coax.  All connectors are wrapped with coax seal and then alot of black tape.  The Ring terminals are covered in black tape and then RTV over the entire connector.  I let it dry for days before installing the antenna so I know that part is water tight. 

I guess I learned something here.  A flat match does NOT mean the load is correct. Clearly, The amp was having trouble loading into that wet antenna.

C

Sounds like you must've boiled the water out of the line by doing that. Maybe if you were on the air while it was raining it might boil the water out as it's coming in?

Traps?

....It will be interesting to see what you find when you next have a look at the antenna....Try pointing it into the wind on this next storm.....Maybe the water is getting in the sides...Good Luck...Steve

Yes, It has Traps but as I understand it, 15 and 20 dont use traps, Only the Coils.  10, 12,17 use the traps. 

Thanks for the tip Steve,  You where 40 over and as I watched the needle, you went down lower and lower over a 30 second period and then where gone.   Funny how fast 20 meters shuts down. From FB to NOTHING in a moment.

C

20 doesn't use the traps, if the traps are functioning normally. They are still part of the physical elements of the antenna, just not electrically on 20 meters. I would think all that could change with if water gets in the wrong place.

That makes sense to me Steve.  For sure, something got wet.

C

You said: "A flat match does NOT mean the load is correct. Clearly, The amp was having trouble loading into that wet antenna."

As indicated in another post, water in the coax will exhibit some of the same characteristics you're describing. A "wet antenna" is the not the issue. Antennas are supposed to work in all kinds of weather. However, if the traps are not sealed properly, rain water can get in there. Most traps have drip holes in them to drain any moisture that may accumulate in them. If your traps have a drip hole(s), the trap should be positioned with the holes facing downward. You have not described the feed mechanism of the driven elements which could also, depending on the design, be a problem for water accumulation. What Mosley is it?

If it was the coax, I would think that ALL bands would be acting up,  In my case its only 20 meters after a rain storm.

The beam is a TA53M Pete. 

When I said Wet I was thinking that water had filled the inside of the coil form or traps.  The drain holes are all downward.  When I got home I took a scope and looked at each drain hole.  Gary at Mosely mentioned this could be the issue on the phone so I double checked. 

The reason why I did not think it was a trap is that Gary said If ONLY 20 meters is acting this way, then HALF the driven element is at fault.  15 uses the other half and he said "the traps are not used on 20 and 15.  20 and 15 use A coil of wire over a form and that form may be damaged or full of water.

But as steve pointed out, The traps could skew the tuning off even on 20.. I really dont know.. I am no antenna expert.

I wonder if I am going to find mud plugging the Drain hole on the coil forms.  We have had very bad sand storms this year and rain with dust makes mud.

C

Same antenna I have Clark and I experienced some similar problems.  You can't keep moisture out of the traps no matter what.  Since you are using the Palomar beads, then it is most likely one of the traps.  They cut the signal off on 10 meters then the traps are added for 15 then they disappear for 20 so the entire element is used.  Do check the termination at the split of the coax for possible problems.

I am betting one trap has one or both of the coil forms split.  They tend to split where the rivet holds the end of the coil to the center piece of tubing.  Once you have the antenna down they are very easy to repair.  Just slide the cover back, remove the screw exposed and put it in a safe place (as me how I know) and pull the coil from the aluminum shell.  The 20/15/10 meter element is coded blue and right behind the director.  The 3rd element is active for 12 and 17.  While on the ground check all traps and both ends of them.  You may find a surprise of two.

You would think so, but it doesn't always happen that way. Back in the 80's with my Tri--bander and using RG-213U coax, I started to develop a problem with erratic loading on 15 meters. When using the antenna during the early morning hours, I could not load the antenna up to the capabilities of the transmitter. 20 and 10 seem to be fine. By noon and throughout the afternoon and early evening, the antenna loaded fine on 15. The coax was about 5 years old. I switched it out with the coax I had running to the 6 meter beam which was also mounted on the mast. No problem on 15 meters no matter what time of day it was. I attributed the problem to moisture in the coax, which depending on where in the coax it was, caused the erratic loading. As the day warmed up, I assumed the moisture evaporated, and things worked as they should. Throughout the night the moisture built up again, and the problem reappeared. Never did find how the moisture got in there and I got rid of the cable.


Whether it's just moisture or actual water gathering in the trap assemblies or the coax, besides cleaning up the problem, you need to find out how it's getting in there. Also, don't discount bugs. When I took all my traps apart last month, I found all sorts of dead critters and even a few small alive ones.

It rained all night.  Guess what?   no 20 meters again.  259B is useless as the antenna SWR plot, impedance ect are all normal at low power.  The 101EE runs full power with not even 1 watt reflected on the bird meter with a 50 watt slug installed.  If I load up the amp, Everything is normal until 250 watts or so.  The max is 500 to 600 watts, and the amp wont load higher.  Reflected power is 5 watts or so.  Flip to dummy load,  1500 no problem.

In the short term, I just wont use power on 20 meters.  Not a big deal.. I am in AZ and rain like this is not common. 

In the long term, I think I will lower the tower down and inspect the traps and coils. I will consider a different type of coax if you think that will help pete.  This is standard RG213 belden.  I used it as Mosley recomends the use of RG8U or RG213 only in the manual.  We happen to have a huge roll of RG217.  Maybe I should run that up to the beam. Mosley is worried that if you use some other coax, the tuning might be off on the beam and this beam is not adjustable.  Well, That is its not easy...

On second thought, I might just order a new 20 meter element and have them ship it out.  Then I can swap the entire thing out, run new coax, and replace that scary 40 year old steel cable on the crank up tower all at the same time.

C

I would first disassemble and check the trap housings on the 20 meter radiator (element assembly labeled Blue Radiator). Actually, all the trap assemblies should be opened, checked, and cleaned if they haven't been done so in recent years.  I replaced the RG-213 with double-shielded RG-214U. Your RG-217U is also double-shielded, slightly lower loss and can handle more power then the RG-214U. It's diameter is also larger then the RG-214U so you need to check if standard PL-259's will mate with it.

You said: "replace that scary 40 year old steel cable on the crank up tower all at the same time." Good idea. Don't wait like I did. Inner cable of my crank-up was thirty years old. Started a crank-up; sections started to rise; inner cable broke; sections dropped; mechanical tower brake stopped the descent but not before it sheared one tower runner completely off and mangled another. Several hundred pounds of steel heading straight down can do a lot of damage.

Yes, the RG217 is larger diameter.  They do make connectors for it but I only need the one, the mosley uses Ring terminals on the antenna side.  I am using rg217 to run from the shack to the EJ johnson room.  Its great stuff.

I rebuilt the beam 2 years ago with lots of new parts from mosley before we put it up. its been just wonderfull for 2 years.  I doubt I am going to find anything major.  It has to be water ingress somewhere.   

I also have a new in the box 40 meter upgrade kit for the little beam. I am torn about installing it.  It really makes for alot of crap hanging around on a small beam.  I got the kit about half price.  A local ham ordered it and never installed it on his ta54. 

Thanks for the tips!

C

LMR-400 and 400UF seems to be the choice these days if your not running a tube with handles. Mosely isnt known for high level engineering and not updating their obsolete coax list is just another example.

You always gotta put that kick to the gut, at the end dont ya Carl?   

C

Pete, I think you where right. It is likely the coax.  It rained all day.. ALL bands are acting up now.  No more then 500 watts on any band.  Radio alone works fine.  Trying to work cambodia on 15 meters right now.   

Mosely is probably ok.   Going to have to lower the tower down next week and fix it.

C

I have been reading on cable types.  Is RG213 considered water proof?   I walked around the back of the house and found about 15 feet of my cable run under water in a flooded section of property next to the concrete slab.  No connectors on that section. But it was under inches of water for all that way. 

I cant find any data showing me if this is ok, at first thought, i would think it would be and the only source of water ingress would be the connectors itself.

C

I'll bet you find the water damage a qtr wave or thereabouts, electrically, from either the antenna or the feedpoint...  On 20 meters.  Then it got more water shoved into it, and now you're experiencing all bands.

You could have my problem, I've got 1/2 inch of radial ice on the dipole...  Makes for wide bandwidth, though.. :)

The fact that their is no coass connector on the beam side is troublesome enough.  Add in the fact of wind driven rain, and you have another good spot for ingress.

No matter if the coass was waterproof when it left the factory, those nice mild summers with the limited sunshine on your lot (tongue in cheek) means you could have problems with the jacket itself....  Gotta check the jacket where it's laying in the water, too.

Good luck.


Shane
KD6VXI

Thanks Shane, I think I will replace it all soon.  I dont know where the water is. I used to have access to a cable tester but no longer have one.  I ran run some tests when I lower it to find out and inspect it.  I weather proofed the bajeesus out of this install with coax seal, Black tape AND silicone. Really.. I was overkill.  I worked on it for days.  Thats why I wondered if the water can go through the jacket itself? 

I do have a Drop loop of 213 up there so the beam can swing around.  Maybe it pulled on something and the jacket got worn. It does slide over the edge of the tower. 

BTW, Did you see my EF johnson room?

C

Newp.  Is it the old radio room, or the storage room LOL.


--Shane
KD6VXI

Naw. Lots of changes here,  There is no storage room anymore. All surplus gear is gone except for a small stack and I have been trying to sell those radios off.  That room is now a small work shop with a desk for repair of old receivers.  The guest room was redone with a new bed for mom/people to visit. 

The EJ johnson room was the old game room/ bar area.  I never use it as I am not 20 anymore :(  So I sold all of that stuff and installed the three johnson stations.

New in the box J500-HRO60,  Ranger1, Johnson Tbolt, and HRO50, Valiant and NC183D   All on Steel case desks from the 50's.

I think the are some Youtube videos of the new room up.

BTW,  10 meters is wide open right now.

C