| Author |
Message |
    
Foxhunter
Member
Username: Foxhunter
Post Number: 67
Registered: 4-2008
| | Posted on Monday, July 28, 2008 - 3:37 pm: | 
|
Last night something happened to my antenna and I can't figure it out. I'm using a Shakespeare Super Big Stick #76SU. We'd had heavy rains & bad lightning earlier that afternoon. Although lightning is the first thing often to suspect when hearing that, please read on and give me any suggestions/help you might have.
So hours after the storm had passed later last night, I was doing some testing up in my "temporary station" and was using the antenna with NO PROBLEMS. I was using a mint Galaxy 99V coupled to a Texas Star 500V. SWR flat with radio, and 1.2:1 with amplifier on. Only running 450W through the antenna (rated 1000W).
I was talking (from NJ) on CH.10 AM to someone in Missouri for a few minutes. I was testing transmit on various vacant channels including SSB. I tested transmitting FM also (was that a mistake?). Then was talking just a minute or two more and the SWR pegged the scale at maximum.
"I can't understand what could've happened".....is probably a phrase some of you have heard many times from more novice base station operators. I am very familiar with mobile installs & operating-----and although somewhat similar I am new to base set-ups and their antennas.
I tested the radio on a small dummy load, flat SWR. Went up on the roof this morning and changed the coax to a new line and still maximum SWR reading. We had alot of lightning yesterday day and even wires down. But all my equipment seems intact and I was using it successfully. Also the fiberglass antenna doesn't appear hit or scorched.
Like I said above-----it did operate fine for 2 hours of use last night then suddenly SWR went off the scale. Any ideas? Would anyone recommend a way of testing the antenna itself to see if somehow internally there is a failure? What, if anything else, could it be??
I wanted to post this on the Copper Forum to see if anyone has any clues----or should I just give up on the antenna? It's ashame, I'd hate to I like the antenna and was getting good reports. Anything you'd have to say I'd really appreciate. Thanks-----Foxhunter |
Bruce
Senior Member
Username: Bruce
Post Number: 4758
Registered: 9-2003
| | Posted on Monday, July 28, 2008 - 6:21 pm: |
|
Did receive go down too ? I know many fiberglass verticals will not take high power well.
As for FM I have run 300 to a A-99 cut for 28.500 on 29.600 mhz and it is still working .
The best way to tell if the antenna is hurting is to get to the bottom and hook a short coax to it and measure VSWR if it looks normal maby your coax conectors are bad or not solder well. you can also check coax with a 50 ohm load on one end and the swr bridge on the other a good coax will look likea good match with that 50 ohm load .
On 6 since 66
|
Foxhunter
Member
Username: Foxhunter
Post Number: 70
Registered: 4-2008
| | Posted on Tuesday, July 29, 2008 - 11:52 am: |
|
Thanks Bruce yes receive and transmit both were affected. The antenna is rated for 1000W and I was only using 450W which is not quite half so I'd figure I would be safe for power-handling.
I've been told and read that the Big Stick is a center-fed vertically suspended dipole housed in a fiberglass enclosure.
As far as with the coax or coax connectors---I substituted the original RG213 I had up for a known good length of Belden RG8X mini-8 with the same max.SWR reading.
Now last night I tested both the radio and the radio & amp----and the SWR had returned close to normal practically, with a radio SWR of 1.15 and a radio & amp reading of 1.2.
???----Why would that be? I know that SWR can fluctuate at times due to certain conditions, but to go from a very low SWR, to pegging the needle, then a day later back down again?? Could water get inside an antenna and cause a situation like this? What could cause an "intermittent" high SWR like this? Any ideas or suggestions? |
Tech291
Moderator
Username: Tech291
Post Number: 513
Registered: 11-2004
| | Posted on Tuesday, July 29, 2008 - 7:11 pm: |
|
Foxhunter,
You pretty much answered your question in your last paragraph.The perticurar bigstick you have could be as many as 30 years old.So it is possible it has developed hairline cracks that let the water in.There should also be a vent hole in the aluminum base next to the so-239,make sure no critters have plugged it over.I've used several of that type(solarcon,antron,archer and shakesphere)and the best of the bunch was the old(mid 70's) original bigstick.it was before C.P.S.C.made them put the rubber or plastic boot over the center connection,and had the half wavelengh sectoon of rg-62 coax as a matching transformer.It was a great working antenna till nieghbor kids pulled thecoax out of the base.well thats enough ramblingfor now.
If you cant find any obvious points of entry in the lower half you could try a good coat of uv proof poly-urethane as a water proofer.just be sure it is dry inside or you could be sealing water in.
Tech291
cef291/cvc6
kc8zpj |
Foxhunter
Member
Username: Foxhunter
Post Number: 71
Registered: 4-2008
| | Posted on Wednesday, July 30, 2008 - 2:06 am: |
|
I didn't notice any drain-holes at the antenna base but I will certainly go back up tommorrow morning to check.
If there aren't any----I'd like to drill some myself but would be afraid/cautious of metal-shavings.
I'm not sure when mine was made it was tucked up inside of someone's rafters in their basement for years, left there by a prior owner.
It is a "Shakespeare Super Big Stick Model # 76SU" and is 16-FT long comprised of two 8-FT sections. The lower section is very thick (1-1/8 inches) and the upper section is thin (3/8 of an inch). It does have the tapered rubber boot you were describing joining the lower and upper halfs.
I'm hoping to have some hot dry weather for the next few days and perhaps will seal the antenna with some sort of sealant (UV is good idea) that has some elasticity that can withstand repeated flexing. I will find something that doesn't have any metallic-content that is hopefully non-reactive. I'm definitely afraid of choosing the wrong product and "supressing" any RF or causing any other problems. The rubber boot I'll try and seal with some GE 50-Year silicone so that won't be an issue.
This is assuming that this is even the problem. I can't figure why the delay before the SWR climbed sky-high. It rained heavily earlier that day and had stopped. I began operating 6 hours or so later and didn't have any problems for a little while. I'd think if water were in there it would've been immediate. Still.....I'll take the antenna all back down again and atleast try once more to do right by it.
It's frustrating because every time I install something---anything---I do a nice, neat and heavy-duty job. Not all "rigged" together slip-shod. It seems like there's always some problem that develops and I find myself having to "undo" all of what I just did. I'm sure I'm not the only one....
Anything you or anyone else has to add would always be appreciated. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2557
Registered: 1-2005
| | Posted on Wednesday, July 30, 2008 - 6:13 am: |
|
If your sure that the radio, amp and coax is OK then it must be the antenna.
Being an old antenna if water has been getting inside I bet there is more than water in there. Not only any insulation could be dry and brittle but corrosion could be built up so even if you do seal it up you can have problems. Also if the antenna is about 30 years old just age itself can cause problems. The sun comes up and starts heating that antenna up and then it cools down. The expanding of the old material under heat and cold.
Sounds like a good time to start shopping for a nice new base antenna.
Got a nice radio and amp with good coax you never want to skimp on the antenna. Get a good antenna.73
KEEP IT REAL!
Kenny
cef491(27.115lsb)
2sf491(27.555usb)
Indiana
|
Foxhunter
Member
Username: Foxhunter
Post Number: 72
Registered: 4-2008
| | Posted on Wednesday, July 30, 2008 - 3:23 pm: |
|
Yes I do hear you what you're saying I understand and is true.
I want the Shakespeare (and maybe another Shakespeare to have them co-phased) separateley for CB/11M. I wanted to keep the ham separate from the CB atleast that's what I'd been planning.
I will get something else of high quality for the Ham equipment I've begun to gather, and use once I'm licensed. I have one 2M, several 10M's and a 10M-160M as well as a couple of really mint recievers. There may be a pair of heathkits in the works if they aren't gone I shouldn't have waited, they are cherry (appear to be---that can be tricky).
I am also a firm-believer that antenna and coax is more than "half the battle"---and that is true. I'll have to see what comes out of this I was just writing on the "Bencher Butternut" thread more about this. Read there if you get a chance I just posted. Thanks Hotwire |
