Antenna(s) Problems

[Carl WA1KPD]

I have 2 HF antennas, a new 160 Carolina Windom put up this fall and an  80-10 G5RV put back up this fall. Both have been working fine although the RFI noise from the Windom is significantly lower. Anyway I was listening this weekend and thought the bands were dead. Long story short after finding another rcvr on a long wire worked fine I started looking into the antenna situation. Both were equally bad. The feed in to different points in the house come up to a 2 position antenna switch in a tuner, then on to a 4 position switch to choose the rig.

I have slowly eliminated the switches, interconnecting cables, antenna tuner and rig, by feeding the antenna cables right into the back of my SDR-IQ and my 756. Both are fine until the outer shell of the coax connector comes into contact with the SO-239 then the signals drop to almost nothing.

I went outside after work, both antennas are in the air and there is no sign of any sort of damage to connections or wires. If I measure the resistance from the shack, the Windom has 0 ohms, so no short, and the G5RV shows 24 meg-ohms (?)

This is a fairly recent development- probably since the blizzard but new, and odd that it is affecting both antennas. Any thoughts out there?

Carl
/KOD

[KK4YY]

< Both are fine until the outer shell of the coax connector comes into contact with the SO-239 then the signals drop to almost nothing. >

That sounds like a shorted coax cable. Loose braid at the connector... or did a neighbor put a pin in it?

[WQ9E]

Carl,

I used a 160 Carolina Windom for several years and I liked the performance.  But on 75 meters running  a Valiant the "line isolator" got very warm and I could see the SWR change a bit during a transmission.  I found some water trapped in it which was probably the main problem but I don't think that part is up to sustained AM anyway.  I had a second 160 Carolina windom used with the contest setup out in the barn and although that one had no apparent moisture it would heat up significantly running contest CW on the low bands.  When I bought the Desk KW the windom was retired in favor of a full wave horizontal loop and I am using a 18HT vertical with the contest station.

[Carl WA1KPD]

< Both are fine until the outer shell of the coax connector comes into contact with the SO-239 then the signals drop o almost nothing. >

That sounds like a shorted coax cable. Loose braid at the connector... or did a neighbor put a pin in it?

Agree.... but

If I measure the resistance from the shack, the Windom has 0 ohms, so no short, and the G5RV shows 24 meg-ohms (?)
Carl
/KPD

Have not put any appreciable power in to either antenna and I am wondering if some moisture got into coax fittings and froze. Not sure if ice would look different to a rcvr then a DVM?

[K1JJ]

Carl,

Sounds to me like the inner wire of the coax is broken - possibly at the antenna junction - or the inner coax connector pin has corrosion.

With the outer shield not connected, the inner acts like an antenna. But when the shield is connected, we have a transmission line that cancels, thus the dead band.  This is what you seem to be seeing there.


I have many, many coax connectors in the shack and outside. Every so often the inner PL-259 connection will get mositure in it and essentially breaks the connection. Whenever I see a dead coax when connecting the shield, I start looking for the inner failure.   Sometimes putting RF thru it will temporarily fix it, assuming it's a poor connection, not a break.


Another sign of a bad coax connection is when we start hearing house appliance noise, like computers, switchers etc., from our receiver.  

T

[KA0HCP]

Sounds like a short.

You need to get a multimeter on each connector and then flex the coax.  All it takes is three hands! 

[KB3WFV]

.......I went outside after work, both antennas are in the air and there is no sign of any sort of damage to connections or wires. If I measure the resistance from the shack, the Windom has 0 ohms, so no short, and the G5RV shows 24 meg-ohms (?)

Carl
 
You mentioned "0 Ohms".
Does this mean the meter indicated "0.00" which is
"continuity" or a "short". Or did it display an "open" circuit ?

You also said the antenna's are still in the air.
I'm not sure a resistance test on the fed lines is reliable
wit the coax still connected to the antenna's..

Disconect the fed lines from the antenna's and check
agian. Werid that both antenna's fail the same way.
Maybe a snow shovel got shoved through the fed lines
during the bizzard ? There isn't any ice still on the
antenna's is there ?

Brian
KB3WFV

[Pete, WA2CWA]

A typical G5RV antenna is a coax run, then connected to twin lead, and ends connected to two dipole elements. Resistance measured at shack end typically should be infinity or many many meg-ohms (depending on the measurement instrument).

Carolina Windom can have a "line isolator" and "matching unit" in the transmission line but a "0" ohms reading seems to indicate a short somewhere in the transmission line stuff. However, that's also dependent on your measuring instrument.

[ke7trp]

Because the Carolina windom uses a 4 to 1 balun, The Center is hooked to the shield. It will show a short with the meter. Lots of antennas are at a DC ground but at RF, they are not a short.  My OWL is grounded through large inductors to ground to stop static buildup in the Dry Arizona winds.  At RF it is not shorted.

its also common to get a big increase in noise in unhooking the coax shield like that.  For example, A 10 meter vertical or a beam makes a Great Recieving antenna if you unhook the coax shield but leave the center pin.

Caution.. You can get shocked if there is any potential from the case of radio to the coax shield.  So be carefull.  FT101 for example has 90 volts and will Nip you good if you reach back and unhook the coax cable while the rig is on and plugged in.

I think the antennas are working but the band is in bad shape right now.


C

[wa3dsp]

"Caution.. You can get shocked if there is any potential from the case of radio to the coax shield.  So be carefull.  FT101 for example has 90 volts and will Nip you good if you reach back and unhook the coax cable while the rig is on and plugged in."

I know that is an older rig but doesn't it have a grounded power cord? There shouldn't be voltage on any rig today properly grounded. 

[KM1H]

You mentioned "0 Ohms".
Does this mean the meter indicated "0.00" which is
"continuity" or a "short". Or did it display an "open" circuit ?

If that is using a "balun" configured as an autotransformer it will read as a DC short but there should be some round trip resistance thru the coax.

Carl

[ke7trp]

The voltage is not on the case of the rig. Its on the Coax center pin.  Its a known issue.

C

"Caution.. You can get shocked if there is any potential from the case of radio to the coax shield.  So be carefull.  FT101 for example has 90 volts and will Nip you good if you reach back and unhook the coax cable while the rig is on and plugged in."

I know that is an older rig but doesn't it have a grounded power cord? There shouldn't be voltage on any rig today properly grounded. 

[kb3ouk]

Some of Yaesu's older rigs I believe might have the filaments tied to ground somewhere, I've got shocked by some low voltage AC off of them before, and no, they don't have a three wire cord, only two, and I'm pretty sure it's nonpolarized too.

[wa3dsp]

The FT101 used tubes in the final. There should be an RF choke from the antenna to ground in any tube rig for protection. If the plate bypass capacitor shorts you would have B+ on the antenna. A 2.5mh choke is fine. If a rig doesn't have it I put it in. I put one in my Ranger when I restored it.

Back to the FT101 - why is there 90 volts on the coax? Is the plate bypass leaky? I did a quick Google check and did not see anything about it. I am sure that Yaesu did not intend for that voltage to be there.

[ke7trp]

No idea.  This thread is about an antenna problem.  I have had a dozen FT101s. All have voltage there.  Never tried to fix it.  It will bite you good if you unhook the coax from the rig while its on. Maybe one day I will look into it.  I am down to one FT101 and its on a shelf right by the bench.


C

[Carl WA1KPD]

.......I went outside after work, both antennas are in the air and there is no sign of any sort of damage to connections or wires. If I measure the resistance from the shack, the Windom has 0 ohms, so no short, and the G5RV shows 24 meg-ohms (?)

Carl
 
You mentioned "0 Ohms".
Does this mean the meter indicated "0.00" which is
"continuity" or a "short". Or did it display an "open" circuit ?

Brian
KB3WFV

Brian,

Good point and sorry about the confusion. Poor wording. I meant 0 ohms as in "no resistance", not as in short. I guess I should have said infinite . The Windom uses a RadioWorks remote balun http://www.radioworks.com/cremote.html. I agree with Pete that most 4:1 baluns have a short, but reading about this one I am not sure. I did a Google search and found schematics that show a design that would read 0 er ... infinite. Note they refer to 2 torrids in their description.

I have solved the G5RV problem. It is on the ground and under the snow. I am not home during the day so I was unable to trouble shoot until yesterday am when I looked out the side window into the woods.  It is under about 6" of frozen snow so it may be awhile before I can pull it out
The wx forecast is not good for the weekend but hope springs eternal!
Thanks for the ideas and advice

Carl
/KPD

[Pete, WA2CWA]

No idea.  This thread is about an antenna problem.  I have had a dozen FT101s. All have voltage there.  Never tried to fix it.  It will bite you good if you unhook the coax from the rig while its on. Maybe one day I will look into it.  I am down to one FT101 and its on a shelf right by the bench.


C

There is a 300 micro henry choke from the antenna side to ground of all FT-101( ) schematics I looked at. Unless it's missing or burned up, there should be no DC on the center pin of the coax connector. However, if the rig is powered up, you place your hand on the rig as you unscrew the male coax connector and as you pull the coax connector away, you fill a tingle(shock, your hair stands up straight, etc.), most likely the .001 mfd or .01 mfd caps that are connected from each side of the AC line to ground are leaky. They should either be replaced or removed completely.  

[Carl WA1KPD]

OK- One solved. Now that I can see, The G5RV balun came completely disconnected from b0oth sides of the ladder line. That could cause performance problems.

Still no clue on the Windom. When the wx dries up I will put a known resistor on this shack side of the coax and go out back to the antenna end of the coax to see what I read..