Off air on 75

[w1vtp]

Well, I'm back in the saddle again.  Bob QV came down - we traipsed around in the snow.  Got the new dipole up just a little after dark.

Steve TAV - good talking to you today.  Too bad you couldn't have stopped in and visited the shack.  At least you know what it looks like from the outside.  One good thing came out of this: I now can raise and lower all three sky hooks.  Shouldn't have to climb up the main roof for the foreseeable future.

Al

[Todd, KA1KAQ]

Was it Karl/Chicken Neck who lit his traps up when he tried out his new Class E rig a few years back? I seem to recall something about 'the antenna is on fire'.

Traps are a compromise at best, and as folks have said Al, just another point for problems. Keep it simple and you'll be happier long term with the results.

[w1vtp]

Well, I'm going to look into a fan dipole so if anyone has dimensions for an ant that is 70 off the ground at the apex, I'd be interested.  Probably not going to happen until spring or at least the snow is gone.

The bands of interest are 160, 75 and 40

Al

[Steve - K4HX]

Hey, Al! You are a prophet. On 12 January 2009 you posted the following.

<snip> Don't bother with those W2AU type commercial ferrite baluns. The are known to smoke at QRO AM.. <snip>

That's what I've been using for the last 25 years and although it seems to be OK with my mere 100 Watts out, I'm worried about putting 300 Watts carrier on it.  The 40 M traps have developed radial hair line cracks in them but they still seem to be working OK.  Looks like I have some fireworks in the making when I go QRO.

Al VTP

Actual post:  http://amfone.net/Amforum/index.php?topic=18246.msg127335#msg127335

[W3GMS]

Hey, Al! You are a prophet. On 12 January 2009 you posted the following.

<snip> Don't bother with those W2AU type commercial ferrite baluns. The are known to smoke at QRO AM.. <snip>

That's what I've been using for the last 25 years and although it seems to be OK with my mere 100 Watts out, I'm worried about putting 300 Watts carrier on it.  The 40 M traps have developed radial hair line cracks in them but they still seem to be working OK.  Looks like I have some fireworks in the making when I go QRO.

Al VTP

Actual post:  http://amfone.net/Amforum/index.php?topic=18246.msg127335#msg127335

We always new Al had special qualities!!

Joe, GMS

[w6tr]

I ran a fan dipole for 20, 40 and 75 for a year and when the wind blew the loading would change significantly.  I have gone to an off center fed dipole using a 4:1 balun and it works great on all the bands from 75 thru 10.  I do use a Millen antenna tuner to touch it up on each band.  I have really good success with the OCF antenna.  Just my .02

[K6JEK]

I ran a fan dipole for 20, 40 and 75 for a year and when the wind blew the loading would change significantly.  I have gone to an off center fed dipole using a 4:1 balun and it works great on all the bands from 75 thru 10.  I do use a Millen antenna tuner to touch it up on each band.  I have really good success with the OCF antenna.  Just my .02

Which OCF design? I'm pondering a second run at an OCF simply because the trees are in the right places. Maybe this time I can do a better job keeping the feed line radiation down and the attendant RFI issues controlled. That's what made me take down the one I used to have. I was talking through the stereo, blinking the lights, pushing the cable modem off line, etc. Still those trees are calling me.

[K5UJ]

I have gone to an off center fed dipole using a 4:1 balun and it works great on all the bands from 75 thru 10.  I do use a Millen antenna tuner to touch it up on each band.  I have really good success with the OCF antenna.  Just my .02

Not to argue but antenna endorsements with no details are not that meaningful.   How high is your antenna?  How much power do you run?  Do you make long transmissions?  What stations have you worked (how far away)?. 

There's a classic article in QST by N6BT called (IIRC) Anything Works.   You can make QSOs with a lightbulb for an antenna if you run enough power and it's a big enough light bulb.  But it isn't a very good antenna.  However the op with the lightbulb might think he's had really good success with it.

[K6JEK]

I have gone to an off center fed dipole using a 4:1 balun and it works great on all the bands from 75 thru 10.  I do use a Millen antenna tuner to touch it up on each band.  I have really good success with the OCF antenna.  Just my .02

Not to argue but antenna endorsements with no details are not that meaningful.   How high is your antenna?  How much power do you run?  Do you make long transmissions?  What stations have you worked (how far away)?.  

There's a classic article in QST by N6BT called (IIRC) Anything Works.   You can make QSOs with a lightbulb for an antenna if you run enough power and it's a big enough light bulb.  But it isn't a very good antenna.  However the op with the lightbulb might think he's had really good success with it.

There actually has been a great deal of analysis and testing of OCF's ranging from the late, great LB Cebik's articles to ON4AA's latest modeling and clever designs (http://HAMwaves.com/cl-ocfd/). There is even a Yahoo group with questions and answers ranging as usual from the completely uninformed to the quite expert (http://groups.yahoo.com/group/windom_antenna/). There are many designs each with something slightly different to recommend it usually in the form of different multi-band trade-offs. It's usually hard to get decent performance on 80 and 40 which, of course, are the two bands I care most about for this antenna. Debates about BALUNs rage on.

As I said, I ran one for years because that's where the supports were and may try one again for the same reason. I'm always curious what someone is actually using, the W8JI design, the ON4AA design, or a commercial one just to get another perspective.

Incidentally, having run fan dipoles, trap  dipoles, OCF's, coax fed full length dipoles, ladder line fed dipoles, in V's and flat tops, and a giant horizontal loop among other things, the only antenna I've ever gotten excited about was the phased dipoles which JJ called possibly the world's best 75M antenna. I still wax nostalgic over that one.

[W3GMS]

It behooves one to measure the feed line current to make sure they are equal when using open wire line.  If not balanced, feed line radiation will occur.  I found out I had about a 15% imbalance when comparing currents in each leg of the OWL.  The physical length was equal but the electrical differences caused the imbalance in the actual current.  Mine antenna is a center fed, 260' long Inverted Vee up 60' at the apex.  I tweaked the physical length slightly and got the currents to be identical and all the RFI issues went away.  In fact I had less EMI problems with OWL than coax.  The key is to make sure everything is balanced from an electrical standpoint. 

Joe, GMS     

[W2VW]

It behooves one to measure the feed line current to make sure they are equal when using open wire line.  If not balanced, feed line radiation will occur.  I found out I had about a 15% imbalance when comparing currents in each leg of the OWL.  The physical length was equal but the electrical differences caused the imbalance in the actual current.  Mine antenna is a center fed, 260' long Inverted Vee up 60' at the apex.  I tweaked the physical length slightly and got the currents to be identical and all the RFI issues went away.  In fact I had less EMI problems with OWL than coax.  The key is to make sure everything is balanced from an electrical standpoint. 

Joe, GMS     

Joe, you are the first person I've seen who has identified this problem and corrected it.

There's a lot of talk about measuring imbalance but not much talk about the cure.

Same antenna but cut to resonance (current IEEE definition) would not have allowed this measurement.

How would you feel about an electrical solution at the coupler?

[w1vtp]

Here's a good way to check your open line balance

http://www.wz5q.net/index/shack_data/tuna.htm

I like this approach

Al

[W3GMS]

It behooves one to measure the feed line current to make sure they are equal when using open wire line.  If not balanced, feed line radiation will occur.  I found out I had about a 15% imbalance when comparing currents in each leg of the OWL.  The physical length was equal but the electrical differences caused the imbalance in the actual current.  Mine antenna is a center fed, 260' long Inverted Vee up 60' at the apex.  I tweaked the physical length slightly and got the currents to be identical and all the RFI issues went away.  In fact I had less EMI problems with OWL than coax.  The key is to make sure everything is balanced from an electrical standpoint. 

Joe, GMS     

Dave,

Yes, you could compensate for the imbalance at the balanced tuner for a given frequency to cause equal but opposite phase feeder currents.  The reason I chose to do  it at the antenna was to make it balanced over a wider frequency range.  I guess it just depends on how much flexibility one has with the users balanced tuner in order to make the required small tweaks on each band of operation.  On some tuners, this would not be a big deal.  The clip lead guys are at an advantage here!! 

I used a high frequency wide band  current probe with my scope to make the measurements.  Any simple toroidal current transformer works also.  Its not a point of accuracy, but rather just a way to make sure the currents are the same in each leg.

Joe, GMS   



Joe, you are the first person I've seen who has identified this problem and corrected it.

There's a lot of talk about measuring imbalance but not much talk about the cure.

Same antenna but cut to resonance (current IEEE definition) would not have allowed this measurement.

How would you feel about an electrical solution at the coupler?

[Pete, WA2CWA]

Joe: Watch your quote brackets; it's hard to figure out who's saying what to whom when you embed your response inside someone else's quote.

It behooves one to measure the feed line current to make sure they are equal when using open wire line.  If not balanced, feed line radiation will occur.  I found out I had about a 15% imbalance when comparing currents in each leg of the OWL.  The physical length was equal but the electrical differences caused the imbalance in the actual current.  Mine antenna is a center fed, 260' long Inverted Vee up 60' at the apex.  I tweaked the physical length slightly and got the currents to be identical and all the RFI issues went away.  In fact I had less EMI problems with OWL than coax.  The key is to make sure everything is balanced from an electrical standpoint.  

Joe, GMS    

Dave,

Yes, you could compensate for the imbalance at the balanced tuner for a given frequency to cause equal but opposite phase feeder currents.  The reason I chose to do  it at the antenna was to make it balanced over a wider frequency range.  I guess it just depends on how much flexibility one has with the users balanced tuner in order to make the required small tweaks on each band of operation.  On some tuners, this would not be a big deal.  The clip lead guys are at an advantage here!!  

I used a high frequency wide band  current probe with my scope to make the measurements.  Any simple toroidal current transformer works also.  Its not a point of accuracy, but rather just a way to make sure the currents are the same in each leg.

Joe, GMS    



Joe, you are the first person I've seen who has identified this problem and corrected it.

There's a lot of talk about measuring imbalance but not much talk about the cure.

Same antenna but cut to resonance (current IEEE definition) would not have allowed this measurement.

How would you feel about an electrical solution at the coupler?

[Steve - K4HX]

What?

[kb3ouk]

The one advantage I can see for compensating for feed line imbalance at the tuner is that it would allow you to adjust for things that are only temporarily causing imbalance, like here where in the summer I have leaves that affect one side of the dipole but aren't there in the winter.

[W3GMS]

The one advantage I can see for compensating for feed line imbalance at the tuner is that it would allow you to adjust for things that are only temporarily causing imbalance, like here where in the summer I have leaves that affect one side of the dipole but aren't there in the winter.

In my case, no leaves near the antenna.   The physical sides are not electrical symmetrical due to angle and height differences in reference to the ground below the antenna.  Once I tweaked one side of the Inverted Vee to produce the same current in each leg of the feeder, the feedline radiation was eliminated.    It has remained balance for years and hence no RFI issues.  

My point is to make sure you measure your feeder current in each leg when using OWL and try to obtain the same current in each leg.  When OWL is balanced it will not radiate!  

Joe, GMS  

[W2VW]

The one advantage I can see for compensating for feed line imbalance at the tuner is that it would allow you to adjust for things that are only temporarily causing imbalance, like here where in the summer I have leaves that affect one side of the dipole but aren't there in the winter.

In my case, no leaves near the antenna.   The physical sides are not electrical symmetrical due to angle and height differences in reference to the ground below the antenna.  Once I tweaked one side of the Inverted Vee to produce the same current in each leg of the feeder, the feedline radiation was eliminated.    It has remained balance for years and hence no RFI issues.  

My point is to make sure you measure your feeder current in each leg when using OWL and try to obtain the same current in each leg.  When OWL is balanced it will not radiate!  

Joe, GMS  

Interesting thoughts.

I recently have been experimenting with feeders with broken insulators and eliminating local neighborhood noise. Good housekeeping sure makes a lot of difference especially during the daytime on 75.

Things cooled off and got much quieter here after ditching coax on the low bands. To be fair I didn't try any BalUnz at the feedpoint though.

[W2NBC]

Very interesting..

Balance is problematic even with pruning of the OWL. The reason is topographic and near field influence with each side of the antenna, as most of us aren't even close to free space on the lower bands for sure.. I am using thermocouple RF ammeters inline with my OWL, and they read almost square on 160, 75 and 40. The higher bands get a little unbalanced.. Wavelength and near field structures (like power lines, houses underneath, TREES, etc) make it almost frequency specific the shorter the wavelength.. So my question Joe was the physical length of the OWL the cure all to the in shack balance?

PS. Glad Al got back on da air!

Inquiring minds..
Jeff

[W3GMS]

Very interesting..

Balance is problematic even with pruning of the OWL. The reason is topographic and near field influence with each side of the antenna, as most of us aren't even close to free space on the lower bands for sure.. I am using thermocouple RF ammeters inline with my OWL, and they read almost square on 160, 75 and 40. The higher bands get a little unbalanced.. Wavelength and near field structures (like power lines, houses underneath, TREES, etc) make it almost frequency specific the shorter the wavelength.. So my question Joe was the physical length of the OWL the cure all to the in shack balance?

PS. Glad Al got back on da air!

Inquiring minds..
Jeff

In my case Jeff, I made some tweaks to the length of one side of the inverted vee until the feed line current was equal.   

Joe, GMS   

[W2NBC]

Here's an example of not reading through the entire post.. Got it! You did pruning on one leg of the inverted V.. I would imagine the same result would be pruning the length of the OWL to that side as well.. I wonder if the OWL then becomes polarity specific with balance not being perfect from tuner or in the shack.. I wish I was completely balanced personally..

Thanks Joe!

[W2VW]

.. I wish I was completely balanced personally..

                !

Personally balanced? That must have been coined by a _____. Answer determines your absolute value profile.

The only people who were ever perfectly balanced personally were Mo, Curly, Larry and sometimes Shep.

[W2PFY]

Is it possible to make one side of the OWL shorter than the other to balance the antenna?

[W3GMS]

Is it possible to make one side of the OWL shorter than the other to balance the antenna?

Terry,

Mechanically that is tough to do while maintaining the line balance.   Either tweak one side of the antenna length or pick your tap points on the tuner to assure the same RF current in each feeder.  Remember the importance of the two feeders being parallel so that cancellation can occur with the opposite phase of the feeder current. 

Joe, GMS     

[W2VW]

Is it possible to make one side of the OWL shorter than the other to balance the antenna?

Terry,

Mechanically that is tough to do while maintaining the line balance.   Either tweak one side of the antenna length or pick your tap points on the tuner to assure the same RF current in each feeder.  Remember the importance of the two feeders being parallel so that cancellation can occur with the opposite phase of the feeder current. 

Joe, GMS     

Ever do any close in (< 10,000 feet) signal comparison on 75 while adjusting for minimum common mode on the feeder?