160m Ant Tips requested

[Todd, KA1KAQ]

Enjoyed some time on 160 last night with Steve 'QIX and John 'FCU. My second time on the band, using the 75m coax-fed dipole into a 'T' with a scroteful broadcast dummy load on the other side. Certainly does the job, but obviously isn't the best solution.

Since I had planned to be out of the house soon, I didn't proceed with getting a 160 ant up before now. With each passing day, it seems less likely that the house will close by Dec 5th and more likely I'll be here until spring or summer. SO.....

Here's what I know: I know that it should be high, and I know I could feed it with open wire line and a tuner, BUT! My current location makes open wire line a bad choice (too many twists and turns to get into the house, reversing direction, etc). I'm also limited to the height of surrounding trees, a couple of which are 50-80 feet high but close to each other.

Here's what I have available: waiting for use is a very heavy-duty, half wave dipole made with large gauge, insulated/stranded wire. Insulators on the ends, large B&W center insulator. Coax-fed, just need to hook up the feedline. Built years ago but never used.

Property has a steep drop off directly behind the house (due west) and also to the north side. Unfortunately, the north side doesn't have enough space or high enough trees to run straight out to, so it looks like I'll need to bend one leg both downward and away from the level plane, into a downward vee. The tall tree out back isn't tall enough or placed well enough for a simple inverted vee unless I run it off the back and point it NNW to Canada.

My main question is: what is the best way to set this up, given limitations and large variations of height above ground? I can get one side up pretty well, but the other side will end up considerably lower and partially vertical if I go with the tallest tree out back for the center support. I know it'll work regardless, but I wonder if I should choose a different spot and droop both ends equally, or? It's not going to be ideal no matter what, but I'd prefer to get it up there the best possible way to start with.

It probably sounds like I'm making a simple issue into a big problem, and maybe I am. Having never worked with anything quite this large and heavy before, the best approach isn't obvious to me. High and flat is best, but my property won't permit this.  My gut tells me to just throw it up where it fits and not worry, but I'm also aware that my knowledge of aerials is anything but extensive.

Any ideas will be appreciated, even if it's just 'throw it up in the air and use it'. Maybe it's more a case of what to avoid doing?

[Steve - WB3HUZ]

Since the antenna won't be that high off the ground in relation to wavelength (e.g. 60 feet is only about 0.125 wavelength on 160 meters), orientation is almost irrelevant. So don't worry if it's pointing at Canada or the Bahamas. It's going to be a high-angle, omnidirectional radiator. With that in mind, put it up so that it's as high as possible along the entire portion of the antenna. Even if you have to do some zig-zagging, it's OK. Higher is usually better than straight, as long as the bends are too sharp or too many.

Hope to hear you on 160 soon.

[K1JJ]

Todd,

Coax feed is FB for your full-size mono-band 160M dipole. There's no advantage to using open wire in this situation.

Despite all the obtacles you described, just put it up as high, flat and straight as possible. The bent legs and downward sloping will cause slight cancellation of the pattern to some degree, but will also lower the feedpoint impedance down into the 50 ohm area for the coax. (and  depending on height above ground)

It will work FB for local work, so don't sweat the minor configuration details since it is only gonna be a 6 month thang. On 160M, it will outperform your coax-fed 75M dipole and dummy load 'T' config by at least 5 db, which is well worth the effort.. That's almost the equivalent signal increase of quadrupling your power.

(I figure a 3db loss in the dummy load, 1db for the shortened dipole and 2db in the coax on 160M at that very high VSWR, depending on length...)

73,
T

[flintstone mop]

Hi Todd,
I'll have to agree with Tom and Steve. Do the best you can for straight and not many sharp ends and setting up for Coax feed 50 ohms. You'll probably get about 50kc bandwidth. The height above ground will be a cloud warmer good for about 2-400 miles. Most of us except maybe Tom are using cloud warmers. I think you have to have the dipole up 1/2 wave?? or 1/4 wave?? before there's any directional affect. An inverted "L" is another thought...IF you can get the vertical wire about 70 feet long. The horizontal wire provides loading and the "L" is supposedly the best of both worlds with some vertical polarization (low angle= distance) and horizontal (high angle=local). Now you have to deal with ground radials with an "L" and a  tuning network.
I have had very gud success with my Inverted VEE. 70 feet Apex, open ladder line, nice K1JJ tuner, Ends of aerial about 40 feet off the ground.
I realize you are trying to have a quickie antenna for the remainder of time in your present QTH. But this is the recipe for 160M. About 200 watts of carrier and away we go!
We'll be listening

Fred MOP radio

[Todd, KA1KAQ]

Thanks guys -

Pretty much what I suspected, but I really don't trust my ant judgement just yet. Haven't done enough of it, either building or testing.

I should be able to get the center up 40-60 feet and one leg will end up being pretty flat to the center. The other one will drop considerably down over the lower side of my property though, approaching 35 degrees or so. I'm not worried about contacting branches since the wire is well insultated. And it's strong enough to just yank through most smaller obstacles.

Looking forward to getting the big ant up. Picked up two 25' sections of 10/3 power cable last night for 50˘/ft, so the Kitchen Kilowatt will get moved back to the radio room this weekend. 160m ant is next in line. Heard you pretty well up here last night, Steve.

[W2VW]

Todd,

Coax feed is FB for your full-size mono-band 160M dipole. There's no advantage to using open wire in this situation.

Despite all the obtacles you described, just put it up as high, flat and straight as possible. The bent legs and downward sloping will cause slight cancellation of the pattern to some degree, but will also lower the feedpoint impedance down into the 50 ohm area for the coax. (and  depending on height above ground)

It will work FB for local work, so don't sweat the minor configuration details since it is only gonna be a 6 month thang. On 160M, it will outperform your coax-fed 75M dipole and dummy load 'T' config by at least 5 db, which is well worth the effort.. That's almost the equivalent signal increase of quadrupling your power.

(I figure a 3db loss in the dummy load, 1db for the shortened dipole and 2db in the coax on 160M at that very high VSWR, depending on length...)

73,
T

5 db? Ya think?

[Steve - WB3HUZ]

Assuming there is an equal power division in the T, Todd's current setup will be 3 db down compared to the 160 dipole. I'd bet the power division is not equal, so probably more power was dumped to the dummy load than to the antenna. Only 5 dB down is probably being optimistic.

[K1JJ]

5 db? Ya think?

Off the hip you'd think it wud be a 10-15 db loss, but even a mobile antenna is only down 15db from a full size dipole on 75M. You'd think  Todd's lash-up wud be better than that.

So, let's see...

Modeling a 75M dipole on 160M shows a 1db loss in wire.  A dummy load that is 50 ohms in parallel shud snag another 3db - assuming the dipole is also 50 ohms which it's not. The dipole is around 12 ohms with a big capacitive reactance, so who knows how much power it would hog compared to the dummy?  That is one variable unless you modeled it.

The RG-213 feedline we once figged out here with a web calculator - found at 5:1 vswr the loss to be about 1db...   So I get about 5db total loss.

What ya think?

T

[W2VW]

5 db? Ya think?

Off the hip you'd think it wud be a 10-15 db loss, but even a mobile antenna is only down 15db from a full size dipole on 75M. You'd think  Todd's lash-up wud be better than that.

So, let's see...

Modeling a 75M dipole on 160M shows a 1db loss in wire.  A dummy load that is 50 ohms in parallel shud snag another 3db - assuming the dipole is also 50 ohms which it's not. The dipole is around 12 ohms with a big capacitive reactance, so who knows how much power it would hog compared to the dummy?  That is one variable unless you modeled it.

The RG-213 feedline we once figged out here with a web calculator - found at 5:1 vswr the loss to be about 1db... so let's say 2db max.  So I get about 5db total loss.

What ya think?

T

I think this is more fun than repairing the clothes dryer which I have in pieces here.

I'd be interested in the model again . Mine was 7 ohms -1385J. Take that and figure out the transformation at the other end of the antenna pipe. We don't know how long that is or the velocity factor. Anyway, if we did then we'd have a giant reactance which has to be conjugate matched before we can feed power into whatever the reflected radiation resistance portion of the impedance is. Then we can throw away the dummy load power.
No way is it only a 5 db loss. That figure is about what you might see with balanced line, a tuner correctly built with the best available parts, large diameter feeders and flat-top 
Maybe Todd will be able to A/B the whole thing when it works.

[K1JJ]

I'd be interested in the model again . Mine was 7 ohms -1385J. Take that and figure out the transformation at the other end of the antenna pipe. We don't know how long that is or the velocity factor. Anyway, if we did then we'd have a giant reactance which has to be conjugate matched before we can feed power into whatever the reflected radiation resistance portion of the impedance is. Then we can throw away the dummy load power.
No way is it only a 5 db loss. That figure is about what you might see with balanced line, a tuner correctly built with the best available parts, large diameter feeders and flat-top 
Maybe Todd will be able to A/B the whole thing when it works.

Oh, I see what you're saying.  Basically there is a super high swr in the coax.  I forgot to consider the capacitance reactance.

I'll have to dig out the coax calculator and check that out - that may be where the big loss is. Open wire would change that dramatically - using a 75M dipole on 160M.

That 5db loss intuitively did not make sense to me cuz when I've tried to listen on 160M with my 75M coax dipole, it seemed down like 20db!   

Unfortunately my ant modeling program is on the other computer out for repair, so I'll have to wait to model the ant portion



T

[W2VW]

Assuming there is an equal power division in the T, Todd's current setup will be 3 db down compared to the 160 dipole. I'd bet the power division is not equal, so probably more power was dumped to the dummy load than to the antenna. Only 5 dB down is probably being optimistic.

That would be true if the antenna was a resonant 160 dipole. It's a 75 meter dipole fed with coax on 160.

[W2VW]

Unfortunately my ant modeling program is on the other computer out for repair, so I'll have to wait to model the ant portion



T

Makes perfect sense. It's easy to blow up tuner components trying to feed a short ant. QRO. So you tried it with your computer and blew it out also.

[K1JJ]

I saved 10% buying cheap memory and paid the price 4 months later.

Dave, since your computer is presently working and feeding a Yagi, what is the swr of a 75M coax fed dipole on 160M ? ie, tranform  7ohms -1385j  into swr and I'll find the loss using 100' of RG-213.

Bottom line is poor Todd oughta be channel master if he was being heard with that lashup... 

If ya want me, I'll be outside freezing my ass off on the 20M tower.

T

[Steve - WB3HUZ]

I think we're saying the same thing Dave, the loss would be more than 5 dB.

From http://fermi.la.asu.edu/w9cf/tran/index.html, the loss in 100 feet of RG213 at 1.9 MHz, with a load of 7-j1385 is 22.84 dB! The input SWR is 1357:1!

Hmmm, maybe 30 dB down is more like it.

[W2VW]

Thanks for saving my computer Steve.

[KB2WIG]

Have you considered using the 75m and StrapinG the coax feedline conductors  and then loading the hole thing??   klc

[Steve - WB3HUZ]

Thanks for saving my computer Steve.

Now we need to keep Tom from falling off the tower.

[K1JJ]

I think we're saying the same thing Dave, the loss would be more than 5 dB.

From http://fermi.la.asu.edu/w9cf/tran/index.html, the loss in 100 feet of RG213 at 1.9 MHz, with a load of 7-j1385 is 22.84 dB! The input SWR is 1357:1!

Hmmm, maybe 30 dB down is more like it.

Wow...   1357 :1    SWR!

That's quite a message.

So, based on this, how much power was going into the 50 ohm dummy and how much into the antenna?  Parallel up a 50 ohm resistor across that circuit.

I'm down and black. About two more climbs this year and I'm done until spring, 2007. The two 20M Yagis point at Eu, ready for Chuck.

Now tiime to finish up the 4X1 and get on the air.

T

[Steve - WB3HUZ]

Now tiime to finish up the 4X1 and get on the air.

yea!

[Todd, KA1KAQ]

Maybe Todd will be able to A/B the whole thing when it works.

I will definitely do this, Dave. It'll be interesting to see the difference (although we already know it will be huge). It's very noticable here to me on receive also, although Richaroni and Steve were both strapping Brent's Class E a$$ up here on 160 last night. Brent is usually a channel master. He probably wasn't even hearing me.

BTW, the 75m is fed with Belden 9913 because that was what I had handy. Maybe a 6' chunk of 213 or crappy foam lashed to the B&W center insulator, can't recall.

The input SWR is 1357:1!

  ouch! No wonder it objects and kicks off the overload when I try to tune just the dipole! Wait 'til the next time I hear someone whine about having a 4:1 swr....

Bottom line is poor Todd oughta be channel master if he was being heard with that lashup... 

Absolutely. Poor @#$! me. This is why I asked the masters, because while I know the 160 antenna will stink due to the limitations of my location, it'll still be better than what I'm using for 160 now. And what I'm using for 160 now is still better than what I was using (nothing). I want to make the most of what I'm able to do.

Scaling the antenna evolutionary ladder can be fun. Soon I'll be able to look down my nose at the G5RV and mag-mount protozoa! Maybe I can get an article into QST after Steve's FB notes on 160m BC transmitter break-in?

[k4kyv]

My second time on the band, using the 75m coax-fed dipole into a 'T' with a scroteful broadcast dummy load on the other side. Certainly does the job, but obviously isn't the best solution.

Wow!  A homebrew Maxcom automatic antenna matcher! 

It would be better to simply load the transmitter into the feedline, mismatch and all.  If you have any big coils and capacitors, see if you can fabricate some kind of tuning unit, using trial and error if necessary.  The astronomical SWR on the coax will generate a substantial loss,  but still not as much as the dummy load.

With coax feed, I don't begin to worry about SWR until it reaches beyond 2.5 or 3:1.

Prior to installing my radial ground system, I used my 80m dipole on 160.  It worked out wery well all over N America.  But it is an average 110' high, and fed with open wire line.  Only thing was that it was extremely sharp tuning.  I couldn't QSY over about 5 kc/s without having to touch up the antenna tuner adjustment.

But when I got the vertical  going, it was head and shoulders above the dipole, except for stations about 50 miles away.  At that distance, which includes Nashville, the 1/4 wave dipole is about 30 dB above the full size vertical.  Skip zone.