Where do the little AM guys hang out?

[N9NEO]

Frank said:

"The shock factor does work but it takes real talent to get make up S#X.
An issue for dopra and Dr. Phil................"

Not really interested in Dr. Phil, But make up S#X with dopra would suit me just fine!  She's sweet!


73
threadbusta

[Vortex Joe - N3IBX]

Al,
   I second the opinions that others made about being intimidated. When conditions are good, please feel free to "jump on in" a QSO.

I sometimes come on with high power and sometimes with the hyellowyest sounding PW rigs using a carbonium microphonium and people will still talk to me.

Fourty-Meters and 75M (when the band is quiet) are good places to start.

Hope to hear you on the band(s)

[ne2d]

Thanks for all the replies, including the song, but I can't find an application that will play it.
(I just got back from skiing in the Adirondack mountains, so I'm just catching up).

I'll have to think about all those ideas. The house is a 2-story modern colonial, or something like that, with attached garage. I think it is around 57 feet or so wide, so it would maybe take a shortened 40 meter dipole or an inverted vee. I saw some plans for a shortened 80 meter dipole that might fit also.
One problem is that the roof is pretty high, and very steep. Add to that the fact that I'm afraid of heights, and it's not easy putting up a high dipole. (I know, I'm a wimp).

I'm thinking in the meantime, maybe I'll try putting up some more radials on my vertical for 75 meters. Will that drop the radiation angle a little maybe? I only have one radial for each band right now.
When I get on ssb I get 59 reports from states to the west of me and to the east of me (which are a lot closer), but it isn't very good to the south for some reason. The one radial I have for 75 runs east and west, and the other radials run in all different directions. I can't run any to the west of the antenna because there's no roof there.

[K1JJ]

Hi Al,

Yes, put up a dipole on the roof of the 2 story house. Make it as long as possible and feed it with good quality openwire on 75M. You will be down only a db or so compared to a full sized dipole, assuming the openwire has low loss and is matched with the ant tuner correctly.

But, rather than this,  I wud use the house as a central support for the center and pull the legs out into the yard, even if they are V configured to make a full sized dipole. Even legs that must come down to the ground will suffice for now. This way the input impedance is higher and losses/matching is easier on 75M.  The input to a 57' long dipole is probably down around 12 ohms or so on 75M.... tough to deal with - losses high, even with open wire if you use the Brown plasdick type.

As for your vertical...the reason for radials is to collect RF energy and return it back to the base. It's all about efficiency.  Read this article about ground systems I've collected from the 160M gurus for some info.  

http://www.amfone.net/ECSound/K1JJ16.htm

I wud not waste my time with that shortie vertical, OM. Put the time into the multi-band dipole. The vert needs to be way in the clear and have down a good 60  1/4 wave radials before it can even hold a candle to your proposed dipole. And if your Earth soil is only fair, like most of us, you will be so PW on it it will never be used.  

I called CQ for 3 days on my 18' Gotham vertical when I was a Novice in 1964 without a single answer on 80M. I put up a dipole and was immediately working stations out 1000 miles like nothing....  :lol:

A vertical system is very difficult to get running to compete with a good dipole. It requires a HUGE cleared field, 60+ radials in ALL directions and excellent Earth soil. Even then, locally you will be pissweak, down -30db from a dipole. Why bother?  On 75M verticals are used for DX only and usually in a four square that takes up a few acres to erect correctly.  If you decide to use that shortie vertical on 75M, lets talk 6 months from now and I'd like to hear what you have to say about the adventure...  :grin:

73,
T

[kz0e]

So Tom, what's the deal with the "Brown plasdick type" twinlead? What's wrong with it, is that a specific brand or style,  and what do you suggest otherwiise? I've got a bit  of 400 ohm (brown)  twinlead from the wireman, and if I could do better with something else I'd rather start that way. My time is what's at a premium here so I need to listen to the voice of experience and not duplicate less than optimum moves if I can help it.

Thanks,

larry

[K1JJ]

So Tom, what's the deal with the "Brown plasdick type" twinlead? What's wrong with it, is that a specific brand or style,  and what do you suggest otherwiise? I've got a bit  of 400 ohm (brown)  twinlead from the wireman, and if I could do better with something else I'd rather start that way. My time is what's at a premium here so I need to listen to the voice of experience and not duplicate less than optimum moves if I can help it.
Thanks,
larry

Hi Larry,

Well, the brown plastic open wire I mentioned is the common stuff seen with the punched square slots... about 2" spacing and about 450 ohms.  Maybe #18 wire or so?

That stuff is OK as long as it has a "reasonable" match (reasonable swr) so that the feedline current points are not too high. It's just a matter of how much loss you consider too much.  

For example, for a 40M dipole of the 3 three wire type or a folded dipole type, the input is about 600 or 300 ohms respectively. Using that 450 ohm line would be excellent and the loss wud be nil on 40M.  It is matched correctly.

However, using say, a standard 40M 1/2 wave dipole on 160M, the input is like 5 ohms and the swr is about 10:1.  That brown feedline would probably melt at the current peaks running a KW thru it for sure. Big losses.  Axe Tim-Tron about his own melting experiences with this stuff.

Running this same 40M dipole on 75M would produce maybe 12 ohms, so the swr is now about  5:1 - you could probably get away with that. This LOW impedance is the killer here.

But most dipoles cut for a band are about 70 ohms... fed with 450 ohm line is about a 6:1 swr ratio.  This is commonly done. I imagine when the swr gets much above this figure is when ya need to worry about it for that plastic line.

And so forth as you use a 75M dipole fed with this plastic open line on the higher bands. There will always be a place where the swr is very high, even if the antenna is MUCH longer than a 1/2 wave for the band. On some freqs you will luck out and be close.

Chuck, K1KW once ran a test wid that stuff. He terminated 100' with a 450 ohm resistor dummy load and  put in 100W on 14 Mhz.  (Probably used an ant tuner) He measured  98W coming out the other end. So, if matched, it works VERY FB.

In contrast, take some homemade openwire, say #12  insulated wire from Home Depot spaced 5"-6" with good Lexan or Teflon spacers.  The IR losses are MUCH lower for both the wire size and for the better insulation. You can then tolerate a higher  SWR that results from running any dipole on bands with high swr.  The bottom line is that every 1/4 wave along the feedline you have a current peak or a voltage peak. This "standing wave" magnitude varies from none when matched, to wild swings when the swr is high. The radical current peaks are the problem and cause heat and loss.... even in open wire.

The db loss is always the same, no matter what power level you run. So when when someone says they are running "low" power so the swr/heat is OK with poor feedline, they are fooling themselves.


Hope this helps. The bottom line is that loss is relative, and it depends upon your own anal/perfectionist factor, the power you run before it melts, and whether or not you can run BIG open wire for XYL-approved reasons... :lol:

Personally, I run hardline and coax for ALL antennas here, simply for convenience. There was a time when I had five antenna tuners mounted on the wall for fast band switching.  There's really little on the air difference in the end if losses are kept in check with any feedline method used..

73,
Tom, K1JJ

[W1GFH]

I called CQ for 3 days on my 18' Gotham vertical when I was a Novice in 1964 without a single answer on 80M.

Ah yes, the Gotham Vertical...better known as THE DESTROYER OF NOVICE CAREERS. :lol:

[w3jn]

You COULD work wonders with a Gotham Vertical

...just like you COULD be a winner in the publishers' clearing house sweepstakes.

I gained about a hundred dB (at LEAST!) after I replaced the JS TV twinlead with honest to god decent openwire line - that and raising the antenner above 10 feet.  I will say that the TV twinlead provided a fine business OM match to the xmitter.  SO does a dummy load.

73 John

[K1JJ]

Ha! Too funny!

Yes, the Gotham Vertical...   I was too poor at 12 years old to buy more than 3' of coax and was afraid of coaxial losses, so I mounted the Gotham outside my window on a steel pipe (no radials).  The antenna was about 1' from the side of the house with the coax stuck thru the window - in December.  

I just used the recommended taps from the instructions - who knows what the swr was - (or what it meant back then)  

The fatal error (besides buying the Gotham) was tying a bare wire from the antenna top to the shingles of the house which were covered with ice - dead short to ground at a high impedance point. I wanted to make sure the ant survived in case of a hurricane - in the Winter.

I called CQ on 3716 khz CW for three days and even violated FCC rules by not entering CQ's into the log after two days. Finally a local General Class ham listened for me 12 miles away and could not hear me. I figgered at that point something was wrong.

Then I got the bright idea that the antenna needed to be up in the air. There was a tree about 150' away that I sawed off the top and strapped the Gotham on the top, about 25' high. I tried to convince my OM to buy me about 1500' of coax so I could have a coax tapped to EACH coil tap and run back to the shack to cover all of the bands. (I was planning for General Class someday)   Can you imagine five coax cables all strapped onto the same coil at the same time? He balked after hearing I also needed about 200 crystals to cover all of the ham bands too. (Didn't know about VFO's)

I brought the Gotham back to Corky at Hatry's, the ham store where I bought it. He forgot that he sold it to me and axed what I was doing with "that piece of crap?".

He showed me how to make a pig tail for a coax connection to a dipole and in the middle of an ice storm I put up a 40M dipole at 40' in the trees. Instantly started working WN4's and WN9's in the daytime!  I was blown away.

T

[W1GFH]

Can you imagine five coax cables all strapped onto the same coil at the same time? He balked after hearing I also needed about 200 crystals to cover all of the ham bands too. (Didn't know about VFO's)

ROTFLMAO!

The thing I liked best about the Gotham vertical ads in QST were the comments they included from their 'satisfied' customers, e.g. "....Put up Gotham V40 and immediately worked 100 countries within 10 mins! --XB9HKY".

[kz0e]

Thanks Tom,

So the tuned open wire fed 'lossless' one size fits all dipole is a bit of a myth, because 18 gague will eat up your power under high swr conditions and that brown stuff isnt an ideal rf insulator either. Makes sense to me. Seems there's no free lunch. Looking at my (low) inverted L with a very jaundiced eye right now.

Larry

[N9NEO]

The oracle of antenna professed the following:

"The db loss is always the same, no matter what power level you run. So when when someone says they are running "low" power so the swr/heat is OK with poor feedline, they are fooling themselves."

If db loss is same regardless of power level then more power translates into more losses. No?  Am I fooling myself again?  


73
NEO

[K1JJ]

The oracle of antenna professed the following:

"The db loss is always the same, no matter what power level you run. So when when someone says they are running "low" power so the swr/heat is OK with poor feedline, they are fooling themselves."

If db loss is same regardless of power level then more power translates into more losses. No?  Am I fooling myself again?  

73
NEO

Hi Bob,

The oracle of class E said:  "If db loss is same regardless of power level then more power translates into more losses. No?  Am I fooling myself again? "

Well, it depends upon the way you look at it...  both are correct.  If it's measuring antenna system performance, then look at db. If it's melting the feedline, then it's raw power to look at.

If an antenna system has say, a 3db feedline loss,  if you "fix" the problem you will gain 3db.   Whether you are running 1 watt or 1KW, your signal level will increase 3db on the other guy's S meter.  

But if viewed from the  pure power point of view, then you are "saving" either 1/2 watt or 500 watts in heat. (3 db).  Same thing.

I prefer to look at antennas in db only, to keep it absolute and simple.
For testing, the value of high power is to run a KW carrier and feel to see if anything in the system is heating up, like matches, baluns,  feedlines, tuners, etc..

You  GGGGotta  PPPPPPPPeeel the PPPPPPPotatoes before PPPPutting them in the PPPPPot., caw mawn.

(I know you're yanking my chain here, but figgered I'd explain it anyway...  :lol: )

T

[N9NEO]

Ok.

Point I guess I was considering was high power may melt feedline.

NEO

[ne2d]

I knew a guy with a Gotham vertical with no radials when I was a novice or general. He got out, but he wasn't exactly the DX king.
My Butternut on the garage works pretty decent for DX (I worked Germany and some other European stations on 80 cw, and I can work almost everyone I hear on the ssb DX contests), but like you guys are saying, it's not real gud for short skip, so I do plan on trying to put up some kind of dipole in the spring.

I looked at the plans for my house, and it is 57' 4" across, including the garage, so I would need a dipole about that long or an inverted vee a little longer (if I keep it all attached to the house, which would be by far the easiest way).
 I did see an article for a 75 meter dipole with loading coils that was only about 48' long, so that might be a consideration. I could probably go as long as 66' for an inverted vee. I know it's not half-wave, but might not be real bad.

[Bacon, WA3WDR]

I did well with low power on 40 and 75 during the day, just using a coax-fed dipoles, not even balun fed - although I recommend a W2DU balun if you can afford one, and a self-resonant antenna.  75 had more d-layer losses and signals were weaker, but there was very little competition other than noise.  When I was running about 80 watts carrier output on 40 meters, someone said I was up with CHU, which was not bad.

At one time I was on 75 with 9 watts carrier from a screen-modulated 6146, and people heard me fine.  Coax-fed 1/2 wave dipole, no balun, up about 40 feet...

The simplest antenna is usually the best.  Coax-feed and a 1/2 wave dipole cut for the frequency of activity, and if you can afford one, a W2DU ferrite-sleeve balun will do it just fine.  But I didn't use baluns way back when, and the self-resonant dipoles worked very well indeed, if they were high enough.

On 40 you can easily put an antenna high enough for good performance.  On 75 it is more difficult.  I found a height of about 40 feet worked very well at 75, and 20 feet was fine at 40 meters.  Higher can be better, but more than 3/8 wave and your local (200 mile) performance can fall off.

So it might make sense to have a self-resonant half-wave 75 meter dipole up as high as you can get it, which will probably be 40-60 feet, and a separate self-resonant half-wave dipole for 40 meters up about 20 or 30 feet.  That's what I did, and it worked great.

If you can't get the 75 dipole up the way you want it, do what you can.  You can bend these things all over the place, and they work fine.  It's the height that matters, and length-pruning usually helps, so you don't have to fiddle with a tuner.  If you are lucky, your local soil will be a relatively good conductive ground (less loss if the antenna isn't that high), but a low antenna usually loses a lot of power into ground losses anywhere.

Verticals are usually really lousy on 75 and 40.  Ground loss issues again, and a big null straight up where the locals are (300 miles).  You would need a big ground radial system, and even then the high angle null would hurt your signal.  Stick with simple horizontal stuff.

If you get really sophisticated, you can play with verticals and advanced designs.  But for simplicity and performance, you can't beat a coax-fed self-resonant half-wave antenna at a reasonable height.

[W2VW]

The db loss is always the same, no matter what power level you run. So when when someone says they are running "low" power so the swr/heat is OK with poor feedline, they are fooling themselves.

This only holds up if your conductor's resistance remains the same when heated. The losses in a hot tuner and feeders are higher than a cold one. Feed power to a small lamp with some light copper wire, heat the wire with a candle and watch what happens.
Also, the reason brown crap feeder does not burn up until you really pour the coal is probably due to the copper's heat conduction away from the current node. I never used the stuff but my guess would be that you could kill it with Voltage sooner than current.

[KL7OF]

I am a big fan of the coax fed dipole cut for the frequency in question...I use them on 75 and 160 on the big rigs without baluns.....Higher is better....Antenna bandwidth is  acceptable for the  freq range I use on AM.......... I once  lived in a duplex in dummy load valley in Spenard Alaska.(West Anchorage) and had a Gotham Vertical mounted on the vent pipe on the flat roof..No radials.......Height above ground was about 10 or 12 ft to the base.......... I worked every Japanese station there was on 10 meters......If they need you, they can read you....

[K1JJ]

The db loss is always the same, no matter what power level you run. So when when someone says they are running "low" power so the swr/heat is OK with poor feedline, they are fooling themselves.

This only holds up if your conductor's resistance remains the same when heated. The losses in a hot tuner and feeders are higher than a cold one. Feed power to a small lamp with some light copper wire, heat the wire with a candle and watch what happens.
.

Now that's a new angle I didn't think of, Dave. Heating the wire so much that the loss gets even worse.  This strengthens even more the reason to use high quality open wire with large diameter and good spacer material.

The point I was making was more for the opposite case where I've heard newbies on the air assume that since they are running low power thay can get away with cheap lossy feedline without any negative consequences.

In fact, probably the worst problem not mentioned is the degradation in RECEIVER S/N ratio using a lossy feedline.  A 3db loss in feedline equates directly to a 3db loss in S/N.  No wonder some pissweakers have trouble hearing too.
Try putting a 50 ohm resistor between the coax connector and the RX input and watch a 3db reduction in S/N. I once stuck a step attenuator pad in there by mistake and was baffled for awhile why I couldn't hear as well when the attenuator was in line on 6M...  :lol:


I learned my lesson on 6M.  Right now I have a 600' run from the shack to the yagis on the tower at 195'.  Even with low loss hardline this is 1/2db loss per 100'.  Total loss in feedline = 3db! This is a 3db S/N receive reduction.  

This is where a preamp at the antenna feedpoint would solve the problem. But how about the transmit power loss?  This Spring I've decided to run quality homebrew openwire for the entire run. This would make the TOTAL feedline loss about 1/2db instead. The 50 ohm Yagis get tied together with hardline at the tower and the open wire gets  tapped  at the 50 ohm point using an open wire stub.  Then 600' of openwire to the shack. At the shack, a 50 ohm coax with a balun is tapped onto the open wire, so now back into the 50 ohm whirl. RX and TX loss problem loss solved.

T

[K1JJ]

I I did see an article for a 75 meter dipole with loading coils that was only about 48' long, so that might be a consideration. I could probably go as long as 66' for an inverted vee. I know it's not half-wave, but might not be real bad.

Hi Al,

So, then let's settle on a 57' dipole at this point for now.  Keep the legs as high/far away from the roof as possible. Remember what the antenna sees - house wiring, copper plumbing, alum siding, etc.

Do you plan to use coax or openwire?  With the loading coils you can adjust them to find a 50 ohm input for the dipole match - good for coax, but one band only. (and maybe 15M)

With openwire, the coils  will need no adjustment, if even used. Just go by the design and an ant tuner will get it on all bands.

But for the sake of discussion, on 75M, I'm wondering what would be the difference in efficiency of using just a straight 57' dipole fed with quality openwire vs: a coil loaded 57' dipole fed with coax. (with coils both out near the ceneter of each leg)

In the case of the coil dipole, the CURRENT point is farther out on the legs like a full sized dipole, giving a higher input impedance. But the openwire dipole does not have the coil losses nor the coax loss, but deals wid a low 12 ohm? input..  I'm thinking the openwire ant might be the better one.  Esp for the multi-band aspect. Both are still only 57' long on 75M.

Any opinions on this???

T

[W2VW]

Now that's a new angle I didn't think of, Dave. Heating the wire so much that the loss gets even worse.  This strengthens even more the reason to use high quality open wire with large diameter and good spacer material.

The point I was making was more for the opposite case where I've heard newbies on the air assume that since they are running low power thay can get away with cheap lossy feedline without any negative consequences.

In fact, probably the worst problem not mentioned is the degradation in RECEIVER S/N ratio using a lossy feedline.  A 3db loss in feedline equates directly to a 3db loss in S/N.  No wonder some pissweakers have trouble hearing too.
Try putting a 50 ohm resistor between the coax connector and the RX input and watch a 3db reduction in S/N. I once stuck a step attenuator pad in there by mistake and was baffled for awhile why I couldn't hear as well when the attenuator was in line on 6M...  :lol:


I learned my lesson on 6M.  Right now I have a 600' run from the shack to the yagis on the tower at 195'.  Even with low loss hardline this is 1/2db loss per 100'.  Total loss in feedline = 3db! This is a 3db S/N receive reduction.  

This is where a preamp at the antenna feedpoint would solve the problem. But how about the transmit power loss?  This Spring I've decided to run quality homebrew openwire for the entire run. This would make the TOTAL feedline loss about 1/2db instead. The 50 ohm Yagis get tied together with hardline at the tower and the open wire gets  tapped  at the 50 ohm point using an open wire stub.  Then 600' of openwire to the shack. At the shack, a 50 ohm coax with a balun is tapped onto the open wire, so now back into the 50 ohm whirl. RX and TX loss problem loss solved.

T

I suspected this for sometime using my 75 metre dipole on 160. Finally changed a bunch of things in the tuner which were getting hot. Mostly connections made of #12 THHN. End result was absolutely no increase in measured antenna current. It just brick walls at around 10 Amperes. The feeders are #12 also and cannot handle 1500 Watts at 1.9 megs. The HuzMan modeled the numbers and my ant. has a feedpoint inpedance of 7 Ohms, J-1385!  
   What is the construction of yer homie open wire?

[W2VW]

I I did see an article for a 75 meter dipole with loading coils that was only about 48' long, so that might be a consideration. I could probably go as long as 66' for an inverted vee. I know it's not half-wave, but might not be real bad.

Hi Al,

So, then let's settle on a 57' dipole at this point for now.  Keep the legs as high/far away from the roof as possible. Remember what the antenna sees - house wiring, copper plumbing, alum siding, etc.

Do you plan to use coax or openwire?  With the loading coils you can adjust them to find a 50 ohm input for the dipole match - good for coax, but one band only. (and maybe 15M)

With openwire, the coils  will need no adjustment, if even used. Just go by the design and an ant tuner will get it on all bands.

But for the sake of discussion, on 75M, I'm wondering what would be the difference in efficiency of using just a straight 57' dipole fed with quality openwire vs: a coil loaded 57' dipole fed with coax. (with coils both out near the ceneter of each leg)

In the case of the coil dipole, the CURRENT point is farther out on the legs like a full sized dipole, giving a higher input impedance. But the openwire dipole does not have the coil losses nor the coax loss, but deals wid a low 12 ohm? input..  I'm thinking the openwire ant might be the better one.  Esp for the multi-band aspect. Both are still only 57' long on 75M.

Any opinions on this???

T

That is exactly what I'm using on 160 here. Dipole is just under 1/2 length necessary for a 1/2 wave. 110' centerfed. I've not maximized the whole thing. Rich, WA2TUM lives nearby with a coil dipole on 160 fed with coax. Unscientific result says the openwire setup kicks the loaded dipole's a$$.

[WA1GFZ]

Tom Vu be careful 50 mhz radiation can hurt you. Why not add a preamp
at the ant say at the bottom of the tower switched out during transmitt.
Then just double your strappage or move the linear out to the ant also.

good info on feed line Dave! Love those old Johnson spreaders!

[ne2d]

I was thinking of using coax because I'm more familiar with it. actually that's the only thing I've ever used.
Also, since my shack is in the basement, it would be easier to bring in coax down there. (I usually drill a hole thru the cement block foundation below the ground.)

If I just run a straight 57' dipole, it wouldn't be resonant at 75 meters, but the tuner should handle that. I'm assuming the coil dipole would be resonant if I tune the coils correctly, but I'm no expert on this, so I don't really know. I could probably use a balun with a straight dipole to transform the impedance, if I knew what it was at the feedpoint.

Also, I was looking at some ready-made antennas by Van Gorden Engineering. They have one that goes on all bands, and is 70 feet long. I'm not sure if I could handle that much length, but I might be able to swing it somehow. I would probably have to use a balun to get it down to 50 ohms.

[K1JJ]

Dave "The ApeMan" Axed:
"What is the construction of yer homie open wire?"


Good question. I haven't settled upon anything yet, still thinking.  

What do you think the maximum spacing can be between wires?  I figgered that 3" wud be the max before feedline radiation occured, but not sure.  The wider the easier to mount and keep apart.

Since I will have a good match in and out of the feedline, the SWR shud be good.  But, still, I was thinking of some heavy Home Depot wire. A friend seemed to think that insulated wire wud cause loss on openwire at that freq... what do you think?  Insulated wire is cheaper, esp the #10 spools of electrical wire.

For spreaders I was thinking of getting 3/8" Lexan rod at Industrial Safety in West Hartford. I plan to use as few as possible on the run over the ground since it will be very tight and tensioned between wooden poles.

BTW, I'm building up a large 40' X 40'  H-frame to hold the four 48' boom 6M Yagis. Rotated by a prop pitch and sproket/chain using a large swing gate on the side of the tower.  Coupled wid the openwire low loss, I'm hoping for the best.

I'm not satisfied wid the triple stack config - good for F2 only and the new config will be 180 degree swichable (top/bottom) to produce high angles for E skip, but still have all in phase to handle horizon stuff.

T  (Nutcase Radio)