Initial low power tests

[VE3GZB]

I put the solderless crimp-on connectors on the cable.....my cable is thicker than what these connectors are meant for (and the braid in this cable cannot be soldered, it just will not flow so it really depends on a mechanical connection).

I put the SWR meter in line (my friend VE3AWA loaned me his SWR meter for a while until I can get my own), fired up the Xmitr, tuned it into the tungsten dummy load, then carefully made a controlled switch over to the antenna, gradually bringing up the plate voltage on the PA keeping the voltage levels low so I don't radiate much power while testing the antenna setup.

I ran tests at both 40 and 80 meters to see where the best SWR can be found. It's rather disappointing to me....40 meter SWR seemed to remain at infinity no matter what I tried.

80 meter SWR came in a little better but it's still far from perfect. The best reading I could get was 3 units forward to 2 units reflected.

Because the braid in this Coax will not accept solder, I know I had some difficulty in fastening it to the Dipole. I may need to mechanically clamp the braid to the antenna wire. The middle conductor is copper plated, I had no difficulty in soldering it to the antenna.

Ironically I may have had better results when I was still using the twinlead...it's rather frustrating I must admit since I have no practical experience in setting up antennas (only in building and designing the electronics) and certainly no money to toss at it, so I'm trying to make do with what I have within the confines of the back yard.

Perhaps I should try using a loop antenna for transmitting and just leave the dipole up for the receiver?

Oh well, anyway, it's late now, I've had a long day driving all over looking for what I can afford in terms of a replacement car (my Hyundai was hit by a pickup truck in late May, the insurance is writing it off so my main focus has to be on finding a suitable replacement....hoping for a Suzuki Swift if possible, took one for a test drive today) and I'll continue to fiddle with things towards a satisfactory SWR.

73s
geo

[N3DRB The Derb]

Geo,

I'm off to K4KYV's  to rescue a pair of 4-400's n a 48" black rack.

I'll be rounding up yer stuff and sending it when the wife is not working next week but it may not be until next Saturday morning, she is going at it 5 days a week at the moment. (I dont drive)

I think the coax is a bad deal. you need open wire line. not plastic coated twin lead either. the swr meter and the rf ammeters will point you in the right direction. i got 25 Birnbach porcelain spreaders NIB for open wire feeders, little ones, 300 ohms. i gave a buck for them, I'll throw them in the box too.

You're going off on a million tangents, just like I do, when things are sucking. Coax sucks for HF anything other than a resonant cut to length center fed dipole. if you havent got that, dont use coax.

just wait a bit until you get my box. It will help.

[VE3GZB]

Wow, yea it's so frustrating...other hams I've discussed this with swear by Coax....others will swear by twisted lead.....now that money has been spent on Coax, it's an awful thing to see it wasted.

I repeated tests this morning, I'm still able to peak the SWR at 3 forward units to 2 reflected units as I approach 3.5 Mhz. Going higher in frequency just causes the reflected units to equal forward units.

I looked closely at the SWR meter, it's rated for 52 Ohms! I didn't realize that! I know my Coax is 72 Ohms and who knows what my antenna is!

But now that I have the Coax, I have to make it work. My wife will make me sleep in the garage if I fail to make this work, she hates to see money spent on things and then it's disassembled and wasted.

If twisted pair didn't work then I have to make the Coax work - it fits in with the general layout since the path to feed the middle of the antenna isn't direct, I have to take a path under the deck diagonally (the feedline is supported by wooden blocks drilled out so it doesn't lay on the ground).

This antenna stuff is so frustrating there are times I'm tempted to just throw in the towel and give up on trying. And my wife isn't happy about me putting holes in the wall, in the siding, or making the backyard look like a lab freak. I love building and designing the electronics part of it, that's where I do best, but in a limited size lot and with constraints, no decent antenna can be set up it seems.

73s
geo
VE3GZB

[W2PFY]

What type of coax did you buy? Is it TV stuff like RG6? Most coax shielding is copper or tinted copper if it is for transmitting service.  If you stay with open wire line then you can build an antenna tuner and use you existing antenna for all the ham bands on HF. Perhaps you'll not need an antenna tuner for a given ham band depending on the length of your lead in and if the dipole is cut to resonance on a band you wish to operate on.   

[VE3GZB]

They had it on clearance, 72 Ohm (Correction, 75 Ohm!) RG6/U, double shielded, indoor/outdoor Coax, they rate it for digital satellite service. Normally up here it's at least $100 but it was on clearance so it was much less.

Nobody carries RF stuff here anymore, it's pathetic! Even the radio shack went belly up, now it's The Source and it's all crap gadgets for people who wouldn't know the hot end of a soldering iron if one was placed in their hands. What's a ham to do!

The thing is that my wife won't tolerate me putting any more holes (or making any of the current holes bigger) in the wall or the siding. I can't blame her either, it looks like crap. So making clearance for anything that's wider than Coax just won't fly with her, she'll hit the roof.

EDIT: What about any military spy or battlefield transmitter designs? Those small transmitters had to work into random wire lengths and still had to transmit a signal effectively under primitive conditions and had to be durable and portable in the field, so they had to be relatively uncomplicated. Does anybody know anything about military HF antennas and matching for 80 and 40m?

Attached is a crude drawing of our rectangular lot and how things are laid out. The only mount points on the property for any kind of antenna are from the old TV antenna tower to the far clothesline pole, that's about 50 feet. Immediately next to our lot is a high voltage 3 phase power line that runs through town so I don't want to run anything close to it.

The feedline runs from the middle of the dipole, diagonally under the deck to a point near the TV tower where it enters our house and into our bedroom, that's where my stuff, my bench, my tools, everything are set up.

The backyard is about 80 feet N-S by 40 feet E-W and very uneven, the house is built on a bit of a mound. This is what I have to work with.

73s
geo
VE3GZB

[Ed-VA3ES]

You can still use your 52 ohm SWR bridge with 75 ohm coax. At resonance, you will see a differential of 1.5:1 or at resonance,  a 1.5:1 SWR.     

Coax is only good with resonant antennas.  75 ohm coax WANTS to see a 75 om load. Losses start to multiply when you have a high VSWR.  A loss of 9dB or greater is not unusual with mis-matched coax.

My yard is similar to yours. I ran an End-Fed Zepp from the TV tower to the near clothes-line pole then out to the far clothes-line pole, thence to the tree at the corner of the lot and out to another far tree (so to speak - I had different supports, but the idea is the same).  It ran 133 feet.  You have no choice but to convince your wife.  Bribe her.  Either that, or take up model railroading.

[VE3GZB]

52 Ohm SWR meter on 75 Ohm Coax giving SWR of 1.5:1.....well if the best I was seeing was a forward power of 3 and a reflected power of 2, doesn't that translate to 1.5:1?

3:2 = 1.5:1 ? Makes me wonder now, doesn't it? Could my antenna system actually then be functioning properly but it's just my loaned SWR meter that's mixing me up?

Your thoughts?

73s
geo
VE3GZB

[Ed-VA3ES]

On virtually every SWR meter I have ever seen, the SWR can be read directly off the meter scale.  Be absolutely sure of what you are reading, and that that your are reading the meter correctly.

Typical SWR meter scale:


Don't forget to set the reference ("set" point).


What kind of SWR meter is it?

52 Ohm SWR meter on 75 Ohm Coax giving SWR of 1.5:1.....well if the best I was seeing was a forward power of 3 and a reflected power of 2, doesn't that translate to 1.5:1?

3:2 = 1.5:1 ? Makes me wonder now, doesn't it? Could my antenna system actually then be functioning properly but it's just my loaned SWR meter that's mixing me up?

Your thoughts?

73s
geo
VE3GZB

[K1JJ]

Geo,

If you're going to stick with coax, then the only way to get a low swr on 40 or 80 meters is to use a flat top that's 65' long for 40M or 123' long for 75M.  Otherwise the swr will be very high with huge losses - just like what you're seeing now.  You see, the flattop becomes a ~70 ohm load at those lengths for those frequencies. At other lengths, the flattop presents a load that is very different with added reactance and a poor match for 50/75 ohm coax.. (Capacitive or inductive reactance creating high swr)

Since you want to use coax, not open wire, try this:  Concentrate on 40M only for now. Since you have up only 50' of flat top,  add another 7.5' to each end and let the extra wire droop straight down on the ends. This will give you about 65' total and shud be a good match on 40M. Measure it to be sure it's ~65' total. Now, to fine tune the swr, simply adjust the length of these drooping ends (equally) a few inches. Ideally, you shud have an electrical 1/2 wave of coax to get a true swr reading, but let's not worry about that now. Using about 65' of center fed flattop wire should get you in the ball park on 40M with a good swr and you will start making contacts.

This 65' wire coax fed antenna will NOT work on 75M, nor will your present 50' coax fed antenna due to the very high swr and mismatch. It is also too short for 40M at present. Add the extra 7.5' to the ends and you shud be OK on 40M.   Openwire with a tuner is the best way to get a multiband antenna to work, since swr is not important with openwire.  (Other than using traps or other gimmicks for coax fed ants)

73,

Tom, K1JJ

[Steve - WB3HUZ]

No. The SWR using forward and reflected power is calculated by

SWR = (1 + SQRT(Reflected Power/Forward Power)) / (1- SQRT(Reflected Power/Forward Power))

So, in your case it boils down to 1 + SQRT (2/3) / 1- SQRT(2/3) or 9.9, if I did the math correctly.

It's not clear to me that you are actually measuring power, so your SWR could be something different.

52 Ohm SWR meter on 75 Ohm Coax giving SWR of 1.5:1.....well if the best I was seeing was a forward power of 3 and a reflected power of 2, doesn't that translate to 1.5:1?

3:2 = 1.5:1 ? Makes me wonder now, doesn't it? Could my antenna system actually then be functioning properly but it's just my loaned SWR meter that's mixing me up?

Your thoughts?

73s
geo
VE3GZB

[VE3GZB]

The SWR meter I have on loan is a QualiComp Model 120. Lou Vermond, VE3AWA, loaned it to me until I can get my own. It used to be his mom's (she was also a ham).

I tried using it the "right" way...but all of my reflected readings stayed in the Red zone where there are no numbers.

If I leave it like that, how can I possibly quantify anything I'm seeing except by scaling things down to remain in the black zone where there are numbers.

That's what I did to arrive at figures such as forward level 3, reflected level 2. Otherwise I'd just be saying "It's all in the red". Not useful information at all.

I took photos of the antenna and the general layout of the place, tried to make things a bit brighter.

[VE3GZB]

More pics...

[VE3GZB]

Still more pics...to mention about the feedpoint at the antenna....the coax doesn't have much mechanical strength at all and we get good winds at times (we had a tornado rip up the town back in 85 too!). So I had to tape the coax to the insulator to prevent the coax from breaking loose. No choice in the matter. The tape helps to prevent moisture/rain from creeping into the open coax.

It's probably not the right way, but it's what I have available to me.

K1JJ - The distance from the old TV tower to the far clothesline pole is about 50-55 feet, it's hard to measure it quite right because the darned Rubbermaid plastic toolshed is in the way, it's very heavy, slippery and we can't move it (we already tried, it's impossible to budge).

Neighbours have trees all over, branches overhang and trees absorb RF. So I can't run pure antenna all the way up to the clothesline pole, nor to the tower.

My radiating element is 45 feet long, loaded in the middle of each "arm" with (if I remember correctly) 67uH homebrew loading coil made from a pair of insulators, empty plastic solder spools and 16ga. speaker wire I scavenged, all taped up to keep direct exposure to rain lessened until I can figure out this whole thing and turn it into something better. It's ugly and I know my wife isn't nuts about it....she'd be much happier if they weren't there.

In the bottom picture "loaded_dipole" you can see the high voltage power lines that run right by our lot, we get a lot of interference from those power lines.

I don't have a lot of space to put up an antenna, and the only mount points I have are the TV tower and the far clothesline. No other.

Oddly enough, when I was still running the ugly twisted line to the feedpoint, I seemed to be able to get somewhat better SWR readings (less reflected power) after I added the loading coils. Now with Coax, it seems to be quite different.

My transmitter isn't stable enough to try to run to 20m, so I need to try to stay in 80 and hopefully 40m with what I have right now, even though I clearly don't have a long enough antenna.

[K1JJ]

Geo,

OK on using loaded coils.  That's fine.

Now, when using coax you must prune the coils to come up with a good match to the coax for a particular band.  This antenna will NOT work efficiently on more than one band at a time with coax.  Pick your favorite band and add or subtract turns on the coils until the swr is close to 1:1.   Only ONE band at a time - all the other bands will have a high swr and be UNUSABLE with coax. (except maybe 15M)

The only other solution is to use that antenna with openwire and the antenna tuner will match the transmitter to the line on ALL bands. The high swr is still there, but will not matter due to the low loss openwire.

Without adjusting the coils or flat-top length, you are spinning your wheels and will never get a good match with coax.


BTW, to support the coax, make a "pipe hitch" knot using rope around the coax and tie it to the center insulator. This uses about eight turns around the coax for a good, distributed, uniform grip.  Look up "pipe hitch knot" on Google.

T

[VE3GZB]

Hmmm.....adjusting the coils when they're already mounted would take a great deal of effort and time, so perhaps that's not the best path...I'm already tied up for time on so many other things at this time, including searching for a car, managing production at work, maintaining electronics at the farm. I was fortunate to have this much time to devote to my hobby so far but it's getting tight.

I don't have enough unmolested antenna wire left, I used everything I had up on getting this far and this antenna I have set up now, well the wire is pretty molested, spliced, just plain messy at this point (I had it set up as a Zepp before and got nowhere with it, now running it as a dipole hasn't proven to be a good choice either).

I'm not sure what you mean by using this antenna with openwire? Do you mean an untuned feedline, like a random length feedline? Or do you mean to change the whole antenna to something other than a Dipole?

Can you link to some image on the internet to show me what you refer to, so I can understand?

What about any kind of military portable transmitting antennas? I'm sure the military must have had some neat ideas back then to allow HF transmission with a piece of damp string or something? How can I begin to research this without wasting so much time chasing info I can't use?

Thanks and 73s
geo

[VE3GZB]

Pipe hitch knot?? Gee!!  I never heard of that, it looks very interesting!! I'll look into it!

But how would I protect the coax against the elements of the weather where the casing is open (to allow me to connect)?

Would RTV Silicone work if I gooped it all over the open end of the Coax?

[K1JJ]

Look up "openwire" on Google.

It's two parallel wires spaced a few inches apart that are held separated by thin ceramic, plastic, Lexan, Teflon, etc, spacers.  You can make it or buy it - the heavier wire the better. #10 wire would be ideal - #14 wire is accepatable.  You will need an antenna tuner to use it. Remember the K1JJ tuner I suggested before?

We've been thru this a few times in past threads. Please reread them.

Bottom line is unless you can adjust those loading coils for a particular band, you will never get a good match to the coax.  The openwire solution is better if you want to put it up and forget about it. I realize the XYL doesn't like openwire, but those are your only options for feeding a 45' long dipole.

T

[VE3GZB]

You mean something like this:



Well, my wife wouldn't stand for that, having some ugly transmission line draped down the middle of the antenna. She'd probably rip it down out of embarrassment to what it would do to the appearance of the yard (she loves to have a nice tidy appearance).

The appearance matters a great deal, my wife won't tolerate an ugly back yard.

Are there any other alternatives I can look at in terms of transmitting antennas which won't look like a science experiment in the backyard and which will work with Coax (since that's what I am stuck with now)?

73s
geo

[K1JJ]

Pipe hitch knot?? Gee!!  I never heard of that, it looks very interesting!! I'll look into it!

But how would I protect the coax against the elements of the weather where the casing is open (to allow me to connect)?

Would RTV Silicone work if I gooped it all over the open end of the Coax?

Yes, tape the coax real well with electrical tape so no water can enter. Then cover it well with RTV. The RTV will last for about 5 years and eventually blow off, but will keep it dry for the duration.  To keep water that DOES enter the connection  from flowing down the coax, let the last foot of coax circle up and over the center insulator and look towards the ground.  Tie the pipe hitch below the insulator with a 3" rope lead holding the coax to the insulator for support for the run to the ground.

T

[VE3GZB]

Yes, tape the coax real well with electrical tape so no water can enter. Then cover it well with RTV. The RTV will last for about 5 years and eventually blow off, but will keep it dry for the duration.  To keep water that DOES enter the connection  from flowing down the coax, let the last foot of coax circle up and over the center insulator and look towards the ground.  Tie the pipe hitch below the insulator with a 3" rope lead holding the coax to the insulator for support for the run to the ground.

T

Interesting!! I'll look into it and try it when I get more time (this week and the next couple of weeks will be impossible for me, just too much work and insurance and car stuff going on, that's why I tried to get as much done today as possible, but without any success, just spun my wheels).

[K1JJ]

You mean something like this:



Well, my wife wouldn't stand for that, having some ugly transmission line draped down the middle of the antenna. She'd probably rip it down out of embarrassment to what it would do to the appearance of the yard (she loves to have a nice tidy appearance).

The appearance matters a great deal, my wife won't tolerate an ugly back yard.

Are there any other alternatives I can look at in terms of transmitting antennas which won't look like a science experiment in the backyard and which will work with Coax (since that's what I am stuck with now)?

73s
geo

Yes, that will work - looks like a G5RV.  But might as well get rid of the 75 ohm feedline and run the openwire to the shack with an antenna tuner.



As I said, don't waste any more time playing with the swr readings for a 50' dipole fed with coax without having the ability to adjust your loading coils for a particular band match. It will not work.

Gotta hit the sack - good luck!

T

[VE3GZB]

What about loop antennas? Does anyone here use loop antennas for transmitting? At least if a loop antenna were usable here, then I could simplify so much by keeping the loop indoors, I could tidy up the antenna I have erected now just for receiving signals and that would make my wife very happy too!

Does anyone have loop antenna transmitting experience at medium power levels on 80m?

73s
geo

[WB2EMS]

I've experimented a little bit with loop antennas. Are you talking about a small transmitting loop for things in the 100 watt power level? Indoors? I'm not sure that's practical.

For a small transmitting loop to work well, it typically has to be in the range of .1-.25 wavelength circumference. For 75 meters, that's pretty large. Check out w2bri's site shown below.

Loops have strong fields close in, I'd be very wary of running 100 watts into a loop I was in the same room with. Maybe in the same house with.    100 watts is also going to require a serious capacitor, probably a vacuum variable or a homemade trombone style.

Small transmitting loops are very hi Q devices, which means they can be twitchy to tune. They also require a lot of attention to reducing any resistance, including choice of materials (copper pipe, large diameter is better) and soldering/welding to make good low resistance connections.

All in all, they are very much harder antennas to make work successfully than the dipole you are working with now. I've gotten some to work reasonably on 10 mhz and up, and have toyed with the idea of one for 75 or 40 meter mobile but the costs and complexities have stalled that project for now.

Check out the following web sites for some info on loops. w2bri has some good ideas on getting started inexpensively on 20 meters, and has an 80 meter loop that will give you a good feel for what it takes to make antenna work on that band.

http://www.standpipe.com/w2bri/
http://www.standpipe.com/w2bri/80meter.htm
http://www.aa5tb.com/loop.html
http://www.iw5edi.com/ham-radio/11/a-magnetic-loop-antenna-for-hf

Good luck in your antenna endeavors.

[ka3zlr]

There's nothing wrong with a Loop (Skywire) Use heavy enough wire an get-r-done heck I ran one with 213 coax feed on 80 and It worked with No Balun...Whoo Hoo....Put one one 40 Vetical man that thing was touchy direction wise  werked great....again heavy wire was used...build it heavy it'll work for ya...Heck I even Like the Double Bazooka, especially for receiving...of my location helps alot.

73
Jack.

[W9GT]

Hi Geo,  

Seems like a pretty frustrating situation for antennas at your location!  Something that hasn't been mentioned, but might work with your limited space is an inverted L antenna. (END FED 1/4 wave) This is a simple antenna and it is very easy to build.  Just run a total of a quarter wave length of wire (approx 60-65 Ft) up your TV tower, through an insulator and then out to the clothes pole with an insulator at the end.  Feed the ant with the center conductor of the coax to the end of the wire and the shield to a ground rod.  Install some radials to improve your ground system by laying out some 30'-60' lengths of wire on the ground and bury them by slitting the ground with a spade or edging tool, then push the wire into the ground an inch or two.  Tie one end of the radials to your ground rod.  The more radials the better, but it will work if you just have a few to start.  You can use any kind of wire for the radials, whatever you have on hand, or can salvage.  Your 72 ohm coax will work, but if you have some 52 ohm coax (enough to reach the feed point), that would be better.  You could also add a loading coil in series with the antenna at the feedpoint, with a tapped coil arrangement and find taps that would work for other bands.  Or....you already have the makings of an L or Pi antenna tuner...that would work great with this antenna.  On 40M, this would be an end fed 1/2 wave antenna and no coil would be necessary.  This antenna might also be considered by the XYL as a little less unsightly, since you wouldn't have the center feedline hanging down to contend with.  Where there's a will, there's a way!

73,  Jack, W9GT