Do you want an HF antenna that performs 20~40 db better than a back stay ?

[deckofficer]

Thanks Chip, couldn't remember the name of it. Like this......
Davis RF Co. - Copperweld Wire

[ka4wja]

Bob,
Nawh, I'm just killing a few minutes waiting on some clients this morning, so no worries....

Originally Posted by deckofficer

Which would you recommend, the 200 watt SG 230 @ $500 or the 100 watt SG 237 @ $360 which tunes 6 meters along with 160 thru 10 like the SG 230?

1) Well, I'd recommend the SG-230....it will have less loss overall (probably negligible difference, but every little bit helps!), more/better tuning profiles, and will handle the 150 watts.....
And, if you need 6m, you'd be MUCH better off with a 54" whip, fed with coax, and your stern rail as a ground/counterpoise...then your backstay or 23' whip!!!


{I don't want to ramble on and on about this, so I'll be brief...
Although I'm not a design engineer, I can read a spec sheet and do real tests....so, on a side note, even if you disregard the IMD specs, your actual/true power output from the AL-500 isn't all that high compared to 100/150 watts....the transistors are spec'd at 100watts each x four transitors = 400 watts (directly off the Toshiba datasheet).....some internet sources quote 120 watts each, but at what voltage and at what IMD????

At BEST the AL-500 is about 45% - 50% eff , @14.5vdc - 15vdc, and a bit lower at 14vdc (and getting worse as the voltage drops more, with the 2SC2879 specs themselves showing 35% at 12.5vdc).....and those voltages are AT the transistor, NOT at the batteries, nor at the input terminals of the amp....
As the voltage sags it tries to pull more current...and the voltage sags more, etc....so, in actual practice, the AL-500 is a 400 watt amp....(not to mention the truly horrible IMD products produced at 12.5vdc, -24db....and even worse at lower voltages....)
And, even if you could provide it with a stiff 14.5vdc supply (if you look at the 2SC2879 data sheet) the IMD specs when driven hard (> 5 watts per transistor) will make you wonder why they ever made the AL-500....
So, if you drive it with 20 - 25 watts, and supply at least 14.5vdc (@70-75 amps) to the amp's power terminals, then you could get 400 - 450 watts out and have it be acceptable for ham radio use....(but never gonna pass any commercial / Part 80 spec!!!)

FYI, Henry Radio made a 500-600 watt mobile amp that had eight 2SC2879's and was spec'd to operate at 14vdc - 15vdc, with a drive power of 30 - 35 watts, and an output of 500 - 600 watts.....it wasn't the cleanest of amps, but very acceptable for the ham bands...although its IMD specs would not allow it to be used on any commercial/maritime service.....

Overdriving any of these low-voltage solid-state amps is a recipe for disastrous IMD....think CB amplifier....

I'm thinking that the Ameritron AL-500 "specs" were probably written by the marketing department... .....}





2) Loops, in general, are some of my favorite antennas....and the second ever antenna I built (in 1973, I think) was a 40m delta loop....(the first was a windom....and then onto verticals and yagis, etc...)

Originally Posted by deckofficer

Now on to a base antenna. What do you think of a delta loop? In keeping with SGC's recommendation of a 9' run from the tuner to radio, I figure on mounting the tuner to my balcony railing on the upstairs bedroom/radio room and center feed the delta loop which will be supported by a telescoping 50' fiberglass mast attached to the railing. The two bottom corners will be tied via egg insulators to trees about 80' apart. Using Pythagorean theorem, total wire length will be 208'. The bottom (base) will only be about 20' off the ground. The only wire I could find that is acceptable is 12 AWG, 259 strand copper wire. Do you have any sources for dipole wire of a heavier gauge?

a) First off loops (whether square, triangle/delta, rectangle, etc.) are very forgiving antennas and provide fairly easy matches on all HF freqs where the loop is one-wavelength or longer, in circumference.....they are NOT critical!!!
Make it about 250' - 270' in circum and it'll work well from 3. 30mhz....(208' should be okay..)
Any wire will work fine.....(I have a friend who used some FREE electric fence steel wire for a 40m loop...and it's been up and working good for years...)

The pattern WILL get "lobey" (lobes and nulls) as you get above 10mhz....and above 20mhz, you'll definitely be able to notice where these lobes and nulls are.....
But, it IS a cheap and easy antenna, that will work well....

You can move the feed point around to attain vertical polarization (on at least the fundamental) and get pretty decent low-angle radiation (~ 20 degrees)....and there are other things you can do with loops as well...
But, a one-wavelength around, bottom-center fed delta loop, is a good basic antenna that will work well over a wide range of freqs and allow for fairly easy matching for the tuner (meaning low tuner losses)....



b) Bottom line with antennas, you should decide:
--- where / when (time of day and time of year) you wish to communicate...
--- what bands/freqs..
--- what modes...
All before you can make specific antenna choices....

The reality is:
Most just toss up a wire and hope for the best....



c) There is NO need to have the tuner 9' away from the radio...(perhaps there is a typo in the SGC papers???)
You can have the tuner 90' away (or 190' away) and have no problems....and you could even have it right next to the radio, as long as you took precaution to protect/eliminate RF ingress into the radio, mic, speaker, etc. radiated from the antenna....

d) There are many antennas that will work well for you....and many that will outperform a single loop (such as yagi's on towers, etc.)....
But, nothing wrong with a loop as a good basic antenna...





I hope this helps...

John
s/v Annie Laurie

[deckofficer]

John,

As always it does help. I wish I could configure it where the tuner is close to one of the skybound legs for a more vertical polarization but the way the trees are in respect to my balcony I'm stuck feeding it in the center of the bottom horizontal leg. I have operated stations with the wide spaced 5 element yagi for 20 meters 85' up the tower with an 8877 final, and as much as I would like to be a big dog like that, it isn't in the cards. Over the years most all of my HF antennas have been either single band inverted vees, dual band single feed inverted vees, or multi band trapped inverted vees, one rotatable multi band trapped dipole by Cushcraft (a disappointment) and of course mobile verticals.

Of my history of antennas (excluding the borrowed station with tower and yagi), for over 1000 mile paths do you think I'll be pleased with the performance of the delta loop over all my inverted-vees that required no tuner/couplers? I can always go back to what I'm familiar with, the inverted-vee, but am willing to try something new if the performance will be better for longer distance contacts.

Thanks.

[SoonerSailor]

Bob -

Don't worry about polarization of HF signals. After hitting the ionosphere it gets twisted all around anyway, and how it comes back down is usually quite different than how it went up.

For what it is worth, I haven't used a big loop before but I have had some experience with small magnetic loops, and found the performance amazing for the size. That is what I carry for a portable and/or emergency HF antenna since it doesn't require height to work well.

Chip

[ka4wja]

Originally Posted by deckofficer

....do you think I'll be pleased with the performance of the delta loop over all my inverted-vees that required no tuner/couplers?

Yes....go with the loop....





BTW, with the exception of my moonbounce array (at about 24dbi gain) most of my antennas are/have been big HF wire antennas or homebrewed vhf/uhf yagi's/helix's/etc.....no pics of my antennas, but you can see one of my Drake TR-7's (my fav radio of all time), that I bought new in '78(??), as well as my old (but perfect!) Alpha 77, and my old Henry 2002 (1.2KW on 144mhz), on my QRZ page....all of them, Alpha, Henry, and my old SB-221 (which I built myself > 30 years ago), still have 30+ year old Eimac tubes in 'em and still output to spec....
(heck the newest things I have in the shack are a 5 year old CW keyer and and a 10-yr old filter...everything else is 30 some years old, some of it 50 years old, and 99% made in USA....)
But, at my old university club station, we had 5-ele monoband yagi's on 10m, 15m, and 20m, and a full-size 3-ele yagi on 40m....on three separate towers 70' - 90' tall...and all these towers mounted on the roofs of two 6-floor commercial buildings, right on top of the 2nd highest hill within 40-50 miles....and two full-sized 80m dipoles @ 140' - 160' high, etc. etc. running a homebrew 4-1000A amp w/ about 3kw output....our main HF rig was a TS-820....etc..etc...(we got an annual operating budget, as well as allocations for equipment purchases.....wish I had that kind of "radio allowance" now!!)





73,
John
s/v Annie Laurie

[ka4wja]

Just for clarity here, there is a BIG difference in antenna radiation angles when looking at horizontally polarized antennas, mounted low to the ground (low = < 1/2 wavelength high), vs. a vertically polarized antenna (even over "poor" / "fair" ground...)

Originally Posted by SoonerSailor

Don't worry about polarization of HF signals. After hitting the ionosphere it gets twisted all around anyway, and how it comes back down is usually quite different than how it went up.

This is what I was referring to when mentioning advantages of low-angle radiation from vertical antennas.....
As an example a horiz antenna (dipole, loop, yagi, etc.) at 1/4 wave, or less, high (loop heights are measured from the center of the loop) can be 20db+ down vs. a 1/4 wave vertical w/ a decent radial field at radiation angles of 20 degrees and below....
(although for easy of explanation, I'm leaving out some details.....with single-band full-wave loops, this is as easy to do as move the feed point....no $$$, no electricity, no tubes, etc. and you can get a real advantage...I can't promise 20db+, but on 80m dx contacts even 10db is significant!!!)




John
s/v Annie Laurie

[deckofficer]

John,

I just measured things and they are a bit different than my eyeballing it. First thing I need to be clear on is a loop type antenna doesn't require counterpoise/radial system that a vertical needs, is that right. Does it need any grounding? That, and a matching impedance is why I always like inverted-vees cut to my operating band/freq. From what I understand you telling me, a great low angle omni pattern antenna would be a ground mounted vertical as tall as possible with 100's of ground radials longer than the vertical going in all directions from the base where the tuner would be mounted? That isn't feasible for me, but if the delta loop requires no ground or counterpoise that is very doable and easy with existing trees and my 2nd floor balcony. Center of the loop (triangle) will be 40' off the ground. This leg I'll call the base leg is 168' long and has to come inward toward the balcony about 10' to meet the tuner on the railing in the center of that 168' run. The distance from the base leg to the tip of the triangle is 45', so dimensions are, base leg 168', top has two 96' legs to the base. Total wire 360'. If major lobes (radiation pattern) is off the ends of this antenna, that would be good as its ends point NW & SE, SE being good for me in Northern California into the Caribbean where a lot of my cruising friends are.

Can you visualize this antenna and how do you think it will play vs an inverted vee and the mentioned hot vertical with lots of radials. I hope better than the inverted vee.

Thanks once again.

[ka4wja]

My enthusiasm took over, and misstated some numbers....sorry about that...

Originally Posted by ka4wja

...a horiz antenna (dipole, loop, yagi, etc.) at 1/4 wave, or less, high (loop heights are measured from the center of the loop) can be 20db down vs. a 1/4 wave vertical w/ a decent radial field at radiation angles of 20 degrees and below....
(although for easy of explanation, I'm leaving out some details.....with single-band full-wave loops, this is as easy to do as move the feed point....no $$$, no electricity, no tubes, etc. and you can get a real advantage...I can't promise 20db+, but on 80m dx contacts even 10db is significant!!!)

Change the "20db" reference to 10db...and change the "10db" reference to about 5db, and this is accurate...

Sorry about that...



John
s/v Annie Laurie

[deckofficer]

Originally Posted by ka4wja

My enthusiasm took over, and misstated some numbers....sorry about that...
Change the "20db" reference to 10db...and change the "10db" reference to about 5db, and this is accurate...

Sorry about that...



John
s/v Annie Laurie

That's OK, this entire thread was predicated on my misplaced enthusiasm as to why my halyard supported inverted vee did so well in the Sea of Cortez into Southern California until you and Bill set me straight as to why I was good on a single short hop. Now I want to be good on a 2000 mile hop and your pointing the way for me.

[ka4wja]

Bob,
In brief:
a) for multiband use, loop dimensions are NOT critical....although keeping it one wavelength or so in circum. on your lowest freq is a good design point....(but again, this is NOT critical...+/- 0.1 to 0.2 wavelengths is fine....)

b) even "random length loops" will work well....although predicting their patterns, etc. is difficult...

c) large loops (~ one wavelength), by their very nature are "ground independent", and need NO counterpoise / ground at all....
(although many are led to understand this easily about horz loops, it IS true no matter what the polarization (or orientation) of the large loop....

d) using a remote tuner with a loop, is as simple as connecting one end to the "antenna stud" on the top of the tuner and the other end to the "ground lug" of the tuner....

e) Loops generally have much lower feed impedances on harmonic freqs, than dipoles/doublets do....and they present a much easier load for the tuner to match to....


f) Low angle of radiation using verticals IS possible, but on middle to high HF freqs, the angles of radiation from horizontal antennas mounted 1/2-wave to 1-wave above ground (such as yagi's on towers) is typically as low as you would get from even the best vertical/radial system, and the GAIN attained by these antennas (yagi's on towers) vs. the vertical is SIGNIFICANT!!! (~10db+)
BUT...
But, once you're operating at freqs low enough that you cannot get a horiz antenna high enough, then the vertical antenna is going to be the choice for long-range comms....and on 80m, a good vertical/radial system can outperform a dipole at 50' - 60', by as much as 10db or more....remember getting a horiz antenna up a 1/2-wave high on 80m, means getting it 130' - 140' high!!!
{I've made many comparisons between my own 80m horiz loop (at about 60' high) vs. my vertically polarized 80m rectangular loop (side-fed) at 10' to 50' high.....over paths to/from UK/EU (5000 miles or so) and Florida....and paths to/from Aus/NZ (8000 - 11,000 miles), and have consistently found my vert-pol rect loop to be 15-20db better.....(although my horiz loop is about 10-15-20db better around Florida, using NVIS..)...}





g) This very reason is one of the biggest reasons that vertically-polarized loops have caught on....I can fit one (and one horiz loop as well) on my city lot....

Originally Posted by deckofficer

...a ground mounted vertical as tall as possible with 100's of ground radials longer than the vertical going in all directions from the base where the tuner would be mounted? That isn't feasible for me, but if the delta loop requires no ground or counterpoise that is very doable and easy with existing trees......

h) Dimensions and exact shape are NOT critical....with multiband loops, used over a wide range of freqs, you'll have various patterns (lobes and nulls) that you'll just deal with, as where/how theantenna is run/installed is going to be mostly determined by what you have to support it!!!
But, you do not need to use all the space you have, use rope/line to support the loop.....and making its length (in feet) about 1005 / (lowest freq of operation), will give you a great antenna....(say about 270 feet, for use from 3.5mhz to 30mhz....360' is a bit big, but would be good if you're looking for 160m operation...)

Originally Posted by deckofficer

.....Center of the loop (triangle) will be 40' off the ground. This leg I'll call the base leg is 168' long and has to come inward toward the balcony about 10' to meet the tuner on the railing in the center of that 168' run. The distance from the base leg to the tip of the triangle is 45', so dimensions are, base leg 168', top has two 96' legs to the base. Total wire 360'.

i) Don't sweat the pattern....it'll be what it'll be....

Originally Posted by deckofficer

If major lobes (radiation pattern) is off the ends of this antenna, that would be good as its ends point NW & SE, SE being good for me in Northern California into the Caribbean where a lot of my cruising friends are.
Can you visualize this antenna and how do you think it will play vs an inverted vee and the mentioned hot vertical with lots of radials. I hope better than the inverted vee..

Sorry, I don't have the time to design an antenna for ya'....

But, in general, when bottom-fed (as you described) on the loop's fundamental (where it is one wavelength around), it will be a broadside radiating antenna, just like a dipole....
As you move up in freq, the patterns change....going to figure-8's and clover-leafs (actually more like "smooth angel wings" than clover-leafs), and then getting very "lobey" on 15m/12m/10m....
Reading some of L.B.'s articles and looking at his models will give you more info than you'll probably want....



I hope this helps...

John
s/v Annie Laurie

[deckofficer]

Thanks again John, I'm ordering parts now and the SG 230. I had bookmarked awhile back a company called Wonderpole that had a stout 50' telescoping fiberglass pole in just 8 sections for $250. They no longer have that pole, largest is a 40' in 6 sections for $350. My triangle shaped loop already has a base leg 80% longer than the two top legs so I don't want to lose 10' of height with that 40' pole. I have found a 60' telescoping fiberglass pole but its nested height is so short that it uses 12 sections, so a bit more flexible with the smaller diameter top sections. It runs $300.

When you say...
c) large loops (~ one wavelength), by their very nature are "ground independent", and need NO counterpoise / ground at all....

Your counting total wire used? So for 75 meters, 244' of wire would be one wavelength, so I'm good with 360'?

[deckofficer]

Here I go again. After finding out the 50' telescoping fiberglass mast is no longer available and others are a bit of a wet noodle due to wall thickness and too many sections because their nested height is short, I'm rethinking a vertical with radials. I live on the eastern side of a ridge in the Sierra foothills. A ground mounted vertical would have a totally blocked view to the west due to my 2 story home and the higher ridge line to my west. One idea would be to mount a 32.5' telescoping fiberglass mast on the crown of the roof in the center with a wire inside it. This placement would allow (8) 36' radials in a 360 degree pattern. These radials would slope downward which might help pulling the radiation pattern closer to the horizon. The best feature of using the crown of the roof is the vertical will see a 360 degree unobstructed view. 32.5' just happens to be a 1/4 wavelength for the middle of the General phone band on 40 meters if I still remember how to calculate. 468 / freq in mhz / 2. My goal is a better long range antenna over the inverted vees I've always used, you and others have told me a vertical is a better low angle radiator. I've also heard the verticals are more prone to man made noise.

John, will a vertical that I've described above in the open setting that is offered by high roof mounting, along with the SG 230 be about the best I can do short of yagis and towers for 20, 40, and 75? I guess since it is a resonant 1/4 wavelength for 40, it should perform good on that band and the auto-tuner will let it work well enough on 75?

[olaf hart]

Can I interrupt this interesting conversation for a minute?
I am sorting out an SSB setup in a 36' boat. The old installation had a manual tuner at the Nav Station and good thick copper strap to the keel bolts, and an external lead keel.
The new one has an automatic tuner (sg239) in a waterproof case, which I want to put high in the lazarette at the base of the back stay antenna.
How important is it to run new copper strap back to the existing strap? The distance is about 15'. Would wire do the job just as well?
Or should I put the tuner at the nav station like the old manual one?

[deckofficer]

olaf, I was waiting for someone better qualified than me to answer, but if nothing else this will bump the thread for a better chance of response. I've always used resonant antennas so my experience with tuners are on other stations or ships that I have served on. Your SG 239 is best suited to operate in a protected area and as close as possible to the antenna. I wouldn't put it in the nav station as that defeats to a degree the advantage of an automatic antenna coupler. On tying back into your boat's ground counterpoise, a copper strap is probably better, but heavy cable should work also. Stay tuned to this thread for Bill or John, they know RF better than most.

[btrayfors]

Originally Posted by mctdog

Do you have a updated link to Marine Antennas (Marine Antennas I get an error with this page? Could someone send me the link to the Alternative Backstay antenna instructions?

The good news is that my website is back up, including info on various marine antennas.

You can access it here: Bill's Marine Pix

Bill
WA6CCA