80M with a 'too small' antenna

[N4AOF]

I'm a long time ham, but haven't had an HF station of my own -- I'm thinking about putting together an HF station and I've got what I expect is a common problem: not enough space.

Certainly not enough room for a full size dipole for 80M.

I might be able to fit a G5RV or similar size antenna on my lot, but a half-size G5RV would be a much better fit.

Most internal antenna tuners aren't rated to handle more than a 3:1 mismatch, but there are several reasonably priced tuners that are supposed to handle a greater impedance mismatch. I'm wondering if it would be practical to use a "mini"-G5RV or other short antenna that way.

Comments or alternative suggestions are welcome.

 

[jwt873]

Are you only interested in 80 meters?

With traps and coils, you can make a shorter dipole for 80 that doesn't need much of a tuner to match. MFJ has a 40/80 meter dipole that's only 84 feet long.. Deployed as an inverted V it won't take up that much room. MFJ Enterprises Inc. But if you're in to building your own antennas, there are plans for loading coils & traps on the net.

If space is really a premium, you can also go vertical... But then you have to start messing around with radials and such. But it is an option.

 

[rfradioconsult]

As a beginner stay away from a HF vertical, you will be disappointed in its performance. Measure you available space and determine how long you can put up either a dipole or inverted vee. Cut your antenna to fit your space, feed it with 450 Ohm ladder line to the exterior wall of your shack, terminate on a 4:1 balun, then run a short run of good RG-8 coax inside and connect to a good mid-priced tuner. Connect to your radio and enjoy the HF bands. You should be able to operate on several different bands with good results. Add a good lightning arrestor to the coax run outside and connect it to a solid ground connection.

 

[AK9R]

Or, don't cut your antenna to fit the space. My lot is 90 feet wide and I have an 80m inverted-V dipole running across the width of the lot. I "bent" the ends to follow the lot line in order to make it fit. Viewed from above, my antenna looks like a wide U. I'm feeding the antenna with coax. I trimmed the antenna so it was resonant at 3900 kHz, but the tuners in my Icom radios and my LDG external tuner will tune it down to 3650 kHz for digital work.

 

[prcguy]

If you run the numbers on a shortened dipole compared to a full size you will find a dipole around 70% of a full size half wave will be within 1dB of a full size half wave dipole. Shorter than that and the efficiency starts dropping off rapidly. This is for the antenna only and does not take into account any feedline loss.

The full size G5RV and its cousin the ZS6BKW both fit within the 70 something % rule and work well on 80m, if you use a short and very low loss feedline. A G5RV is designed for 20m and has a horrible match everywhere else but the ZS6BKW is a modern computer designed version that has a good match on 40, 20, 17, 12, 10 and 6m. Its a better choice since it operates with low VSWR on 6 bands where a G5RV can incur more loss due to the coax feedline operating under very high VSWR conditions. Plus the ZS6BKW is a little shorter at around 93ft long. I ran a ZS6BKW for many years and was very happy with it.

The mini G5RV is basically a 10m version of a full size at 51ft long and reaches that 70% rule on 40m, so 80m is very difficult to match and the efficiency is way down. However there was a local guy here who ran a 50ft dipole fed with 600 ohm open wire line to a modified Johnson 1kW matchbox for wider tuning range. He put out a very respectable signal on 80m but he had eliminated any feedline loss using the 600 ohm line and tuneup was a bit tricky.

You can also put up a dipole that fits your property and feed it with 450 or 600 ohm balanced line as mentioned to preferably a balanced tuner and if you transition to a coax tuner use a very good 1:1 choke balun and not a 4:1 as mentioned. On an antenna like this the feedpoint impedance is all over the map and could be a few ohms or a few thousand ohms. A 1:1 choke balun will work better across the entire range where a 4:1 would incur more loss at low impedance points and the goal is to isolate the unbalanced tuner from the balanced feedline and force a balance with the 1:1 choke balun.

1:1 baluns are not created equally and they range from useless to really good with some junk costing more than the good ones, so if you go that route there is another conversation to bring up.
prcguy

I'm a long time ham, but haven't had an HF station of my own -- I'm thinking about putting together an HF station and I've got what I expect is a common problem: not enough space.

Certainly not enough room for a full size dipole for 80M.

I might be able to fit a G5RV or similar size antenna on my lot, but a half-size G5RV would be a much better fit.

Most internal antenna tuners aren't rated to handle more than a 3:1 mismatch, but there are several reasonably priced tuners that are supposed to handle a greater impedance mismatch. I'm wondering if it would be practical to use a "mini"-G5RV or other short antenna that way.

Comments or alternative suggestions are welcome.

 

[N4AOF]

Are you only interested in 80 meters?

Not ONLY 75/80, but definitely not just 20 & up.

The local HF nets are mostly there, so I'd at least want to be able to get on the band.

If space is really a premium, you can also go vertical... But then you have to start messing around with radials and such. But it is an option.

Multiband verticals are an even bigger pain than multiband dipoles and the various derivatives. With kids and pets, my mounting options for a vertical aren't great.

 

[N4AOF]

A G5RV is designed for 20m and has a horrible match everywhere else but the ZS6BKW is a modern computer designed version that has a good match on 40, 20, 17, 12, 10 and 6m. Its a better choice since it operates with low VSWR on 6 bands where a G5RV can incur more loss due to the coax feedline operating under very high VSWR conditions. Plus the ZS6BKW is a little shorter at around 93ft long. I ran a ZS6BKW for many years and was very happy with it.

I'll take a look at the ZS6BKW.

I knew the G5RV wasn't a great match (or even a good match) but it was the one shortened compromise that I was at least somewhat familiar with -- and it almost fits on my lot

The mini G5RV is basically a 10m version of a full size at 51ft long and reaches that 70% rule on 40m, so 80m is very difficult to match and the efficiency is way down.

That's pretty much what I expected, even though I was hoping otherwise.

However there was a local guy here who ran a 50ft dipole fed with 600 ohm open wire line to a modified Johnson 1kW matchbox for wider tuning range. He put out a very respectable signal on 80m but he had eliminated any feedline loss using the 600 ohm line and tuneup was a bit tricky.

I wonder how well any of the better auto tuners would do with a short non-resonant dipole

You can also put up a dipole that fits your property and feed it with 450 or 600 ohm balanced line as mentioned to preferably a balanced tuner and if you transition to a coax tuner use a very good 1:1 choke balun and not a 4:1 as mentioned. On an antenna like this the feedpoint impedance is all over the map and could be a few ohms or a few thousand ohms. A 1:1 choke balun will work better across the entire range where a 4:1 would incur more loss at low impedance points and the goal is to isolate the unbalanced tuner from the balanced feedline and force a balance with the 1:1 choke balun.

Many years ago, when I put up a 40' tower for my VHF antenna, I did erect a fit-the-yard dipole with 600 ohm balanced feed line - but the other stuff happened and I never got an HF station set up to use it. Time, plus air pollution and a few storms took that antenna down quite a while ago. I'm neither as athletic nor as agile as I once was, so I'm hoping that by now a low maintenance and somewhat simpler solution might be available.

1:1 baluns are not created equally and they range from useless to really good with some junk costing more than the good ones, so if you go that route there is another conversation to bring up. prcguy

Not-Created-Equal is true across almost everything, and certainly all ham gear. That's why I'm picking the brains of the guys who have been actually using this stuff rather than reading what the marketing and sales guys say about their "great" stuff.

 

[SCPD]

A 75 metre antenna?.... I love it!
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Anyone familiar with my posts knows I am a great fan of ground mounted verticals.
They can be constructed simply, they are very efficient, and don't take up much space. The following is an example of one I use at home, with some of its pro's and con's.
Its a ground mount, on a 3" diameter iron pipe ~6 feet deep. The insulator is a section of industrial plastic pipe separating it from the radiator, which begins about 18" above ground. There are about 20 radials streaming off the base, buried an inch or two- varying between 12 to 18 feet in length-- the radiator is about 20 feet high, an un-guyed 2" irrigation pipe couple thru an Icom marine band auto tuner, which gives me an in-station SWR of better than 1.2:1 across 1.8 to 30 Mhz's (the efficiency, of course, will vary across said frequencies for obvious reasons.... but its got a great SWR.)
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How good does it work?? Well, I don't chase DX, but with an Alaskan callsign I am often mistaken for being in Alaska - I get called by some rare DX often*. With this antenna I can talk to virtually anyone I can hear with 100 watts. I have another, similar antenna for 160-- a longer radiator, longer radials-- and a heftier manual tuner (kilowatt)- manually set to one frequency---- on this band I don't often QSY-- this, I use on 160 (though not very often anymore.... )
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The Pro's? -- these antenna's have low angles of vertical(!) radiation. This is especially important on 160 and 80/75. At the height's ham string wire antennas, most of the radiation angles will be very high-- as in NVIS-- on these two bands. On 160 these wires might as well be called Dummy Loads.
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Okay, I can hear the grumblings .... ...... but Hey Guys!... this is my experience- ham and professionally.
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Another plus?... these things are sturdy. They don't blow down, they don't get taken down easily by trees,... they don't have coax dangling from centre fed insulators to ensare the innocent ,... you don't have to cut-and-try ...endlessly... them into resonance like a dipole...., ground mounted they offer some degree of better lightning/static protection,... they have a small 'foot print,'.... did I mention their low angle of +vertical+ radiation?..so essential on 75/80 and 160??...Oh, good,-- I did.
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The Negatives? Did I mention the low angle of radiation?.. well, not a good thing if you are surrounded by anything looming over 6 or degrees in the near field (as in: Mountains.) But in the 1.5 to 4 Mhz, the vertical ground wave and higher incidence of incoming sky wave make this less important than if it were 10-30Mhz.
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Want something simple to try?... get a Hustler mobile 75 meter resonator; then by cleverness, adapt it to the end of a 12 foot aluminum 'painter's pole" from Home Depot. Make an insulated base,... string out the best array of counterpoise you can get away with... feed it with coax (72 Ohm's will do- 50 is even better)... on low power resonate the coil-- you will have to shorten that upper whip above that coil...... and see how great That works on 75.... and then tell me about it....
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Regardless of what you decide on, have fun with it all, N4AOF... !
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........................................................CF
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____________________________________________________
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maybe its also the female voice?? or so I have been told....

 

[ka9ucn]

inverted L?
joe ka9ucn

 

[jwt873]

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Want something simple to try?... get a Hustler mobile 75 meter resonator; then by cleverness, adapt it to the end of a 12 foot aluminum 'painter's pole" from Home Depot. Make an insulated base,...

I run the Hustler system on my car. I have their 56 inch mast and I screw a 75 meter resonator on top of that. In the mornings when the band is in decent condition I talk to friends up to 300 miles away.

Because of the size, they are horribly inefficient.. (Probably radiating around 10 Watts with 100 Watts in), and they're very tight. You can't go much off the resonant frequency (about +/- 10 Khz).

But they do work

 

[wyShack]

If you are planning on local nets, I would not go the vertical route. The low angle of radiation will work against you for contacts out to about 300 miles ( "local" area for hams). The principle mode for communication in this range is NVIS and is best with high angles of radiation-sometimes known as 'cloud warmers'.

Many years back I used a vertical for 75 meter phone and often needed a relay into the statewide net. Now I use a random wire (about 67 feet) and a tuner and do just fine.

Remember to consider what you are trying to do-often a good DX antenna is poor for shorter range where you want continuous coverage which means overlapping 'skip' zones.

Just my two cents --

73

 

[wb6uqa]

short ant. for 80 meters

I like the W5GI antenna for 10- 80 meters. It is 100 feet long. Has 6 db gain on 20 meters and works very well on 80 meters.

 

[N4AOF]

If you are planning on local nets, I would not go the vertical route. The low angle of radiation will work against you for contacts out to about 300 miles ( "local" area for hams). The principle mode for communication in this range is NVIS and is best with high angles of radiation-sometimes known as 'cloud warmers'.

Many years back I used a vertical for 75 meter phone and often needed a relay into the statewide net. Now I use a random wire (about 67 feet) and a tuner and do just fine.

Remember to consider what you are trying to do-often a good DX antenna is poor for shorter range where you want continuous coverage which means overlapping 'skip' zones.

Just my two cents --

73

And a very valuable two cents it is.

The low angle radiation of a vertical is a major negative for me - as you point out, getting into state-level nets is accomplished primarily on groundwave and NVIS, low angle radiation is great for DX but not for 100-300 miles.

Another drawback to a vertical is the need for radials, and the need for those radials to be all the way around the antenna for omnidirectional performance. Although my yard is too small for a full size dipole on 80, it would be at least as hard to find a good place to put a vertical and its radials while keeping them all away from kids and pets.

As CF mentioned, a vertical CAN BE simple and sturdy -- but both of those are generally characteristics of a single-band vertical. Although I have been talking about wanting to be able to get on 75/80, that has been mostly because that is where the size of the yard presents a problem that I was looking for ideas to solve.

 

[gonefishn1]

How about a Tarheel antenna?

 

[prcguy]

+1 on the vertical not being a good choice if regional comms are needed. At a remote HF station I have a ZS6BKW at around 25ft and a 43ft vertical with about 33 radials 30ft long each over a wet marsh connected to the same radio. When I listen to regional nets on 40 and 80m many stations just go away on the vertical and all are louder on the horizontal wire antenna.

A vertical can be better for DX but it depends on the antenna. In my case the 43ft vertical with good ground system and an auto tuner at the base does outperform the low horizontal dipole on 40, 30 and 20m DX. However, the low horizontal dipole kicks it butt on 80m DX and 17m through 10m for not only local regional comms but also for DX. I often run propagation tests on all bands day and night between the horizontal dipole and 43ft vertical from my home near Los Angeles to the remote station near Boston and its quite revealing.

A 43ft tall antenna is getting fairly large but not large enough to be more efficient on 80m than a large but low cloud burner dipole. You would probably have to go with a full length 80m 1/4 wave vertical or about 65ft tall to get a vertical to outperform a low dipole on 80m DX. And you would still have lousy regional comms in the 75 to couple hundred mile range.

If you consider some of the other suggestions of using a 20ft vertical or Hustler mobile whip, Tarheel mobile screwdriver, etc, the difference between them on 80m compared to a low dipole can be as dramatic as having a great signal on the low dipole and you don't exist on the short mobile antennas.

In my experience a multiband dipole like a G5RV, ZS6BKW, offset center fed 80m dipole, 80m end fed half wave (64:1 transformer type), etc, will get you on the air on all HF bands easier and cheaper than any vertical and with better overall performance including DX.
prcguy

And a very valuable two cents it is.

The low angle radiation of a vertical is a major negative for me - as you point out, getting into state-level nets is accomplished primarily on groundwave and NVIS, low angle radiation is great for DX but not for 100-300 miles.

Another drawback to a vertical is the need for radials, and the need for those radials to be all the way around the antenna for omnidirectional performance. Although my yard is too small for a full size dipole on 80, it would be at least as hard to find a good place to put a vertical and its radials while keeping them all away from kids and pets.

As CF mentioned, a vertical CAN BE simple and sturdy -- but both of those are generally characteristics of a single-band vertical. Although I have been talking about wanting to be able to get on 75/80, that has been mostly because that is where the size of the yard presents a problem that I was looking for ideas to solve.

 

[SCPD]

WyShak makes a good point- select your antenna design on what you want it to do. NVIS antennas are popular with the military and government... we use them frequently at remote site to communicate in a the 200-600 mile radius. A low height, horizontal terminated long wire is extremely easy to set up... needs no tuner, and I know I can talk to anything with 100 Watts within that circle on 8Mhz (I love 8 for this-- it is the ideal band for daytime NVIS, 5 Mhz at night...40/75 mtr's are much the same.) Most hams, though, don't realize that the majority of their low horizontal antennas are operating +primarily+ as NVIS when it comes to the 3 - 7 Mhz range.
I know, believe me, -- when conditions are right they 'work the world'- but as a physicist I have trouble seeing beyond the science... usually

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I say, Usually.....
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Anecdote ---- Were any of you there in the wee days of the opening of the 60 metre band for the US? I was-- I was living in Washington DC at the time. I wanted to see what this new band was all about, so I strung up one of my favorite NVIS terminated longwires, about 60 feet in length, about 10 feet high- oriented East-West. I thought the "DX Frequency" of 5.403 would be impossible to use- that all the US hams in the Eastern US would be trying to contact the UK..... but the night I took to the band-- Nothing! Just mild static crashes-
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"Is something wrong?" I thought.
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But I tried a short "Is anyone out there? (I don't use the call CQ very often)
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And to my pleaasnt shock, a GI3 in Northern Ireland came back to me!
A G3 in London joined in, and we had a pleasant roundrobin for quite some time. When I remarked about the poor antenna I was using, the GI3 remarked....
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"Aye, Lass, the Fae's* are a-playing a good with ya' tonight"
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And I will always remember that comment-- when one of my antenna designs works better than anything the design says it should- I thank the Fairies....
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Ah, but now I have to get back to work- maybe this, to be continued at another time...........?
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..........................CF
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____________________________________
*Faires
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[prcguy]

I was playing on 60m from day one and had a very unusual contact a couple years later. At my work I had a 165ft long T2FD antenna about 30ft high and horizontal. Its got a great match everywhere but its not known as a high performing antenna on any band. The radio was a commercial Harris RF-3200.

One day a little after lunch time on the US west coast I was scanning through some pre programmed channels and heard a very faint conversation on 60m 5.3715MHz and when the stations cleared I called the odd callsign that ended in 3FF. Turns out it was Budd from the Buddipole company on his bicycle mobile on one of the Caribbean Islands, St Kits I believe, and we had a brief but definite two way contact from Southern California to the Caribbean Islands on 60m.

Budd's usual call is W3FF and he had procured a similar callsign for his Caribbean trip and I think he was using an FT-857 on his bicycle with a short loaded Buddistick. That should have been an impossible contact on 60m, especially that time of day and my antenna was essentially a cloud burner with poor low angle properties on 5MHz. After that contact the 60m band was dead as usual that time of day. I will always be in awe of the surprising contacts you can make with a low horizontal dipole.
prcguy

WyShak makes a good point- select your antenna design on what you want it to do. NVIS antennas are popular with the military and government... we use them frequently at remote site to communicate in a the 200-600 mile radius. A low height, horizontal terminated long wire is extremely easy to set up... needs no tuner, and I know I can talk to anything with 100 Watts within that circle on 8Mhz (I love 8 for this-- it is the ideal band for daytime NVIS, 5 Mhz at night...40/75 mtr's are much the same.) Most hams, though, don't realize that the majority of their low horizontal antennas are operating +primarily+ as NVIS when it comes to the 3 - 7 Mhz range.
I know, believe me, -- when conditions are right they 'work the world'- but as a physicist I have trouble seeing beyond the science... usually

.
I say, Usually.....
.
Anecdote ---- Were any of you there in the wee days of the opening of the 60 metre band for the US? I was-- I was living in Washington DC at the time. I wanted to see what this new band was all about, so I strung up one of my favorite NVIS terminated longwires, about 60 feet in length, about 10 feet high- oriented East-West. I thought the "DX Frequency" of 5.403 would be impossible to use- that all the US hams in the Eastern US would be trying to contact the UK..... but the night I took to the band-- Nothing! Just mild static crashes-
.
"Is something wrong?" I thought.
.
But I tried a short "Is anyone out there? (I don't use the call CQ very often)
.
And to my pleaasnt shock, a GI3 in Northern Ireland came back to me!
A G3 in London joined in, and we had a pleasant roundrobin for quite some time. When I remarked about the poor antenna I was using, the GI3 remarked....
.
"Aye, Lass, the Fae's* are a-playing a good with ya' tonight"
.
And I will always remember that comment-- when one of my antenna designs works better than anything the design says it should- I thank the Fairies....
.
Ah, but now I have to get back to work- maybe this, to be continued at another time...........?
.
..........................CF
.
____________________________________
*Faires
.