Delta Loop 4 Meters 70 MHz

I'm thinking about building a Delta Loop antenna for the 4 meter FM band because I have limited space for antennas outside and I can't have all the bands I want, I do have some attic space where an antenna can be installed.

I did try a vertical half wave dipole cut for 70MHz and it performed like garbage I ended up taking it down as range was about 3 miles on 20 watts. I couldn't even join the local net so it wasn't worth having it. I then tried a wire 5/8 wave antenna which was better and I was able to join the local net but then it started giving a weird issue so I made a Slim Jim today but in order to use that, I'll have to take down my 2/70 antenna to put up the 4 meter antenna which I really don't want to do. The 4 meter Slim Jim antenna is too long to fit in the attic.

I was thinking a Delta Loop in the attic might be a better option and that way I can permanently have a 4 meter station setup but I'm becoming skeptical of how well a Delta Loop would perform... are Delta Loops compromise antennas?

Is it worth building for 4 meters?

Theory says a delta loop will have a bit of gain over a half wave in a couple of directions. How much gain and which directions are going to depend how and where you set it up. I have found the delta loop to be a very effective omnidirectional radiator in my loft. I have made and used them on 70cm, 2m, and 10m in the configuration I detailed in this thread:
charlietangodxgroup.forumotion.com/t5702-vertically-polarized-delta-loop-for-10m

Haven't made one for 4m yet. Let us know if you do make one and how it works for you.

By the way, if you didn't know, with slim jims and j-poles you can bend that bottom quarter wave section at up to a 90 degree angle and it will still work fine. Whilst that part may radiate something, the main purpose of it is just for matching. It's the top 1/2 wave section that's doing most of the work. Just thought I'd say so if you want to try it in your attic space you could try bending to fit.

Thanks for the info... I watched a YouTube video of a 4 meter delta loop antenna that shows how to make some of it but isn't very detailed. I've never built a delta loop before so I don't really know what the overall diameter of the antenna should be.

The top of the boom is 4.7 foot but I'm unsure of what the overall length of wire should be and whether its just one wire that shorts from center pin to braid I'm assuming it is?

If that is correct then all I really need to know next is what length the wire should be for the loop?

Edit: does 4.332 meters sound right as the total length of wire for the loop?

What polarisation do you use for 4m over there?  I assume vertical, but wanted to check.....and unlike HF, as you're talking line of sight, you don't want to lose 20dB from running differently to the other party.

A loop is fullwave, but where you feed it will change the impedance, and hence what matching you will need....I have a vertical 20m loop, matched with a stub of 75 ohm coax which works well, and will give some gain.

A coaxial dipole, double bazooka, worked well for me when I first got going on 4m.

Had it up in the loft and during Es season regularly worked into Gibraltar.
There was not much local stuff and only a few countries back then.

Double Bazooka

By me locally most use vertical pol for FM and horizontal for SSB, like other VHF bands.

What shape you make the delta and where you feed it are the main factors that effect the impedance of the feed point. If you narrow one of the angles (i.e. have 2x long sides and 1x short side) the feed point will be close to 50 ohms and you will not need a matching stub or balun, just connect the coax straight to it.

I don't know which video you watched, but this one shows a 50 ohm feed point one:
youtu.be/CZ4m4DGAexw?si=RjxWTjVz3LXKry12
This delta, although taller than it is long will be horizontally polarized.

If you turn on it's side so that it is longer than it is tall like my design, it will be vertically polarized..


I would start with a full wave length of wire, plus a bit, so you can trim it back to tune. Your calculated amount looks good for that. And yes, it is one length of wire that shorts from centre pin to braid. If it's a bit short you can always add a bit of wire like I did with electrical choc blocks..



If you want to make a different style vertical pol delta loop, the antenna design site Victor recently posted shows a different version and where you can directly put the feed point with no matching device.
portable-antennas.com/deltalp.php

I am planing on having it vertical as its going to be for FM use. My attic is quite small tho so it will just about fit any larger than that and I'll be back to square one. I have no line of sight I'm surrounded by several dense big trees with a hill one side of me and big blocks of flats on either side so I've pretty much got no signal path. 

Range tends to be limited regardless of where antennas are put whether that be outside or indoors there isn't a huge amount of difference on both RX & TX I'm probably in the worse spot for radio. Now all the leaves are falling off the trees, I am hoping my range will improve a bit.

My range on 2 meters is about 10 to 15 miles simplex 20 watts outdoor antenna. 15 miles being my drop off point and that is only in some directions, other directions I get as little as 5 miles before my signal fads into the noise

Range on 70cm simplex hasn't been tested yet but I predict it to be about 2.5 miles simplex.

I setup a horizontal antenna in my bedroom for 10 meters and local range varied between 5 & 10 miles on just 4 watts, I was heard slightly better on 20 watts but power didn't seem to boost range a whole lot. I would have gone vertical but with antenna restrictions its not possible to put a 18 foot vertical outside so horizontal was easier.

When I tested 4 meter range when I had the half wave dipole, range was very poor about 3 miles and wasn't any better when tried outside. Thankfully I have the London WebSDR to use as a range tester which gives me an idea of how well my antenna is working. When tested with the half wave 70 MHz dipole my signal on the waterfall was very faint on full power 25 watts barely visible. Nobody could hear me either.

When I got the viper 4 meter wire antenna, its a 5/8 wave with a matching section, that gave me range but it kept dropping out then coming back and making my radio do weird things while keyed up so I tried other 4 meter radios with the same issue so there is a problem with the viper antenna unfortunately but when it does work it puts a signal on the water fall of the WebSDR, not a strong one but reasonable and people can hear me so this tells me with a bit of gain on a 4 meter antenna I could have a 4 meter station going with reasonable range although not the best but good enough to make some local contacts and join a local net, it may even be good enough in lift conditions for DX.

I now built a Slim Jim hoping I can get some results from that range wise, I haven't yet tested it against the WebSDR. Its 9 foot in length so too tall for the attic even with the bottom part bent at 90 degrees it will be a very tight fit at best.

When I build the 4 meter delta loop that will be a tight fit but doable.

I tested the viper antenna again and found what was causing the strange issue... I tacked the fault to the power supply I was using to test which I have always used for years but its dropping current so something inside has become faulty the power supply was good for 10 amps so it would have been more than capable of powering a transceiver. I tested with another power supply and the issue was gone so the Viper antenna is working fine. Slim Jim also works fine but its hard to say if one works better than the other until I can make some contacts. Neither antenna will fit in the attic so I'm still going to build the Delta Loop I just need to find a bit of 75 ohm coax for the matching section and then I have everything I need to build it.

does anyone remember the electronica special that was around in the 80's

After measuring the attic space there is no way I can squeeze a Delta Loop antenna up there. I just don't have 14 foot of space I have about 9 foot length ways and just over 5 foot upwards. I will have to scrap this idea. I don't know if its possible to add coils to shorten the two antenna sides, I expect it will just make it perform lousy.

Otherwise I will have to go with a simple L shape dipole antenna with a choke and leave it as that. Range will be crap but its better than nothing and good for testing at the very least. Unless there is something better that is a "reasonable size" then this is the only solution unfortunately.

I got a 16 mile contact with the viper antenna strung up in the bedroom which surprised me, I was a clear signal but the station that heard me is high up so maybe not so surprising. Its not all lousy and disappointing, making this 16 mile contact tells me that something can be done... Its a shame the viper is just a couple of feet too long to fit in the attic otherwise that would have been a much better solution.

Well done on the 16 mile contact, that's good. That's about the distance I am getting for line of sight FM on 4m.

I think you could fit a delta in that space. If you made using my plan and if I've calculated correctly in feet, the measurements would be roughly 4'6" for the vertical wire and 5'3" for the two other wires.


skyrider Lionel, I don't remember the electronica. What style antenna was that, and was it any good?

Spider281 wrote:

Its a shame the viper is just a couple of feet too long to fit in the attic otherwise that would have been a much better solution.

 
I believe the Viper antenna is a coaxial dipole. The 1/4 wave driven element will be only 1m. You can lay the bottom section along the loft floor or in a wide circle.

Deb

VanRougeT4 wrote:

Spider281 wrote:

Its a shame the viper is just a couple of feet too long to fit in the attic otherwise that would have been a much better solution.

 
I believe the Viper antenna is a coaxial dipole. The 1/4 wave driven element will be only 1m. You can lay the bottom section along the loft floor or in a wide circle.

Deb

The one I have is the more complex 5/8 with the matching sections. Viper made a few different types.

SangueG wrote:

Well done on the 16 mile contact, that's good. That's about the distance I am getting for line of sight FM on 4m.

I think you could fit a delta in that space. If you made using my plan and if I've calculated correctly in feet, the measurements would be roughly 4'6" for the vertical wire and 5'3" for the two other wires.


skyrider Lionel, I don't remember the electronica. What style antenna was that, and was it any good?

Thanks I will follow your plan.

That is interesting that 16 miles is about the distance you get for line of sight... I wonder if I'll do the same again.

I will have to wait for conditions to get back to normal then test again. Conditions have been all over the place for weeks now so maybe it was conditions that helped my signal get out that far plus with the other station being so high up with a very good take off in my direction then I expect his station did most if not almost all of the heavy lifting. I normally really struggle with being heard on 4 meters with 20 watts. The other thing with 70MHz is that its going to get by obstructions better such as hills, buildings and trees than higher frequencies at 2/70.

Spider281 wrote:

The one I have is the more complex 5/8 with the matching sections. Viper made a few different types.

Then why not DIY one that will fit? Low angle of radiation, what's not to like? Coaxial dipoles are very simple to build, even I can do it.

Deb

EDIT to add dimensions for 70.250mhz T2LT. 

the electronica was like a silver rod with four long radials at the bottom , after i had gone out one night at the weekend my dad went on my rig (a ham international multimode 2 ) and he was talking to a guy in san francisco so it couldn't have been too bad 

skyrider wrote:

the electronica was like a silver rod with four long radials at the bottom , after i had gone out one night at the weekend my dad went on my rig (a ham international multimode 2 ) and he was talking to a guy in san francisco so it couldn't have been too bad 

I had one in am day's but it had nothing to do with a 4m delta loop.

VanRougeT4 wrote:

Spider281 wrote:

The one I have is the more complex 5/8 with the matching sections. Viper made a few different types.

Then why not DIY one that will fit? Low angle of radiation, what's not to like? Coaxial dipoles are very simple to build, even I can do it.

Deb

EDIT to add dimensions for 70.250mhz T2LT. 

I have already done this...

A halfwave dipole wont fit in the attic unless its horizontal. An L shape dipole would but they generally suck on 4 meters with zero elevation.

no totally different Alan 

skyrider wrote:

no totally different Alan 

11m antenna V 4m delta loop antenna ????.
Well both are antenna's.

Alan Pilot wrote:

skyrider wrote:

no totally different Alan 

11m antenna V 4m delta loop antenna ????.
Well both are antenna's.

The thing with 11 & 4 meters is that they are mostly used locally with verticals so having horizontal antennas is no good. I have a 11/10 meter horizontal antenna and it is rubbish but works, if it was vertical I can hear people better and people can hear me. I can't have a vertical on 11 meters where I am so a horizontal one has to do. Even though its crap locally, it might be good for DX contacts... I have heard Europe come though on it quite strong but I've not managed to make any contacts with it just yet. I figure a horizontal 11/10 meter antenna is better than no antenna at all so it will be left up.

4 meters has to be vertical because its better for local and DX but I rarely hear any DX and if it is there its often in SSB which I don't have. I only have FM which is good enough for me. FM local vertical. 

I find with vertical antennas they are better in general. Horizontal tend to be more of a compromise.