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Discones


#1

Hi all
I know I occasionally post with antenna questions but I hope no one is to weary of them yet!
Is a discone any good? A wideband transmit discone will do 50,2 and 70cms. I have read that whilst good for receiving they radiate poorly in all directions. Is this correct? Does anyone have any experience with a discone? I currently only have a 2mt colinear in use for vhf. If I swapped it for the discone I would get two extra bands to play with. However how much of a difference will I notice on 2mts? Would the discone give a better horizontal coverage for ssb/cw than the colinear, or will it just be worse all round?
I am desperate to get out better on 2mt ssb/cw and am still trying to figure out the best route. Bearing in mind my disabilities prevent me from climbing any ladders and also limitations on what I dare attach to the side of my house! I know that ideally a beam and rotator is the answer but financially it is not currently an option.
Any opinions?
Cheers
Q GW3BV


#2

Hi Quentin,

My personal opinion is that they are are complete waste of time - full stop.
Having played with several over the years, my dual band co-linear has outperformed all of them every time by a considerable margin, both on RX & TX.

I too would be interested to hear how others have found them.

73, Mike G4BLH


#3

In reply to GW3BV:

Hi Quentin

Whilst it may not help so much with the ssb/cw I use the Watson 2000 co-linear which covers all three bands. I have used it for ssb/cw with some results.

73 Glyn


#4

In reply to GW3BV:

I would suggest a halo. Whilst not comparable to a beam/rotator combo, they at least are horizontally polarised and omni-directional.

I have one, whilst not perfect, is better than nothing. A 2m one is fairly small too.

Ian
G7ADF


#5

In reply to GW3BV:

Hi Quentin,

As a compromise wide range receive antenna discones undoubtedly have
a place - for example for scanner use. The vast majority of VHF/UHF
signals are vertically polarised, and despite its appearance the
discone is vertically polarised which will suit this application,
but I doubt it would work even as well as a dedicated vertical
dipole, and certainly notnothing like as well as a colinear. As others
have stated, the smallest omnidirectional antenna is probably the halo.
I have heard that concentric nests of halos have been tried as a multiband option, but I have no idea of the results. What is certain is that in
a given direction a horizontal dipole will outperform a halo, so a switchable combination of dipoles and/or a halo might be an option.

Happy New Year

73
Dave G0ELJ


#6

In reply to GW3BV:
Hi all Happy Christmas, I have just bought one for the new scanner when and when it arrives i will give it ago and let you know.
regards Nigel


#7

In reply to 2E0HJD:
Actually Mick an aluminium or Steel kettle would fair slightly worse due to skin effect. A copper one however would be about 10db better (IMHO) :wink:
Back to wine hic…

Roger G4OWG


#8

In reply to GW3BV:
The discone will in theory operate over a 10:1 frequency range but it has a number of disadvantages. The loss relative to a dipole has been mentioned already, but in addition the SWR deteriorates sharply at the lowest frequency, and a more subtle problem is that after the first octave the radiation angle starts to rise above the horizontal which makes it useful only for local work.

The vertical polarisation of the discone is OK for FM but since the convention for SSB is horizontal polarisation you can expect a theoretically infinite cross-polarisation loss, which in practise is 20 to 30 dB - although I have noticed a few misguided activators using vertical polarisation for SSB recently! Misguided because vertical polarisation is less effective for weak signal work and there is no point in using SSB unless you are interested in weak signal work!

The halo is horizontally polarised but it has a loss of, if I remember correctly, about 3dB relative to a dipole so although it is compact it is best suited to local work, and relatively few people use horizontal polarisation for local work. Its heyday was the 60’s before the repeater network was dreamed of!

A really effective omnidirectional antenna for horizontal polarisation is the turnstile, consisting of a pair of dipoles crossed at 90 degrees but with one dipole fed with a 90 degree phase difference. This has a roughly square radiation pattern with a gain of about 1 dB at the corners: a pair mounted one above the other would have a gain of about 4 dB at the corners. This is a simple antenna to make, it could even be contrived with wire taped to bamboo garden sticks. The quarter wave (90 degree) phasing is achieved with a length of coax but you need to know and correct for the velocity factor.

I hope this helps!

73

Brian G8ADD


#9

In reply to GW3BV:
Hi Quentin

I would seriously suggest thinking about a pair of stacked halos.

Horizontal polarised for SSB/CW and relatively cheap (2m halos are £15 each at Moonraker), and a shade under 3 dB gain in all directions with just one pole with no rotator to worry about.

Have a look at this link for Callum’s experience:

http://www.mccormick.uk.com/stacked-halos/index.html

GL 73 Marc GØAZS


#10

In reply to G8ADD:

I’m not sure that vertical ssb is misguided. Its about stacking the odds in your favour. There are many more chasers with 2m co-linears than horizontal beams (or whatever).

SOTA is not about DX really, although its nice when you get it.

Is vertical polarization worse for weak signal due to the lack or directivity of the most simple antennas. When your on a hill and have managed to get some shelter from the wind and rain,the last thing you want is to keep getting up to turn the beam.

In essence vertical ssb should be more practical for activators than horizontal.

Sorry for hi-jacking the thread.

Ian
G7ADF


#11

In reply to G0AZS:
The 3 dB gain in all directions of a stacked pair of halos can only be relative to a single halo, but as I point out above, a halo has a LOSS relative to a horizontal dipole. The gain of a stacked pair of halos should bring them to approximate equivalence to a single turnstile. Stacking a pair of turnstiles in the same way will give you a 3 dB better performance, about equivalent to an HB9CV in the direction it is beaming. Add the fact that a turnsile stack can be easily constructed for just a few pounds, against a cost of £36.90 for the Moonraker halos, and I know what my choice would be!

73

Brian G8ADD


#12

In reply to G7ADF:

Is vertical polarization worse for weak signal due to the lack or directivity
of the most simple antennas.

It’s worse for vertical polarisation in general. Hence the use of horizontal polarisation for weak signal work.

Moonraker? Not a company I would give business too. Your mileage may vary!

Andy
MM0FMF


#13

In reply to G7ADF:

Hi, Ian, were you one of the vertical SSB activators? I didn’t keep my notes.

A couple of days before Xmas I heard one of the Brum mafia calling an SSB portable which was so weak I could not resolve the signal, from the end of the contact that I could hear it turned out to be an activation of one of the highest peaks in Snowdonia, a peak from which I expect the average signal here to be at least S7. I went downstairs and outside and looked at the beam but it was pointing in the appropriate direction, I then started checking the plug on the coax for dry joints and then the continuity of the coax, but finding nothing wrong. It was only later that I discovered that the activation had been vertically polarised on SSB, something that for an old hand like me is almost an oxymoron!

This in a nutshell is why I used the word “misguided”. It is partly about expectations. An SSB specialist (which I am) does not expect to encounter vertical SSB with the attendant horrendous cross-polarisation loss. And horrendous it most certainly is, much greater than the diffractive and indirect ray effects!

The other point is that a lot of work has been done into the relative efficiency of horizontal and vertical polarisation. It has been shown conclusively that horizontal is much more effective than vertical on long paths, and whilst SOTA is not about DX, some of our summits are so remote and difficult to get out from that you need all the help you can get!

I agree that in terms of physical practicality a vertical antenna makes life somewhat easier for an activator, but it is less effective and for SSB defies expectations, costing you contacts.

73

Brian G8ADD


#14

In reply to G8ADD:

A simple answer here Brian.

The activator is king.

We are chasers, so we have to chase what is on offer, be it fm, cw, ssb, vertical or horizontal, end of story.

If an activator has taken the time and effort to gain a summit for our benefit, then he/she calls the shots and we should be grateful for his/her efforts and chase them on their terms.

73 Mike GW0DSP

P.S. Apologies to Q for going slightly off topic.


#15

In reply to GW0DSP:

Very true, Mike, but it seems I didn’t make it clear that it was the activator and his/her ability to make contacts that I was concerned about, not my ability to score points. Not only is the activator king, but he deserves every effort of support that the chasers can provide. I was pointing out that using vertical SSB without making this intention widely known will cost contacts and could possibly cost a qualification. Using vertical has other costs which can be lived with, and is the chief cause of the relatively short range of FM, but cross polarisation loss is pretty fatal, as my description of what happened with me should illustrate!

73 & HNW

Brian G8ADD


#16

In reply to G8ADD:

In reply to GW0DSP:

Using vertical has other costs which can be lived with,

and is the chief cause of the relatively short range of FM

I disagree with that Brian, why are all amateur repeaters vertical FM if the range is limited? Why do the emergency services us vertical FM?
The only comment I would make is that FM is probably the most inefficient mode as far as current consumption is concerned.

but cross
polarisation loss is pretty fatal, as my description of what happened
with me should illustrate!

All it illustrated was that as a chaser, you dropped a clanger by not switching antennas to check the polarisation of the incoming signal.

I do agree on the cross polarisation issue though, massive losses, I hear the big vertical sigs only on my horizontal quagi array, no problem though, I just flick a switch and work them on the vertical colinear.

73 and a Happy New Year to you and yours Brian.

Mike GW0DSP


#17

I only hear a faint dribble from the horizontally-polarised 2m SSB activators here, while those very occasional v-pol 2m SSB signals come booming in.


#18

In reply to G8ADD:

Hi Brian,

In many ways I sympathize with what you are saying. Indeed, I am quite a stickler for pointing out to people such things as the huge losses incurred when one uses the wrong polarization. I am one of those people who strive, when constructing an antenna system to have every aspect of its construction be as close to ideal as I can muster.

I recently led an expedition up NW-011 Arenig Fawr in Snowdonia a few days before Christmas. As well as myself, there was my YL (Katy) and two good friends. This was Katy’s first proper high-level walk and conditions up there were savage. Roger MW0IDX measured the temperature up there two days prior, under very similar conditions to be -5C. Couple this with a wind speed of 35mph and you have a wind-chill of about -15. Visibility on the top was 50yds at best and ice was forming on my gloves and my beard. Thats a cold place to be playing radio. I was also the sole navigator and the most experienced hillwalker of the group and as such the comfort and wellbeing of the other three rested on my shoulders. This is why I chose to activate 2m SSB with vertical polarization. I had simply to attach a 1/2 wave whip to the front of the FT-817 and stick the whole lot on the edge of the cairn. Portable operation started! Even working quickly, it took me about 1/2 hour to work 14 stations, with best DX being Don G0RQL at over 140 miles. Not bad for 5W out of an antenna coupling into my own body at 1m AGL.

I’m certainly not saying that vertically polarized sideband is “right” from a technical standpoint. But when you need to get some calls in the log under some extremely uncomfortable conditions, and you do not have the time for every ham and his dog coming back to you on 2m FM, it is fairly safe to assume that the dedicated band of chasers will find a way work you regardless of polarization. Its a lot easier for the chaser sat in his shack to flick the coax switch over to vertical than it is for an activator to assemble a mast and beam, activate and then disassemble it all again. The time spent playing with equipment can easily take 1/2 hour in cold weather - in the case of my activation alone it would have increased the time up there from 1/2 hour to a full hour and in the given circumstances, that was not acceptable. Additionally, I and others tend to point out in our alerts if we are going to be doing anything unconventional, making it really quite easy for the chaser to select the ‘correct’ polarization. Forewarned is forearmed after all.

I agree with a good many of the points you make, they being indisputable. Perhaps the best way to lead is by example - how about getting up a few of those high peaks this winter and showing us how its done? Activator’s discretion and all…

I’m certainly not trying to teach you to suck eggs and I don’t claim to be an SSB specialist (or an anything specialist really), but I would probably have had a listen around between 144.400 and 144.500 for a few beacons before systematically disassembling and checking my equipment.

Anyhow, my apologies for a somewhat length and OT message.

A peaceful New Year to all,

73,

Dave 2E0BYA


#19

In reply to 2E0BYA:

In reply to G8ADD:

Anyhow, my apologies for a somewhat length and OT message.

A peaceful New Year to all,

73,

Dave 2E0BYA

Dave PLEASE PLEASE don’t apologise for putting on a superb activation under extreme conditions, with friends and or family present. An apology is an admission to doing something wrong, you did absolutely NOTHING wrong.

We are chasers, the word has meaning, we chase. That, to me any way, means that we chase what’s available to us, 80/60/40/30/20 whatever the band, RTTY PSK32 FM CW SSB SLOW SCAN VERT HORIZONTAL, whatever the mode, it is up to us as chasers to use our skills and available equipment to get the summit in the log. If we don’t get the summit, then that’s our fault.

Every activator should be applauded for taking the time effort and expense to gain each summit, sometimes in horrific wx, whereas we can sit back in our centrally heated shacks with a mug of hot beverage, or stronger stuff in our hand.

One activator once told me an important fact of sota chasing, “You can’t work them all, some will escape.” That’s a fact we have to live with.

73 Mike GW0DSP


#20

In reply to GW0DSP:

“I disagree with that Brian, why are all amateur repeaters vertical FM if the range is limited? Why do the emergency services us vertical FM?”

Surely the repeaters need restricted range or the qrm would be terrible and the numbers of hams able to use one at any time would be limited. The emergency services are in the same position, its a matter of service area and user numbers. Vertical polarisation for mobile operation was chosen for two very good reasons. Firstly the degradation due to reflections in an urban environment is more accptable with vertical, secondly the mobile antenna is more easily set up: horizontal polarisation over a metallic ground plane needs precise spacing to hold the radiation pattern close to the horizon. Add to this the greater ease of accommodating an antenna with gain. Stacked halos or turnstiles would be quite unwieldy atop a mini!

Incidentally, there used to be a horizontal FM group which demonstrated that FM was only a little inferior to SSB if a horizontal antenna was used. That group faded away but the idea is being revived by another band of enthusiasts, I have worked some of them over quite good distances!

“All it illustrated was that as a chaser, you dropped a clanger by not switching antennas to check the polarisation of the incoming signal.”

In fact I so rarely use FM and vertical polarisation that I would have to change antennas manually (and search for the right coax!) but a crossed yagi would be great if they were not so infernally visible and likely to arouse the attention of the planners! I keep my head down and hope!

73

Brian G8ADD

PS re your reply to 2E0BYA above : Amen!