More Flag advice needed !

Medium & long wave antenna discussion
simbeav
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More Flag advice needed !

Post by simbeav »

Sorry to be a pain.

I see from the Ken Baird site (David 's corner) dimensions of 34ft x 16ft and a few other sites have similar.

But Stuart has 10m x 2 m and unless I got it wrong, John has only 8ft between his verticals and both are getting great results.

What is the most important ? Length / Height / both ? Is the ratio important ?

Puzzled of Cardiff.

satnipper
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Re: More Flag advice needed !

Post by satnipper »

8m x 4m is probably the optimal. The vertical section is the most important (along with the balun...) as a Flag is a pair of phased verticals and the horizontal sections act as earths.

My flag is "wrong" but it is still working brilliantly as my location is very good now for NA MF.

Stuart

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John Faulkner, Skegness
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Re: More Flag advice needed !

Post by John Faulkner, Skegness »

Large flags can exhibit poor directivity problems. I have witnessed this with my own and with Julian's. Stick to the stated dimensions 25 feet across, 10 feet up.

tvdxrools
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Re: More Flag advice needed !

Post by tvdxrools »

there is no set rule ,, go with what u can fit in but dont go to big with them , i would try what john or stuart says but go all in with the balun , David

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

satnipper wrote:
29 Oct 2018 10:31
8m x 4m is probably the optimal. The vertical section is the most important (along with the balun...) as a Flag is a pair of phased verticals and the horizontal sections act as earths.

My flag is "wrong" but it is still working brilliantly as my location is very good now for NA MF.

Stuart
Does this mean that if for example the vertical elements are larger than the horizontal elements it should work as well? The reason I ask is because I have a rather narrow garden area to use but I can extend the wires upwards?

tvdxrools
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Re: More Flag advice needed !

Post by tvdxrools »

dont worry about the size , use what you can that will fit in the garden it will still work , David

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John Faulkner, Skegness
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Re: More Flag advice needed !

Post by John Faulkner, Skegness »

As with all antennas, try it and see.

When I suffered bad noise here, I found that placing the vertical elements close together cured a lot of it. SIX FEET APART! The horizontal wire was just tied up so it didn't sag too much. The horizontal elements do not play any part in the reception, other than to connect the vertical elements together. It is the phasing together of the vertical elements which gives the flag its amazing directivity.

If anybody can be accused of using Bodgitt & Scarper Ltd. designs then it's me. I don't have the time or the inclination to mess around with antennas. I have to be in the mood for that., but it's amazing what can be done by trial and error .... and by luck. Hopefully you'll have plenty of the latter.

Extending the height of the verticals increases gain.

The physics behind antenna design never changes and it is great if you understand it, but just get it done and try it.

The only down side of the flag is it's relative lack of gain, but in addition to being a very directional antenna, the flag gives you two other very useful things. Same with a loop, a flag is a very quiet antenna. Signal to-noise is very important and I've heard some argue that it is the most important thing in antenna design. You should have both with a flag.

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

Thanks for the advice John. What I would like to do is a similar set up to yours with 2 flags: one pointing roughly NE for North America and another pointing NE for Asia. My idea is to have 3 poles on a small part of the garden arranged in a triangle with the resistor boxes and wires for both coming down the pole at the south and the horizontal elements crossing the garden to the transformers/preamps. Is this feasible or are the 2 wires heading down to the resistors likely to interfer with one another?

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John Faulkner, Skegness
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Re: More Flag advice needed !

Post by John Faulkner, Skegness »

I would guess that they will interfere. Since it's the verticals which are phased together, the addition of a third at fairly close proximity might affect the directivity. I have never tried this.

The only thing I can say, which is irrelevant to this, is that the horizontal lengths and positions are not critical. In fact, I used to have a longer bottom wire (longer by about three metres) and it was wrapped randomly around some bushes on the garden. There was zero apparent affect on directivity.

When I first made my flag movable, I fastened a few copper pipe saddle clips to the fence in such a way that I could drop the flag's vertical supports into the clips.

41615.jpg

I might go revert to this method as my current system of a completely mobile flag, with the vertical supports anchored into concrete-filled parasol bases, is falling apart. Another job to do ...... one day ...... maybe.

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

So would it be fair to say that the ratio of the vertical to horizontal lengths should be around 3 to 1 but that the physical distance between the two vertical elements doesn't have to be?

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John Faulkner, Skegness
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Re: More Flag advice needed !

Post by John Faulkner, Skegness »

That's where it gets too technical for me. :oops: I don't know if there is a ratio for this but I wouldn't be surprised as it's all about ratios anyway. I will point you to the original EWE antenna article where this all began for me. A EWE and a FLAG are the same antenna, more or less, but the flag has no ground connection. The flag gives a better rear null than the ewe, hence many of us moving over to the flag.

http://www.dxing.info/equipment/ewe.dx

There may be some good articles about flag antennas, so I hope somebody might post if they know of one.

Just found this:

https://www.qsl.net/wa1ion/flag/flag_antenna.htm

Now this shows that most of us probably don't construct or use our flag antennas correctly. I remember somebody telling me that it is better to connect into them midway up the vertical elements. I hope this is of use. It's much bigger than the flag I use and no doubt the proper way to do it. Looks way too complicated for me.

Paul_Logan
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Re: More Flag advice needed !

Post by Paul_Logan »

From what i remember ratio between vertical and horizontal parts of a closed loop should be something like from 1.5:1 to 2.5:1 I used a 12 x 27 foot loop for years and it worked great.

See the plots here: https://www.bamlog.com/superloop.htm

the triangular KAZ loop worked well at my place too:

http://www.dxing.info/equipment/kaz_bryant.dx
https://www.qsl.net/wa1ion/pennant_v_kaz.htm

I have a feeling that vertical sections of two antennas supported on the same pole are going to interact. How about hanging one from the same pole with fishing line or twine with a feww feet separation.
Paul Logan
Fermanagh, N. Ireland

FMDX: Elad FDM-S2 with 5 el Yagi by K6STI, 9 el yagi.
MW / SW: Perseus / Elad FDM-S2 with EWE / Wellbrook Loop / MFJ1026 Phaser.

satnipper
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Re: More Flag advice needed !

Post by satnipper »

MikeyRepublic wrote:
15 Feb 2020 12:47
So would it be fair to say that the ratio of the vertical to horizontal lengths should be around 3 to 1 but that the physical distance between the two vertical elements doesn't have to be?
You're getting a bit confused here as the ratio IS referring to the physical distance between the two vertical elements as this distance is the horizontal section. As Paul L says aim for a 2:1 ratio - that is to say the vertical sections are half the size of the horizontal ones.

I am going to re-engineer my Flag as a 8m x 4m as I need to do some maintenance on it anyhow. However as Davey H said the balun is probably more important than the ratio itself as long as the horizontal portions are longer. Anything will work but it's a question of what works optimally for any given situation.

Stuart

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

I have seen designs that suggest that the ratio should be 3 to one but of course there are lots of variables not least the transformer. I, like John have been using Bodgett and Scarper as consultants and the results I have found are quite bizarre. I have an antenna mounted roughly North West. This antenna is almost square shaped with very little difference between the vertical and horizontal dimensions. When it comes to ground waves it is unidirectional with a good front to back ratio. In fact using SDR Console to measure indicated a ratio of 12dB. But when it comes to skywaves, it offers very little nulling of The South. The second antenna was much closer to the 2 to one ratio that you all seem to have success with. About 2m by 4. This one was less unidirectional but on the plus side was an excellent short wave antenna. This one was dismantled this morning and I used the wire to make an antenna that was 3m by 6m. It looked great but proved useless because it was overloaded with IMDs. Not sure why but I suspect that connecting various lengths of wire together probably wasn't the best idea.

Paul_Logan
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Re: More Flag advice needed !

Post by Paul_Logan »

This might be of use to some: turns count on BN73-202:

7 and 2: 9:1 (EWE / beverage)
9 and 2: 16:1 (closed loop)
10 and 2: 19:1 (triangular KAZ loop)

2 turns on the coax end.
Paul Logan
Fermanagh, N. Ireland

FMDX: Elad FDM-S2 with 5 el Yagi by K6STI, 9 el yagi.
MW / SW: Perseus / Elad FDM-S2 with EWE / Wellbrook Loop / MFJ1026 Phaser.

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

Curiously I tested the North West flag again early evening after removing the other antenna that was very close to it. Whilst it is still picking up signals from Spain, they are being attenuated. Many of you did say that it was likely that having the 2 flags close together was likely to cause some form of interaction between them. Maybe that was what was happening.

satnipper
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Re: More Flag advice needed !

Post by satnipper »

You are not going to get perfect nulling with skywaves. That’s just the nature of the beast. It’s best to test nulling with the ground wave. However the nulling is frequency dependent. ON4UN has written the low band bible (use google) and the 8x4m design was reckoned to be optimal for top band.

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

What I find odd is the fact that the antenna that is nowhere near the correct ratio works much better than the one that was. The point about skywaves is a concern. Where I live gets swamped by Spain at night. I have solved this by phasing loop antennas placed a right angles to each other. But of course the effectiveness of this is limited due to the relatively high angles of loop antennas.

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John Faulkner, Skegness
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Re: More Flag advice needed !

Post by John Faulkner, Skegness »

One of the bonuses of the flag is its broad nulling, so it tends to work better in nulling rear skywaves than others. The null is impressive. I wish I could find an image to demonstrate this - somewhere on the internet, if the page still exists, there is a 3D plot of the flag antenna. I hope somebody can find this as it's worth seeing. Recent searches have been unsuccessful, but try to imagine an inflated balloon where somebody has poked their finger in one 'end' (the null). The opposite end resembles a huge dome, indicating a broad spectrum of reception (and not a tight beam). The null to the rear is also equally broad and able to reject a lot. This is the theory of course. The practise may be very different.

A few years ago, daytime, admittedly, I was able to remove virtually all of local Absolute Radio 1242 and hear Vietnam. I have used a number of beverage antennas over the years, including some carefully adjusted beverages in Scotland which have given good rear nulling. In my opinion, NONE of them have matched the nulling abilities of the flag. Flags just lack the gain, but their F/B ratio is impressive.

The really clever thing about this antenna is the fact that the null, once set up, should be good for the whole of the medium wave, although some users find that a minor adjustment is needed for the edges of the band. Some find it still works well up into 48 metres.

MikeyRepublic
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Re: More Flag advice needed !

Post by MikeyRepublic »

When it comes to daytime reception, the current pattern does resemble what you are describing. Compared to a loop pointing in the same direction, reception at the front is a lot broader, reception at the back attenuates more from the sides than the 180 degree point (12dB compared to about 5 or 6dB). This appears to make a kind of hyper cardioid shape. Not sure if this is normal, but I suppose what I could do when the wind dies down is use this to move the antenna so that it is closer to 300 degrees than 315. That way most of Spain would be in the line of maximum attenuation. In theory at least.

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