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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
G4YVM wrote:
ei9ju wrote:
G4YVM wrote:
We have taken SWR reading at the base and further afield. The aerial seems unaffected by coax length, height AGL, surrounding terrain etc etc etc. All of which is very good but all of which rather plays into the hands of the "snake oil!!" cryers.

We had one chap come up and quote text book references at us telling us why the aerial was a fake and would never work. Oddly enough the Asian stations I later worked with it hadnt read the same text books, so worked me anyway.

Like I say in the notes, we make no claims at all for this aerial, except that it works. They now operate in many countries and I have no one come back and tell me it didnt work as well as I say.

If you do play with one and make some interesting finding, do please tell us!

Regards

D


As I said to Tony on another thread only last week when i first became licensed i worked stations for an entire week using only the coax as unknown to me I was sold a faulty antenna as it's so-239 chassis connector wasn't making contact with the PL259 centre pin.
I don't doubt this antenna works to some degree and i'm not pouring scorn on it, even a less than ideal setup is better than none at all but surely it must be accepted the other half of this antenna can only be the coax feeding it, the coax braid must be the antenna ground and that being the case my fear in a built up area would be causing RFi.
Read my sig, being told it works doesn't cut it with me.....I want to know why it works. :D



Oddly enough I tried using just the coax by unplugging the aerial. Castle electronics reckon my PA stage will be fixed in a week.

No, youre right. The aerial doesnt really work at all. I dont know why we bother. If I sound a bit fed up of your comments its because I am. Go away, analyse the aerial, rip it apart and find out why it works. Then come back and tell us. In the meantime, perhaps, just accept that some people are working global Dx on QRP power and having a ball. They dont know why, they probably dont care. They saw an article, they built the aerial and now, using the skills of their own hands, they having fun. Is that so bad?

I wont read this thread again...it winds me up.

D


Jesus Christ, talk about being an unfriendly quick tempered sod!!

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Tue Jun 30, 2015 1:04 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
Sangoma wrote:
Maybe people could give some credit to the original article?

Would be fair after all, even if not asked for.


Duly noted Sangoma. I have put a credit to the designers and a link to the origin al article by Davis and Jim, on my website.

Thanks again

Pete

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Tue Jun 30, 2015 4:18 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
ei9ju wrote:
G4YVM wrote:
ei9ju wrote:
G4YVM wrote:
We have taken SWR reading at the base and further afield. The aerial seems unaffected by coax length, height AGL, surrounding terrain etc etc etc. All of which is very good but all of which rather plays into the hands of the "snake oil!!" cryers.

We had one chap come up and quote text book references at us telling us why the aerial was a fake and would never work. Oddly enough the Asian stations I later worked with it hadnt read the same text books, so worked me anyway.

Like I say in the notes, we make no claims at all for this aerial, except that it works. They now operate in many countries and I have no one come back and tell me it didnt work as well as I say.

If you do play with one and make some interesting finding, do please tell us!

Regards

D


As I said to Tony on another thread only last week when i first became licensed i worked stations for an entire week using only the coax as unknown to me I was sold a faulty antenna as it's so-239 chassis connector wasn't making contact with the PL259 centre pin.
I don't doubt this antenna works to some degree and i'm not pouring scorn on it, even a less than ideal setup is better than none at all but surely it must be accepted the other half of this antenna can only be the coax feeding it, the coax braid must be the antenna ground and that being the case my fear in a built up area would be causing RFi.
Read my sig, being told it works doesn't cut it with me.....I want to know why it works. :D



Oddly enough I tried using just the coax by unplugging the aerial. Castle electronics reckon my PA stage will be fixed in a week.

No, youre right. The aerial doesnt really work at all. I dont know why we bother. If I sound a bit fed up of your comments its because I am. Go away, analyse the aerial, rip it apart and find out why it works. Then come back and tell us. In the meantime, perhaps, just accept that some people are working global Dx on QRP power and having a ball. They dont know why, they probably dont care. They saw an article, they built the aerial and now, using the skills of their own hands, they having fun. Is that so bad?

I wont read this thread again...it winds me up.

D


Jesus Christ, talk about being an unfriendly quick tempered sod!!


Thats probably because ever since this antenna was designed / discovered, there has been a certain element who will not believe that this antenna works..... BUT IT DOES!

I would be very interested to read how some one has built, analysed and can then explain how / why it works. We all know that sometime, especially in this hobby of experimentation, thing shouldn't work but do.

If you have the equipment to do so, PLEASE build one and then let us all know the results of your findings.

Pete

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FISTS #16592
SKCC #12173C
RSGB
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Tue Jun 30, 2015 4:25 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
G4YVM wrote:
ei9ju wrote:
G4YVM wrote:
We have taken SWR reading at the base and further afield. The aerial seems unaffected by coax length, height AGL, surrounding terrain etc etc etc. All of which is very good but all of which rather plays into the hands of the "snake oil!!" cryers.

We had one chap come up and quote text book references at us telling us why the aerial was a fake and would never work. Oddly enough the Asian stations I later worked with it hadnt read the same text books, so worked me anyway.

Like I say in the notes, we make no claims at all for this aerial, except that it works. They now operate in many countries and I have no one come back and tell me it didnt work as well as I say.

If you do play with one and make some interesting finding, do please tell us!

Regards

D


As I said to Tony on another thread only last week when i first became licensed i worked stations for an entire week using only the coax as unknown to me I was sold a faulty antenna as it's so-239 chassis connector wasn't making contact with the PL259 centre pin.
I don't doubt this antenna works to some degree and i'm not pouring scorn on it, even a less than ideal setup is better than none at all but surely it must be accepted the other half of this antenna can only be the coax feeding it, the coax braid must be the antenna ground and that being the case my fear in a built up area would be causing RFi.
Read my sig, being told it works doesn't cut it with me.....I want to know why it works. :D



Oddly enough I tried using just the coax by unplugging the aerial. Castle electronics reckon my PA stage will be fixed in a week.


D



Clearly then I'm not as stupid as him because even as a newly passed M3 I made sure using a sniff of RF and the aid of an ATU the load the rig was seeing closely matched 50 ohm. :thumbsup:
By deliberately unplugging the coax as this guy claims to have done before then preceding to blow the PA's must rate as one of the dumbest acts of stupidity owned up to on a radio forum.....no wonder he gets cross thinking about it :lol:

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Tue Jun 30, 2015 4:40 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
G0PNM wrote:
ei9ju wrote:
G4YVM wrote:
ei9ju wrote:
G4YVM wrote:
We have taken SWR reading at the base and further afield. The aerial seems unaffected by coax length, height AGL, surrounding terrain etc etc etc. All of which is very good but all of which rather plays into the hands of the "snake oil!!" cryers.

We had one chap come up and quote text book references at us telling us why the aerial was a fake and would never work. Oddly enough the Asian stations I later worked with it hadnt read the same text books, so worked me anyway.

Like I say in the notes, we make no claims at all for this aerial, except that it works. They now operate in many countries and I have no one come back and tell me it didnt work as well as I say.

If you do play with one and make some interesting finding, do please tell us!

Regards

D


As I said to Tony on another thread only last week when i first became licensed i worked stations for an entire week using only the coax as unknown to me I was sold a faulty antenna as it's so-239 chassis connector wasn't making contact with the PL259 centre pin.
I don't doubt this antenna works to some degree and i'm not pouring scorn on it, even a less than ideal setup is better than none at all but surely it must be accepted the other half of this antenna can only be the coax feeding it, the coax braid must be the antenna ground and that being the case my fear in a built up area would be causing RFi.
Read my sig, being told it works doesn't cut it with me.....I want to know why it works. :D



Oddly enough I tried using just the coax by unplugging the aerial. Castle electronics reckon my PA stage will be fixed in a week.

No, youre right. The aerial doesnt really work at all. I dont know why we bother. If I sound a bit fed up of your comments its because I am. Go away, analyse the aerial, rip it apart and find out why it works. Then come back and tell us. In the meantime, perhaps, just accept that some people are working global Dx on QRP power and having a ball. They dont know why, they probably dont care. They saw an article, they built the aerial and now, using the skills of their own hands, they having fun. Is that so bad?

I wont read this thread again...it winds me up.

D


Jesus Christ, talk about being an unfriendly quick tempered sod!!


Thats probably because ever since this antenna was designed / discovered, there has been a certain element who will not believe that this antenna works..... BUT IT DOES!

I would be very interested to read how some one has built, analysed and can then explain how / why it works. We all know that sometime, especially in this hobby of experimentation, thing shouldn't work but do.

If you have the equipment to do so, PLEASE build one and then let us all know the results of your findings.

Pete


Errmnn...but it's bound to work 40m and above given the electrical length and the matching, there's no mystery there, the mystery lies in claims that it's performance is "awesome" on bands below 40m, and why the need to get all ratty, had he not wanted any reaction he should've bloody PM'ed you.....geezus, had I been derogatory about the bloody antenna I may have understood his reaction but I wasn't, directing someone to notes that basically consist of "jim said this" and "jim said that" mean nothing without giving a clue which bands that performance was seen....."Jim said it got better reports than his beam"....20m beam, 15m beam, 10m beam???? :scratch:

...and another thing, all I did was offer a suggestion of why it's working without the aid of a manufactured ground system before he went off on one!

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Tue Jun 30, 2015 4:51 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
I found a couple of hours today to try to bring some objectivity to this debate. Here's what I did:

Wound 43ft of wire on a 7m fibreglass pole and mounted it at the corner of my garage. Built a 4:1 unun comprising 6 bifilar turns on a T130-26 core and connected it to the base of the antenna. Fed the unun with 50ft of RG58 from my VNA. I installed a good CM choke at the shack end of the coax.

Test 1
SWR sweep from 160m thru 10m. SWR was impressively low - never above 4.7:1 and elsewhere below 3:1. That would put it comfortably within range of most internal tuners on 80m thru 10m.

Test 2
Noted the frequencies where SWRmin occurred: 4.2MHz, 6.8MHz, 20.5MHz
Moved the choke to half-way along the coax.
Noted the frequencies where SWRmin occurred: 5.9MHz, 21MHz
Moved the choke to the antenna end of the coax.
Noted the frequencies where SWRmin occurred: 2.3MHz, 12.2MHz, 25MHz

SWR values on each band also changed with choke position, sometimes significantly. For example the 17m SWR changed from 1.7:1 to 2:1 to 2.6:1 for the three choke positions.

Conclusion: the coax braid forms an inherent part of the antenna system

Test 3
Repositioned the choke to the shack end.
Replaced the Type 26 unun with one wound on Type 2 material.
SWRs were much worse on 160m and 80m (17:1 and 15:1 respectively) and generally higher (5:1) on 40m thru 10m.

Which raises the question: why is the SWR so much better with the Type 26 unun?

Test 4
Measured the complex impedance of the unun secondary winding using the VNA.
Surprisingly low Q (lossy) on all bands. Q varied from a high of 2.2 down to a low of 0.5. The equivalent Q of a Type 2 unun would be in the 100s. This is consistent with the intended low frequency use of Type 26 material - it is not characterised by Micrometals for use at HF.

Test 5
Measured the input SWR of the unun with no load connected
SWR was 5.9:1 on 160m and mostly below 4:1 on the other bands

Conclusion: the unun is very lossy

Test 6
Calculated the unun efficiency and input SWR from its measured secondary impedance and the vertical's feedpoint impedance.
The calculated SWRs were close to those measured.
The calculated efficiencies were:
160m: 0.09% (-30dB)
80m: 3.4% (-14.6dB)
40m: 37% (-4.2dB)
30m: 17% (-7.6dB)
20m: 20% (-7dB)
17m: 63% (-2dB)
15m: 65% (-2dB)
12m: 29% (-5dB)
10m: 93% (-0.3dB)

Overall conclusions:
1) The coax braid forms an inherent part of the antenna system
2) Impressively low SWR figures are achieved because the unun is wound on a high loss material
3) The system is particularly inefficient on 160m and 80m
4) If you have little space, and you must have an antenna with low SWR, and you are prepared to trade low SWR for efficiency, this is a contender
5) If you have a wide range tuner and can tolerate higher SWRs, there are more efficient options.

Steve G3TXQ


Wed Jul 08, 2015 6:55 pm
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 80m antenna for limited space. 
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Nice one Steve all that in 2 hrs or was a couple a loose term lol

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Wed Jul 08, 2015 7:26 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
Started at 1.00pm and finished at 5.00pm ....... but I had a few breaks along the way to watch Wimbledon, Tour-de-France, and make the XYL a cup of tea :good:

What surprised me most was just how lossy the Type 26 material is at HF - actually worse than some of the "lossy" ferrites we use for HF chokes.

Steve G3TXQ


Wed Jul 08, 2015 7:32 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
Steve,

So judging by your tests etc... if I wanted to build one of the above antennas, but make it more efficient... lets say.. an "upgrade" of the original..

What would be your suggestions for doing so, bearing in mind that it uses no radials... keeping to a 7mtr pole as well...

BR

Lyndon

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Wed Jul 08, 2015 8:12 pm
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 80m antenna for limited space. 
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If you want all-band (80m thru 10m) operation, and provided the coax run is not too long (say less than 50ft), use an unun based on a Type 2 core; you will get a higher SWR back at the shack, but assuming you have a tuner that can cope you'll have higher overall efficiency.

Of course, best of all is a remote tuner at the base of the vertical.

Steve G3TXQ


Wed Jul 08, 2015 8:19 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
cheers Steve for the prompt reply....

Although you have done your tests on the above antenna... what's your views on how it is that at least 3 operators have got this antenna to work.... in other words... why does it work..even though your tests show it to be so inefficient

cheers

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Wed Jul 08, 2015 8:45 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
Almost anything will "work".

Look at the efficiencies on the various bands. From 40m thru 10m the worst-case efficiency is equivalent to a signal reduction of around 7dB. That's not going to stop you making lots of contacts - it only becomes an issue when a path is marginal.

On 80m the 14.6dB loss would be equivalent to running 14W instead of 400W - again, still lots of contacts to be had!

I'm not saying it's a "bad" antenna, or that it wont "work" - those are emotive terms. But if your tuner can tolerate a higher SWR, simply swapping out the unun would avoid most of those losses 80m thru 10m; of course 160m is always going to be inefficient with an antenna that length.

Try comparing the efficiency figures with those in the third chart here:
http://www.karinya.net/g3txq/unun/

By the way, I checked the 160m efficiency by feeding 10W CW to the antenna; the unun core was warm to the touch after one minute, so there's no doubt where most of the power is going on that band.

Steve G3TXQ


Wed Jul 08, 2015 8:58 pm
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 80m antenna for limited space. 
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Post Re: 80m antenna for limited space.
G3TXQ wrote:
Almost anything will "work".

Look at the efficiencies on the various bands. From 40m thru 10m the worst-case efficiency is equivalent to a signal reduction of around 7dB. That's not going to stop you making lots of contacts - it only becomes an issue when a path is marginal.

On 80m the 14.6dB loss would be equivalent to running 14W instead of 400W - again, still lots of contacts to be had!

I'm not saying it's a "bad" antenna, or that it wont "work" - those are emotive terms. But if your tuner can tolerate a higher SWR, simply swapping out the unun would avoid most of those losses 80m thru 10m; of course 160m is always going to be inefficient with an antenna that length.

Try comparing the efficiency figures with those in the third chart here:
http://www.karinya.net/g3txq/unun/

By the way, I checked the 160m efficiency by feeding 10W CW to the antenna; the unun core was warm to the touch after one minute, so there's no doubt where most of the power is going on that band.

Steve G3TXQ


Personally the best thing I ever did was have my entire back garden up and lay around 100 radials. My roach pole in inverted L config with remote auto ATU at the base pulls in a hell of a lot more than I ever managed with a loaded vertical on 160/80/40/30 (I guess I'm lucky that the 'Freznel' zone is mostly pastoral on heavy clay).


Last edited by G0FVI on Wed Jul 08, 2015 9:24 pm, edited 1 time in total.



Wed Jul 08, 2015 9:19 pm
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Post Re: 80m antenna for limited space.
Wow Steve! That's what I call a thorough test :thumbsup:

When I constructed this I used a T106-26, with no choke and my SWRs were much lower than those in your test.. Does this mean I have even more losses than yours? (using approx 15ft of RG58)

Cheers

Dave
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Wed Jul 08, 2015 9:23 pm
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Quote:
When I constructed this I used a T106-26, with no choke and my SWRs were much lower than those in your test.. Does this mean I have even more losses than yours? (using approx 15ft of RG58)


There will always be some differences between what we measure - remember that the coax braid is effectively a counterpoise for the vertical, and changing its length changes the impedances.

Here are the SWRs I measured with the choke at the shack end of the 50ft coax run:
160m: 4.7:1
80m: 2.3:1
40m: 1.4:1
30m: 2.9:1
20m: 2.6:1
17m: 1.7:1
15m: 1.3:1
12m: 2.4:1
10m: 2.5:1

If your SWRs are very much lower than those I would be looking at whether the changed core size could account for it. I wonder why you chose a smaller core?

Steve G3TXQ


Wed Jul 08, 2015 9:32 pm
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