2m beacon to bridge Indian Ocean

[VK4ABW]

I reckon the beacon should be set up to chirp on 6mtrs & then 2mtrs (obviously into an appropriate antenna system) pointed that way. South africa has been worked on six a couple of times from various parts of australia, so more investigation is required...

Gary
VK8AW / VK4ABW

[ZL1RS]

... I have an 11 element optimised yagi which is around 12DBd according to the designer so I am not sure how they would get 11.86DBd from 8 elements. You need to double the number of directors to get a 3DBd increase. Antenna gain is just about always overstated.

There are several 8 element 2m designs about that will produce 12dBd or more gain ... I0JXX and DK7ZB designs immediately spring to mind, the latter I built for 3D2RS 2M EME dxpedition and with a pair of them worked more than 200 EME QSOs in just over a week. Just for giggles I let the antenna modelling software optimise a 2M8 Yagi file solely for gain and within a few seconds it produced a new design with 12.3dBd gain (but a rather poor f/b).

73

[VK3PY]

For those who are interested in the DJ9BV family of yagis and how they compare, see:

http://www.ifwtech.co.uk/g3sek/diy-yagi/dubus/bvo2.htm. 12dBd on 2m is quite achievable with 8 elements on a 4.25m boom.

But now we're straying a little off topic.

Tony - always use dBi for path loss calculations. dBd is a bit useless for this. In any case, it doesn't matter so long as the reference is specified.

Peter (VK5PJ): Yes, it would be great if that beacon could switch directions towards us in some pre-determined manner.

73,
Chas
VK3PY

[VK6ADF]

Info today june 18 2013 on a local vk6 email thingy from VK6RK :

VK6RIO is completed, operational on test but not installed at NCRG.
The reason for this is there are no stations at the other end capable of receiving the Chirp signal.
Phil VK6APH and I are working on this now and are hoping to have some news to report soon.
We have interest in ZS and V51, which we are nurturing, and our Reunion Isl contact has many obstacles in his way ( few thousand metre mountains )
So all is not lost, we just need the other end to do their bit.

Cheers
Keith [VK6RK]


de vk6six

and may I just add it was posted to the local VK6 email thingy in reply to an email I posted there because I asked the question
to find out the status because this thread was running.

I would have posted the reply but Graham beat me too it but I would have changed it to UPPER CASE TO OVERCOME THE CONE OF SILENCE

[VK6ADF]

[SNIP]
Maybe we can convince the VK6's to run it to the EAST for a short spell if there is no one yet listening to the west of them?

regards,
Peter, vk5pj

Peter, I have asked the question. I will post any replies unless Graham beats me to it again..hi

[VK3BSF]

So the consensus is 10Kw ERP...is that enuf with path losses and receiver noise floor and other end antenna gain?..guess it is..hope the event is successful and us east coasters can somehow hook up!!..u can't be too careful with antenna calculations can u?

[VK4TS]

No the consensus is 10kw ERP but apparent power is 100 Megawatts equivalent -

My next email will be to VK6APH about setting up an equivalent this end so they can test the system before they get some ZS stations on air...

[VK2JDH]

No the consensus is 10kw ERP but apparent power is 100 Megawatts equivalent -

My next email will be to VK6APH about setting up an equivalent this end so they can test the system before they get some ZS stations on air...

My thinking would be that they are saying the power is equivelent to a SSB signal at 100 Mw. ie taking into account the narrower bandwith and increased rx decode capability.

[VK3ALB]

My thinking would be that they are saying the power is equivelent to a SSB signal at 100 Mw. ie taking into account the narrower bandwith and increased rx decode capability.

No, I think someone simply made a mistake in the original post.

ERP is the product of the power supplied to the antenna multiplied by the gain of the antenna compared to a reference antenna - usually a dipole. It has nothing to do with bandwidth or mode.

[VK2JDH]

ERP is the product of the power supplied to the antenna multiplied by the gain of the antenna compared to a reference antenna - usually a dipole. It has nothing to do with bandwidth or mode.

I understand that fact, but here is a quote from the original published article:
Phil Harman, VK6APH. 2012. Chirp Modulation: A sophisticated radar-like technique for propagation study that makes 100W act like 100 megawatts http://www.rsgb.org RadComm 2012(3):32-38.

Abstract here http://www.fotogravett.com/Docs/The%20C ... beacon.pdf middle of page 2

[VK5ZD]

I understand that fact, but here is a quote from the original published article:
Phil Harman, VK6APH. 2012. Chirp Modulation: A sophisticated radar-like technique for propagation study that makes 100W act like 100 megawatts http://www.rsgb.org RadComm 2012(3):32-38.

Abstract here http://www.fotogravett.com/Docs/The%20C ... beacon.pdf middle of page 2

Ah, I see. It was published in an article so it must be true

On the page 2 that you mention they state, quite clearly, that 50 of the 80dbW is due to techniques used at the receiver. i.e. The ERP is actually 1KW; fancy modulation techniques and receiver systems make this equivalent to a 100MW ERP transmitter and a standard (voice bandwidth) SSB receiver.

My 2c worth...

[VK6ADF]

[SNIP]
Maybe we can convince the VK6's to run it to the EAST for a short spell if there is no one yet listening to the west of them?

regards,
Peter, vk5pj

Peter, I have asked the question. I will post any replies unless Graham beats me to it again..hi

The question was asked, the reply was received

Perhaps you can post for me Phil.
The system is fixed in ZS direction.
I dont think too many locals would be happy with the effective erp blasted at the suburbs
Also I'm not sure if any of them over there do actually have the required gear to receive it, except maybe one.
I'll stand corrected if they do.
73
Keith

Does not look too good to pointing it east. Don't know about the locals being upset. Not sure how much local activity would even notice. I would have thought a brief period would have been worth a go.

The cone of silence continues (you might be right Leigh).

[VK3ALB]

I understand that fact, but here is a quote from the original published article:
Phil Harman, VK6APH. 2012. Chirp Modulation: A sophisticated radar-like technique for propagation study that makes 100W act like 100 megawatts http://www.rsgb.org RadComm 2012(3):32-38.

Abstract here http://www.fotogravett.com/Docs/The%20C ... beacon.pdf middle of page 2

Hi David,

I don't want to start an argument nor take away from the very important work that Andrew is doing but our hobby is based on a science which uses specific terms to mean specific things. ERP is ERP and is all about the sending end of the system. I don't think one can take a term with a specific definition and just make it something else.

[VK2AAH]

Lou,

I've also been scratching my head about this one for a couple of days. The term ERP is clearly defined so no matter how others choose to spin it they are wrong, wrong, wrong! This is not something that can be a matter of opinion- there is a definition. Period.

Though I think I can understand how someone who is from a microwave system "bent", trained to think in terms of total system gains & losses could be programmed to think that a gain or a loss can be moved anywhere within the system & still be "true". But it isn't... if you put a power meter at the input to the phasing harnesses & measure the input power, then multiply that by the total gain & losses in the antenna system- the effective radiated power result will never come to 10MW no matter how hard one tries! What they may be should be talking about is "receiver system gain", because that is where the hard work is being done.

Cheers

Richard
VK2AAH

[VK3OE]

Hello,
Oh dear,,,,,?
You are missing the point.......
Read "act like" and "normalize to a 2kHz bandwidth" and you may get the idea.

Good thinking.

Andrew.
VK3OE

[VK2AAH]

From the extract:

"As an example, a 100W 2m beacon using an antenna array with 10dB gain, using a 2kHz by one
seconds chirp and integrating for 60 seconds at the receiver will have an Effective Radiated Power of
20 + 10 + 33 + 17 dBW = 80dBW = 100,000,000W or 100MW"

Sorry, but that is totally flawed & is not compatable with the accepted definition of ERP. Call it something else but don't call it "Effective Radiated Power" because it isn't true... the term ERP has an important role in determining compatability of services in spectrum planning & this misuse of the term doesn't help.

Think of it another way... if the receiver at the far end is turned off what is the ERP of the transmitting end? 10kw ERP? If you turn the receiver on it increases to 100MW... Remarkable!!!

Even the smartest engineers get their terminology wrong sometimes...

Cheers


Richard

[VK3ES]

Always use DBd not DBi subtract 2.14DB from DBI figures. My calcs were in DBd. No antenna refers to isotropic in the real world.
VK2TS

I've never understood why hams insist on using dBd. It's unheard of outside of amateur circles and only seems to add confusion. A dipole might have a theoretical directivity (not gain) of 2.14dB in some directions and in free space and away from anything else, but so what? Why not use dBch (dB referred to a coat hanger)?
As someone else mentioned, you have to use dBi for any useful link calculations anyway.

I'm now stepping off the soap box...

73,
Andy VK3ES

[VK4OX]

Always use DBd not DBi subtract 2.14DB from DBI figures. My calcs were in DBd. No antenna refers to isotropic in the real world.
VK2TS

I've never understood why hams insist on using dBd. It's unheard of outside of amateur circles and only seems to add confusion. A dipole might have a theoretical directivity (not gain) of 2.14dB in some directions and in free space and away from anything else, but so what? Why not use dBch (dB referred to a coat hanger)?
As someone else mentioned, you have to use dBi for any useful link calculations anyway.

I'm now stepping off the soap box...
,
73,
Andy VK3ES

I'm with you Andy... I was not going to get involved with this topic...We're on a hiding to nothing, but dBi is THE standard of comparison when comparing apples, oranges, coathangers, dipoles or any device radiating electromagnetic energy.

73, Adrian. VK4OX.

[VK2AAH]

dBd unheard of outside amateur circles? I don't know who you mix with Andy but the antenna manufacturers I deal with normally discuss antenna gain using dBd. They probably aren't hams just seeking a bigger number to make things seem better than they are...

Cheers


Richard
VK2AAH

[VK2OMD]

Always use DBd not DBi subtract 2.14DB from DBI figures. My calcs were in DBd. No antenna refers to isotropic in the real world.
VK2TS

I've never understood why hams insist on using dBd. It's unheard of outside of amateur circles and only seems to add confusion. A dipole might have a theoretical directivity (not gain) of 2.14dB in some directions and in free space and away from anything else, but so what? Why not use dBch (dB referred to a coat hanger)?
As someone else mentioned, you have to use dBi for any useful link calculations anyway.

I'm now stepping off the soap box...

73,
Andy VK3ES

Hi Andy,

I wrote some notes on dB, dBi, and dBd at http://vk1od.net/antenna/concepts/dBd/index.htm .

It is interesting to quantitatively examine the arguments put forward in favour of either antenna (neither of which physically exist ideally). Of course, the fact that neither exist means that your proposed dBch could be used by applying the appropriate factor at each out of context use just as dBd users must.

For example, if we wanted to know the field strength of 100W radiated isotropically at a distance of 100m in free space, the solution from first principles is quite simple. The area of the sphere at 100m radius is 4*pi*100^2, so S, the power passing through a square metre of surface is 100/(4*pi*100^2)=7.96e-4W/m The field strength is simply (S^R)^0.5=(7.96e-4*120*pi)^0.5=0.547V/m.

I challenge anyone to caclulate the field strength at 100m broadside to a half wave dipole from first principles (ie WITHOUT foreknowledge of dipole directivity) as simply as this. Yes, it can be done, and any good antenna textbook has the workup... a page of trig integrals that requires a much higher level of understanding.

I suspect that it is fudamentally conceptual, and numeracy plays into it.

The strange thing is that the less inclined people are as mathematicians, the more likely they will prefer to use a dipole in free space as a reference on the ground, even though it is not a fundamental unit of directity and the derivation is beyond them.

But, most importantly, people are very resistant to change... so even if they became aware of a better way, it is so difficult to change... and the safer option is to not consider these things with an open mind, so avoiding all the stress that comes from learning that one might have been wrong (or less correct) all these years.

Owen