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Old 22-02-2018, 09:20   #46
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

"Left to their own, most hams will complicate a simple subject beyond recognition."
Art, W6RMK [SK]
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Old 22-02-2018, 12:25   #47
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

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Originally Posted by SoonerSailor View Post
"Left to their own, most hams will complicate a simple subject beyond recognition."
Art, W6RMK [SK]
Not so fast there SoonerSailor - I think I am getting to grips with it...

Radio + Battery + transmission = live output through oscillating lines that match up with wire of certain length over rum x many G&Ts. When added to rigging and mermaids the flux capacitor controls the hot dog that will soon be used as the grounding plate if it's filled with charred onions.

This is my current understanding of comms!!
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Old 22-02-2018, 13:11   #48
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

That bit of wisdom might have some truth in it.

But what we are talking about is the very basics, like not putting a hole in your yacht hull and not go sailing. Radio physics might be hard to grasp for some but its just the very basics that is being discussed that some find so hard to understand.

If we all get scared away by technicalities we would still be sailing paper bark yachts with bark covered hulls. You can make your own choices in life if you want to live like a ignorant caveman.

Then lets talk about "sailors" taking a simple subject beyond recognition. Just read the VHF antenna thread. Hundreds of pages of verbal diarrhea and you struggling to find 1 technical fact or a radiation pattern that supports the supposed claim this "this VHF antenna is better than that because I bought it"

Then lets not forget who anally over complicates RF grounds, not hams but ignorant sailors. The only hobbyists on the internet who can talk about a simple thing like RF ground for 10 years with 1000 pages of technical nonsense.

Not wise to throw stones in glass houses. Its just better to stick to the technical facts because the technical facts dont tell lies.

Thats todays generation they want to obtain everything the easy way. If its all too hard you might as well sail around the world on your Playstation. Its so easy, just turn on the virtual SSB that you dont have to install and it, and it comes delivered in a box for $199! So easy dude.


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"Left to their own, most hams will complicate a simple subject beyond recognition."
Art, W6RMK [SK]
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Old 22-02-2018, 13:43   #49
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

OK Plebian, a question for you:

I certainly understand about the desirability of low take off angles for a transmitting station if working DX is one's aim. Is that angle so important for receiving a signal from some random WEFAX transmitter when neither the distance nor the frequency is predetermined on a given day? In our part of the world, we depend upon broadcasts from two stations in Austrlia (E and W coastal areas) and one in New Zealand. We move around a lot, and all three stations broadcast on several frequencies, so there are lots of combinations of distance and frequency that may be currently best.

So, shouldn't one be designing a receiving antenna with the best all around performance rather than optimizing it for one particular angle/frequency ?

73 de Jim VK4GFT/N9GFT
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Old 22-02-2018, 13:59   #50
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

Speaking of G&Ts (and complicating things), the main factor in a good receiving antenna is Signal to Noise Ratio (SNR). For transmitting you want good gain, and in the appropriate direction and angle. These aren't always the same thing, and some good receiving antennas actually have a pretty low gain. An example of such a receiving antenna is the "Beverage" design. Actually, "Beverage" isn't a drink, but somebody's name.

Now on a boat we are lucky to get an antenna that works reasonably well for both transmitting and receiving. About the only optimization possible for a receiving antenna is to put the sensitive part as far from on-boat noise sources. A whip antenna inside the cabin may be sensitive enough for general use, but it is likely to pick up interference from your electronics, refrigerator controller, etc. If you can put an antenna up in the rigging, and use good coax (etc) you may reduce your local noise pickup enough to make a big difference.

Even with zero local noise, you will still have the atmospheric noise that will be the limiting factor. Antenna directionality will further improve the SNR, but more gain usually isn't helpful. Again, on a boat it's pretty hard to get a better than average multi-band antenna setup, let alone a directional one that's pointed in the right direction. On land I might take heroic measures to optimize my antennas, but on a boat I will happily settle for "good enough".
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Old 22-02-2018, 14:42   #51
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

So, a major step to an Rx only set up to get weather faxes has been taken. I have just won an Ebay auction for a Tecsun PL 680. I have read all of your comments regarding the different radios available and which ones you'd recommend on past/current experience. I, like you, have taken it seriously. But when it came down to it, I had to add my own concerns and circumstances so opted for this radio (I must have watched in excess of a hundred Youtube reviews on Tecsun, Grundig, Degen, Tivdio, Sony and Sangean). Only time will tell if it was the right choice. It was much cheaper than a new one so how can I fail!?

As for antenna, the reason for starting this thread, well I shall try the telescopic that is fixed to it followed by the 7m(?) wire that comes with it. If no joy there, then I shall revisit mermaids and gin!
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Old 22-02-2018, 15:48   #52
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

Well done!
Next step.... download and save this... http://www.nws.noaa.gov/os/marine/rfax.pdf

And read this ...

'Unless otherwise stated, assigned frequencies are shown, for carrier frequency subtract 1.9 kHz. Typically dedicated radiofax receivers use assigned frequencies, while receivers or transceivers, connected to external recorders or PC's, are operated in the upper sideband (USB) mode using carrier frequencies.'

So if a frequency is listed on the NOAA pdf as 11030.0 frinstance you will have to tune your radio to 11028.1 .... that is a common trap for new players....

Using Cocoamodem2 I normally fine tune using the waterfall ...

Next point.... reception in a marina and possibly in your house may be very difficult due to RFI... go outside and find somewhere quiet...

On a mooring in a quiet location? Your boat may be making a lot of noise ... your inverter, your charger for your computer ( more of a problem in my case on VHF frequencies ), and your fridge compressor are likely culprits.... also LEDS.
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Old 23-02-2018, 02:00   #53
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

You have have very clear thinking about RX antennas.

1. The angle is also important for receive. The height of the ionosphere varies hence the take off angle and the angle of arrival will vary.

If at a particular moment in time the angle is extremely low, and your antenna does not have a gain response at that angle you wont receive the station at all.

We are fortunate operating over seawater because of the so called "Brewster Angle" its relatively easy to get great low angle performing receive antennas, even short ones. Something that is not possible on land with poor conductivity. Rig a low dipole on deck and then switch between a low dipole and say a backstay and watch long distance stations disappear totally. Thats just having gain at the arrival angle.

2. Yes, never optimise an antenna for 1 arrival angle or 1 frequency. That is something you must avoid. You are right to optimise your antenna for the broadest range of frequencies and angles. Going too long like the 22 meter wire recommend to the OP results in a very high angle response that does not make a general purpose antenna.

3. The best antenna will always be one that maintains its pattern and gain over the most frequent angles of arrival. This is generally considered to between 5 degrees and 20 degrees. This is a relatively easy thing to do on receive. A short vertical of between 7 and 10 meters will do it and likewise something like a 14 meter backstay. The 14 meter backstay will have an undesirable response above 14 mhz. The radiation pattern and lobes are split and creates nulls at common angles of arrivals which you dont want.

4. The signal to noise ratio as one poster mentioned is also a critical issue. If for example you use a antenna that has lots of gain at high angles, which is also the angle that noise largely propagates at, you can have a horrible time receiving even strong fax stations. You will have a favorable responsible to lightning and tropical storm noise. Having an antenna that has a less favorable response in tropical areas to natural storm noise is a big advantage. Shortening the antenna to reduce gain and takeoff angle can yield dividends. We dont have to worry about wasted power loss in matching networks and ground loss like on transmit.

In short:

A good receive antenna is simply this for the HF frequency range.

1. Maximum gain at the desired angle and direction
2. Has more gain at the desired takeoff angle rather than wasting gain because of high angle lobes and having no gain at low angles.
3. Has the best signal to noise ratio
4. Not sensitive to noise pickup because of stupid design or feed solutions.
5. A uniform radiation pattern over say 5 to 20 degrees, without creating nulls in the critical takeoff angles.
6. Gain is not important because on most HF marine frequencies our receivers are noise limited and have way too much sensitivity.

On yacht and over seawater a moderate length passive vertical will almost be an ideal antenna. A final reminder is that when installing any vertical receive antenna the feedline will always be part of the antenna unless you take great care to isolate the antenna from the feedline. Use a lot of common mode chokes or use isolated feedline with something like a isolated feedline transformer. A wideband beverage transformer is almost ideal offering a certain measure of receive protection, especially for those portable Chinese receivers whose front ends you can blow by breathing on the antenna!

I would also use a very high quality multi shield coax like.

https://messi.it/en/catalogue/50-ohm...ystal-100m.htm or the Belden Equivalent. This kind of coax can reduce noise tremendously on noisy boats. Its available worldwide including the USA.


Quote:
Originally Posted by Jim Cate View Post
OK Plebian, a question for you:

I certainly understand about the desirability of low take off angles for a transmitting station if working DX is one's aim. Is that angle so important for receiving a signal from some random WEFAX transmitter when neither the distance nor the frequency is predetermined on a given day? In our part of the world, we depend upon broadcasts from two stations in Austrlia (E and W coastal areas) and one in New Zealand. We move around a lot, and all three stations broadcast on several frequencies, so there are lots of combinations of distance and frequency that may be currently best.

So, shouldn't one be designing a receiving antenna with the best all around performance rather than optimizing it for one particular angle/frequency ?

73 de Jim VK4GFT/N9GFT
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Old 23-02-2018, 02:07   #54
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

Try to get the coax feed plug that allows you to connect a coax fed antenna directly to the radio. I would try also to feed this piece of random wire with a RX only 9:1 Unun. You will pick up a lot of noise connecting a 7 meter wire to the whip antenna ruining your receiving experience.

Quote:
Originally Posted by settlednomad View Post
So, a major step to an Rx only set up to get weather faxes has been taken. I have just won an Ebay auction for a Tecsun PL 680. I have read all of your comments regarding the different radios available and which ones you'd recommend on past/current experience. I, like you, have taken it seriously. But when it came down to it, I had to add my own concerns and circumstances so opted for this radio (I must have watched in excess of a hundred Youtube reviews on Tecsun, Grundig, Degen, Tivdio, Sony and Sangean). Only time will tell if it was the right choice. It was much cheaper than a new one so how can I fail!?

As for antenna, the reason for starting this thread, well I shall try the telescopic that is fixed to it followed by the 7m(?) wire that comes with it. If no joy there, then I shall revisit mermaids and gin!
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Old 25-02-2018, 05:15   #55
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

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Originally Posted by El Pinguino View Post
Well done!
Next step.... download and save this... http://www.nws.noaa.gov/os/marine/rfax.pdf

And read this ...

'Unless otherwise stated, assigned frequencies are shown, for carrier frequency subtract 1.9 kHz. Typically dedicated radiofax receivers use assigned frequencies, while receivers or transceivers, connected to external recorders or PC's, are operated in the upper sideband (USB) mode using carrier frequencies.'

So if a frequency is listed on the NOAA pdf as 11030.0 frinstance you will have to tune your radio to 11028.1 .... that is a common trap for new players....

Using Cocoamodem2 I normally fine tune using the waterfall ...

Next point.... reception in a marina and possibly in your house may be very difficult due to RFI... go outside and find somewhere quiet...

On a mooring in a quiet location? Your boat may be making a lot of noise ... your inverter, your charger for your computer ( more of a problem in my case on VHF frequencies ), and your fridge compressor are likely culprits.... also LEDS.
That list is a great resource, thanks Pinguino! It is now safely stored on my desktop...

Cocoamodem has been downloaded so now it's time to play around with it
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Old 25-02-2018, 05:19   #56
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

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Try to get the coax feed plug that allows you to connect a coax fed antenna directly to the radio. I would try also to feed this piece of random wire with a RX only 9:1 Unun. You will pick up a lot of noise connecting a 7 meter wire to the whip antenna ruining your receiving experience.
Is going from the coax feed into a 3.5mm ext. antenna socket going to affect the reception? It would be a terrible shame if all the hard work of choosing the right antenna and setup were to be undone when it comes back to the radio through that little socket.
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Old 25-02-2018, 06:19   #57
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

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Originally Posted by settlednomad View Post
Is going from the coax feed into a 3.5mm ext. antenna socket going to affect the reception? It would be a terrible shame if all the hard work of choosing the right antenna and setup were to be undone when it comes back to the radio through that little socket.


Nope, no problem doing that.
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Old 25-02-2018, 10:39   #58
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

Forget about ground planes, a tuner or unun for a receive only antenna. Reread Paul Elliot's message. If the radio, tuned to your desired frequencies, noise floor goes up when the antenna is connected vs. not connected then you have a good enough antenna. The length is unimportant except that longer is generally better but once it's long enough then, well, it's long enough.

Why is a tuner unimportant? Well for the simple reason that the receiver provides a near perfect termination to the antenna. So there are no reflections coming back from the receiver to create a standing wave on the antenna. When transmitting, the exact opposite is true and that's why tuners are important for transmit. But for receive mainly what they do is create extra losses.
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Old 26-02-2018, 00:59   #59
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Re: Is length of antenna for MF/HF frequencies (Rx only) important?

Quote:
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Is going from the coax feed into a 3.5mm ext. antenna socket going to affect the reception? It would be a terrible shame if all the hard work of choosing the right antenna and setup were to be undone when it comes back to the radio through that little socket.
Well.... my best RX ant down on the campo is that one I mentioned earlier https://www.gwhip.co.uk/receive-only-antenna

From the box with the balun in it there is about 4 metres of coax to a 3 way Diamond antenna switch.... from there a few feet more coax to a Stridsberg receiver multicoupler and from there another metre of coax ends in a 3.5mm plug....

Current propagation conditions are such that this simply blows away the radio whips or included long wires...

Wasn't always so... used to be fine sitting outside with just the whip... not at present though.

You could do worse than speak to the nice G-whip man and ask him if he could knock you up something with a wire maybe 30 or 40 foot long that would fit on your boat.

Another handy site for you ... Short-Wave Radio Frequency Schedule for BBC in ENGLISH
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