Getting into scanning/Listening - antenna help.

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Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Sat Aug 31, 2019 9:19 am

Hi all, just joined - looks a great forum, I'm East Herts area and have an Icom IC-R20 plus an Icom R8500 on the way to me :)

I need two aerials for the R8500 - HF and VHF/UHF

I have a telescopic 9m pole but no space for ground radials etc. I have been using a straight wire on the pole for the R20 on HF with very good results, it seems ok up into air-band as well.

Is there a better option for the R8500 on HF- I can do a loop around the loft space, some sort of vertical dipole, stick with the vertical wire etc. or get an MLA30 loop??

Next there is VHF/UHF - things get confusing here, whats recommended for listening, seems most stuff is below 500Mhz so best to concentrate down there?

Is there a wide band aerial for 30-500Mhz? Or am i looking at Slim-Jim style focused on a certain area like air-band??

Thanks for any help

Dave
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Re: Getting into scanning/Listening - antenna help.

Postby m0lsx » Sat Aug 31, 2019 11:22 am

Welcome to the forum.

The Icom handhelds are renowned for being poor at handling strong signals so take care when connecting your R20 to any external antenna, as you could reduce it's ability to hear stations as the strong signals will desensitise the R20. Overloading could also cause signals to pop up where they should not & a number of other issues too. So NEVER use a pre amp with a Icom handheld scanner.

But despite the above, as a handheld radio with a handheld antenna the R20's are a reasonable compromise scanner which cover a lot of spectrum half reasonably. As nothing cheap is ever going to be a good MW, HF, VHF & UHF RX, so radios like the R20 do make a good compromise option, if that is what you want.

For a HF antenna on the 8500, a simple length of wire fed via a balun is probably the best option, as you will presumably want to listen across all of HF's spectrum & thus the end fed wire makes a good option for broadband reception. Baluns help level out the antenna mismatch a little & across a lot of spectrum almost all antennas are always going to have a varying mismatch. T2FD's are one of the few wideband antennas that would give a SWL a reasonable level of spectrum coverage without too much mismatch & they use a big resistor in the design to achieve that low SWR.

A balun at your antenna feedpoint gives you an electrical break between antenna & radio. Which helps reduce electrical noise a little at the radio & gives a better signal to noise ratio & in today's noisy world, every little helps. Radials are not as important on RX, as TX. And you really need a few radials for each frequency you listen to. So they are reasonably useless for a SWL listening across a lot of spectrum, unless tunable anyhow. And if using a tunable radial, then that will complicate your set up a little more.

The Short Wave Listener balun, is generally a 9:1 & I would recommend using a Balun connected to an earth stake, as that does reduce the signal to noise ration a little bit more in your favour.

If you are going to listen seriously on HF, then an ATU will probably be worth investing in. But I would leave that until you are sure it is what you want. I use a Global SWL ATU with bandpass filtering & adjustable Q, so that I can peak a signal & not be effected by out of band signals.

I have some antennas in my loft. But I would not recommend using your loft for you main antennas, or not unless you really have to. As first the loft will attenuate your signal a little & secondly & more importantly, you will almost certainly increase the electrical noise you pick up, as you loft will have electrical wires laying around up there. But the loft can be a great place for antennas if you are space limited, or to stop your home from looking like a porcupine. But it is a compromise, but that does not mean it is one not worth taking.

On VHF a discone is probably the best broadband scanner antenna. But beware. Not everything sold as a scanner discone is what it claims to be. A Discone, should be a disc of horizontal radials & a cone of the angled radials. A discone does not need a vertical, on transmit or RX. Yet many commercial scanner discones have a vertical & occasionally even a base loaded vertical.

Slim Jims make great antennas on airband etc. But you will need several of them. A easy to make variation on the slim jim is a Bow Tie or Hourglass antenna. these are wider band than a slim jim. So make better RX antennas. Especially on a massive band like the civil airband.

http://www.arrl.org/files/file/QST/This%20Month%20in%20QST/December2018/Stanley.pdf

There are things to listen to over 500 mhz, but most of us do not listen to much up there. If anything at all. And the higher we go, in MHz, the more important coax & antennas become. So we tend to hear less of what is higher up the bands, as our scanner set up's are by nature, compromise set ups designed to cover a lot of spectrum quickly & nothing really well. So we hear less & less well as we go up the spectrum.

A simple set up is a compromise as we have a lot of things to consider. But over complicating our set up's can mean that we make things harder for ourselves & induce compromises in that way too. So often it is the simplest set up which is operated the best & which thus achieves the most.
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Re: Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Sat Aug 31, 2019 1:21 pm

Many thanks for the in-depth reply.

So for HF i need a long-wire - does it matter if vertical or horizontal? I have only got a small back garden but the end walls of the house are exposed as its detached so going upwards may be better?

A 9:1 balun - that sounds easy enough, ground spike adds an issue as garden is block-paved :sad:

Then a discone for VHF/UHF - i have seen endless adverts for these, all of different styles and promises so will have to tread carefully here i think.

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Re: Getting into scanning/Listening - antenna help.

Postby m0lsx » Sat Aug 31, 2019 3:20 pm

Although I always use to use wires of 50 meters plus. More recently I have stuck with shorter 10 meter wires, as they are easier to work with & do not seem to make any real difference to received signal across 90% of shortwave.

Have a listen to the university of Twente's SDR over in Holland. They, so I understand it, use a one meter whip. Which yes is on top of a tall building, but it is still a tiny antenna & that gets some amazing signals.

http://websdr.ewi.utwente.nl:8901/

Another excellent RX antenna, is a tiny miracle whip. They are designed for amateur radio low portable operation & they make really excellent RX antennas for what they are.

Noise wise, an antenna seems to pick up more electrical noise vertical than horizontal. But put what you can up. I often just use a 10 meter, or shorter telescopic fiberglass pole with a wire taped to it. At other times, I use a horizontal wire. Mostly I use a coax fed 10 meter wire up the side of the house, with the last few meters sloping downwards from under the gutter. But if I am using my small portable radio, I use just a few meters of wire hung around the room that I am in.

The antenna I generally use with my small portable radio is 10 meters of bell wire, stripped in half to make 2 X 10 meter single core wires. I have then attached a small crocodile clip to one length & I clip that to the retracted telescopic antenna, after wrapping a couple of coils of wire around the antenna first. I find more than 10 meters of wire tends to overload portable radios designed to work on a small telescopic whip.

With the earth stake for the antenna. Could you not simply hammer a stake in close to the boundary? It is all I use.
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Re: Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Sat Aug 31, 2019 4:36 pm

Thanks

I can see i'll have to play around with this, the garden is a pain, concrete block all over apart from a small strip by the fence, high trees along the back and one side, my radio room will probably be the office so 1st floor at the rear. I can't get to the roof myself - no ladders and hate heights :sad:

I do have a 9m fibreglass pole and don't mind fitting a mast to the side wall if needed.

Lots of options i think but need to settle on a direction to go in :smiles:
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Re: Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Mon Sep 02, 2019 11:13 am

Hi alll,

I think i'm just about settled on a 1st aerial for my Icom R8500 on HF range, will start with a longwise and 9:1 balun, I have a wellbrook loop on my christmas wish list ;)

In UHF/VHF would you say it's best to concentrate on 2m and 70cm or more?

Would an aerial for air-band reach into 2m well enough?

I would be making these so i can mess around a bit but looking for an area to focus on :)
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Re: Getting into scanning/Listening - antenna help.

Postby m0lsx » Mon Sep 02, 2019 12:35 pm

Dave In Herts wrote: Would an aerial for air-band reach into 2m well enough?


In short yes. I use a three band amateur radio white stick (white fibreglass colinear antenna.) As my scanning antenna. Mainly because I use to use 2 meters & 70cm at one time. But despite not using 2 or 70 for years I have not got round to using something different yet.

A airband antenna will possibly be more of a compromise on other bands than a decent discone would be. But a discone would be a compromise on airband if that is where your main interest is.

If we want to listen across a lot of spectrum, then almost everything is going to be a compromise, as in the real world, no matter what some might try to claim in their advertising. Nothing works great every where.
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Re: Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Mon Sep 02, 2019 1:16 pm

Thanks,

So if i start experimenting with something like a slim-jim made from 450ohm ladder or a coax dipole from RG213 centered around 125Mhz maybe?

I like a bit of airband so would want that in there.

For receiving, Can you somehow mount several antennas on one feeder? Does it work as well as several antennas and separate feeds?
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Re: Getting into scanning/Listening - antenna help.

Postby m0lsx » Mon Sep 02, 2019 3:53 pm

Do you have a antenna analyser? If not take care with ladder line. It's velocity factor can effect the wavelength of the antenna you make from it & drastically. My local amateur radio clubs childens group made some ladderline 2 meter slim jims using measurement they had used before. All the antennas ended up being resonant around the top end of airband. Being off frequency does not matter too much with RX antennas, but it will mean your airband antennas are not optimised for airband, if you use the wrong type of ladderline for your measurements.

And the answer to can you use a single feed for several antennas is both yes & no. If you want one feed for several antennas use, what is called a NEST of antennas. A nest would in general be a series of half wave antennas fed off a single coax.

But take a look at Chris P's post on the following link. His interest is similar to yours & after many years listening this is his choosen antenna..

https://ukradioscanning.com/viewtopic.php?f=7&t=5270
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Re: Getting into scanning/Listening - antenna help.

Postby Dave In Herts » Mon Sep 02, 2019 4:42 pm

Thanks,

no analyser yet (spent all money on receiver :wink: )

Yes, i have calculators that show vf for cables etc so pretty good idea what to expect there.

The link shows a new to me antenna, the bowtie - sounds good and pretty simple. A few questions...

Is it effective at lower end like 125Mhz? - the size will be pretty large but do-able i think.

Also where do you centre the frequency? On the spot of most interest is my guess.

I gather they are mounted with the 'shield' side V towards the bottom?
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