Wondering...

[datainmotion]

I was thinking of putting up an inverted V (for RX only) and have a couple of amateurish questions:

1. I'd like to have the apex at the chimney with the wire radiating out and down towards the rear fence (simply for more length). It will slope at a 45° angle - will this compromise any advantedge I might gain by using an inverted V?
2. Can I connect both legs to a 9:1 balun for this?

Thanks!

 

[SCPD]

A couple of points:

1. An inverted V is just a dipole that is oriented such that it will give a directional radiation pattern. By changing to a 45 deg angle you'll have more of a NVIS antenna -- which is designed for short range communications.

2. In terms of receiving, it will still pick up DX stations but probably more local (< 1000 miles) In theory, the more vertical (so zero degrees) the better DX. If I recall, I think it was determined by ARRL Labs that 25 deg was the "ideal" angle but I can't recall off the top of my head. A 90 deg angle (so the inverted V would be lying down and aiming straight up toward the sky) is a true NVIS antenna -- for TX < 500 miles.

3. For RX the balun won't really make much of a difference. If you use a 9:1 then go with long legs (100ft or more.) The 9:1 will work best if you're looking for broadband coverage DC-30 Mhz.

4. One obvious downside to using the chimeny for your apex is local RFI. House borne RFI becomes an issue especially at the lower frequencies. Are there are any trees away from the house that could serve as the apex?

5. Regarding the receive gain, the Inverted V is a good antenna but not designed for DX. It should work fine for RX but it's more of a compromise antenna in this case. A 45 degree angle might be too sharp... perhaps a 30 degree would be better for DX reception.

6. In answer to your next question... you may be better off trying the 9:1 balun with a simple 100ft random wire parallel to the house. The key is getting the wire away from the house as far as possible and far from any local noise sources. This means a longer run of coax but LMR240, RG8 or 213 would be fine. I'd recommend at least 30ft from the house -- the farther the better. Also, if you can get it up high -- 40ft or more would be ideal.

Obviously, the best way is to give both a shot and see which works best.

 

[datainmotion]

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Thanks for the detailed response. It sounds like, at least in this case, I'd be better off with a long wire. You correctly assumed I'm seeking another DX antenna and I could string that between the two 20+ ft. tall trees in each corner of the rear of the yard. If I do, is the long wire's best RX abeam or off the end?

Thanks

 

[k9rzz]

Ask 100 different people and you'll get 100 different answers. Here's mine!

Go for it.

What if you move your antenna away from your own house (which may be very quiet in terms of RF noise) and closer to a neighbor who might have all kinds of noisy appliances? You'd have a tuff time tracking down his noisy junk and getting him to change it.

Try it with the 9:1 balun, and without ... see which is better in real life. I'm guessing that you're not going to need it.

Any antenna less than 30 ft off the ground on HF is going to be pretty much omni-directional below, say, 10mhz. Too much interaction from the ground. Even so, if the wire is more than 1/2 wave long for whatever frequency you're listening to at the time, you're going to have lobes of best reception is all sorts of weird directions, so although you point you wire in a certain way hoping to peak the signals from a certain part of the world, only time testing it will determine if you're correct or not. As you change bands, the lobes will be different. (unless you've got a rhombic or something like that).

Any sloping of the wire towards the horizon is going to lower the angle of attack and improve it for DX.

So, I agree, put it up and try it. If you're not happy, then take it down and try something else. Even better, have more than one antenna, then you can switch between them to find the best performer at the time.

 

[ka3jjz]

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Thanks for the detailed response. It sounds like, at least in this case, I'd be better off with a long wire. You correctly assumed I'm seeking another DX antenna and I could string that between the two 20+ ft. tall trees in each corner of the rear of the yard. If I do, is the long wire's best RX abeam or off the end?

Thanks

A random wire's (which is really what we're talking about here) pattern is going to be all over the place depending on the frequency and height above ground. I suspect you will probably have a number of figure 8 type lobes off the sides.

However if we're talking a real longwire (one that is a wavelength or longer at some frequency), the longer the antenna the more those lobes tend to flatten out toward each end. The classic way to make it unidirectional is to ground one end through a resistor.

There are many other possibilities depending on your layout. I don't know what you have there now, but if you have the room, I understand a Skyloop is a heckuva performer. Your approach is sound however - having 2 antennas of different types can be an advantage. One antenna might not hear something well, but the other might, simply because propagation is flipping the signal constantly.

Mike

 

[SCPD]

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Thanks for the detailed response. It sounds like, at least in this case, I'd be better off with a long wire. You correctly assumed I'm seeking another DX antenna and I could string that between the two 20+ ft. tall trees in each corner of the rear of the yard. If I do, is the long wire's best RX abeam or off the end?

Thanks

Wire antennas have that doughnut pattern. Picture a giant doughnut so that the lobes extend 90 deg from the wire. So if you string the wire from E-W -- the lobes are N-S and vice versa. The size, number and direction of the lobes are based of length of antenna, height above ground, etc.

If you terminate the end of a longwire (at least 1 wavelength long) then it'll be directional toward the terminated end.

I had a 300ft+ random wire in the backyard as well hooked to a DX Engineering 9:1 balun. The other end was grounded to a ground rod. It worked quite well across the DX band. My wire was anything but pretty. It was routed all over the place but it worked well considering its small cost.

I've since moved on to the loop antennas -- since their performance is hard to beat. Yes, they require a small financial investment but their performance for a 3ft antenna is incredible. It rivals any wire antenna that I've ever had.

 

[prcguy]

Any dipole or mostly horizontal antenna less than about 30ft high will be an NVIS antenna within the sub 1MHz to about 10MHz range regardless if it's a flat top or inverted V.

Trying to make a dipole into a wide band antenna with coax feed is difficult at best and adding an impedance transformer/balun may help or maybe not.

Instead it's best to run a balanced feed line alll the way from the radio to the antenna and if coax is required to get through walls use the shortest length of coax and place an appropriate 1:1 choke balun at the coax to balanced line junction.

With all that said I've used every kind of end fed, center fed, balun fed, coax and balanced fed wire antenna for HF reception and the best so far is a center fed dipole with balanced feed line. You can make it as long as your property will allow and get it as high and far away from household noise generators as possible and it will be quiter than many other antennas and provide more consistent and predictable performance across a wide frequency range.
prcguy

Ask 100 different people and you'll get 100 different answers. Here's mine!

Go for it.

What if you move your antenna away from your own house (which may be very quiet in terms of RF noise) and closer to a neighbor who might have all kinds of noisy appliances? You'd have a tuff time tracking down his noisy junk and getting him to change it.

Try it with the 9:1 balun, and without ... see which is better in real life. I'm guessing that you're not going to need it.

Any antenna less than 30 ft off the ground on HF is going to be pretty much omni-directional below, say, 10mhz. Too much interaction from the ground. Even so, if the wire is more than 1/2 wave long for whatever frequency you're listening to at the time, you're going to have lobes of best reception is all sorts of weird directions, so although you point you wire in a certain way hoping to peak the signals from a certain part of the world, only time testing it will determine if you're correct or not. As you change bands, the lobes will be different. (unless you've got a rhombic or something like that).

Any sloping of the wire towards the horizon is going to lower the angle of attack and improve it for DX.

So, I agree, put it up and try it. If you're not happy, then take it down and try something else. Even better, have more than one antenna, then you can switch between them to find the best performer at the time.

 

[prcguy]

And another thing....
Hf reception on the lower bands like maybe 15MHz and lower is governed more by signal to noise ratio rather than raw signal level.

What that means is if you have say a wire antenna 25ft long in a place that is not too noisy and it picks up signals in the lower HF range at a particular signal to noise ratio, adding wire to make the antenna 100ft or 200ft long will generally not have any effect on the overall signal to noise ratio and the ability to pick out weaker signals.

Unless your receiver was starved for signal with the small antenna, going to a larger antenna in the same spot will generally give you more signal but the noise will also increase by the same amount and even though your signal meter reads higher you may not pick up any weaker stations than you did before since your noise floor is now higher.

Every case is different of course but these are general rules. An exception would be at higher frequencies like CB or 10m where atmospheric noise has dropped off and point to point ground wave is common. In this case raising antenna gain or efficiency may bring up signals and the noise contribution is minimal so weaker signals can be improved.

Another problem can be receiver overload with a large antenna. I have a POS Yaesu VR-5000 thats comfortable to listen using a VHF/UHF Discone on SW (and it works great) but the radio is almost unusable when connected to my main large HF antenna. It seems the VR-5000 and many other poorly designed HF receivers will overload and create internal IMD with a large HF antenna connected. So, going big is not always better depending on your equipment.
prcguy

 

[Danoman]

Something to consider with that inverted V is to close the two far ends and make it a Delta loop.

I put up a delta loop last weekend.
Currently have a Alpha Delta DX-SWL sloper to compare to.

Both antennas seem to work equally well but the loop is much quieter.

 

[datainmotion]

WOW...get off my frequency Danoman :lol:
After Mike mentioned the Skyloop earlier in this thread, I got to researching and came across the delta loop which would be a good fit for my yard. I also have an AD DX Sloper, but don't really suffer from noise until the plasma gets turned on.

What is the total length of your loop?

 

[Danoman]

The original idea was to cut a loop for 7mhz so I could pick up the pirate radio broadcast better.
However, I ended up just stringing as much wire as I could fit in my back yard.
It's a "compressed" delta as the bottom is about 120ft. and the sides are somewhere around 80 to 90.

I used what I had on hand as I did'nt want to spend any money.
With that being said I fed the loop directly with some cheap dollar store coax at the center of the bottom.

I'm sure the experts will say you can't feed it the way I did, but trust me, it works as well as the DX-SWL commercial antenna but with less noise.

 

[ka3jjz]

Receive only skyloops are much less critical than their transmitting counterparts insofar as the total length goes. I believe the Chief has a 150 foot one, and I'm quite sure he hears his share of stuff. I would definitely do some research and planning, but if you have the room for one, it sure seems hard to beat.

We have a little about this subject in our Loops wiki...

Loops - The RadioReference Wiki

Sadly it seems that the SkyWires yahoo group has been overrun with spam crap, but the links and files areas might also hold useful information

best regards..Mike

 

[kb2vxa]

I don't know where that NVIS idea came from, I worked plenty of DX on an inverted V. I don't know where that 9:1 balun came from either, they're made for long wires and one side of the balun is grounded. This application calls for a 1:1 current balun you can order from any Amateur Radio dealer. BTW, while dipoles exhibit a figure 8 pattern broadside at the fundamental frequency with it moving toward the ends at higher frequencies the inverted V is essentially non-directional.

 

[datainmotion]

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I believe the NVIS was in response to my original question about proposed orientation of an IV. I brought up the 9:1 as its what I have, without a good understanding of the various ratios and their recommended use.