Dual band ant questions to access distant repeater

[Om_Audio]

I built this antenna and it works excellent on 15' mast on my roof (25ft total height above ground):
A Simple 2m/70cm Vertical Dipole Antenna
It consists of 2 vertical bent rods- asymmetrical U shape- longer side is for 2m, shorter for 70cm. Upper element connected to center, lower element connected to shield. No balun/choke.
2m=18 5/8"
70cm= 6 1/4"
SWR is excellent below 1.2:1 (for what that is worth)

pic of installed antenna attached and shown below

I currently only have a 5W handheld I use with it. I can full quiet repeaters over 50mi away.

Goal:
There is one repeater located 80mi away I can only get into with a LOT of noise and cannot receive it reliably. It is also very noisy on my scanner with ST2 scanner antenna. It is at 8000' and looks to be clear path as far as any other ridges or mountains obscuring the path.

The repeater in question is Keller Peak machine: Web:KPRA-The Keller Peak Repeater Association
RepeaterBook-Running Springs, Keller Peak, , 146.385, KE6TZG Repeater

I want to full quiet this repeater as it is a great community with nets I want to participate in. (Their EchoLink rarely works) Considering more gain would be a solution by modding my current antenna or building a new one if I have to. (amps for 2m are too pricey for me now)

I could easily swap out the elements of the current dipole with longer- even full wave. I know there are different radiation patterns with different element lengths.

Any comments or suggestions appreciated-

Clifford

 

[n4yek]

A beam will be your best bet with doing what you want at that distance.
You could try a 5/8 wavelength antenna but I would not go anymore than that. When you start adding more than 5/8 wavelength to antennas, the radiation pattern changes and your signal will move from near horizon to higher angles of radiation. Making your antenna longer than 5/8 will not help you, probably hurt you.

 

[Om_Audio]

Thanks Danny. I will try 5/8 wavelength elements for starters and go from there. I have a large TV antenna for parts so will build a beam or Yagi eventually as well just curious to see what 5/8 will perform like.
C

 

[K5MPH]

I'm going to 2nd that go with a beam antenna and also you going to need more than 5 watts if you really want to get 80 miles away.............

 

[Om_Audio]

Really just depends on the path- I have accessed Keller very well from 100mi from a 1900ft peak in Topanga with a ridge obstruction on 5W and a 15" Nagoya. I am hoping to have some luck from home as Keller is at 8000ft. Will be a fun experiment!
Thx,

C

I'm going to 2nd that go with a beam antenna and also you going to need more than 5 watts if you really want to get 80 miles away.............

 

[mmckenna]

What kind of coaxial cable are you using? I can't tell from the photo, but it looks pretty small.
A directional antenna would probably help, but the problem is, well, it's directional. If you want to talk to other repeaters, this might not be your best choice.
Increasing antenna gain will help, but you can do a lot by using a lower loss coaxial cable.

 

[Om_Audio]

It is Belden 9175, not desirable at all but I had 1000' of it on hand when I started experimenting a few months ago. Just got my lic in Nov. I do plan on Obtaining better coax but running less than 50ft of it I suspect I am losing a few db prob not enough to be audible. If money was not an issue I would have LMR400 and a base rig with more than 5W.

What kind of coaxial cable are you using? I can't tell from the photo, but it looks pretty small.
A directional antenna would probably help, but the problem is, well, it's directional. If you want to talk to other repeaters, this might not be your best choice.
Increasing antenna gain will help, but you can do a lot by using a lower loss coaxial cable.

 

[techman210]

How does the radio perform just outside of your house? If it sounds better, that COULD be the effect of not running through the coax, but if it's like night & day, then experiment a bit by rotating and then relocating the antenna as a last resort. It could be "parked" in a null.

 

[Om_Audio]

Apples and oranges I think. Outside I have to use 15" Nagoya at ground level unless I go up on my roof. The rooftop dipole works dramatically better in my location that much I have verified many times. A null spot is a good suggestion but I have really only 1 place I can put the mast so I am limited there. I have done experiments with my scanner antenna and sometimes could pull things with handheld I could not with scanner but was weak and I would be holding the handheld up on my roof in a super specific angle and location- so I have some sense of how placement can affect things.

I suppose I could enlist the help of a friend when I take down the mast and walk it to diff locations on my roof and test before changing the antenna.

Also if the SWR is 1.2:1 or less would that not indicate the coax is not too lossy? I have a 50ft length of old mil spec RG8/U but it is not great for 2m/70cm to begin with in addition to being bulky and very stiff.

C

How does the radio perform just outside of your house? If it sounds better, that COULD be the effect of not running through the coax, but if it's like night & day, then experiment a bit by rotating and then relocating the antenna as a last resort. It could be "parked" in a null.

 

[mmckenna]

Belden 9175 is a pretty low end TV grade 75 ohm coax, similar to RG-59. It certainly isn't helping your situation.
The low SWR doesn't mean it's working well, it just means that not much of your transmitted power is being reflected. It doesn't mean that it's getting radiated well from the antenna.

Increasing the antenna gain by adding longer elements might add a few dB, but you are losing more than that in coaxial cable loss.

While I understand the cost issue, upgrading to a higher grade coax will help.

 

[Om_Audio]

I have learned some interesting things about coax today. Multiple sources show that 50ft of RG-59 even at 400MHz would attenuate the signal less than 3dB. You cannot even identify an audible change until 3dB and it takes 2x the power (+ or -) to create every 3dB of signal change. I am not sure I am even using a 50ft length. Although the coax is certainly a weak spot it is pretty minor and I will focus on antenna and transmit power first then replace coax later. I think I would be better served to begin with improving radiation and output power. Switching coax at such a short length in my case would likely get me 3dB of gain at best which is not even audible.

I used various online resources and also Bill Cheek's "Scanner Modification Handbook" to learn about the losses my coax might be imparting.

Thanks a lot for the input- this is all really helping me consider my options!

C

Belden 9175 is a pretty low end TV grade 75 ohm coax, similar to RG-59. It certainly isn't helping your situation.
The low SWR doesn't mean it's working well, it just means that not much of your transmitted power is being reflected. It doesn't mean that it's getting radiated well from the antenna.

Increasing the antenna gain by adding longer elements might add a few dB, but you are losing more than that in coaxial cable loss.

While I understand the cost issue, upgrading to a higher grade coax will help.

 

[Om_Audio]

If you all have any suggestions for DIY dual band beam projects please fill me in. I have a big TV antenna for parts I was going to make a 3 band Yagi but I think avoiding a strong directional design would be best at this point.
C

A beam will be your best bet with doing what you want at that distance.

 

[mmckenna]

You are correct, at 50 feet on the 440 frequencies, you are losing somewhere around 3.5dB in the cable.
Keep in mind that loss works both ways, not just your transmitted signal, but also what you receive. A similar run of LMR-400 will give you about 1.3dB of loss.

Nothing wrong having to work with what you have. That 2dB of loss probably isn't going to make or break things, but on the fringes of coverage it can make enough difference between a scratchy/barely there signal and being understandable. Trying some additional antenna gain would help. See if you can scrounge up some RG-6 cable. It'll have a bit less loss than what you have. It's pretty popular with cable TV companies, satellite antennas installers and cabling contractors. You might be able to score some scrap for free.

Also, don't overlook your connectors. Any water ingress/corrosion will add to the issue. If you've already sealed things up well, then you should be OK.

Increasing the length of your elements isn't going to give you a whole bunch on it's own. You are running what looks like a dual band 1/4 wave dipole right now. Jumping up to a half wave will give you about 2dB of additional gain. Adding some elements to make it directional will help even more at the expense of giving up the omni-directional performance of your current set up.

One thing I can suggest is that the spacing between your antenna and the mast is probably making it slightly directional. That might be working in your favor if the antenna is on the side of the mast you are trying to talk to. You might even be able to lower it so the top of the mast and the top of the antenna are even to get a bit more directional pattern out of it.

 

[mmckenna]

I would like to add that it's a pretty good looking antenna. I've built a few over the years for use on 6 meters and 2 meters, and it adds to the enjoyment.

Old TV antennas are a great source of parts.
Heck, if you weren't on the opposite end of the state, I just pulled down a 9dB gain VHF vertical antenna off the roof at work. It's tuned for 157.740, but there are some good innards inside there that could be salvaged. Trouble is it's about 20 feet long.

 

[Om_Audio]

Thanks very much. I will see if I can score some RG-6 for free. Only 2 connections and the exposed one at the feed point is sealed well with Lexel which seems very durable. The other is in the shack attached to my radio.

I intentionally used plastic for the top most section of mast which is parallel to the antenna and the horizontal distance is about 18". I was thinking the upper element was he radiator and figured plastic would affect the system less. It is pointing NE which is not the direction of the repeater in question which is more SE. Lowering it to the metal portion of the mast (hollow aluminum) and pointing it SE certainly never crossed my mind but is an intriguing suggestion!

I was actually thinking a 5/8 wave upgrade in the elements. I think each 2m section would be around 4' which is no prob. Just have to find metal rod long enough. As I understand it 5/8 wave radiates roughly 16deg which may or may not be better than 1/2 wave in this urban location.

Appreciate the compliment and thought regarding that vertical!

Thanks again for the help!

C

... See if you can scrounge up some RG-6 cable. You might be able to score some scrap for free.

Also, don't overlook your connectors. Any water ingress/corrosion will add to the issue. If you've already sealed things up well, then you should be OK.

One thing I can suggest is that the spacing between your antenna and the mast is probably making it slightly directional. That might be working in your favor if the antenna is on the side of the mast you are trying to talk to. You might even be able to lower it so the top of the mast and the top of the antenna are even to get a bit more directional pattern out of it.

... I would like to add that it's a pretty good looking antenna. I've built a few over the years for use on 6 meters and 2 meters, and it adds to the enjoyment.

Old TV antennas are a great source of parts.
Heck, if you weren't on the opposite end of the state, I just pulled down a 9dB gain VHF vertical antenna off the roof at work. It's tuned for 157.740, but there are some good innards inside there that could be salvaged. Trouble is it's about 20 feet long.

 

[popnokick]

I don't think lowering / reducing the height of the antenna to get it next to the metal portion of the mast for some possible directional gain will be helpful. You may get the directionality, but lose the height advantage. Height is king... ensure all is as high as you can get it. Why not replace the plastic mast with another section of metal.... and preserve (or increase) the height advantage?

 

[mmckenna]

I think if you start going with 5/8ths elements, you might start having impedance issues creeping up. I could be wrong, though.

Just look at the entire package. While upgrading coax will only add a dB or so, it will combine with other changes.
You could try making a 3 element beam. While they are directional, they get enough coverage in other directions that it wouldn't be useless. I have an old Spectra hooked up to a unused 5 element Yagi on the roof here at work. It's designed for 154MHz, but it works well enough on 146MHz. It's pointed at my house about 20 miles away, but I get enough off the sides/back that I can talk to my wife while she's around town.

 

[nd5y]

The antenna that the OP built using the design on the web site he linked to has a very poor radiation pattern on the 70 cm band and won't work well.
I modeled one using MMANA-GAL.
It's another case of people believing everything they see on a web site or YouTube video.

 

[Om_Audio]

Regardless of what your software tells you it full quiets 70cm repeaters for me all over the LA basin on 5W. In addition the repeater I am trying to gain access to is a 2m machine. The project was described as simple, cheap, and easy for a new ham. That was me. The design works great for my first home made and I'll take real world experience over a non helpful post on a user forum any day.
C

The antenna that the OP built using the design on the web site he linked to has a very poor radiation pattern on the 70 cm band and won't work well.
I modeled one using MMANA-GAL.
It's another case of people believing everything they see on a web site or YouTube video.

 

[Om_Audio]

Indeed I agree with you on the system being the sum of it's parts just not going to start there in my case (the coax that is). Money is tight right now unfortunately. I will look more into the impedance issue and also start seriously looking into a beam design I can make from the TV antenna I have. Ideally I would have a switch and a few antennas to work with and 1 100' tower but then reality happens.


Also, many manufacturers market what they claim to be high gain verticals usually with 3 ground plane reflectors at the base, is this type of design worth looking into in your opinion?

Thank you sir!

C

I think if you start going with 5/8ths elements, you might start having impedance issues creeping up. I could be wrong, though.

Just look at the entire package. While upgrading coax will only add a dB or so, it will combine with other changes.
You could try making a 3 element beam. While they are directional, they get enough coverage in other directions that it wouldn't be useless. I have an old Spectra hooked up to a unused 5 element Yagi on the roof here at work. It's designed for 154MHz, but it works well enough on 146MHz. It's pointed at my house about 20 miles away, but I get enough off the sides/back that I can talk to my wife while she's around town.

Noted, thx.

I don't think lowering / reducing the height of the antenna to get it next to the metal portion of the mast for some possible directional gain will be helpful. You may get the directionality, but lose the height advantage. Height is king... ensure all is as high as you can get it. Why not replace the plastic mast with another section of metal.... and preserve (or increase) the height advantage?[/QUOTE