Tuned vs un-tuned antenna

[csxcp55]

I am using a Ringo Ranger ARX-2B - without its radials - and tuned to 146MHz for receiving in the railroad band (160-161.5MHz).
The antenna seems to perform fairly well, but I have been toying with the idea of re-tuning it for 161MHz. That would involve shortening the elements, and adjusting the tuning ring at the bottom. I have an antenna analyzer, so can do this without a problem.

The question is whether or not it is worth my trouble to do this. There seems to be some controversy over whether tuning significantly affects the received signal strength.

While I realize that the best method to improve signal strength is to raise the antenna, I'm kind of stuck with it up no higher than about 40ft here in northern NJ. And there are lots of obstructions between me and the trains I like to follow, especially from the north.
So I'm searching for other methods to improve signal strength, while fully understanding that if the signal is being blocked by an obstruction, and isn't getting to my location in the first place, nothing I do, short of raising my antenna is going to matter.

Of course, re-tuning the antenna to 161MHz precludes my using it for transmitting on 2m (146MHz), as the SWR would be very high.

Your thoughts?

Thanks
CP

 

[jwt873]

I wouldn't bother.. You're only about 12 Mhz off the antenna's resonant frequency. You'd only be trimming it by a few inches. I doubt you'd see any difference at all in incoming signal strength.

 

[csxcp55]

I wouldn't bother.. You're only about 12 Mhz off the antenna's resonant frequency. You'd only be trimming it by a few inches. I doubt you'd see any difference at all in incoming signal strength.

Thanks for the advice. Maybe I can raise it a bit higher. I will need some guy lines though.

I have also been considering building a Yagi for 161MHz. With the Yagi, I believe that having it tuned for the correct frequency is more important, since it has a much higher Q than the omni, and gain falls off quite rapidly as you get even a few MHz off the resonant frequency. I have done some modeling with 4NEC2 which clearly shows this. But that's a project that may never come to fruition. I just don't have the support for a larger (higher wind load) antenna at this time.

Another possibility is replacing the 2m with a dual-band for 2/70cm. Something like the Diamond X300A.
Not that I would expect better performance at 161MHz, but at least I would have a decent antenna for 70cm as well as 2m.

 

[Ubbe]

Using the antenna above the frequency its tuned to will direct the loob more up in the sky and even more so when you're not using any ground plane radials. Where there any particular reason to not install them?

The ARX-2 had a take off angle of 16 degree over the horizon and the ARX-2B have a stated angle of 7 degree and that changed the gain from 5.5dBi to 7dBi but also made it narrowbandet from 6MHz to 3MHz where the angle are still low over the horizon. One could only imagine what would happen when you use it 15MHz above the tuned frequency with a properly installed antenna.

A less optimized antenna without its ground plane will mellow out the differencies between tuned and out of tuned frequencies as everything would probably be low gain.

/Ubbe

 

[csxcp55]

I didn't install the three 20in radials because I could not get them up past the eave of the house. I was installing onto wall mounts outside the attic window, and had to do everything while reaching out that window. I didn't feel comfortable as it was, and was using 1ea 10ft length of 1in and 1-1/4in EMT conduit as a mast,which makes the whole thing too heavy to handle without proper leverage/stable position to stand on.
There are no guy wires on the mast either - I don't have access to the roof where they would need to be anchored.

The radials and the collar that secured them to the mast were problematic in another way as well. When I was first installing them, I found at least one hole in the collar wasn't properly tapped for the threads of the radial, so I had to re-tap it myself.
I am not particularly happy with the ARX-2B. It doesn't come close to the build quality of it's older brother, the ARX-2.
I no longer have the radials or the collar, so re-installing isn't an option.

What I am now considering is moving the whole thing to the (lower) garage roof, but in doing so I would need 15 more feet of mast just to reach the height the antenna is at now, and then another 75ft of LMR400 coax, which doesn't have too much loss at 160MHz.
I would like to buy a push-up mast (either fiberglass or aluminum) to mount on the garage roof. This mast would be guyed.

 

[csxcp55]

Ubbe; Is that list in your sig all the radios you own? If so, which one do you like best for VHF (railroad band if you do) scanning?

 

[prcguy]

I would tune the antenna to 161MHz as you are loosing a good amount of signal with it tuned 15Mhz away. I've got some 2m antennas that are deaf at 162Mhz weather channels and when retuned they perk up 10dB or more. You won't know what your missing until you tune it.

 

[csxcp55]

I would tune the antenna to 161MHz as you are loosing a good amount of signal with it tuned 15Mhz away. I've got some 2m antennas that are deaf at 162Mhz weather channels and when retuned they perk up 10dB or more. You won't know what your missing until you tune it.

I think that before I do any work on this antenna, I need to replace the heavy EMT conduit mast (20ft total) with lighter aluminum tube. At least then, I can feel somewhat confident raising and lowering it.

If I decide to tune the antenna to 161MHz, I will also add three radials.
And I will need to do something else for 2m...

I should probably make this decision soon, as it's getting pretty cold now...

 

[nanZor]

Also consider that the special radials are there to reduce common-mode coupling to the mast - which skew the pattern.

So without any radials - whether you end up tuning the main element or not, put some Type-43 ferrites around the coax where the radials would have gone. Snap-ons, multi-turns around a circular core etc.

Also if you can isolate the mast somehow - plastic, plexiglass rod etc near the antenna that would help also.

Like the secondary cone of the AEA isopoles, the ringo's decoupling radials are pretty important to keep those angles down low.

 

[cessna_172]

If you are planning to primarily use it around 161Mhz then I would definitely re-tune it. It will make a difference on receive. Especially on weak or more distant stations that you may be trying to receive. Tuning will affect both transmit and receive. 146Mhz-161Mhz is enough spread that it will make some difference. If you are relatively near the transmitters that you are wanting to listen to and don't have any issues receiving them with the antenna as it is currently tuned, then it really won't matter if you decide not to tune it.

 

[JoshuaHufford]

I've always been the type of person that if there is a better way to do something, even if the gain is small, if you have the ability to do it, then go for it.

Maybe 90% of the time you won't hear a difference, but that 10% of the time when your able to understand a transmission that you would not have been able to before, then it was wroth the effort.

 

[iMONITOR]

What are those wall-mounts anchored into? I would not depend on them to support very much weight, or wind load. Of course a longer mast would exacerbate the risk.

 

[Ubbe]

Are those railroad signals comming in from all directions or could you use a more directional antenna pointing to a rail yard?

Normally it's easy to adjust the antenna by loosing the hose clamps and adjust the telescope elements and the bottom ring but as it is so difficult to reach the antenna, and that you also use it for amateur radio, I would leave it alone and use another antenna for 160MHz.

Buy a cheap and small TV antenna either a logperiodic antenna, that's the easiest to modify, or a yagi. Get some aluminium rods and use an on-line calculator to see where to drill new holes in the boom to attach new elements of proper lenghts. It's enough with 3-4 elements on each side of the boom. Yagis often use a folded dipole that are harder to modify compared to log periodic. The logperiodics I've seen have the rods pressfit and you drill new smaller holes than the rod and then take a hammer and force the rod into the boom. With 3-4 elements you have an almost 180 coverage. At 160Mhz you can use any lenght of RG6 coax. https://www.changpuak.ch/electronics/lpda.php

I have more gear than the signature have room for. For receiving analog signals the most sensitive and interference free receiver are "real" radios and not scanners. Even the $100 TYT MD380 are superior to any scanner I have and as it doubles as a DMR receiver and is an amazing performer for its low cost.
The Icom R-2500 are my best "scanner" even if features and options are limited in a communication receiver as Icom calls it and are rock solid as a real radio but lacks just a little bit in sensitivity compared to a MD380. The UBC780XLT are the best of the rest as it has tracking filters in the VHF range. Other scanners needs external filtering and careful adjustment of signal levels as there are pager transmitters in VHF nearby where I live and FM trapfilters are needed in some configurations.

/Ubbe

 

[csxcp55]

Hey guys;
Thanks for all of your advice.
To answer some of your questions:

I am planning to re-install the radials once I have the antenna down and am experimenting with it.
I will do this before re-tuning the antenna for 161MHz.
I am hoping that, using my SDRPlay and SDRtouch on my phone, and tuning to one of the more distant weather stations at 162.500Mhz, I can get some before/after readings.

This experimentation will be done while the mast/antenna is easier to reach; the mast stuck into a fence post to support it and easy access to raise/lower the telescoping mast.
Then, when I am happy with the results, I will re-mount it on the wall outside the attic window.

The brackets I used are heavy-duty with the bottom one being a tripod and the upper a bipod. They are mounted to the wall of the house using carriage bolts with nuts and washers on the inside.
It has survived for more than 5 years with up to 15ft of exposed, un-guyed EMT conduit above the roof.
I have lowered it several times when wind was forecast, and left it so that only 10ft of conduit is now exposed above the roof.
The purpose of my changing to aluminum mast is to reduce the weight (about 8.5lbs compared to 17lbs) to make raising and lowering easier.
I had been considering a Max-Gain fiberglass push-up mast, but decided I didn't want to spend that much, and that the fiberglass would probably bend too much if left un-guyed. Of course in that case I would also be lowering the mast on windy days.

I realize that this is not an ideal situation, but it's what I have to work with right now. Eventually, I will move to another QTH and put up a 100ft tower in my backyard... hi.

Log Periodic:
I have used the link Ubbe provided to guestimate the size vs gain of the antenna. I don't know how long a boom I could use, considering that my masting is not guyed. I have to consider wind loading vs the vertical. If I wind up moving the whole thing to a more stable location (with guys), I would certainly be interested in either the Log Periodic to cover the entire 2m and RR band, or maybe a Yagi for only the RR band with a new vertical for 2m and 70cm above it?

The railroad signals I am most interested in receiving are pretty much from one direction, so yes, the directional antenna would be a plus. It might also help to reduce the interference I get from other services.
If I re-locate the antenna I should be able to install a small rotator as well.

All of what I want to do now is make easy improvements that will get me through the winter. In the spring, I will re-evaluate the entire situation.
If I do move the VHF antenna to the garage roof and install a well supported mast there, I can also raise the apex of my HF inverted vee's - one for 40m (with 15m stubs) and the other for 20m.
Currently those wires (at least the 40m one) are a bit too low for a good take-off angle, with much of my signal apparently going into outer space... hi.

But that's a subject for another post.

CP

 

[csxcp55]

I did some experimentation with the Ringo Ranger ARX-2B today.
After having taken it down from the mount at the attic window, I set it up with the EMT conduit (2x 10ft) using a fence post to anchor it so I could easily raise and lower, and remove it as necessary.

With the antenna lengths set for 161MHz, I adjusted the tuning rod for the best SWR at 161MHz (using my antenna analyzer). I got it to 1.5:1 and didn't try to get it any lower (for now).
The radials were not installed for the first test.
I tuned my VX-150 to several of the NOAA weather stations.
Using the standard R-S signal reporting system, where R =1 is unreadable, and 5 = 100% readable, and S=1 faint, barely preceptible, and 9= very strong signal:
The s-meter on the VX-150 is a 7 segment bar graph.

162.500MHz (Hardyston NJ, approx. 50Km/32mi air dist.): 7 bars 5x8
162.475MHz (Highland NY, approx. 92Km/57mi air dist.): 4 bars, 5x5
162.450MHz (Howell twp/Lakewood NJ, approx. 84Km/52mi air dist.) : 1-2 bars, 4x4

Next, I added the three 20 in radials at about 50 in down from the base of the antenna, as per instructions.
There was no improvement whatsoever. If anything, the signal strength dropped slightly.
I tried moving the radials around the mast, trying to get them to be equidistant from each other, but that had no effect at all.

I thought that perhaps I need to shorten the radials slightly, and maybe move them a tad closer to the base of the antenna for the higher frequency, but didn't bother to try that.

Next step was to tune the antenna back to 146MHz again and compare signal levels.
I did this, and with a center frequency between 145 and 146MHz, I got a best SWR of 1.2:1
Then I checked the signal strength again:

162.500MHz: 6 bars, 5x7
162.475MHz: 2 bars, 5x3
162.450MHz: 0 bars, 3x2

My conclusion: Tuning the antenna most definitely affects receive signal strength and readability.

Whether or not adding the radials will do anything for receive is still undetermined, as I may need to adjust the exact length and position of the radials.
In addition, I did not break the coax cable at the point where the radials were attached, leaving only the metallic mast to bond the antenna to the radials.
That said, I hardly think that using the coupling to bond the coax outer to the radials will have any effect when using a metallic mast.

I suppose that the radials would make a difference for transmitting, but since I am re-tuning the antenna to 161MHz, I will not be using it for any transmissions.

Once I receive the aluminum tubing I ordered from DX Engineering, I will set the whole thing up again - from the fence post - and do some further testing/evaluation. At that point, the max height of the mast will be about 25ft above ground. Once it is mounted on the house, the max height will be about 45ft above ground.

I am also going to look into the reason I was not able to get the SWR at 161MHz down to the 1.2:1 that I could at 145MHz. Perhaps I just didn't move the tuning rod far enough, or maybe it's just the characteristic of the antenna. In any case, I hardly think that getting the SWR at 161MHz below 1.5:1 is going to have any effect on the received signal.

 

[dispatch235]

When you added the radials did you also use the phasing harness that comes with the antenna? I have used the Ringo Ranger II for years, as it came and also in the other 2 configurations of the antenna. Adding the radials WITH the harness definitely helped me on 2 meters. I had a commercial version of the Ranger I used on 154-155 mhz for dispatching our Fire Dept and swapped in the radials and harness and could hear depts probably another 30 miles out with a solid signal that had a lot of static and lower signal strenght without them.
your mileage may vary, it's a good antenna to experiment with.... the only problem i had was when it rained or snowed and the antenna got wet it detuned drastically. A plastic "cool whip" bowl slid upside down over the radiator to cover the ring and tuning rod cured the problem although it looked a little strange lol.

 

[JoshuaHufford]

Interesting results, thanks for posting.

 

[csxcp55]

When you added the radials did you also use the phasing harness that comes with the antenna?

If you're referring to the 50 in coax cable and the ring that holds the 3 radials, no. I don't have the ring or the radials anymore. I do still have the cable though. I just attached the copper wires to the mast using a hose clamp, and did not install the coax coupling, so the coax just continued past the radials unbroken.
When I do the permanent install, I will be using a coupler mounted to the mast along with the radials.
I'm also going to try using a short PVC section at the very top to isolate the antenna from the mast, so the only path from the antenna to the radials is the coax.

I have used the Ringo Ranger II for years, as it came and also in the other 2 configurations of the antenna

What are the other two configurations?

the only problem i had was when it rained or snowed and the antenna got wet it detuned drastically. A plastic "cool whip" bowl slid upside down over the radiator to cover the ring and tuning rod cured the problem although it looked a little strange lol.

Exactly. I have measured the 'wet' SWR to increase significantly at the frequency I tuned the antenna to. The resonant frequency jumps down about 1MHz.
I may try the cool whip solution. Thanks.

BTW: Should I change the length of the radials and/or the distance they are from the antenna for the higher frequency?

Edit: Should I also use a choke in the coax between the antenna and the radials, or just below the radials, assuming the coax outer is bonded to the radials at their point of attachment.

 

[dispatch235]

The AR-2 configuration ( Cushcraft Amateur Radio Antennas ) and the ARX-2 configuration of the antenna ( http://www.cushcraftamateur.com/Product.php?productid=ARX-2 ). There are links for the manuals that have the dimensions to measure

 

[csxcp55]

Thanks for the links. I had already visited the one for the ARX models, but had not seen the AR models.
I can see that adding the radials increases the gain from 3dBi to 5.5dBi. My ARX-2B manual states a gain of 5.5dBd, but I see that the website has gain as dBi, not dBd, so it's pretty much the same.

What may have skewed my 'test' results with my ARX-2B and my VX-150 radio was that:
1. The radials were too long for the re-tuned frequency of 161MHz.
2. The radials were not at the proper position on the mast. The 50in indicated in the manual is for 146MHz, so I need to move them up the mast a bit.
3. When I attached the radials using a hose clamp, I did not break the coax cable to bond the outer to the radials at the point of attachment. So I probably had currents on the coax, and currents in the mast that were not in phase or whatever.

When I set it up for the next test, I will have the radials cut to length, positioned at the proper point on the mast, and the coax outer will be bonded to the radials at that point.

Someone suggested installing an inverted 'Cool Whip' dish over the bottom radiator and covering the tuning ring to prevent rain/ice from affecting the antenna's performance. Cushcraft should have considered this problem when they designed the antenna.

If I decide to replace this antenna - after all the experimentation - then it will be with one that is encased in a fiberglass radome, so no problems with the weather.