Can't Tune 1/4 wavelength vertical for 17 m and higher

[kn6msc]

I built a 1/4 WL vertical with slopped down radials for 20 m (using a PVC post, and aluminum radiating vertical element, and insulated stranded wire for the radials) and managed to tune it well to SWR 1.1:1 and close to 50 ohms at 14.2 Mhz.
I've been having difficulty to get anything lower than 1.5:1 in similar verticals for 17 and 15 m. I kept reducing the length of the radiating vertical element, but the frequency of best SWR does not move up much from 17.5 Mhz.
In both, the 17 m and the 15 m versions ( with corresponding radials of the same length as the vertical element) seem to hit some frequency above which the SWR will not go down not matter how much I shorten the radiating vertical element and the radials....Is there some capacitance/inductance built in the system that prevents them from tunning well above certain frequency?

 

[krokus]

How are you measuring your VSWR? Do you have access to a NanoVNA?

 

[FreqNout]

Is the Vertical elevated? If elevated:The number of radials, length of the radials, radials sloping greater than 90 degrees from the vertical element, etc. can all impact your swr.

Edit: Rudy Severns N6LF has a number of online studies on verticals.

 

[kn6msc]

In response to Krokus: I am using an MFG 259 ( incidentally, I have gone through two NanoVNA's and both did not last too long ( a couple of months))

In response to FreqNout: The base of the antenna is about 5 ft from the ground. The coax connector is at the base between the lower part of the radiating element ( Aluminum molding about 1/2" by 1/2" cross section) and the connector for the radials, which consists of a 4 inch galvanized washer with holes around the perimeter where the radials connect. The coax runs vertically along the post to the ground and then horizontally to the shack. There is only 50 ft of coax total to the rig.

 

[FreqNout]

I can only suggest looking at the radials (length/slope angle/number) in addition to the vertical element to fine tune your antenna.

You could also try modeling your antenna with a program called 4nec2 or eznec. A bit of a learning curve, but well worth it when building antennas.

A web search for N6LF antennas, you will see a lot of his real world test results on how to improve vertical performance. Good stuff!

 

[kn6msc]

Thank you FreqNout! I am a little familiar with EzNec2, so I will give it a try. I will check the N6LF as well. Thank you for your help; I appreciated it!
J.L.

 

[popnokick]

To provide some practical implementation experience that may help -
There is an antenna known as the Eagle One Vertical that can be found here https://eagleoneantenna.com with eHam reviews here -

https://www.eham.net/reviews/view-product?id=8094

The Eagle One is an extremely simple vertical antenna consisting of 31 feet of 16 gauge bell wire in a collapsible tubing. I have one, as do two others members in our ham club. We have found that a set of ground radials help, or when mounted on a camper / RV ladder the shield of the coax should be connected to the frame of the camper / RV to provide an RF counterpoise. The antenna will work in these configurations, but a good external (not rig-internal) tuner that will handle matches greater than 3 to 1 is needed.
To improve upon the tuneability and efficiency of the Eagle One, a 9 to 1 impedance transformer balun (un-un) should be installed at the base. These are available from Palomar Engineering, MyAntennas, and other sources. Or you can build your own.
Even more effective is an ICOM AH-4 or similar tuner installed at the base of the Eagle One. This provides not only the proper impedance transformer but also an autotuner. Personally I use my Eagle One with an LDG IT-100 tuner and a Palomar 9 to 1 impedance transformer. I am able to use my 31 foot Eagle One on all bands 40M up to 6M. I cannot get it to tune on 80M but am told that a tuner such as the AH-4 will let it work on 80M. In fact, I've heard that whenever the makers of the Eagle One show the antenna at a hamfest, there is an AH-4 at the base.

 

[kn6msc]

Thank you Popnokick for the info.
Best regards,
J.L.

 

[RadioDXfun]

Hi there, on the face of it there should be no reason why. A 1/4 is a 1/4 is a 1/4 wave assuming radiating and radial elements
are trimmed up to frequency. However, I wonder if there might be the possibility of a little CMC on the coax for 17m/15m ? I have read a source that 1/4 waves ideally need de-coupling using a choke of some kind.. (ugly balun or a ferrite ring with coax turns) It may be this lack of de coupling could be having some unforeseen effects which you are getting away with on 20m.

Here is the material I read:

Ground Plane Verticals

I hope one day we can make a QSO. I love speaking into California and the Western states, they are tricky to work as I am mainly out in the day times. I was out the other day at 5AM but chose the wrong band sadly, I was on 15m and I made the wrong call, in the early morning 15m needs longer to charge up I think at least at recent SFI's (indicator MUF remained low) so it was dead as far as DX goes just one YB station heard at 1/0 with QSB just before I QRT'd at 8:15AM. I was too tired to change band (I use 1 antenna per band)

If you want a cracking DX vertical.. I mean one to outperform them all (if you can get it up very high - close to 1 wavelength).... I suggest a mono band EFHW elevated as high as possible off the ground. In models I am seeing very significant gains at very low DX angles on 15m and 10m and my DX results on a 100W are bearing that out.

1.5:1 is fine actually but I do like to see lower SWR myself as well. Even though for balanced/ladder line users SWR is less of a concern and as I gather field strength is a better indicator of RF radiating out of the antenna than SWR.

What happens across 15m it is a pretty wide band ? Are you getting lower/higher readings at band edges than 1.5:1 ?

 

[prcguy]

The AH-4 does work well on 40 through 6m but a 31ft vertical is only good through about 17m due to the extreme upward radiation angle you will get on 10 and 6m. You should not need a 9:1 balun with a good auto tuner at the base.

To provide some practical implementation experience that may help -
There is an antenna known as the Eagle One Vertical that can be found here https://eagleoneantenna.com with eHam reviews here -

https://www.eham.net/reviews/view-product?id=8094

The Eagle One is an extremely simple vertical antenna consisting of 31 feet of 16 gauge bell wire in a collapsible tubing. I have one, as do two others members in our ham club. We have found that a set of ground radials help, or when mounted on a camper / RV ladder the shield of the coax should be connected to the frame of the camper / RV to provide an RF counterpoise. The antenna will work in these configurations, but a good external (not rig-internal) tuner that will handle matches greater than 3 to 1 is needed.
To improve upon the tuneability and efficiency of the Eagle One, a 9 to 1 impedance transformer balun (un-un) should be installed at the base. These are available from Palomar Engineering, MyAntennas, and other sources. Or you can build your own.
Even more effective is an ICOM AH-4 or similar tuner installed at the base of the Eagle One. This provides not only the proper impedance transformer but also an autotuner. Personally I use my Eagle One with an LDG IT-100 tuner and a Palomar 9 to 1 impedance transformer. I am able to use my 31 foot Eagle One on all bands 40M up to 6M. I cannot get it to tune on 80M but am told that a tuner such as the AH-4 will let it work on 80M. In fact, I've heard that whenever the makers of the Eagle One show the antenna at a hamfest, there is an AH-4 at the base.

 

[popnokick]

Every antenna could be better. Since last Sep I've had to use my Eagle One on my camper trailer... or not be on the air at all. I miss my Off-Center Fed Dipole. Since last Sep my Eagle One has only gotten me 727 QSOs in 29 CQ Zones, 33 ITU Zones, and 85 distinct DXCC countries on all bands 40 thru 6 Meters. Nothing on 80M.

 

[popnokick]

A correction: I have a Palomar 4:1 impedance matching transformer on my Eagle One. The manufacturer recommends a 9:1, but I had better results with a 4:1. Here's their recommendation - https://eagleoneantenna.com (scroll down to the Key Features section).

 

[paulears]

A thought. Replace the antenna with a dummy load and repeat the VSWR test - I bet the problem is the feeder. If you disconnect the antenna at the feed point, and stick the dummy load there, you should see 1 to 1. I bet you find it's the 1.5 to 1 or close that is causing grief.

 

[prcguy]

My DX Engineering 43ft vertical came with a 4:1 balun. Tossing that and installing an auto tuner made it into a completely different antenna and the performance went through the roof compared to just the balun.

A correction: I have a Palomar 4:1 impedance matching transformer on my Eagle One. The manufacturer recommends a 9:1, but I had better results with a 4:1. Here's their recommendation - https://eagleoneantenna.com (scroll down to the Key Features section).

 

[popnokick]

I came close to getting an AH-4 but since my days of 100% reliance on the Eagle One exclusively are coming to an end (as soon as I get my OCFD back up) I opted to stay with the 4:1 impedance transformer.

 

[AK9R]

As an aside, the AH-4 is being replaced with the AH-730. The major visible difference seems to be that the coax and control cable connections are on pig tails so you don't have to remove a zillion tiny screws and open the case to make connections (which most AH-4 owners did anyway). There must be some other differences because the price has gone wayyyy up. Ham Radio Outlet shows the AH-4 as in stock for $330 (seems like I only paid about $250 for mine 15 years ago) while the AH-730 is out of stock and $550! Yikes!

 

[prcguy]

Here is secret a tip for ya'll, so don't advertise and blow it for potential buyers. The older Alinco EDX-2 tuner is compatible with Icom and it covers 160m through 10m and is a better performer than the AH-4. The Alinco handles up to 200 watts where the AH-4 is about 120 watts. I think you have to repin the power/control cable to match the Icom. These tuners are also much cheaper as the demand is very low, I remember paying about $75 for mine used.

 

[popnokick]

The AH-4 covers 6 Meters in addition to other bands down to 80M. None of the others do.

 

[prcguy]

You trade 6m for 160m on the Alinco tuner. Besides, your not going to make very many contacts on 6m with a 31ft long whip, it needs to be half that size at most. Otherwise the radiation pattern is way up in the air and not at the horizon.

The AH-4 covers 6 Meters in addition to other bands down to 80M. None of the others do.

 

[alcahuete]

If you need a tuner for 6m, you're doing something wrong.