MAAS DP-27 dipole antenna tuning

Hello all,

I just bought a Maas DP-27 dipole (Yes yes I know I could have made one etc etc but I had no materials and for the price of this and my time it was definitely easier and cheaper to buy this one). Anyway the quality of the dipole on first impressions is great, with stainless wire and connections and high quality plastic parts. Its a 1/2 wave at about 5m long












So I threw it up last night on my balcony (basically identical to the balcony in the pic from google images) I just left it resting on the timber face and swr'd it, the swr was sky high. I proceeded to shorten it and did get the swr to 1-1.5:1 but i had to shorten it a lot ! (I didn't cut it).



My question is, how much should I be shortening it at a time to make a difference ? It was pretty late and I wasn't giving it my absolute best, will be trying again tomorrow but would like some advice, Does it ideally need to be suspended and not lying on a surface ?

I would like to operate from 26.965 MHz - 27.855 MHz predominantly

Cheers & 73,

Mark

You need to tune it for where it's going to be used so that'll probably mean putting it up and down a fair few times and it's times like this where an antenna analyser becomes worth the money because you can take a reading then adjust it a bit and see how many kHz that amount of adjustment gives you. You can't do this with a SWR meter nearly as well.

Where you had it it'll have been capacitively coupling to loads of stuff, including the house wiring, so will appear electrically longer. You'll find when you move it to where it's going to be installed you're likely to need to lengthen the elements so it was a good job you didn't cut.

So I stuck the antenna back up today, (in an inverted V due to space) SWR was sky high and gradually shortened it and re tested and was still high until it just dropped off a cliff. Basically 1:1 at both ends of the band. Heard a small bit of chatter on 27.555 but I’m getting some really bad QRM. Not sure if this is because my power supply is about 1.5m away from the radio or just due to the fact that QRM is almost a guarantee in a relatively built up area.

Hi - welcome to the world of interference, which is sometimes not a nice place. If you’ve mounted the dipole on a hand rail as in the picture, I’d just try moving it. Pickup from nearby ADSL broadband cables and AC power cables would be my first thought. Re the power supply question - perhaps try bringing the antenna end close to the supply and see if it gets worse and worse. I have also tried a car battery to power the radio and turned the house power off to try to find the noisy thing, if that makes any sense. Happy hunting .

Thanks for the feedback Wilko88. My intention was never to have a permanent homebase as it so easy for me to drive 25 mins and be at ASL 4000ft which is why i'm predominantly static mobile but i did put this up to see if i could have some QSO from home but im not going to put massive effort into eliminating the noise. I will bring the dipole out with me mobile and string it up off a tree so all is not lost.

73's Mark

I have this antenna recently, and something confuses me about the settings. 
If anyone knows or has experience... Is it allowed to adjust the SWR by shortening or lengthening the ends? 
Or do the ends always need to be the appropriate length for the frequency at which the antenna is used?

The second thing that interests me, if anyone has an idea how to set it up to achieve the best performance for DX... 
My idea was to have it in an inverted V.

Image

Hello Dejan,

Yes you will need to lengthen or shorten the legs to tune the antenna to the frequencies that you are using. A dipole should cover the majority of the 11 meter band with an acceptable SWR.

The inverted V configuration will be fine for DX and should also help a bit with local contacts as well.

Best 73 Gary.

GaryWilson wrote:

Hello  Dejan,

Yes you will need to lengthen or shorten the legs to tune the antenna to the frequencies that you are using. A dipole should cover the majority of the 11 meter band with an acceptable SWR.

The inverted V configuration will be fine for DX and should also help a bit with local contacts as well.

Best 73 Gary.

Hello Gary,
Thank you for the comment.
It confused me that it's a bit longer than it should be according to the calculation.


Here is the image, as seen by the Nano VNA:





73's Dejan

Hello Dejan,

The legs of an inverted V dipole will need to be a little bit longer than those of a horizontal dipole. If you used a calculator for a horizontal dipole this is why you're experiencing a difference. The height of the ground it's mounted will also effect your results.

Best 73 Gary.

GaryWilson wrote:

Hello Dejan,

The legs of an inverted V dipole will need to be a little bit longer than those of a horizontal dipole. If you used a calculator for a horizontal dipole this is why you're experiencing a difference. The height of the ground it's mounted will also effect your results.

Best 73 Gary.

Then everything should be OK

I live on the fourth (last) floor.
I am at an altitude of around 200 meters above sea level.

73's Dejan

Short update. 
After just three months of use, I managed to burn out the balun.
I wouldn't recommend connecting this antenna to the amplifier.
The balun can barely handle 5 times less power than declared.

I found quite a few bad antennas on Ebay and elsewhere over the years. Often with very thin wiring, and poorly rated small toroids inside.

In the end I made my own with thick copper enameled wire large toroids and soldering by myself which is was good quality.

Some of these ready made dipoles and baluns never achieve get a low SWR. One place uses potting compound for the toriod and wiring which is 100pct unnecessary and that somehow that messes up the SWR, I never saw less than 1.8:1 and all my own baluns and transformers I get 1:1 at the radio.

Then you are likely to get the efficiency and reliability and risk of overheating, any heat is RF that was not radiated. Some hams are trying to make a few bucks on the side form the hobby and they make pure junk.

Frankly it's not good enough so it is worth trying to make your own even if it is just to avoid junk.

I know many hams parrot the saying "1.9 to 1 does not matter etc." The problem is it sets a precedent for other small issues that you are also not meant to worry about. Not elevating the antenna, not using the best coax money can buy, running radio on 80W instead of 100W, not worrying about SWR, not having enough radials, poor soldering and connectors, lossy in line items, not resolving noise sources where possible, poor antennas with crummy patterns on some bands. All these losses then add up. It is a much better approach to try and perfect every part of the station and not let these issues slip. 

Each to their own though.

Power in Watts and RX microvolts lost, are losses plain and simple.

It all adds up in the end, losses and mismatches.