Building basic antennas with thick materials?

[-Jimmi-]

Hello everyone! Happy to found RR! Dozens of knowledge etc.!

As a former 90's cb:er, I found myself planning antennabuilds again. The trigger was cheap rtl-sdr dongle.

First, antenna at the time. First is for airband. Goal is to catch distant airport towers. 1/4 magnetic whip seems to catch something but nothing strong enough.

Antenna options are 1/4 gp, discone, 1/2 dipole and lastly yagi, if squelch wont crack..

Basics is on my head somewhere, and question is stretching bandwith. After reading tons of posts, and having various aluminum tubes (from 8 to 50mm diameter) laying around; is it worth to make 1/4gp vertical of 40-50mm pipe instead of random wire (broadband-wise)?

Other option is to make thick dipole from 40-50mm tubes, and convert it to yagi by adding more (thinner elements (8-10mm) if I need directivity..

Making discone is another story..

I Hope you are getting my idea, although english isn't my language 😀 Simply omnidirectional broadbanded antenna is nice first step, because I don't have fancy tools like antenna analyzers etc.

 

[merlin]

For DXing airports, perhaps the best antenna is a 1/4 wave vertical ground plane. You also need to get the antenna as high as practically possible, and use low loss coax such as RG-8U or RG-213. Anything lower than utility poles or 2 story homes, is just not going to perform well.
Because vhf air band is so close to fm broadcast band, you also need a good broadcast trap and/or an air band bandpass filter.
I use a stub that work reasonably well.
If you elect on a preamp, it must be very low noise. 5 to 10 Db will work fine. Mount that at the antenna after the trap/banpass filter
Now for DIY antennas, in theory a larger element vs wire is more broadbanded. I use 4.5 MM copper tubing for mine with excellent results.
40 or 50 MM pipe might be better suited for a mast.
There are a couple alternatives to the ground plane, such as a 1/2 wave J-pole or vertical folded dipole.
If you want to start from scratch fabricating antennae, I would recomend the ARRL antenna book. There are also numerous online antenna calculators if your math is not so good.
I have built countless antennas for various bands and frequencies including Yagis and discone, so hope this helps.
A note about my stub trap. It is cut for 98 MHz, so it will trap frequencies every 98 MHz going up the spectrum.
Inserted to the coax with a 'T' connector.
I have a Nano VNA H4, excellent for antennas and under $100 US.

[PDF] ARRL antenna book 21.pdf - Free Download PDF

Download ARRL antenna book 21.pdf

epdfx.com

 

[-Jimmi-]

About 90´s when internet wasn´t available, studying from books was almost only option. No we have online almost everything.
I´d better stick with tried and trued antenna designs, there would be less unwanted complications. Building antennas by own hands, studying and analyzing, or modifying existing designs is more satisfying for me, than just buy commercial version. I am an old school electrical engineer, now refreshing my memory of old "radiohobby" I know antennas on basic level, but not familiar with the nuances

Feeder cables I'm using are about 10m long RG-6 and 2x LMR-210. They are already on the roof, as an option that never needed. Everything is flowing on optical fibres under ground... Now I know how could I use those. 50Ohm LMR:s for discone/gp and RG6 for dipole

Anyway, some manufacturers in Europe (where I live) have inspiring designs, like SIRIO GP -series & airband yagis. Also US origin (?) DPD OmniX antenna is interesting design. They all use thick elements like 0.75" ... 1,5" or so.

When searching information on internet, I found K7MEM:s website. There was Fat-dipole calculator. A wire dipole with center freq. 127MHz gives 16% bandwith on 30mm spacing of two wires. I guess I could have same results with 30mm tubing?

Discone or Biconical variant is also on my list; any suggestions for lowest freq on calculation? If target range is like 118-500MHz?

Vertical Biconic antenna (sold here as a double discone !?!) I thing it is just Broadband "stretched" dipole, or "copypaste boomerang" centered at some freq. Anybody familiar with performance of these compared to other omnidirectional antennas?

 

[-Jimmi-]

..Little inventory of garage. I'm gonna make fat gp antenna for civil airband of 40mm aluminum tube. Propably stupid idea, but why not! Let's see how it performs.

Nano-vna would be nice to have, but there is so much options on ebay. Cheapest at about $40..

 

[AK9R]

I'd stay away from Ebay.

R&L Electronics, who is a ham radio dealer with a long history, sells this one: NANOVNA NANOVNAH4 [NANOVNAH4] - $89.95 : R&L Electronics, Amateur radio store

 

[John_S]

The nanoVNA H4 is a very handy tool for antenna work. There are some good vids on Youtube to get you started with calibration and other stuff. EZNEC is also good for design work.

 

[-Jimmi-]

....

Great tips, thanks!

Now I'm modelling antennas with mmana-gal... It takes some time to learn, but what a great tool!

1/4 civil airband gp is in progress and goes up to mast some day.

Meanwhile: is there some tips for making a discone or bi-conical antenna? Preferred calculators etc.? Someone has make these for sure, and know do's and dont's for diy -costructions. Is there some good starting points for "minimum" freq for calculation based on ARRL book? I mean lowest calculating freq vs good first resonant freq? It is hard to see without vna how design works, and is there harmonics visible. Also how is resonance/matching behaving when there is, say, 4 elements shorter and 4 elements longer on both disc&cone etc.

Seems that I'm not able to find any calculations for biconical antenna (even on ARRL book).. I am assuming, that it could be made just by "mirroring" cone design of discone. Commercial version claims in specs that it's a bit better beamed to horizon than a discone? Any real life opinions?

Slow progress, but going on !!

 

[John_S]

Discone antennas probably don't get that much usage in the ham community because they don't have much gain. The military uses them where a wide band of frequencies needs coverage in one radio. You'll probably find more just using Google than in books. If you need a little more gain for VHF/UHF frequencies, try a slim jim vertical...easy to build with 450 ohm ladder line.