Yagi

[dmchalmers]

will a yagi aimed towards a fringe area 800 p-25 tower site possibly improve picking it up? Yes i'm aware terrain such effect, general question if it might improve?

 

[merlin]

Yes, and you should get the antenna as high as practical. Yagi, more elements, more gain, tighter beamwidth.

 

[Ubbe]

As long as the signal are above the noise floor it will help with a more powerful antenna with a higher gain, and also a low noise amplifier at the antenna with a lower noise figure than your scanner but pretty much all amplifiers will help more or less, if the scanner doesn't overload from very strong transmitters in the same frequency band.

/Ubbe

 

[dmchalmers]

Thank you guys i'd like to try an pickup treetops site (mi) but i'm 5-10 miles out of its radius, even when i've done an overnight tower search nothing.I'm on a30' tower with discone.

 

[Ubbe]

Discones are the worst antenna type to receive frequencies above 500MHz. It's direction pattern, that are best at the horizon below 500MHz, starts to point into the ground at higher frequencies and the signal level are down 10 times compared to a short steel rod antenna or the antenna you have on a portable scanner. This is the Sirio D2000 discone:

/Ubbe

 

[merlin]

Discones are the worst antenna type to receive frequencies above 500MHz. It's direction pattern, that are best at the horizon below 500MHz, starts to point into the ground at higher frequencies and the signal level are down 10 times compared to a short steel rod antenna or the antenna you have on a portable scanner. This is the Sirio D2000 discone:

/Ubbe

I seem to have lost my plots to my discone, but this Sirio you show is awful. There are a few discussions of discone, their gain/loss patterns
and SWR plots elsewhere. I don't know who made mine, but it has a lot better (flatter) insertion loss from 110 MHz to 980 MHz, then rolls off a bit. Receiving sites beyond their range, I get several from Utah state line, north to Rexburg, NW to Borah peak, W to Rupert.
East Butte, the furthest, the RSSI is just too low into noise, so 10 sites, 3 are 20 Db above noise. My discone on 2 meters, the long shot is scout Mountain, 14.5 mile, a little noise from a 30 watt repeater. I'm full quiet with 10 watt to discone.
For the OP, I might suggest a GOOD preamp with filtering below a 5 element Yagi and RG6/LMR400 coax on your 30' tower.
The preamp should have a good 10-15 Db gain, < 1.2 DB noise and good IP3.
Even then, no guarantee the signal you get is usable.

 

[Ubbe]

I don't know who made mine, but it has a lot better (flatter) insertion loss from 110 MHz to 980 MHz, then rolls off a bit.

By design a discone should have a good SWR over it's whole frequency range, but it is its direction pattern that are the problem. Most discones are designed to start work at 100MHz but above 500MHz its direction pattern starts to be less than optimal to the horizon. If you cut its horizontal elements to half size it works good from 200MHz to 1000MHz. Cut them to a 3/4 length and its a 150-750MHz range.

Where a horizontal elements points to are its reception angle. If you have all 700-900MHz system in one direction then cut only the element or elements that point to those sites and the rest of the directions will still have its original frequency range.

/Ubbe

 

[AB5ID]

@Ubbe So discones in general perform well over a 5:1 ratio above its lowest design frequency?

 

[Ubbe]

@AB5ID It's the SWR that usually has a 1:10 range. Can't remember what discone this is, but already at 437 it is 3dB down at the horizon.

/Ubbe

 

[AB5ID]

@AB5ID It's the SWR that usually has a 1:10 range. Can't remember what discone this is, but already at 437 it is 3dB down at the horizon.

/Ubbe

Thanks! I was doing some back and forth with Chat GTP and the recommendation was a Bicone antenna gives better performance over a 10:1 frequency range?

 

[Ubbe]

Ive only seen 1:5 bicones and then they have an even smaller frequency range for a good SWR.
Do you have a link to anyone you are considering?

/Ubbe

 

[AB5ID]

No, just looking at theory. And attempting to use GTP for answering questions (not a great idea without citing references)

https://www.mathworks.com/help/antenna/ug/vhf-uhf-biconical-antenna-for-testing-applications.html

ChatGPT - Bicone vs Discone Antennas

Shared via ChatGPT

chatgpt.com

 

[Ubbe]

A problem with ChatGPT and similar programs are that they have no intelligence of their own and can only look thru the internet for statements regarding the subject and compile them and present them as the truth. But most info written on the internet are false and it can't filter out those and can include a lot of garbage in its answers.

/Ubbe

 

[AB5ID]

Absolutely true! ChatGPT is fun to use, but sometimes it lies with confidence. It's like that one friend who swears they know everything, but you’ve learned to double check what they tell you just in case. 😄

 

[dmchalmers]

Yes, and you should get the antenna as high as practical. Yagi, more elements, more gain, tighter beamwidth.

Thank you Merlin i'm trying to improve my range to pickup one more just out of range p-25 site thats a higher populated area. I found one inexpensive one on amazon for $25 so its seems to be worth a try.

 

[dmchalmers]

thanks guys was wondering IF a yagi aimed towards tower might improve my chances.

 

[Ubbe]

thanks guys was wondering IF a yagi aimed towards tower might improve my chances.

It will. They are usually narrow in its frequency range. If you have a dipole antenna with one reflector element pair at the back it will start to reduce signals from the rear but increase the same amount from the front. Adding 10 pairs of elements will make it very directive like a 10-20 degree angle and usually even more narrow banded. 2-way radio signals are vertically polarized so any yagi needs to have its elements positioned vertically.

10 pairs of elements are more than 10dB in gain, 10 times stronger signal.

/Ubbe