Triax FM5 vs a "Korner 9+0"

FM antenna discussion
Post Reply
daveB
Posts: 1187
Joined: 07 Oct 2014 16:49

Triax FM5 vs a "Korner 9+0"

Post by daveB » 15 Mar 2017 12:20

This for John and his house move.

Some screen shots of the 4nec2 results to go with my comments re John's house move. All gain figures are dBi - so take off 2.1 to get gain relative to a dipole.

Triax FM5 in free space - published dimensions (reflector 31.1 inches half-element)
Triax FM5 freespace Gain_FB.png

Triax FM5 in free space - reflector extended to 32.0 inches half element
Triax FM5 ext freespace Gain_FB.png

I wish I found out about this before I had my Triax FM5s installed!

Korner 9.2 with the outer elements removed - in free space
Korner 9+0 free_space Gain FB.png

Five/six element yagi 1830 mm boom length - in free space
Band II 5-6 ele yagi free space Gain_FB.png
This one is something I've modelled in 4nec2 based on the Antiference dimensions - but with the parasitic element 2.5 inches in front of the driven element . It achieves 14-15 dB f/b ratio

Finally - my antenna based on the K6STI design in free space
My K6STI style yagi in free space.png

With 20dB f/r and 22-25 dB f/b it was worth the effort to build it to get 8-12 dB improvement over the Triax.

Note - I did try extending the elements on my spare FM3 - by pinching the reflector elements from an antiference aerial. Crude measurements confirmed the marked improvement of F/b rejection on BBC R2 stations. That was done before I constructed the compact yagi and installed it on the garden mast.

David
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

User avatar
John Faulkner, Skegness
Posts: 4925
Joined: 19 Sep 2014 15:55
Location: Skegness, Lincolnshire. JO03dd
Contact:

Re: Triax FM5 vs a "Korner 9+0"

Post by John Faulkner, Skegness » 15 Mar 2017 21:48

Thanks David. Very interesting.

My methods at the moment are very crude and I am still yet to install a larger antenna than the ones I have been playing with so far.

I spent an hour this morning using a Triax FM3, pressed right up to the east facing window, but plugged into my Degen DE1103. Luxembourg 100.7 was a solid, noise free signal. German transmitters at Bremen and Steinkimmen were also peaking to noise free levels and would certainly have been at RDS levels on the XDR or FDM-S2, etc. I heard Brocken very weakly and I also heard Brocken, Hoher Meissner, Eisenberg, Kleve, Tentative Inselberg, Bonn and Nordhelle. No Langenberg! The south was quite impressive with Villers Cotterets almost noise free and there was a weak Bourges on 91.8.

I don't think there were any enhancements, i.e. tropo, but scatter was obviously pretty good.

Flipping to vertical produced fluttery but solid-peak signals from Egem and a few other Dutch transmitters.

Peter Körner
Posts: 33
Joined: 21 Oct 2014 10:05

Re: Triax FM5 vs a "Korner 9+0"

Post by Peter Körner » 16 Mar 2017 09:37

> Korner 9.2 with the outer elements removed - in free space

Why remove the outer reflectors? You would get worse F/B and slightly lower gain...

And, if you for some reason want a single-reflector design, the remaining reflector must be shorter than for a three-reflector design, so shorten to 1.68m, due to the mutual coupling effects between the reflectors. This is also the reason why the reflectors of the 9.2 have different lengths.

daveB
Posts: 1187
Joined: 07 Oct 2014 16:49

Re: Triax FM5 vs a "Korner 9+0"

Post by daveB » 16 Mar 2017 21:59

Hi Peter,

Purely because John has moved house and was considering an FM3 or and FM5. I just wondered what it would perform like and whether he could get something up and running at no cost. It was interesting to see that just taking the outer ones off it was still markedly better than the FM3 or FM5 ! I doubt he could mount a 9.2 indoors :D

What I would really be interested in is your thoughts on making the antenna out of 10 mm elements - I'm restricted on what I can put into the sky and 10mm elements on a 20 mm boom would reduce wind load significantly. I've put all the info into 4nec2 and the only change I made was the rod diameter. It is not as good mid band but still manages 29 dB f/r ratio - which is 9 dB better than I get with the compact yagi. But I don't know how much faith to put in 4nec2 - so far when modelling various antennae the figures 4nec2 gives are pretty close to published results. I modelled it over 'good' ground at 5.65 m the height it would be mounted at. I'm in a coastal area in area which was clay used for brick making and a couple of km away it becomes marshland and then estuary and finally the North Sea.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

Peter Körner
Posts: 33
Joined: 21 Oct 2014 10:05

Re: Triax FM5 vs a "Korner 9+0"

Post by Peter Körner » 17 Mar 2017 10:03

> What I would really be interested in is your thoughts on making the antenna out of 10 mm elements

No problem, you would only get 0.1 dB less gain and 0.5-1 dB less F/B midband (less elsewhere). In reality, very hard to notice.

If you are really picky, for 10mm elements, make the directors 4mm longer and the reflectors 10mm shorter. This would compensate for some of the (small) differences.

daveB
Posts: 1187
Joined: 07 Oct 2014 16:49

Re: Triax FM5 vs a "Korner 9+0"

Post by daveB » 17 Mar 2017 21:06

Hi Peter,
Thanks for your comments - I've found a uk company that 'only' charges £12.50 post and packing for all the 2500mm length of ali tubing I would need (one or two others wanted £20-£25, which was more than the cost of the materials. I've found a source of element clamps for 20 mm - so I shall place some orders and see what I can achieve.
SDRPlay, AirSpyMini, RTL dongles, SB920s, Yamaha TX930. 5 ele compact yagi on rotator at 18ft agl. FM5 facing east, FM5 facing south, FM3 facing NE, OIRT dipole, 3-ele Moxon vertical facing east.

Post Reply

Return to “Antennas”