Yes, here is the long awaited comparisation between the homemade HB9CV and the mighty 4 element LFA beam. Both on same height in the same tower, same coax, same test station with same antenna and same power levels. I tested with neighbourstation PA4O Peter who is living about 15km from my QTH.
TX best signal was 6,5-7 at PA4O
RX best signal was 6 from PA4O
Last evening we tested with the LFA. Of course the LFA has 2 more elements and a closed loop as radiator. It is a incredible design and much better as conventional designs from last century. Of course this is not a fair comparisation but I wanted to be shure it the LFA is really that good. Not theoretically but under real conditions.TX best signal at PA4O 8,5-9
RX best signal from PA4O 7,5-8
Theoretically because of the test results the LFA would be better as the HB9CV on this distance. I don't know what the actual specs are from the LFA. When I look around I see something like 14,2dBi. In dB that would be 14,2-2,15=12dB. The HB9CV would be doing something like 4dB but probabely on another angle. Difference between the antennas would be 8dB. In that case you would expect less as 2 s-unit difference. But of course a s-meter like we use in the IC-7300 and in Peter's case the IC-7410 is not that accurate and just a indication. The big difference actually is the front/side and front/back ratio. Wow, what a difference it is...
Yes.....I believe now, after this test, the LFA definitely is a better antenna. But what would happen if I extend the HB9CV with 2 directional elements?
If allowed to say....
ReplyDeleteIm afraid, the 4el LFA does not "really" have 14,2 dBI.
It most likely has around 8dBI. Gain primairly comes from boomlength and that 4el is limited to about 8dBi.
The 14,2dBI number provided, includes "ground gain" (which is around 6dBI).
The 14,2dBI is to be specified at a certain height, and im pritty confident Justin would have done that.
In aspect to compare... I would start with a dipole....and compare both antennas in reference to that dipole. (you cant really make mistakes with a dipole (make sure u include rf chokes) and its a rather reliable to compare. That cant really be said of the HB9CV.... Or you sure it actually has 4 dBD ? It would not suprise me if the gain actually was lower, infact...i can imagine it would suprise you hihi.
Another thing you could do to improve the test you are doing: is download a programm called "polarplot" that is really helpfull to get a "rough" idea of the antenna pattern. For sure its not 100procent accurate...well it actually isnt that bad ! ...but due to reasons (soundcard etc) it is to be taken as a "indication". BUT !! it will show "pitfalls". For instance commen mode currents providing a bad FB etc. Just google "polarplot" im sure it will show up, it is easy...and you are allready "ready" to use it (if you have a rotor and can do digital modes your oke !)
ps....im more then willing to function as a "beacon" for you on 10m just let me know if you want to try some test. Then you could "narrow" things a bit down :-) As it is wise to have several references over different distances.
Hoping the response helps a bit ? Always fantastic to see what you are doing Sebastiaan ! Kind regars, enjoy the weekend Henry PG0DX
Henry, of course you're allowed to write something. I know not even half you know about antennas. Yes, the comparisation between these antennas is not correct. It is only to show the difference in real time. The difference is 2 s-units and a lot better F/S en F/B. The 14,2dBi is something I picked from the internet, I see it is not correct. But both antenna's were at 13m high, so it gives another gain number!
DeleteI will look around for polarplot. Seems to be a interesting program for documenting a test.
O yes, both antennas featured RF chokes Henry. By the way 10m is open every day, propagation.....or is it the antenna?
73, Bas
Hi Bas
ReplyDeleteI'd agree with Henry, the real gain of the LFA is not 14 dB. That figure probably includes ground gain.
The LFA is probably around 8-9 dBd. The HB9CV around 4-4.5dDd.
One thing to try is perhaps to put known attenuaters in line to see that the difference might be. Another is to get your S meter calibrated by someone with a good signal generator. Find out what S4,5,6,7,8,9 mean in terms of dBm. At least then you can get a reasonable comparison.
Also test with more than one station. The more samples the better.
73's de John, EI7GL
Yes John, I should have test it with more stations. If there were more stations equipped with a reasonable 10m antenna in the neighbourhood. Henry is too far away, groundwave will have influence. Same for other stations around me. Nearest stations are PA4O and PA0O that I know have reasonable equipment and could give me some data. The S-meter is not calibrated of course it it would take too much for a test like this. It is more a real live test between the beams. In favour of the LFA, but I knew that already of course. Overall I'm not dissappointed ;-)
Delete73, Bas