maco 3 vs 5 element

[skullman64]

Ok have a question ive got a 3 element maco and a 5 element maco both mounted on towers 200 feet apart my problem is when switching between them the recieve on the 3 element is 2-3 s units better at time ive checked both ant measuerment and match is good on both the transmit is better on the 5 but recieve is lower anyone have any ideas?? thx

 

[Robb]

Bad location relative to the other?
Coax problem?

 

[C2]

The M5 should have a narrower beam width so it sees less (has a smaller aperture). Once you're pointed to a station, the M5 should sound quieter, but give higher signal to noise. You might not see that on the needle though, but you should be able to hear it.

If the noise floor is the same or louder on the M5, then there is a problem. Could be something else in the system or the antenna.

Same thing with telescopes, when you crank up the magnification, the objects get dimmer (not as loud).

 

[wavrider]

The M5 should have a narrower beam width so it sees less (has a smaller aperture). Once you're pointed to a station, the M5 should sound quieter, but give higher signal to noise. You might not see that on the needle though, but you should be able to hear it.

If the noise floor is the same or louder on the M5, then there is a problem. Could be something else in the system or the antenna.

Same thing with telescopes, when you crank up the magnification, the objects get dimmer (not as loud).

Antennas are Reciprocal.

If you have MORE gain on transmit then you should also see MORE gain on Receive.

Thus the 5 element should be more noise or a higher signal received than the three element.

As far as the three element receiving better? So many variables, coax, height above ground, grounding issues, etc etc etc.

The Five element should have a slight advantage over the three, maybe a 3db difference in TR and RX. 1/2 an S unit on a linear calibrated receive meter at 6db per S unit.

Three element will give you more useable band width due to the design and less elements than the five.

Signal to noise is a specification in performance of your receiver in the radio nothing to do with an antenna.

Antenna is F/B, I E rejection per say.

 

[C2]

Thus the 5 element should be more noise or a higher signal received than the three element.

Are you sure on the noise? More signal, yes... I figured the narrower beam width and higher F/B ratio, all the noise from those directions will be suppressed, more so than in the M3. Perhaps the higher gain will more than offset this? I would expect the noise to be roughly equal if anything else.

A loop is far quieter than a dipole and has gain over a dipole. That is just my experience, not that has anything to do with the beams we are discussing, just noting the affect an antenna can have on received signal and noise.

Here is a handout hosted on the Stanford University site, not notable for their studies in RF/Microwave, but the section on Antenna Temperature is a little interesting.

http://www.stanford.edu/class/ee252/handouts/antenna_noise.pdf

It is interesting to note also that the OP says the M5 has much stronger TX, so being the antenna is a passive reciprocal device, how could that be...

 

[wavrider]

The Yagi-Uda Antenna - Yagi Antennas

Out the door going to work but here is a link for some reading.

 

[C2]

The Yagi-Uda Antenna - Yagi Antennas

Out the door going to work but here is a link for some reading.

The article is a very basic and generalized discussion of Yagi antennas and does not address the topic here. I've used that information before to build a number of antennas, as well as info from the antenna elmer site.

The site author appears Dr. Peter Joseph Bevelacqua, who has written his doctorate thesis on optimizing antenna arrays, in where he discusses some theory about increasing signal and reducing interference and noise in the antenna system.

The illustration is that you have on the order of 12 dB reduction in signals from the side and 20 dB from the back, and around 12 dB gain from the front.

http://www.antenna-theory.com/Bevelacqua-Dissertation.pdf

 

[wavrider]

Yes Exactly,
20db front to back ratio. F/B. not signal to noise ratio.

12 dbd reduction on the sides I.E. 45 degree angles from front of yagi and from back of yagi. Picture a clover leaf pattern for the nulls for the sides of the yagi.

12dbd gain from the front of the yagi, correct for discussion purposes that is ALSO a 12 dbd gain in receive from the front of the yagi, so no matter what direction you point the yagi the receive will be stronger than a three element that has maybe 5.9dbd gain which is one S unit at 6db per S unit.

The more elements spaced correctly the more F/B ratio the yagi will have.

Yagi is a compromise antenna, power is not created it is redirected at the expense of losing some radiated power in other areas. Thus the side rejections and F/B. I.E. nulls per say.

By creating those nulls and redirecting the signal it increases the ERP of the signal.

The best thing about a yagi is you can turn the yagi to NULL out offending QRM, this may be what you are referring to as being quieter??

Of course you already understand this as you have mentioned you have built some yagi's before. Nothing new.