Phasing Antennas

[taco6513]

How would you go about Phasing 2 DB420's together?

Thanks 

WCRW870

[coryb27]

How would you go about Phasing 2 DB420's together?

Thanks 

WCRW870

 

For what reason? The 420 is already a great antenna, I can't electrically see any benefit to phasing two of them together.

 

Corey

[Elkhunter521]

Hi Taco6513,

The only benifit of stacking your antennas, considering the line of sight characteristics of the frequency, would be area saturation. A 3 element yagi would be simpler and more effective.

[Jones]

I also ask: WHY?  The DB420 is already a stacked phased array of 16 folded dipoles with an omni gain of 14 decibels. Why do you need more?

[taco6513]

The antenna is a 9.2db gain in omni set up or 10.4 and  the pattern looks like an egg. Every time you double the antenna size you gain 3db. This would take you from 9.2 to 12.2 db gain in omni set up. Would give you a more sensitive system for walkie talkies. So if you could phase 4 together you would get 15.2db gain. The better the antenna gain and the lower the feed line loss the better a repeater would preform. If you can do it why not?

[RCM]

The antenna is a 9.2db gain in omni set up or 10.4 and  the pattern looks like an egg. Every time you double the antenna size you gain 3db. This would take you from 9.2 to 12.2 db gain in omni set up. Would give you a more sensitive system for walkie talkies. So if you could phase 4 together you would get 15.2db gain. The better the antenna gain and the lower the feed line loss the better a repeater would preform. If you can do it why not?

Depends on the terrain. In a mountainous area for example, more gain is not necessarily better.

[Jones]

I agree with RCM.

 

As I explained elsewhere on this site, too much gain is not a good thing on UHF.  You will wind up with such a narrow beam-width that you wont be able to hit the repeater when you are in close to it.

 

Antenna height is king.  You will get better results from a 3dB antenna at 100 feet than you would with a 12dB antenna at 50 feet... especially in hilly or mountainous terrain.

[coryb27]

Also, Gain has nothing to do with RX..... If you need better sensitivity try using a filter tuned to the frequency, into a pre amp and then you need to pad out any gain from the preamp that is above the noise floor.

[RCM]

Gain works both ways. RX as well as TX.

[coryb27]

I guess everything I have ever learned is wrong, guess I should sell my Areoflex and Sitemaster.

[RCM]

Point a Yagi antenna at a weak signal, then turn the antenna away and see what happens to the signal. You won't need high dollar test equipment to hear the difference.

[berkinet]

Gain works both ways. RX as well as TX.

Antenna “Gain” might reduce your S/N ratio, especially in the case of a directional antenna, because you will be receiving less noise and competing signals. But, it will not impact the signal strength of the desired signal. In the case of an omni directional antenna, the impact is really minor since you really don’t hear much from

directly overhead or below the antennna.

[coryb27]

Antenna “Gain” might reduce your S/N ratio, especially in the case of a directional antenna, because you will be receiving less noise and competing signals. But, it will not impact the signal strength of the desired signal. In the case of an omni directional antenna, the impact is really minor since you really don’t hear much from

directly overhead or below the antenna.

 

Trouble is most people dont understand what S/N ratio, insertion loss, return loss, impedance, noise floor, velocity factor etc even are. The Yagi example has noting to go with gain at all. I have shown countless people using calibrated industry standard equipment RX gain is nothing more then S/N. If you take a 3dB Yagi and a 18dB yagi, mount them in a fixed position at a fixed signal the uV level received by the test equipment is going to be the same. This is why filtering, pre-amps and attenuator's have a place. Simple really, a filter to reduce the S/N ratio and provide adjacent channel rejection, pre-amp to boost the signal and proper attenuation to lower the noise floor.

[RCM]

Call it whatever you like, but antennas with greater gain also have greater effective area which increases received signal strength. When you double or quadruple the size of the antenna you pick up more noise and more of the desired signal equally.

[coryb27]

Antenna gain is selected based on the site and required coverage area. It is a total misconception that more gain is better. Depending on the antenna height and terrain you can do more damage then good with higher gain. Site engineering is an important part of any system, science and methodology will always provide the best results over what one may think. Unless you are stacking UHF Yagis you will gain nothing by phasing omni's together, you would be better off setting them up diversity using power dividers but this involves its own engineering and the proper test equipment. Co phasing omni's was and still is popular for 10 and 11 meter but that is HF AM not UHF.

 

I currently have several DB-420, DB-411, DB-408, DB-404 and a single Sinclair SC329-HF2LDF in use at different sites both part 90 Commercial and GMRS. Each one selected for the installation and desired coverage. The antenna is the biggest factor in any radio system with the coax the second, trust the science. I have and still do see allot of people wasting money and being unhappy with system performance over bad antenna selection.

 

Just my $.02 

Corey

[quarterwave]

What is the emoji for Nauseated? 

[rfmedic]

This whole thread hurts and is an absolute waste of time for the actual results. You would have more loss in the phasing harnesses than you would gain.

 

Put up the DB420 and enjoy the hell out of a kicka** antenna.

[n4gix]

Now this is a phased array! It is the infamous "Duga Woodpecker" in Russia.

[coryb27]

OMG the Woodpecker, I remember this famous numbers station from the 80's

[PastorGary]

Speculation was that it was an over the horizon missile launch 'radar' detection system. ERP was thought to be over 10 megawatts and was heard back then on a number of HF frequencies between 7 and 19 Mhz.  It routinely wiped out the transmissions from WWVH in Hawaii.

[n4gix]

That is precisely what it was, an OTH backscatter array. The transmitter was located about 70 km from this receiving array so it wouldn't cause any desense issues.

[w2xab]

If you are talking about stacking one antenna atop the other to get 3-db of additional gain, it requires a new factory phasing harness.

 

If you plan on mounting them otherwise, you would be better to us a voter and a second receiver for phase diversity on receive and can gain 6-db or more on RX.

 

If you are using a duplexer and the antennas are phased incorrectly (harness and/or spacing); it can create some bad TX patterns including rapid fading for mobiles.

 

One of the advantages of using a voter is you can add a high gain preamp (may require a bandpass filter also) and greatly improve handheld coverage.

 

 

[taco6513]

Going forward with one single DB420 and 220 feet of 1 5/8 heliax cable. Just told by tower owner that is all free for me to use. So I can't bit*h to much.

Trade off is I buy, install, service, and maintain a standby generator. It is on it's way. Be here next week. 

WRCW870