Super Yagi
- Thread starter click23
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nd5y
Member
Sounds like BS to me. It is impossible for a 800 MHz yagi with 14 elements
on a 40" boom (about 3 wavelngths) to have that much gain.
It is probably more like 14 or 15 dB max.
You would also lose half of that gain in the 30' of RG-58 that comes with it.
Tom
on a 40" boom (about 3 wavelngths) to have that much gain.
It is probably more like 14 or 15 dB max.
You would also lose half of that gain in the 30' of RG-58 that comes with it.
Tom
click23
Member
Do you think that refletor at the end has anything to do with it?
nd5y
Member
click23 said:
No.
Tom
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I agree with Tom. The front-to-back ratio may be 24db but not the forward gain. Also curious is the horizontal polarization. Phone cell transmissions from commercial towers sure look like they are vertically polarized to me by looking at the antennas on them. They are always vertically oriented. And you will definately want to hunk that rg58 coax into your junk box and use bigger cable.
click23
Member
Sorry double post 
click23
Member
I thought that sounded a little to good to be true. I cam currently bidding on THIS yagi. I can pick up a TRS about 50 miles away with a squelch turned down on my RS mag mount. I am hoping for a big improvement with this antenna. Now all I have to do is tell the wife about it and convince her to let me put it up on the house, this is my first real antenna. Should I replace the 20' section of RG58? I am planning on usig RG6QS, will this work or should I get something better? If I can't put this on the house it is going to have to go into the attic. I am also looking at a RS discone to go up there, how far apart should I put them??
Thanks,
Robert
Thanks,
Robert
Check out using LMR-400 or some other low-loss cable. At 800 mhz, you lose quite a bit unless you use premium cable.
...jim
...jim
N
N_Jay
Guest
If you can receive the signal today (scratchy) you only need 6 to 10 dB more signal to get it solid.
Don't go for over kill.
Moving an antenna outside will give you 2 to 6 at VHF and 4 to 12 at 800 MHz. Doubling the antenna height will typically give you 4 to 6 dB also.
Subtract your cable loss to see if you are going to make an improvement.
Big gain antennas are usually not needed unless you are hunting for a signal that you can not hear at all.
In that case, it is hard to tell what yoy need since you don't have a reference point to start with.
Don't go for over kill.
Moving an antenna outside will give you 2 to 6 at VHF and 4 to 12 at 800 MHz. Doubling the antenna height will typically give you 4 to 6 dB also.
Subtract your cable loss to see if you are going to make an improvement.
Big gain antennas are usually not needed unless you are hunting for a signal that you can not hear at all.
In that case, it is hard to tell what yoy need since you don't have a reference point to start with.
JnglMassiv
Member
I don't think you can say at this point that you should replace the the RG58. It couldn't hurt but that yagi is going to make a big difference from your mag mount with its own (likely) crummy cable.Click23 said:
You may be just fine with the new antenna and the included cable alone. A hunk of LMR or other low loss cable with the N connector can quickly double your antenna outlay and since you may not need it at all..why spend more?
rdra90
Member
Okay guys, just how directional is a good Yagi??? I need to hit two different 800mhz trunked systems - basically in the same direction *but* not identical degree angles from my monitoring location. Can I "split the difference"; e.g. point the yagi halfway between the two towers - or does that blow the advantage of the yagi and I'm better off trying to get a better omnidirectional discone for 800mhz? I don't really want to blow $100 on a yagi if it's not going to buy my anything. Your advice would be appreciated.
K5MAR
Member
A quick rule of thumb, the longer the boom, the higher the gain, which means the narrower the pattern. For a highgain yagi, the pattern can be very narrow. It's hard to say in an individual case. If you don't need too much gain, and there is only a couple of degrees of seperation between sites, then you should be ok. YMMV
Mark S.
Mark S.
N
N_Jay
Guest
rdra90 said:
Lets try the scientific aproach.
How well can you receive the signals today?
Breaks Squelch, but can not hear = Need 10 to 20 more dB (Minimum)
Can hear but very scratchy = Need 6 to 15 more dB
Hear fine but a bit scratchy = Need 3 to 10 more dB
Good signal but want to improve reliability = Need 0 to 6 more dB
A few extra notes:
An outside antenna providing the exact same signal level to the scanner will have less variance in sifgnal and provide more consistant results.
A directional antanna can provide some protection for interfering signals in other directions.
The lowest gain antenna that does the job can reduce interfering signals, and improve signal to noise ratios.
OK, have fun! :twisted: :twisted:
rdra90
Member
Thanks guys - I guess should have also indicated that these are APCO P-25 digital systems. So I have to translate your "scratchy" gain guidelines to degrees of "cats in the blender" sounds. The tips re: low-high gain were helpful but I have to say that there will definitely be more than a couple of degrees separation in the direction. My concern is that I'll point between the systems and suck in never-never land as opposed to either system. Oh well, more head scratching.... I'm leaning now toward a better quality discone than the RS 20-176 I have - probably will look for one that's tuned for 800mhz. If you have any suggestions, I'd love to hear them.
N
N_Jay
Guest
rdra90 said:
If all you want is 800 scrap the discone and get an 800 MHz ant.
What do youy have now? and how bad is the reception? and where is it mounted? ANd how much of what type of cable? and how many of what type of connectors and adapters?
rdra90
Member
What I have now is a RS 20-176 (http://www.radioshack.com/product.a...me=CTLG_008_009_010_001&product_id=20-176) mounted 10' above roofline on a standard single-story home. 50 feet of RG-58 with PL connectors on each end. A PL-to-BNC adapter on the radio end (296d). Flat terrain; closest 800mhz system tower about 10 mi. away. It works just fine on VHF-UHF, but when they converted some systems to 800mhz digital; the antenna just doesn't hack it. I do monitor everything from Low VHF (air) to 800 mhz so I don't want to dump the other bands but am willing to take some analog degradation down there to get better digital audio at the 800 end (e.g. I can live with scratchy analog but when your digital drops out, well, I don't need to tell you--it's cats in the blender). The reception on 800 digital is variable - at best it's fair-to-middlin' and most of the time, it's fair to poor. So, I don't think I need a ton of additional gain. When I switched to an 800mhz rubber ducky, it definitely improved the portable results - if I could get the same improvement on the base side, I'd be a happy camper.
N
N_Jay
Guest
rdra90 said:
I would start with new cable.
If it is good you have between 10 and 12 dB of loss in teh cable and connectors at 800.
Change the cable out and use the best connectors you can get.
White insulated PL259 are not too bad, if that is what the antenna needs.
USe N, TNC, BNC, at the radio end and avoild adapters unless you need them.
The Next improvement I would look at is trying to double the antenna height above ground. But only if you ahev GOOD cable.
You will hope to gain about 6 dB (and loewer muiltipath noise) doing that but can lose even more with the wrong cable
rdra90
Member
Thanks for the scoop. I've seen alot of discussion about cable. Sounds like best bet is to use only the maximum amount of cable needed and to use your own connectors; vs. precut lengths with connectors attached. Better to go short on cable with manually crimped connectors vs. using extra feet of unneeded cable just to get factory crimped connectors. Any specific type of cable you would recommend? I'm looking probably at needing about 35-40 feet. This whole thing sound like the audio gear analogy. You can have the best amp (antenna) in the world but if the speakers (antenna cable) suck, so will the sound.
N
N_Jay
Guest
rdra90 said:
It depends on the connectors and the person putting them on.
I would keep 10 to 20 foot of cable to have quallity factory connectors.
As for cable, buy the best you can afford and can run.
1/2" LDF or Air is good 7/8 LDF or air is better. :twisted: :twisted:
Now I will let the guys here flame me.
DaveH
Member
click23 said:
Check the specs for a Sinclair SRL-406, 7-element yagi. It is not exactly the same, but close. Sinclair being a reputable company, doesn't inflate their specs. The forward gain is 12dBi, or about 10dBd. Looks like the other antenna is high by at least 10dB, if not more.
Dave
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