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Yaggi antenna not that great ...whats the problem??

B

beveridge2sw

New Member
Hi guys here is the problem..... I have a magnum dynalab md-10 yaggi antenna that about 35-38 feet high above ground with rotor ...sitting in my car in the driveway i can get 90.9 wdcb collage of dupage station CLEAN on my 03 toyota camery why is it i cannot get this station in my home i have tryied changed deg's of rotation etc.. i have many tuners... all do not pick this up....FYI other stations come in with a strong signal.....but there may be other problems too..like 98.7 is a strong classical chicago station but ....when i rotate the antenna it still comes in real strong....I thought a yaggi antenna is very directional??

what the heck can be wrong :scratch2:
 
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90.9 khz might just be outside of your particular antenna´s range?:dunno:

This is just a wild guess, but it seems any antenna has an optimum receiving frequency, its efficiency declining as you move to each side of it.
 
G'day all, a well designed Yagi antenna should be a very potent antenna! As an active Ham Radio operator myself who has designed and buillt several yagi antennas for the VHF Radio bands and also for the FM broadcast band, I know this is true!

To answer your question, I wonder if the reason is signal polarisation. On your car, you would be using a vertical antenna with vertical polarisation. Is your yagi horiziontally or vertically polarised? A station transmitting only vertical polaristation will incur a loss in signal strength of at least 20 db if received on a horizontally polarised antenna.

Also the FM band is quite 'wide' in the frequency sense, going from 88 to 108 Megahertz, and designing a yagi for full frequency bandwidth is difficult, if not impossible unless operational bandwidth is traded off for gain. A couple of possibilities to check. Regards, Felix (vk4fuq) aka catman.
 
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How far away is the station, what kind of power do they put out. What kind of cable are you using, how many tuners to you have hooked to the antenna, (any splitters?).

I have an APS 13 at 35 feet and I pick up stations that I loose in the car 20 miles away.
 
Beveridge said "I thought a yaggi antenna is very directional"

That's very true, at least the ones I am familiar with (Felix and Mike prolly know a lot more about yagis for home tuners than me).

I've used Yaggis for radio-telemetry work (tracking animals) as well as trying to locate the source of radio transmitters. In both applications, changing the orientation (horizontal vs. vertical) does sometimes make a difference. Also, when I've used Yaggis for telemetry work, the yaggis were 'tuned' for particular frequencies.
 
catman said:
To answer your question, I wonder if the reason is signal polarisation. On your car, you would be using a vertical antenna with vertical polarisation. Is your yagi horiziontally or vertically polarised? A station transmitting only vertical polaristation will incur a loss in signal strength of at least 20 db if received on a horizontally polarised antenna.
Click to expand...

I think that may be the reason. This and that a car body can make a great ground plane.
 
catman said:
G'day all, a well designed Yagi antenna should be a very potent antenna! As an active Ham Radio operator myself who has designed and buillt several yagi antennas for the VHF Radio bands and also for the FM broadcast band, I know this is true!

To answer your question, I wonder if the reason is signal polarisation. On your car, you would be using a vertical antenna with vertical polarisation. Is your yagi horiziontally or vertically polarised? A station transmitting only vertical polaristation will incur a loss in signal strength of at least 20 db if received on a horizontally polarised antenna.

Also the FM band is quite 'wide' in the frequency sense, going from 88 to 108 Megahertz, and designing a yagi for full frequency bandwidth is difficult, if not impossible unless operational bandwidth is traded off for gain. A couple of possibilities to check. Regards, Felix (vk4fuq) aka catman.
Click to expand...

Hello this is not a home grown antenna and as far as i know this is strickly for the fm band its a magnum dynalab md-10 this thing is 350.00 dollars!!!! what the heck good is this expensive antenna if i cannot even get stations that my friggen car gets!!!

ok i am calm now :music: ok so is there a way to check if my antenna is working correctly?

as an experiment my coax rg6 quad is not grounded but grounded on my tuna ....i lifted my ground and the signal gets worse....

next... i reverse my shield and center conductors...I still have a signal although less in strenth....? how can this work this way??

lastly i just use the sheild only for my signal i still get a decent signal....:scratch2:

is something wrong??
 
Beveridge,

I don't know anything about that antenna but the first thing that came to mind after seeing your last post is whether the elements are properly mounted. Not meaning to imply anything but I do remember from using these in telemetry work that they need to be parallel to each other, and the antenna is directional with the shortest element being the 'front' of the antenna that you point at the 'target.'

Try this: connect the coax to the tuner but not to the antenna and see what you get. If the antenna is working properly, when you connect the antenna you should (hear) big improvements. I'm sure others here can give you better help than this ...

Again, my apologies if you already know all this!
 
Punker X asked a bunch of questions about the setup...

I'm interested because I could use some gain myself, thinking about putting something up, so I'm reading antenna threads these days.
 
G'day all, in thinking about this issue, I'm almost sure that polarisation is the issue. On VHF frequencies, if 'cross polarised' (one side vertical and the other horizontal, for example) you will lose a great deal of signal, at least 20 db.

In my Ham Radio work, our VHF repeaters are vertically polarised and likewise so is my receiving antenna (mounted up and down). This complicates the physical mounting arrangements but it is unfortunately necessary.

Many FM stations use 'mixed' polarisation giving good results regardless but I suspect that your college FM station probably uses only vertical polarisation, perhaps aimed at cars and domestic FM receivers with inbuilt telescopic whip antennas. Sadly, if that is indeed the case, heaps of antenna gain won't really make much difference as the antenna polarisation becomes the dominant issue in determining receivable signal strength.

Reversing the position of the coax wires will only make things worse. The 'inner' wire carries the RF energy and the outer is the shield (or earth), or should be the case ideally!

Attached is a photo of one of my VHF Ham Band yagis, vertically polarised. Regards, Felix (vk4fuq) aka catman.
 

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The MD-10 is an excellent Yagi-type antenna. I doubt there's anything wrong with it, other than being ridiculously overpriced. (If you want to throw it away, throw it at me! :D )

Much more like that there's something specific to your location and the transmitter; maybe polarization. Punker X has it right (and he should know!): you need to go to FMFool.com and enter your address. The resulting chart will tell you what signal strength to expect and the heading of every transmitter within a certain range.

Anything conductive is an antenna, which simply collects electromagnetic energy; a directional antenna designed for a specific range of frequencies is simply better at it. The MD-10, and any other directional antenna, is not absolutely directional--nothing is. It will pick up a strong signal no matter how it's oriented, but the signal strength will be weaker--hence the "front to back ratio", which is a simple indicator of directionality and gain.

I think you're going to have to go for a rotator to get the best results. Keep trying and telling us what happens; you should be able to get that station! We'll figure this problem out.
 
Did you answer the question regarding polarization (they spell it with a "s" in Australia, what's with that)??
The car's antenna is vertically polarized. Is the Magnum the same way?
If you want a truly directional antenna they do make something called a Beverage antenna. Probably won't work very well at the higher frequencies though!
JimB
 
Damon Hill said:
The MD-10 is an excellent Yagi-type antenna. I doubt there's anything wrong with it, other than being ridiculously overpriced. (If you want to throw it away, throw it at me! :D )

Much more like that there's something specific to your location and the transmitter; maybe polarization. Punker X has it right (and he should know!): you need to go to FMFool.com and enter your address. The resulting chart will tell you what signal strength to expect and the heading of every transmitter within a certain range.

Anything conductive is an antenna, which simply collects electromagnetic energy; a directional antenna designed for a specific range of frequencies is simply better at it. The MD-10, and any other directional antenna, is not absolutely directional--nothing is. It will pick up a strong signal no matter how it's oriented, but the signal strength will be weaker--hence the "front to back ratio", which is a simple indicator of directionality and gain.

I think you're going to have to go for a rotator to get the best results. Keep trying and telling us what happens; you should be able to get that station! We'll figure this problem out.
Click to expand...


Hello My antenna is rotor mounted (can be rotated) I have been to fm fool here is my address

"Edited by moderator" portage IN 46368

my friend has a shorter(less gain) antenna then me but is only 3 miles closer to the transmitter station..he get a much better signal :tears:
 
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Yeah, polarization could be the key here. Your desired station is extremely weak and I'm surprised your car radio pulls it in strong; changing the MD-10's mounting to vertical polarization won't be easy, it's not designed for that. Sometimes moving the antenna to a different physical location makes all the difference.

Well, that's OTA reception for you. Getting a desired station is sometimes an exercise in frustration; every installation is unique and so are the reception rules. Makes for a fun but occasionally maddening hobby...
 
Also, what kind of FM tuner do you own? How long has it been since it's had a servicing. Some tuners are better than others on reception ability. I don't judge a tuner section until I have verified that it meets specification when new. Your antenna is an excellent one.
 
Ok found something out

using the antenna backwards the station comes in much better signal strenth is the same :scratch2:sounds good:music:meaning i now have the last rod (rejection rod pointed at the transmitter) this works much better why?

whats the heck is wrong with my setup?
 
Based on the details you've been able to convey to us so far, I can only see that you're trying to receive a low power (5 KW) station 50 miles away. You have what is probably an optimal antenna setup in a difficult reception area (probably intervening terrain), and what you now describe might well be a reflected signal off an object like a building or some other structure that has a better "view" of that station's transmitting antenna.

There may be adjacent channel interference and turning the antenna to another direction might minimize the signal from an interfering station, allowing your tuner to more cleanly receive the desired station. Or the direction you're pointing the antenna now really is towards the station and you've just been pointing it the wrong way before. If so, problem fixed?

Aside from that, I suppose there could be problems with the antenna, the wiring and other installation. A better tuner may also be required. What are you using now and how is the coax connected to it? That is, is there a coaxial receptacle to screw the coax connector into, or are you using a "balun" transformer to connect to screw terminals?

I'm just fishing here for details to best understand your particular setup.
 
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Have you tried changing the physical location of the antenna?

The reason I ask is because a couple of months ago I was playing around with the location of my FM discone antenna. It was originally mounted to a mast that was suspended from a roof truss in the attic near the rear gable end. I put it on a chimney mounted mast that is located at the center of the house about 15' from the rear gable end. The reception got worse. Yet it was a few feet higher and outdoors. That 15' change seemed to put the antenna in a dead zone. I put the antenna back in the attic where it was and there it will stay until we get some warmer weather.
 
adam-ads said:
You could try hooking the tuner up to the antenna on the Camry:smoke: If it works, go buy a junkyard camry and put it on your roof.
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Might fix my AM reception problems too, but after looking at his neighborhood via Bing Maps I'm pretty sure it'd violate community standards. :) Nah, we're going to have to find a non-redneck way of doing this...
 
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