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

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.
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Have you tried turning the antenna so the elements point up and down and then aim it towards the station (vertical polari...z...or...s...ation or whatever), Also what is the cable? Is it cheap stuff...kinked...wrong impedance...ran right against metal with no standoffs? In the RF world, cable makes a world of difference as opposed to audio frequency cable like speaker wire. I'm using 9913 on my Icom receiver, a world of difference in a 60 foot run from the antenna, from the RG cable I was using. Big as a cigar though.

How about the termination of the cable? Right connectors? Good, clean connections? Is the tuner in good shape?
 
Sounds as if you have a bad connection somewhere. If it was me, I would be checking all my connections, making sure all was tight and no corrosion from the antenna all the way to the F-connector on the back of your tuners. You might have a bad spot in your RG6. Any kinks anywhere? Once 'squashed', the kinked area sould be cut out and a connector installed. But, I'm guessing that you have a bad connection rather than a bad antenna or whatever. BTW - only one 'g' in yagi. You might also ask your question over in the http://tech.groups.yahoo.com/group/FMtuners/ forum. While folks here are very knowledgeable, there are several dozen folks over there that not only do this for a living, they live and breathe this FM tuners and antennae and everything associated with the art and science of same. I'm a refugee from there. Down to only six tuners at the moment.

Also, the question by Punker X about splitters in the line is quite important. Every splitter takes an equal share of the signal. One split and each gets half. 3-way split and each gets a third, and so on.
 
G'day all, Tripqzon's earlier comment about the actual position is an excellent one.

Likewise in my VHF Ham Radio, FM Radio and even TV antenna work, sometimes the exact position of the antenna can make a massive difference and even locations that would seem 'better' can actually be worse!

At VHF frequencies even a shift of a few inches can be critical, due to the effects of signal reflection and whatever. I have personally witnessed many, many examples of this kind of thing over the years.

I've even written articles in Ham Radio journals about it! That's one of the most annoying, yet endearing things about (VHf) antenna work, that whilst the laws of radio antenna physics always apply, sometimes the 'real world' can make that more than a little blurry! Regards, Felix (vk4fuq) aka catman.
 
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I certainly don't have the level of knowledge and expertise (or is that expertize in Aus?) that Felix and others here have with radio frequencies, but as a user of radio for many decades I can tell you that antennas and the capture of radio waves sometimes seems like black magic.

I know personally that sometimes having an antenna arrayed or using it in exactly the manner it's not supposed to work gives one the best results. I think (but I don't know for sure), that this is often the result of very localized effects that make frequencies bounce or attenuate in unexpected (at least to me) ways.
 
Make it vertical and point the side of the shorter element to your station. The longer one faces away.
 
Geeze.. just spend too much time writing a response and lost it.

Edited the street address out. Town and zip are good enough.

Still haven't seen the set up. Tuners used, cabling, how many connections, any splitters, switches or other connections. Amplifiers, lighting supressors, or ground blocks? Cabling used, 300 ohm twin lead, Coax RG59, RG6, The length of the cable run. Etc.

Was it confirmed the station is 50 miles at 5K watts? If so that's fringe, trees, buildings just about anything could affect reception. Placement of the antenna by a few inches could greatly affect reception.
 
Punker X said:
Geeze.. just spend too much time writing a response and lost it.

Edited the street address out. Town and zip are good enough.

Still haven't seen the set up. Tuners used, cabling, how many connections, any splitters, switches or other connections. Amplifiers, lighting supressors, or ground blocks? Cabling used, 300 ohm twin lead, Coax RG59, RG6, The length of the cable run. Etc.

Was it confirmed the station is 50 miles at 5K watts? If so that's fringe, trees, buildings just about anything could affect reception. Placement of the antenna by a few inches could greatly affect reception.
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Hi guys thanks for the response...

balun at the antenna...rg6u solid copper core quad shield cable about 60 feet going to no splitter directly connected(without added balun) this tuna has a balun internally i am using the micro cpu tuna

the only thing i changed is from using the front and putting the back of the antenna pointed at the transmitter...it works much better this way???
 
Your Sherwood Micro-CPU is a good tuner but you may need to step up to the plate. Try some different tuners and see what might work better. I use a HH Scott 312D Broadcast Monitor for weaker FM stations that far off. I am 50 miles between two medium sized cities. I get all but the weakest signals and many adjacent signals are present. The Scott takes less signal strength for Stereo to lock on than any other tuner I have had at home and excellent sonics. Do you have another station adjacent to your preferred station? If so, good selectivity is a godsend. Has your Sherwood been recently checked over by a good technician? It was one of the supertuners back then. :tresbon:
 
reneborg said:
Beveridge,
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!
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I use a simple dipole forty feet up on my chimney and it is vertically polarized. Signal strength has been great from as far as 100 miles away in Ontario. As far as I know a dipole has no gain I could be wrong on this. I would say the yagi should offer significant improvement in reception and as others have said the polarization may be the problem. I would set the yagi horizontal as most FM stations transmit both vertical and horizontal. I would just want it to be oriented that way and the reason why is most usually are.

I have a feeling I would go nuts installing a yagi (as much as I want one) if there are so many tweaks involved. No way am I gonna move that mast once its all installed and cabled in. (ohhhh... :sigh: )
I would definitely try what Rene has suggested. Disconnect the cable at the antenna and see what happens to your signal. Also if you want to take a dipole up there and wire it in to check your cable if you want that may be a good idea at least you can make some compariasons in the gain characteristics.
 
G'day Ron, I'm not sure if I understand your question? If you're referring to the picture of the five element yagi, well there's a bit of a story to it. It was actually designed and made by me, but it belongs to a Ham Radio friend of mine who lives much further north.

It is designed for the VHF 'two metre' Ham Radio band from 144 to 148 MHz. I optimised the design for the repeater segment around 146 MHz. It is shown vertically polarised as all the VHF repeater antennas are vertically polarised in Australia.

The antenna isn't in a tree. It's on a mast which is just visible, with trees behind it. The upper section of the mast has to be non metallic (e.g. wood) to avoid unwanted interaction with the elements of the antenna. Regards, Felix (vk4fuq) aka catman.
 
catman said:
G'day Ron, I'm not sure if I understand your question? If you're referring to the picture of the five element yagi, well there's a bit of a story to it. It was actually designed and made by me, but it belongs to a Ham Radio friend of mine who lives much further north.

It is designed for the VHF 'two metre' Ham Radio band from 144 to 148 MHz. I optimised the design for the repeater segment around 146 MHz. It is shown vertically polarised as all the VHF repeater antennas are vertically polarised in Australia.

The antenna isn't in a tree. It's on a mast which is just visible, with trees behind it. The upper section of the mast has to be non metallic (e.g. wood) to avoid unwanted interaction with the elements of the antenna. Regards, Felix (vk4fuq) aka catman.
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Interesting Felix. Thank you I was just worried a bit about the tree and you up in it mounting an antenna...
I guess I could not make out the mast in the picture.
 
beveridge2sw said:
the only thing i changed is from using the front and putting the back of the antenna pointed at the transmitter...it works much better this way???
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You haven't answered the one important thing that everyone is asking you, is the antenna FLAT (horizontal) or Pointing up and down (vertical)? The car antenna is vertical, college stations tend to vertical polarization. A horizontal receiving antenna will get a very weak signal from a vertically-polarized transmitting antenna. The reason that you are getting better reception off the backside is that the design may reject in-phase polarity but might accept some out-of-phase or untuned signal from the "wrong" part of the antenna construct.

ALSO a reflected signal usually has its polarity scrambled, producing some more signal that matches the antenna's polarity.

Commercial stations tend to be circularly polarized, which can be received with some loss of gain by either horizontal or vertically-phased antennas.

Is your antenna vertical or horizontal?
 
G'day all, yes he seems to be very evasive on this point. :scratch2: As I keep on saying, correct polarisation makes a massive diifference (at least 20 db).

As an example, one of our semi local area FM rock stations who use only vertical polarisation, are only weakly readable on my horizontally polarised yagi, but are virually full scale when it is vertically polarised! Regards, Felix (vk4fuq) aka catman.
 
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Given the design of his antenna, a Magnum Dynalab MD-10, it is horizontally polarized in construction; I'd give 99.9% odds that's how he would have installed it.

The station he wants to receive is way down (-88db) in the mud at his location, according to Antenna Fool, so he's got a challenging reception issue that demands the best possible setup, including a tuner. If the station is vertically polarized, yeah, that'll make things worse. I can't find any clear indication of polarization in the FCC database, just that it's a 5 KW station about 300' high.

Near as I could tell from his response, he's now getting an acceptable signal off the back of his antenna and is understandably confused.

You know, he's going to be pretty mad if it turns out a simple vertical whip or dipole instead of that big $ Yagi would have been all the antenna he needed... :)
 
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G'day all, well then if the OP is using a large horizontally polarised yagi, he has a problem.

The only solutions I can think of, is to properly install a small (3 element) yagi vertically polarised separately, and pointing in the correct direction and if the signal is still too weak, use the blend or mono switch on his tuner (assuming they are transmitting in stereo).

A difficult situation. Interestingly enough, it is quite possible that he may be getting an improved signal with his yagi looking away from the intended station direction, due to signal reflections and incidental polarisation 'reversal', as I have seen it happen in my Ham Radio work at a Ham friend's location (QTH). Regards, Felix (vk4fuq) aka catman.
 
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