Ok, so I'm building a completely adjustable, lightweight, field portable yagi antenna. As of yet, I am not utilizing any baluns or matching devices in order to reduce weight and decrease the complexity of tuning. I am utilizing a straight dipole for the driven element (it is not folded) and feeding it directly. I am modeling my yagi to be adjustable in both element length and element spacing along a long square boom as to adjust for any desired band/frequency. The entire antenna is designed to be broken down into 3 foot sections for ease of portability. I really like the mechanical design, but I'm not too sure how electrically efficient it will be.
I want this antenna to be as versatile and fool proof as possibly. I am using yagi design software to get a base configuration to start with for any particular frequency I desire. I do not expect this to be a high performance antenna like some expect their yagi's to be.
I am modeling mine similar in design to a military version like the one in the following ebay link:
My questions are as follows:
• What is the best way to fine tune the yagi?
o I read that only the dipole should be adjusted to lowest SWR and to leave the reflector/director element length and spacing alone.
o I also read that to tune the beam on the ground you should point it skywards with the reflector on the ground.
• How do I know when the yagi is actually in tune?
• Is SWR alone the only/best indicator that the antenna is in tune?
• The best SWR I have gotten yet has been 1.5, is this a decent SWR for a non-perfect yagi?
• If I end up using a balun or choke, do I tune the antenna with the choke in place or disconnected?
• By not using a balun, will the common mode currents pose a threat to the radio even if the SWR is low?
When I tune the dipole alone (off the boom) and away from the other elements, I find that the point of resonance is pretty far out from the theoretical/ideal calculation. For instance, if tuning it to 440Mhz, I find I need to adjust the element beyond the theoretical length by approx 20Mhz.
• Is +/-20Mhz at 440 ok, or is something way out of whack?
-As of now, the boom is made of 4 three foot sections of 1" square tubing totaling 12 feet long when assembled.
-I have a total of 5 elements (including the driven) that are insulated from the boom.
-The elements consist of a 1/2" OD outer aluminum tube with a 3/8" OD inner telescopic tube
Thanks,
Jared
I want this antenna to be as versatile and fool proof as possibly. I am using yagi design software to get a base configuration to start with for any particular frequency I desire. I do not expect this to be a high performance antenna like some expect their yagi's to be.
I am modeling mine similar in design to a military version like the one in the following ebay link:
My questions are as follows:
• What is the best way to fine tune the yagi?
o I read that only the dipole should be adjusted to lowest SWR and to leave the reflector/director element length and spacing alone.
o I also read that to tune the beam on the ground you should point it skywards with the reflector on the ground.
• How do I know when the yagi is actually in tune?
• Is SWR alone the only/best indicator that the antenna is in tune?
• The best SWR I have gotten yet has been 1.5, is this a decent SWR for a non-perfect yagi?
• If I end up using a balun or choke, do I tune the antenna with the choke in place or disconnected?
• By not using a balun, will the common mode currents pose a threat to the radio even if the SWR is low?
When I tune the dipole alone (off the boom) and away from the other elements, I find that the point of resonance is pretty far out from the theoretical/ideal calculation. For instance, if tuning it to 440Mhz, I find I need to adjust the element beyond the theoretical length by approx 20Mhz.
• Is +/-20Mhz at 440 ok, or is something way out of whack?
-As of now, the boom is made of 4 three foot sections of 1" square tubing totaling 12 feet long when assembled.
-I have a total of 5 elements (including the driven) that are insulated from the boom.
-The elements consist of a 1/2" OD outer aluminum tube with a 3/8" OD inner telescopic tube
Thanks,
Jared