Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Efficiency of 200-ohm hairpin matching
On 19 abr, 19:02, "Antonio Vernucci" wrote:
After running the required simulations it was possible to conclude the following: - the antenna impedance can clearly be transformed into 50 ohm or into 200 ohm by just changing the driven element length and the hairpin length. By selecting the proper lengths, an identical SWR curve can be obtained for the two cases, this meaning that the matching system impedance has virtually no influence on the SWR bandwidth of the antenna under simulation - however, for a given RF power, in the 200-ohm case the RF current in the hairpin is about 1.8 times higher than in the 50-ohm case. This means that in the former case the power lost in the hairpin ohmic resistance would be about 3.2 times that of the latter case. 73 Tony I0JX Hello Tony, Probably you convinced yourself for 100% that the antenna limits the bandwidth. One can generally say when the bandwidth of the L network is far greater then the antenna bandwidth (without matching, with respect to a reference impedance equal to the resonance [real] impedance), the overall BW is just a little less then the antenna bandwidth. Or you can say when the antenna Q is far higher then the Q of the matching network, overall Q factor is determined by the antenna. The Q of an L network is about sqrt(Zin/Zout –1), when ZinZout, uses sqrt(Zout/Zin-1). For a step from 20 to 200 Ohms, the VSWR=1.5 Bandwidth is about 11% (5.72 MHz in your case) A nice exercise can be modeling your antenna's impedance (without matching) as a LCR series circuit and put this into a lumped circuit simulator (for example a PSPICE simulator). Some simulators allow direct entry of S-parameters. Now you can add every other component (also lossy and lossless transmission lines) and see the effect on the overall BW. As other people said, the Q of a hairpin made of 5…10mm tubing is over 100. As the BW of your L match is far below that (also for the 200 Ohm case), losses in the hairpin are that low, that they can practically not be measured via field strength measurement. So 3.2 times higher then in the 50 Ohms case is still negligible. After all the calculations and simulations, I hope your 6m Yagi is still useful for you. Best regards, Wim PA3DJS www.tetech.nl please remove abc from the mail address when replying directly |
#2
|
|||
|
|||
Efficiency of 200-ohm hairpin matching
Probably you convinced yourself for 100% that the antenna limits the bandwidth.
Yes, I had overestimated the effect of the matching system, and, as you say, the antenna Q is far higher then the Q of the matching network. The fact that the capacitance (corresponding to the capacitive reactance of the shortened D.E) varies with frequency does not change things. As other people said, the Q of a hairpin made of 5…10mm tubing is over 100. As the BW of your L match is far below that (also for the 200 Ohm case), losses in the hairpin are that low, that they can practically not be measured via field strength measurement. So 3.2 times higher then in the 50 Ohms case is still negligible. I agree with the conclusion After all the calculations and simulations, I hope your 6m Yagi is still useful for you. Yes, after precisely tuning the D.E., it shows a good SWR all over the band of my interest. Nevertheless, before mounting the antenna, I would not have suspected such a narrow SWR response. 73 Tony I0JX |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Efficiency of Vertical | Antenna | |||
Efficiency | Antenna | |||
Request for information on phase matching and set / batch matching | Antenna | |||
Yagi Hairpin Match | Antenna | |||
Building a Matching Transformer for Shortwave Listener's Antenna using a Binocular Ferrite Core from a TV type Matching Transformer | Shortwave |