This is a report about a Yagi that i built during my holidays.
Here is some information about it:
| Gain: | 11dB |
| F/R ratio: | >26dB @ 145 MHz |
| Boomlength: | 3.30m (~1.6 λ) |
Here are the Element dimensions:
| Element diameter | 4mm | 6mm | 8mm | 10mm |
| Reflector | 1019mm | 1016mm | 1014mm | 1011mm |
| Driven Element | -- | -- | -- | 978mm |
| Director 1 | 959mm | 951mm | 945mm | 940mm |
| Director 2 | 933mm | 924mm | 916mm | 909mm |
| Director 3 | 916mm | 906mm | 898mm | 891mm |
| Director 4 | 915mm | 905mm | 897mm | 890mm |
| Director 5 | 904mm | 894mm | 885mm | 877mm |
Important: The driven element is always 10mm !!
Here are the distances:
| Element No. | related to the previous Element | related to the Reflector |
|---|---|---|
| 1 | 0mm | 0mm |
| 2 | 360mm | 360mm |
| 3 | 240mm | 600mm |
| 4 | 545mm | 1145mm |
| 5 | 675mm | 1820mm |
| 6 | 805mm | 2625mm |
| 7 | 620mm | 3245mm |
The antenna which has 28Ohms is matched to the Transceiver's 50Ohms using 2 parallel 75Ohms lambda/4 cables.
 |
Attention: | The connection to the boom is very important!! (on the picture i haven't done that yet) and should offer little resistance to HF -> cable with large surface (->coax braid) to avoid eventually occurring common mode current making the VSWR worse. |
|---|
| Tip: | Use 2 parallel 56Ohms/2W metalloxide resistors as dummy load. And if you need a higher power dummy load use 8x220Ohms/2W resistors (=27.5Ohms/16W). But keep the connections to the dummy load as short as possible!! if they're too long your SWR is at least 0.2 worse compared to the optimum. If you pay attention to this there should be no more problem to achieve a nearly perfect SWR.... |
|---|
| 1. experiences: | The antenna seems to work really good in spite of my bad
measurements with a tolerance of about ±2mm. The antenna has a really broad range where the VSWR is <1.2. I measured from 140 to 148.5 MHz and between 140 and 147.0 the VSWR was <= 1.2. |
|---|
The final antenna:
Another site with info about this antenna: DF8GH's antenna page