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Rock & Roll. Never in my wildest dreams did I think my Hy-Gain 20 Meter 203BA monobander would work this well on 17 Meters. By the way, I should stop calling it a 203BA. Now that it's been converted to 17 Meters, they call it a 173BA.
You're probably reading this post because you're thinking of doing the same thing, converting your 203BA to 17 Meters. I'll tell my story with the conversion so maybe it will help a Ham or two. Information on converting a 4 element 204BA seems readily available, but there's also some information I couldn't get to work for me out there too. Maybe this will help you cut through to the chase. I'll supply the dimensions I found, and also the compromised dimensions I ended up using.
The final result is a SWR across 17 Meters of less than 1.1:1. 1.08:1 is the lowest I got it, and it's 1.08:1 all across 17 Meters, top to bottom (18.068 through 18.168). The front to back is hard to believe but in initial tests with GI0EJU, here's what we found - with the beam pointed straight at Northern Ireland from Colorado, I was hearing Victor S9+5db. I turned around 180 degrees and could barely hear him as he was in the noise at S2. I couldn't understand a word he was saying, but I could tell he was there. From Victor's vantage point, I was +20db head on, and S4 off the back. That's mighty impressive to say the least. That math doesn't add up at 6db per S unit, but that was a "real life" test, what can I say? It is what it was.
Here's how I got there:
First thing of note is I only shortened the elements. I DID NOT change the element spacing on the boom. I left the element spacing exactly as it is for 20 Meters.
Searching the Internet, I found this for the individual sleeve lengths: 173BA dimensions.
Hy-Gain 173BA Rev 1.0
3 elements, inches
4.0000 1.2500 0.8750 0.4375
0.000 3.6250 69.3750 55.0000 44.6250
86.000 3.6250 69.3750 47.0000 42.1250
189.250 3.6250 57.3750 47.0000 50.5000
This design is a modification of the HG203BA.
It was developed by Hy-Gain using
YO 4.0. VSWR only verified. RC 9-8-93
But (always a big butt), make sure you continue reading this post because those dimensions did not work for me. I used the "modeled numbers" to shorten up the lengths of the elements (per the chart) but once done, tested and erected, the SWR was 1.9:1 on 18.125. After deciphering the rows into Reflector lengths, Driven Element lengths and Director lengths, I shortened the 203BA to those specs and I was quite disappointed in the final result. The antenna was resonant well below 18.125 Mhz so it still needed to be shortened up quite a bit. I did remember that "to raise the resonant frequency, the elements get shorter". Damn it, back to the drawing board.
Searching the Internet again, I stumbled upon VE7SNC's QRZ page where he mentioned he had already done the conversion. I emailed VE7SNC to see if he had retained the dimensions he used. Bingo! VE7SNC sent me a reply that he would look for them. A little bit after that, he emailed me with the numbers he used:
Director each side 147.5 inches
Driven Element each side 159.5 inches
Reflector each side 170.25 inches
Brent (VE7SNC) also sent me a .pdf with the dimensions for the conversion of a 4 element 204BA into a 3 element 173BA. The pdf file showed that they simply left Director #1 OFF the 4 element breakdown sheet and used D2 now as the single Director of a 3 element. The problem with these "total" numbers was I wasn't quite sure how to set the individual sleeves to get to the correct element length.
Since I had already shortened up the sleeves to fit the modeled numbers, I calculated those total element lengths then subtracted VE7SNC's numbers and there was the solution. 11" off each side of the Director, 2 5/8" off the Driven Element and 2 3/8" off the Reflector. I went out, lowered the antenna, and shortened the outer, smallest sleeve elements to get to VE7SNC's final length numbers on the Director and Driven Element. To do the Reflector, I'd have to stand the tower back up, rotate it 180 degrees then drop it back down again.
Let me tell you something. I didn't have any assistance (human or mechanical) putting that booger up and down, and since I'd already done it twice by myself, after the Driven Element and Director were shortened, I ran some tests. 1.08:1 SWR across 17 Meters, and the front to back numbers I saw with Victor in Northern Ireland (above). If something's not broke, you don't fix it! I left it up, left the director 2 3/8" a side longer than VE7SNC's numbers and I'm happier than a bug in a rug because I don't have to take it down and stand it up again.
Here's my final N0UN "combined" (and individual) dimensions from both the modeling and VE7SNC numbers:
R: 3.6250 (center), 69.375 (inner), 55.000 (middle), 44.625 (outer) = 172.625 (172 5/8")
DE: 3.6250 (center), 69.375 (inner), 47.000 (middle), 39.500 (outer) = 159.500 (159 1/2")
D: 3.6250 (center), 57.375 (inner), 47.000 (middle), 39.500 (outer) = 147.500 (147 1/2")
Thanks again to Brent, VE7SNC for assistance with the numbers! Now it's time to go play on 17M.