Thread: 91 XG Modified
View Single Post
Old 14-Jun-2020, 6:35 PM   #26
bobsgarage
Antenna Enthusiast
 
bobsgarage's Avatar
 
Join Date: Mar 2016
Location: Beach Park IL
Posts: 318
Quote:
Originally Posted by bobsgarage View Post
Tripleo thank you. It's all very clear to me now. I will take it step-by-step pictures, and I will report back. I also want to thank my other friends sheer on TV Fool and the other forums. Sev, Rabbit, Tim and Calaveras.

Seems like I always pick something complicated to do and it's hard to get input that way. So, I really appreciate it.
Yeah, I spoke too soon. I guess I wasn't clear on how many antennas I was trying to stack. I'm only looking to stack two at this time. I had some rude awakening when I was PMd.

"OK, I understand about the ferrite to form a choke balun around the coax, but there are two questions I have in mind: 1. If you connect two 300 twinleads together in parallel, that would give you 150 ohms. Wouldn't that be a 2:1 missmatch with the 75 ohm coax? 2. When you connect the two twinleads in parallel, they must be in phase. It's like connecting two batteries in parallel: + to + and - to -. How will you know which way is correct?It will work, but there will be some loss because of the mismatch which causes an SWR of 2:1. It is difficult for me to predict how much additional gain two antennas connected that way will give you compared to just one antenna.
There are two problems to be concerned about when you connect together in parallel the two 300 ohm lines from two antennas.
The first problem is the mismatch loss because two 300 ohm lines in parallel will give you 150 ohms, which you will then connect to a 75 ohm coax line.
You aren't going to like to hear this, but you would need a 1/4 wave matching section of 106 ohms between the 150 ohm point and the 75 ohm coax for a perfect match.
The second problem is getting the two 300 ohms lines in phase (or polarity if you prefer) when they are connected together in parallel. You have a 50/50 chance of getting it right. If they are connected out of phase the main lobe will split in two like this"


https://imageevent.com/holl_ands/sta...f5v5sec1.goose
Ooops... looks like I have another problem to solve? Now that we're in the 11th hour I'm so glad that I did not execute my plan fully. I'm kind of glad it was chilly Friday after work and I had to do some deck work around the house. That kept me off the roof! Anyhow what should I do? What do I do to achieve the correct match?
bobsgarage is offline   Reply With Quote