EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: veedub565 on November 01, 2024, 07:14:43 pm
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Just looking for some opinions on adding a boom to my antenna mast.
Currently I have a 5m long aluminium pole, 2" dia and 3mm thick, with a Diamond X50 on the top. It's mounted to the side of the house with T&K brackets spaced about a meter apart.
I want to add an extra antenna (DPD OmniX) for the scanner. So I was thinking of putting a boom at the top of the 5m pole, with the X50 at one end and the OmniX at the other end. Couple of questions though..
What dia would you use for the boom 1.25" or 1.5" ? and how long would you make the boom? I was thinking around 1m.
Ben
2E0KYS
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What dia would you use for the boom 1.25" or 1.5" ?
why not keep with 2" then you can use standard scaffold clips to join the boom to the mast
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Ben the bigger issue is that when transmitting on your X50 you will put a lot of RF into the scanner antenna and blow the front end of the scanner (if it is connected, and not through a change over switch).
If you have already bought the scanner antenna, I would look to mount it well away from the X50 to avoid blowing the front end of the scanner, if you haven't bought it, do you really need it? An X50 will pick up signals well away from 2m and 70cms.
73 SJ
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keep the current antenna tied to the mast, add the boom (say) 20" below the mast top, place the other antenna at one end of the boom and use a piece of rope running between the other end of the boom to a lower point of the mast (angle 45° or more) to "balance" the boom
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Ben the bigger issue is that when transmitting on your X50 you will put a lot of RF into the scanner antenna and blow the front end of the scanner (if it is connected, and not through a change over switch).
If you have already bought the scanner antenna, I would look to mount it well away from the X50 to avoid blowing the front end of the scanner, if you haven't bought it, do you really need it? An X50 will pick up signals well away from 2m and 70cms.
73 SJ
Yes I did wonder about the power from the X50 going straight into the scanner antenna, and then into the front end of whatever's connected to it. I have already ordered the OmniX, but I don't think it would be too late to cancel it (the emailed to say it would be delayed anyway).
The X50 does receive out of band, but surely it's never going to be as good as a dedicated broadband antenna (alright such thing really exists but you know what I mean).
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Yes reading about it now there seems to be quite a few cases where scanners have been fried by RF power from nearby TX antennas.
I don't really have the option to mount it anywhere else. Disconnecting the scanner each time I use the X50 will get old real quick. I could put a switch in, but guaranteed I'll forget at some point to switch it and fry the scanner. Some sort of RF power limiter ?
I guess another possibility would be some automatic switching that disconnects the scanner antenna whenever my rig is keyed up. Still, it would have to switch pretty quick to prevent damage. And if there's enough power coming down the coax to fry the scanner, wouldn't it jump across an open switch anyway ?
I've got a couple of switches like this might might work ? https://www.torontosurplus.com/hp-8761a-agilent-8761a-spdt-rf-switch-dc-18-ghz-12-15-v-solenoids-option-001.html (https://www.torontosurplus.com/hp-8761a-agilent-8761a-spdt-rf-switch-dc-18-ghz-12-15-v-solenoids-option-001.html)
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does your trx offer an external "ptt" plug ? If so you may consider a relatively easy solution
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No I don't think it does unfortunately (Yaesu FT-480R and 780R) only on the Mic circuit. There's other ways an means of achieving it I suppose.