Mr. Carlson uses BNC jacks on some of his receivers that were designed for either twin lead or ferrite bar antennas. He has a circuit that uses a .01 uF capacitor in series with the antenna and resistors to ground to “bleed off” static. Does anyone know: 1) Where and how does he hook to the radio and match the impedance? 2) Which YouTube or Patreon video describes how to do this? 3) Which value resistors does he use and why? Thanks for any help.
🤔 My comment on this would be that for shortwave frecuencies impedance matching in receivers not critical. Shortwave frecuencies are like DC compared to other frecuencies where impedance is really critical.
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I’m looking for the video where mentions the matching the 50 ohm coax to a 450 ohm input for a shortwave receiver. I seem to remember a video where he made one of these in a little white box. It might be for a communications receiver, which is more fussy about being properly matched. It was similar to the scope/ equipment protection box. I might be getting my wires crossed (pun intended).
@ryan-w1rmd The only protection box Video I can recall that has to do with radios is on YouTube, where he presents the construction of a protection box (in fact 2 identical boxes) that he has to use in conjunction with his HP 3585A (a 40MHz spectrum analyzer that is used to do radio alignments with) in order to protect it from high voltages while working in vacuum tube dangerous radios. That is a 50 Ohms input box and some attenuation as well but I don’t recall it as being an impedance matching as as well. The video is about 8 years old (by now) and is called: Build This Spectrum Analyzer Circuit. There is however another 2 protection boxes presented on Patreon but they are both to do with the curve tracer project so, nothing to do with radio alignment as such. If there is anything regarding Impedance matching box ? well… I’m not aware of it (yet!)
I remember a restoration that the IF filter shape was critical and if I am not mistaken that needed some antenna adapting. But I might be wrong
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From my memory, he did mention creating a box for this, but it was never revealed to us. Instead, he advised to search “RMA dummy” and build one to correctly align the radio. Don’t ask me which video this was but possibly the HQ140 rebuild?
Radios + Tubes + Scopes + Cars= Nothing better!
I have this in my favourite photos album for ages. Never built it.
Mm, I realize I cannot attach files 🙄
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@cpechiar There are many variants of a RMA Dummy Antena (adaptor) but in all fairness they should/would achieve pretty much the same thing.
Also, sometimes (this usually applies for old radios ) in the service manual of certain radio manufacturers you’ll find a suggested RMA circuit diagram to follow:
@ovi4 Agree, and now that you mention I’ve seen them in some schematic or service manual sometime. Is this what @ryan-w1rmd was looking for?
BTW, how did you attach the images to your post?
CH
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@cpechiar The best and easiest way to attach a picture I found to be via IMGUR (a free version) of an online picture hosting service. All you need is a free account. that’s it. So once you have the account setup post a picture there then go to your images tab and click on the image you want to be shown here. Once clicked you’ll be presented with a series of links. Choose the one that is named “Direct Link” this way the desired image would directly appear in your post (instead of just a link). NOTE: if the picture resolution and/or size is big (as in HUGE!) sometimes posting it here wouldn’t appear as full size and in order to see it (the viewer) will have to “inconveniently” scroll up/down/left/right. So an easy fix to that is to adjust the image size by selecting the appropriate size from the SIZE box (that is the last box show in the picture @ the bottom right hand corner). However to see the results of your picked picture size you’ll have to paste that (direct link) to your post (before publishing your post) have a look at it and if it is still too big (or too small for that matter) right click on the picture here (within your post) to select “CUT” to get rid of it then via a new tab (in your browser) go back and choose another size and repeat the process to get the picture just right. TIP: always, always choose the picture as big as possible so it would be seen clearer and more convenient by the viewers.
@cpechiar The best and easiest way to attach a picture I found to be via IMGUR (a free version) of an online picture hosting service. All you need is a free account. that’s it. So once you have the account setup post a picture there then go to your images tab and click on the image you want to be shown here. Once clicked you’ll be presented with a series of links. Choose the one that is named “Direct Link” this way the desired image would directly appear in your post (instead of just a link). NOTE: if the picture resolution and/or size is big (as in HUGE!) sometimes posting it here wouldn’t appear as full size and in order to see it (the viewer) will have to “inconveniently” scroll up/down/left/right. So an easy fix to that is to adjust the image size by selecting the appropriate size from the SIZE box (that is the last box show in the picture @ the bottom right hand corner). However to see the results of your picked picture size you’ll have to paste that (direct link) to your post (before publishing your post) have a look at it and if it is still too big (or too small for that matter) right click on the picture here (within your post) to select “CUT” to get rid of it then via a new tab (in your browser) go back and choose another size and repeat the process to get the picture just right. TIP: always, always choose the picture as big as possible so it would be seen clearer and more convenient by the viewers.
QUESTION MARK: Now…that’s kind of “peculiar” but I’m not quite sure why my last post (above) has been published “TWICE” and now of course I cannot erase one of them since it has gone past the 2-3 minutes EDIT time threshold (allowed by this site),
Hmmm this is a first ! Well….it could have well been “ME by mistake” but still… is a mystery since I really don’t know how it happened !?
Anyways…no a big deal as long as the message of the post gets across to the viewers.
@ovi4 And I’m trying to make an imgur account but it doesn´t alow me because of my country !!! So.. no igmur..
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@cpechiar the same has happened to me but somehow by just simply downloading the IMGUR app to my android phone…it would then the account creation be allowed. I have been trying to do it on my Windows PC first with no luck! I’m not exactly sure how I did it but I think that there was an option that might have appeared at some point saying something like: sign in with a Microsoft account or Facebook or a google account and in the end I might have chosen Google but again….it was quite some time ago and don’t quite remember how I did it. And did not need a mobile phone number at all.