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| davelectronic:
Ok, I never thought 50 ohms connectors would be alright, I just had the mindset of TV / radio 75 ohms etc. But if bnc is fine I'd prefer to use that. What I'm concerned about is the connection coax between the chassis socket and the RF input to the receiver. 8f possible I don't want to compromise the built in telescopic antennas performance. The reason I thought I might need an isolation switch to disconnect the chassis socket when not in use. As if left connected to the same termination as the built in antenna, it might decrease its performance. |
| Richard Crowley:
You are really overthinking this. Consider that the built-in telescopic whip antenna is a COMPLETELY RANDOM impedance depending on how long you make it and what frequency you are receiving. If you are really that obsessed, then connect the built-in antenna to a short pig-tail coax cable with a BNC connector on the end. Then plug in the pig-tail to the BNC receiver input when you want to use the built-in antenna, and alternately disconnect the pig-tail and plug in your external antenna when you are using that. All your concerns about impedance, etc. would be significant if you were TRANSMITTING as you would need to monitor and minimize standing wave ratio (SWR). But working with a casual, consumer short-wave receiver the exact impedance is of no practical significance. |
| davelectronic:
Yes maybe I am over engineering the idea so far. It practical opening the case back and fitting a bnc chassis socket shouldn't be to much of a problem. My only thoughts where if I needed to disconnect the chassis socket when it's not in use, and the telescopic antenna is used instead. Might appear over engineers, but more practically a tidy solution to have the option of an external antenna. I can see now impedance is of no real concern as a receiver. Thank you for the comments and help, much appreciated. |
| Richard Crowley:
Use a pig-tail, use a switch, whatever. I would use a mini-toggle switch like this: This is of almost zero significance compared to the nature of your external antenna. (Height, length, etc.) And remember to use a lightning arrester where the antenna lead comes into your house. Connected to a good ground-rod under the arrester. Or at least always disconnect the external antenna connection 3 feet (1m) away whenever you aren't actively using it. You could seriously fry your electronics or even burn down your house. That seems infinitely more important to me. |
| davelectronic:
Sorry for the late reply.. Yes I will use an isolation switch, as for a lightning arrestor, I'm not sure its necessary. Having said that I did have a cb radio wiped out bang, whilst transmitting during a lightning storm. Bad on my part really. |
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