Radio antenna socket - Page 1
Forum section: electronics / projects

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 24, 2019, 10:35:09 pm
content: Recently picked up a DAB radio, portable Robert's retro RD-37. It has a telescopic antenna which is in good condition. I would like to fit a chassis socket of some type to allow connection of an outdoor antenna. Firstly would this be possible, and would I need to add an isolation switch to disconnect the internal telescopic antenna. Kind of like a selection switch, I'm looking for thoughts as its digital, I've done it on an analogue radio receiver and that worked ok.Thoughts and ideas appreciated. Also if possible, chassis socket type to use, N type F type etc.Thanks for reading.

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 25, 2019, 08:56:35 pm
content: Wow 56 views not a single reply....It wasn't click bait, I really wandered if adding an external chassis socket for an outside antenna might upset the signal on the telescopic antenna. Mainly as its digital signal.Go it alone taste it and see.

author: CJay
author_rank: Super Contributor
timestamp: April 26, 2019, 12:23:32 pm
content: Shouldn't be a problem, I'd probably use a premade pigtail and test first before I drilled the case though.

author: Benta
author_rank: Super Contributor
timestamp: April 26, 2019, 12:52:51 pm
content: You can call it digital, if you like, but the radio part is all analog and has the same demands as, eg, FM reception.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 26, 2019, 01:17:17 pm
content: RF is RF. There is no "digital" or "analog".The typical solution is to use a plug-in telescopic antenna. So you plug in the telescopic antenna when you want to use that, but then you unplug it when you want to connect an external antenna. That way there is no fiddly switching of the RF signal.Plug-in telescopic antennas are available in a variety of lengths and with various connectors ranging from PL-259 ("UHF") to BNC to RCA and even 3.5mm.The choice of exactly which connector to use is a matter of available space and aesthetics. Only you can identify the appropriate options. You can install the connector in the same hole where the existing telescoping antenna is. Of course, if you want to ADD another connector and switch, then you must identify where you can put them without destroying the appearance of the gadget.

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 26, 2019, 06:11:58 pm
content: Thank you for your replys, yes I knew the signal coming in wasn't binary. But thought there was some kind of DAC type thing going on. It was really just to obtain more stations, but wasn't sure if a connection coming off the exciting antenna termination would upset the received signals. Good idea to try it before drilling the case back for sure. The screw in telescopic antenna sound like a scanner screw in type, or bnc maybe. I'm still not sure if I need an isolation switch to disconnect any external chassis socket, as the short coax might cause problems with the telescopic antenna Unsure.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 26, 2019, 06:28:23 pm
content: Depends on what your external antenna is.It is rather common for an external antenna to be simply be a random length of wire strung out the window over to the tree.And in that case people often simply attach an alligator clip on the external antenna wire.Then just clip the alligator onto the existing telescopic antenna (whether extended or collapsed).If your external antenna is coming in on a coaxial cable then you may still just make a PL-259 or BNC to alligator clip adapter.Remember if you live in an area with lightning storms, be sure to use a proper lightning arrester connected to a good earth ground.AND detach the antenna connection to your radio when not in active use, or during a storm.Collapsing the attached antenna when using an external antenna may make is somewhat less susceptible to local QRM and QRN. Switching the attached antenna out of the circuit when using an external antenna may not be such a big deal simply for receiving. And depending on what kind of interference you may encounter in the immediate vicinity.

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 28, 2019, 11:27:13 am
content: That's where if I had an external antenna socket, I've got options in choice of antenna. Probably something with a good gain, and covers the band width of dab radio stations.Going to give it a go. Just work out best chassis socket type. I don't think bnc is any good as it's 50 ohms etc. Maybe N type chassis socket.

author: Benta
author_rank: Super Contributor
timestamp: April 28, 2019, 11:35:03 am
content: You can get BNC as 75 ohms, no problem.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 28, 2019, 02:06:32 pm
content: If you don't have an antenna yet (or the lead-in cable) then how did you arrive at: "I don't think BNC is any good as it's 50 ohms"? First, 50 ohms is a very common impedance for RF connections, and Second, the impedance is of practically no importance for HF reception. Now, if you were transmitting, then impedance would be important.An "N" type connector seems like nuclear overkill. You may be overthinking this.

author: davelectronic
author_rank: Frequent Contributor
timestamp: April 30, 2019, 01:11:51 am
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 30, 2019, 02:01:56 am
content: 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.

author: davelectronic
author_rank: Frequent Contributor
timestamp: May 01, 2019, 01:19:31 pm
content: 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.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 01, 2019, 05:31:11 pm
content: 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-rodunderthe arrester.Or at least alwaysdisconnectthe 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.

author: davelectronic
author_rank: Frequent Contributor
timestamp: May 04, 2019, 08:40:46 pm
content: 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.