Newbie. I am totally ignorant. How to connect antenna?

**SharpyWarpy** · Wed 23rd Nov 2011, 00:39

Hi, all. I am completely new to radio communications. I dabble in electronics for the past 3 or 4 years. I pick up electronics of all types that are discarded by people I know and mostly from a local thrift store. I use these electronics devices of all types -- televisions, printers, etc -- for parts and for the learning experience breaking them down. The other day I acquired an interesting device -- a Realistic DX-160 Communications Receiver. It does not transmit so I know I don't need a license. I am very curious to see what I can pick up with this unit. It powers on and that is as far as I have gone with it physically. I have downloaded an owner's manual and a service manual. This thing looks so good I can't bring myself to tear it apart for parts. I want to replace all the caps and try it out. I have good headphones. I have read a brief amount of the owner's manual but it is not specific about what is required for an antenna. I have about 8 feet of what looks like the top section of an old radio antenna. Possibly Citizen's Band, it's just a straight piece of hollow aluminium, two sections. How do I secure this to the antenna connections on the back of the receiver? I know there are three connections there -- a ground and two antenna screws. Let's say I sand clean a spot at the bottom of the aluminium aerial and drill a small hole. Then screw a wire (with appropriate lug soldered onto the end of it) into the hole. Now which antenna connector on the back of the receiver do I use? If required I will attach a photo of the rear of the receiver, specifically of the antenna connections in question. Also in one of the manuals mention is made of alignment using a dummy antenna. What is the necessity of this procedure? Please bear with my ignorance but I am excited to learn what is possible with this well built unit.

**5B4AJB** · Wed 23rd Nov 2011, 03:31

Originally Posted by SharpyWarpy

with appropriate lug soldered...

You already sound like a radio amateur

Welcome, you're on the right track, the antenna's physical length dictates which frequency it will be resonant on (or most sensitive to).

The formula for this is the speed of light divided by the length, which gives the frequency.
Simplified further 300 divided by the MegaHertz will give the approximate length in metres.
For example, say you wanted to build a dipole for the centre of the 2m amateur band, which is 145MHz, then 300/145=2.07

This is the total length of the dipole, so each leg will be just over a metre long.

Now, a dipole is 75 Ohms impedance and your radio is 50, so you will need a balun, or transformer to connect it, here is a good diagram for making one.

Try to mount the antenna vertically, away from large metal objects as high as possible.

**G4LNA** · Wed 23rd Nov 2011, 07:03

I have used that receiver many years ago and at the time it was a well respected little receiver, the nice thing about it is the bandspread dial. You want to try and get that working as it is now in the vintage class of receiver and is sought after these days by collectors, so what ever you do don't pull it apart.

You will probably find just stuffing a long bit of wire in the back of the aerial socket will work just fine for receiving, at a later date as you get more interested then start looking into antennas, but be warned, there is a lot of misinformation out there along with wild claims about antennas, but you will find out all about that in your learning curve. In the meantime, welcome to the hobby.

**druid** · Wed 23rd Nov 2011, 15:19

If it's got two terminals marked "antenna" it's looking for a balanced line - probably 300 ohms (so you don't need a balun). The simplest is what's called a "longwire" and it's just what it sounds: a long wire. The longer the better. I used a 165ft longwire on my old Hallicrafters receiver and it worked fine. I believe you hook the wire to one terminal and ground the other. (and make sure you have some sort of lightning arrestor on the antenna!)

And as 5B4AJB says, the higher the better, and as straight as possible, horizontal or vertical.

Dipoles and other resonant antennas are great but restricted to fairly narrow frequencies: if you find you like, say, the 40 Meter band (7-7.3 MHz), you can make a 40 Meter dipole (physically 1/2-wave, so it would be about 20 meters long). But for general listening, hard to beat a longwire!

druid
VA7LAS

**K7KBN** · Wed 23rd Nov 2011, 15:28

For receiving, just get a length (a long length; say 50 feet) of light copper wire. #20 is fine. Connect one end of it to the antenna connection point (don't forget to strip the insulation off). Run the other end as far and as high as you can get. You have a pretty good receiver there, and it doesn't require an antenna cut to a specific length in order to pull in lots of signals. Now, if and when you get licensed, you WILL need to worry about the antenna's length and other factors. Not so with general shortwave listening.

**SharpyWarpy** · Wed 23rd Nov 2011, 22:29

Thank you all for the replies. I did not receive any emails stating I had replies. Is there such a service with this forum? If so how can I activate that? That said, I'm sorry I took so long responding. Thanks again to you all. Very, very helpful.
@ G4LNA : Yes the receiver looks very well made and I will not tear it down for parts. I love high quality machines and this one impressed me immediately when I took the bottom off to have a look. It powers up so I'm going to hook up a makeshift antenna using my new information from my new friends and see what happens. Wish me luck.

EDIT:
I modified my user settings to send an email instantly when there are posts to threads to which I am subscribed. I check my email at least twice a day. I hope in the future when my knowledge of radio improves I can contribute to this forum. Thanks again.

**SharpyWarpy** · Sat 26th Nov 2011, 19:27

Okay I rigged up a simple antenna, about 20 feet of 16 gauge copper wire 7 feet off the ground and connected it to terminal A1. I connected A2 to GND. Plugged my headphones in and turned the unit on. Not even a hiss at 80% gain. Tried several bands, no sound at all. I looked at the circuit boards with a good light and a magnifying glass and found one trace that had been intentionally cut. So I dismissed that. Found a zener diode and measured 6.7 volts on one side and 0.0 volts on the other, so that's not it. I'm at a total loss so I guess I'll have to give up on this receiver. Does anybody know if it would be worthwhile to change all the electrolytic caps? I did not see any signs of swelling or leakage but this thing was made back in the late '70s so I'm wondering. Shouldn't I at least get a hiss? My headphones are known good 'phones, stereo but I should hear something out of one of 'em. Anyway, I sure hate giving up on anything.

EDIT:
I looked at the troubleshooting section of the service manual and found several possible causes. One is electrolytic cap #66, a coupler to speaker/headphone jacks. So I'll try replacing that. It's 100uf, 16v. Another possible cause (there are 7 possibilities) is the power amp IC. Another is a short in the DC regulator circuit. I don't think the latter is an issue here. It's not blowing the fuse, voltages on the PCB don't look bad. Another is "Faulty power switch on AF GAIN VR3". I don't see how that is possible since the unit powers on and there are good voltage readings all over the place. And lastly "Faulty stand-by switch". Which I think is not likely. I'm going to replace the output coupler cap first. Then short the stand-by switch. Then replace the power amp IC. I suppose it could also be a bad pot for the AF gain. This thing has so many switches and bands I'm bewildered and excited at the same time. If I get this thing fixed I'm going to be so elated they'll have to reel me in with deep water tackle.

**G4LNA** · Sat 26th Nov 2011, 21:20

I think it's time to get the test meter and signal generator out, you need to find out what's not working before you start changing things. Why not start with the easy things first like the audio stage and inject a signal into the audio stage and see if you get an output. If it isn't working then that's a start, get that working then once it is then go to the IF and inject a signal. Process of elimination.

here are the circuit diagrams on this site.

http://bama.edebris.com/manuals/shack/dx160

**SharpyWarpy** · Sat 26th Nov 2011, 21:35

Originally Posted by G4LNA

I think it's time to get the test meter and signal generator out, you need to find out what's not working before you start changing things. Why not start with the easy things first like the audio stage and inject a signal into the audio stage and see if you get an output. If it isn't working then that's a start, get that working then once it is then go to the IF and inject a signal. Process of elimination.

here are the circuit diagrams on this site.

http://bama.edebris.com/manuals/shack/dx160

What is a signal generator? I'll have to Google that. Also you say the audio stage, inject a signal there. Can I do that by connecting the output from an mp3 player? And at what point in the audio circuit? I also need to Google IF. Thanks. And thanks also for the link to the circuit diagrams. I hope they are better quality than the ones in the service manual I downloaded. It is poor quality. I think I might invest a little money in a good service manual. I know a guy who can sell me one.

**G4LNA** · Sat 26th Nov 2011, 22:08

An MP3 player would do, I would help you, but I've got a crap internet connection at the moment, so I'm have trouble downloading those files, thanks Virgin Media, I'm kicking you into touch when I get a chance.

Without looking at the diagrams I guess you need to inject the signal into the volume control, that's as good as anywhere for a start.
IF means the Inter-frequency circuits, they could be around 455KHz in that type of receiver. If my internet picks up later I'll try and help you.

**G4LNA** · Sat 26th Nov 2011, 22:39

Right, the internet has speeded up now, on the circuit diagram you need to inject the signal into the AF Gain potentiometer VR3, inject it at the top end and start with the pot at its lowest setting to save blasting your ears out, run the MP3 player and slowly increase the audio gain and listen if you get a signal. Let us know how you get on?

Just to add, the circuit diagram has got the voltages marked on it which it really useful when it comes to fault finding. Again, don't start replacing anything yet, otherwise you are just working blind without carrying out any tests first and if you do start replacing things it will make it more complicated as you might not know what changes you have made to get the receiver working, you have got to be systematic from here onwards.

**techiesteve** · Sat 26th Nov 2011, 23:19

I've been looking at the service manual here http://radiopics.com/1.%20Manuals/Ra...%20Manual).pdf

The schematics were clear on screen. You have a DVM and the manual lists typical voltages, are any drastically out? If you turn up the volume control, hold the metal shaft of a small screw driver and scrape it against the top of the control, this connection goes to the mode switch. Do you hear any hum or clicks?

As you don't have a signal generator, it is easy to make a simple cross coupled multivibrator from 2 transistors, 2 resistors and 3 capacitors and a potentiometer to vary the output. This outputs a square wave, rich in harmonics from AF to RF, and makes an ideal simple generator for basic fault finding. I built one, along with a simple RF probe many many years ago. This would enable you to inject a signal at the AF stage, then if OK work backwards. An RF probe would indicate if the oscillator was running.

I wouldn't start randomly replacing components. The fault guide is very simplistic and typical of most, written at the design stage before any history of real faults is recorded.

**SharpyWarpy** · Sat 26th Nov 2011, 23:58

Originally Posted by G4LNA

Right, the internet has speeded up now, on the circuit diagram you need to inject the signal into the AF Gain potentiometer VR3, inject it at the top end and start with the pot at its lowest setting to save blasting your ears out, run the MP3 player and slowly increase the audio gain and listen if you get a signal. Let us know how you get on?

Just to add, the circuit diagram has got the voltages marked on it which it really useful when it comes to fault finding. Again, don't start replacing anything yet, otherwise you are just working blind without carrying out any tests first and if you do start replacing things it will make it more complicated as you might not know what changes you have made to get the receiver working, you have got to be systematic from here onwards.

Unfortunately the schematic is not the correct one for my dx160. It has an 8 pin PDIP chip whereas mine has a 14 pin chip. The owner's manual I downloaded has the 14 pin chip but it's not very clear. I'll download the service manual suggested by techiesteve and see if it is better quality. Just for kicks and giggles I tried to find a datasheet for the chip and it is apparently non existent. So I wouldn't know what to use as a replacement should that become necessary. Here's an update. This last time after I replaced the coupler cap (I know, I shouldn't have but oh well, I'm anxious) I tried it out and I noticed I got a reading on the meter. I used the fine tuner on the left to increase it to the max which was about 1/6th of the way up the meter. So I know it's trying to pick up. And that was without an antenna. I'm on dial up so it's probably gonna take a while before I can download the service manual techiesteve suggested.

**SharpyWarpy** · Sun 27th Nov 2011, 00:24

Okay I downloaded the service manual suggested by techiesteve and it is MUCH better quality than the one I downloaded from another source this morning. Yes, the values of the components are very clear and this will help tons. As I said earlier I am getting a signal on the meter even without an antenna so I'm leaning toward the audio part not functioning. I have a question. Why would somebody cut the trace coming off pin 9 going to the standby switch? That aside the next thing I'm going to do is connect one channel of an mp3 player to the gain pot like G4LNA said (thank you, G4LNA) and see if I get sound. I've been working on this off and on all day so I might not get back here until tomorrow morning. But if I don't get sound I'm gonna have to make my own amplifier. Shouldn't be that hard, I've built hundreds of cmoys and Pimetas. Thanks to you too, techiesteve. I'm so pumped.

**SharpyWarpy** · Sun 27th Nov 2011, 02:10

One more post before I go to bed. (yes, I'm a country boy.) I had a look at the audio portion of the schematic and saw pin 9 is where IC1 gets its power. I repaired the trace that had been cut there and now I get a hum. The hum does not go up in volume with an increase of the gain pot. I could no longer get a signal however, so I put it on hold until tomorrow -- after I disconnected the trace again. I suspect the previous owner did this trying to diagnose the loss of audio and then gave up. Tomorrow I will wire in an external headphone amplifier to the center connector of the AF gain pot and ground the other lead. That will bypass the audio amp of the board. It will be interesting to see if I get the same hum with no adjustment with the gain pot or if it does perform as it should. If it works like it should I'll hook up the antenna and try to home in on something.

**techiesteve** · Sun 27th Nov 2011, 08:36

I very much doubt you'll find an equivalent to the NEC UPC20. Page 4 of the manual does show the chips internal circuitry, the pre amp pin out 4, input to the PA pin 5, and the simple regulator circuit. I think that's the best you'll find.

I presume you've tried the receiver on both AM and SSB, as SSB uses a separate product detector and AF pre amp.

What you've proposed will break down the fault to either RF or AF, which is logical.

**G4LNA** · Sun 27th Nov 2011, 08:40

Obviously pin 9 is the supply voltage for the chip, there are some voltage reference points around the chip so check some of the voltages and see what you get, if that has gone it is an obsolete chip, so you might have to build an amp for it. Hopefully that is all that's wrong with it.

**SharpyWarpy** · Sun 27th Nov 2011, 16:36

Originally Posted by techiesteve

I very much doubt you'll find an equivalent to the NEC UPC20. Page 4 of the manual does show the chips internal circuitry, the pre amp pin out 4, input to the PA pin 5, and the simple regulator circuit. I think that's the best you'll find.

I presume you've tried the receiver on both AM and SSB, as SSB uses a separate product detector and AF pre amp.

What you've proposed will break down the fault to either RF or AF, which is logical.

Yes I did try both AM and SSB. I found a replacement for the NEC UPC20. Mouser has it, it's an NTE1075A. $12.00. Should the need arise. I have yet to try the headphone amp -- I'm going to try that today. First I'm going to disconnect the input and output to the chip. The power to pin 9 is already disconnected. Thank you.
Here's a link to the PDF for the NTE1075A:
http://www.nteinc.com/specs/1000to1099/pdf/nte1075a.pdf

**SharpyWarpy** · Mon 28th Nov 2011, 00:04

Okay I tried the headphone amp today. With the power supply to the onboard audio amp chip disconnected. I disconnected the input and output on the volume pot. I then connected an input for the headphone amp to the wire that had been connected to the input of the volume pot. Then I connected the ground from the headphone amp to ground on the chassis. I have a volume control on the headphone amp. Now I have sound, not just a hum. And I can turn it up and down, whereas before it made no difference if I turned it up or down, it was just a hum that stayed the same volume. But the headphone amp only has a gain of 11, not enough. But it was enough for me to hear several stations, some in spanish some in english, just weak. So if I want this receiver to work I've got to either buy a replacement chip or build my own amp with higher gain. I can't tell from the schematic how much gain is there so I'd have to try several levels of gain, probably starting with 21 or so. I'm tempted to buy the NTE1075A replacement from Mouser but I don't think it's worth that much. Almost $20.00 with shipping and not sure that's all it needs? Of course everything around the chip is passive stuff, not hard to change out but I just am not sure which way I want to go. Any thoughts? Oh, I have a question. In the schematic around the amp circuit I'm seeing circled numbers like 9.4, .25, .75, 4.0. @G4LNA -- Are these the voltage reference points to which you referred? Because if they are I'm thinking they aren't going to be correct if the chip is pulling too much power, are they? The reason I ask is because the illumination lamps dim a bit when I connect the power to pin 9.