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View Full Version : Morphy Richards DRM radio, and a possible solution?


ljones
10-01-2007, 21:02
Hello all,

While I don't have a PC/software-based DRM radio yet I have just recently gotten started with listening to DRM-based transmissions. To start off with, I bought the Morphy Richards DRM radio which is currently being mentioned all over the internet. It is quite dissapointing that it has no option for an external ariel but I am thinking I might have a possible solution, though I am no expert and I am guessing on this.

After reading about the MR (Morphy Richards) radio online (and finding out it dosen't have an external ariel socket) I noticed one person suggested (I forget which forum though!) that to attach an external antenna all you need to do is to connect a longwire ariel to the MR's telescopic antenna via a short cable and crocodile clips.

In my case, I do not have a longwire ariel, however I do have a wellbrook ALA1530 loop ariel. I usually use it with my (analogue) scanner - both of which are 50 Ohm impedance.

So I tried to connect this to the MR with a short cable and crocodile clips, but it made no difference. A reading on the same forum where I found this information out about trying to do this ( I forget where it is ) someone later mentioned that it didn't work for them either.

Not sure as to why, I decided to repeat this with a different radio. For this, I tried connecting the antenna using crocodile clips to an old Grundig City boy 1100 - this radio like the MR can receive LW,SW,MW and FM - but being around 30 years old no sign of digital(!). Intrestingly, the same thing happened - namely there was no improvement by attaching the ariel to the grundig's telescopic antenna in this way.

However - and this is a *guess* as I am not an expert in this I am thinking maybe all of this has to do with impedance. The wellbrook and my scanner are both 50 ohm so no impedence problems there, but connecting the wellbrook onto a telescopic antenna means connecting a 50 ohm device onto something with (and I am really guessing, I have no way of testing this) a much higher impedance (the telescopic ariel).

So prehaps the answer to the MR not having an external antenna input is to use some sort of balun? I dug out an old 75 to 300 ohm balun as a test (really ment for TV antennas) and tried this (I did not expect it to do much really) - it had no effect really on the MR but on the grundig (analogue) it made a slight difference, though only slight.

I am thinking if a balun (in my case) converting from 50 to (maybe) 300 or 600 ohms that this would enable an external antenna to be clipped on. Though I am guessing about the MR/Grundig telescopic antenna impedance, I don't really have any way of telling, just guessing here.

Am I right in all of this, or is there something I am missing?

Thanks

NB: I apologise if this thread appears twice, apon posting I got an "invalid thread" error.

ljones

bk227865
12-01-2007, 15:36
Maybe you already know , but check that the morphy is actually using the whip antenna and not the internal ferrite.

There are 2 antenna symbols . If the antenna symbol resembles a capital I then it is using the internal ferrite antenna and whatever you clamp to the whip wont have any effect.

richard
12-01-2007, 16:29
I think I have seen a Degen loop which you can clip onto the telescopic aerial of a receiver. In theory you should be able to do the same with any active loop. I would also earth the loop to the receiver chassis. A balum may help transform the signal voltage up a bit but I guess the high impedance input of the receiver should be sensitive enough anyway.

Richard