Local MW station being received on Shortwave Band
 

Hello,

I have a strange problem which affects two old Perdio PR73 radios, they both pick up the local County Sound radio station 192m MW in three/four places on the shortwave band ! I do live very close to the transmitter (its about a mile away), but other radio sets are not affected like these two Perdios. Anyone got any suggestions as to why they should be doing this ?

Howard :)

Re: Local MW station being received on Shortwave Band
 

Hi Howard,

What frequencies are involved, please? Ie. where are you hearing it on SW and what is the IF of the sets in question?

My guess is a simple harmonic or mixing problem of some kind, exaggerated by a lack of RF shielding in the radios.

Best regards

Frank N.

Re: Local MW station being received on Shortwave Band
 

Your reception of MW stations on Short wave could be down to a number of things, particularly poor front end rejection/alignment or bad local oscillator purity allowing multiple mixes to the I.F.. On old valve radios it was easy to fit a wave trap to the aerial/earth sockets tuned to the offending station that broke through but I think it is a bit more difficult with a tranny portable like the Perdio.

Re: Local MW station being received on Shortwave Band
 

Thanks Frank, top cap,

The wavelength of this radio station is 192m MW, the shortwave band on this PR73 is 87 - 197m and the IF is 470 kHz. I notice also that on these Perdios and also with later Perdio PR36s that this local radio station is picked up yet again at around 440m MW ! I guess therefore that this is a quality/design fault of Perdio radios ???

Howard :)

Re: Local MW station being received on Shortwave Band
 

Hello Nick,

Ive never considered using switch cleaner on a VC, I daresay it works for a while but if the VC is mechanically worn then I suspect its eventually going to fail again :( I know someone with several spare R200 chassis so I'll pinch one off him :)

Howard :)

Re: Local MW station being received on Shortwave Band
 

I had a bit of a problem getting used my head round these wavelengths in metres.... Translated to the more usual frequencies:
Local station 192m = 1563kHz
Interference freq 440m = 681kHz
This is probably a straightforward image problem:
1563- 2x470 = 623kHz give or take errors in your dial readouts.

All radios suffer this to some extent, certainly I would expect it to be normal with a very strong local station.

You say 'shortwave' is 87-197m. This is 1523kHz-3448kHz and is not what most of us would call shortwave. In fact there is only one shortwave band in this (90m, around 4000kHz, not widely used in Europe). Are you sure of this range?

In short, I would say this is a general shortcoming of receivers overloading with strong local signals. Very common in all receivers with a single conversion 470kHz IF.

Dave

Re: Local MW station being received on Shortwave Band
 

Thanks Dave,

Yes that Shortwave band is correct according to the radio servicing sheet I have here (its described as MSW). It doesnt worry me this "feature" as long as this old radio is working OK, in fact it picks up this local station better on SW than it does on MW cos 192 is right at the end of its MW range :)

Howard :)

Re: Local MW station being received on Shortwave Band
 

I live a few miles away from the BBC Radio Bristol medium wave transmitter on 194m, on many radios old and new the second channel image from this potent signal can appear anywhere between 450-500m depending on the radio concerned.
My guess is that if your local medium wave station is breaking through on short waves its probably due to an overloaded front end causing cross modulation.

Re: Local MW station being received on Shortwave Band
 

Hello Simon,

You're spot on, its exactly the same problem here with 192m County Sound.
I just consider it a feature of my Perdio radios. Other radios I have seem to cope better and this feature is less obvious.

Howard :)