Medium Wave Circle - Radio

O.K, so it's a pretty essential piece of equipment, but what do you need to make all the effort you've put into antennas, finding a location, extra equipment, time off work and away from loved ones worth the while? A receiver that will maximise your chances of hearing those weak, distant signals.

There are numerous figures and specifications provided by manufacturers and test panels which will point you in the right direction towards a DX dream-machine. If were to purchase a receiver for the prime intention of MW DX, the factors I'd be most interested in are:

*Selectivity
In the crowded MW band where stations are separated by as little as 1kHz, the ability of the receiver to discriminate between adjacent stations and to provide loggable audio is essential. What's more the width of the filter's skirt is as important as its quoted width and is often determined by the type of material the filter is manufactured from. For example, ceramic filters have very wide skirts allowing interference to ingress whereas mechanical or crystal filters provide very sharp skirts. Look for a receiver with a filter of around 2.5kHz at -6dB and a skirt width of less than 5kHz at -60dB (the narrower the -60dB figure in relation to the -6db the better - don't worry too much what that means, just use it as a point of comparison between receivers). If you're tossing up options at purchase time, between a VHF converter, external speaker or a sharper filter, take the latter!

*Sensitivity
Some receivers aren't designed to apply all of their features to MW and sensitivity is often affected by internal attenuation to prevent strong local signals over-loading the receiver. In many receivers the attenuation can be readily set to zero by a front-panel control, or a simple software fix. In others, (e.g. Kenwood R-5000) it's a soldering iron job which, given the complexity of modern receivers, not all will be keen to tackle.

*Preamps
Generally useful devices that may be handy for giving a weak signal that extra nudge. Pre-amps that do not degrade the signal-to-noise ratio are extremely useful, though often they have been disabled on MW or require a user software fix to be enabled. Check to see if they will work on the MW band or can be adapted to do so.

*Memories
Some may consider having a receiver with 400 memories as more than sufficient, though for the MW DXer, the ability to program in every MW DX channel in the best mode, with the optimum filter setting etc. is a real bonus. This allows swift tuning between channels which in a strong opening is very handy for analysing the best frequency(s) to monitor.

*Noise Floor
And there's little point in erecting long antennas, spending heaps on coax, preamplifiers, tuners, baluns etc, if the weak signals you're chasing can't be heard under the receivers internal noise! A simple test to see how noisy a receiver is, remove the antenna and turn the volume right up - should be very quiet, a low-level background noise, ideally the noise level would be near zero and you would hardly notice the volume had been increased. I'm fortunate to have an ultra-quiet 25 year old Drake SPR-4 that has allowed reception of weak signals at loggable levels, which have been buried on colleagues' receivers.

*Hash
Modern receivers with all their synthesisers, microprocessors and fluorescent displays can produce a fair amount of internal noise. This can effect the use of indoor loop antennas near the receiver, as they'll pick up the noise radiated from the electronics. Another simple test is to hold a transistor radio about 50 cm from the set and see how much hash it picks up.

*Operating Voltage/Current Consumption
If battery operation is required (for example when running mobile or on DXpeditions) the amount of power drawn by a receiver will dictate how long a battery will last (and if you can start the car after a nights DX!). The Drake R-8A uses 2 amps when running (i.e. 30 hours operation on a fully charged car battery) though the drop in voltage will see the set turning itself off well before the 30 hours are up and 1 amp switched off on the front panel. The consequences of high battery drain mean that you'll need to be prepared for long stints at the dials by bringing extra batteries or charging between uses. Most receivers are designed to work off 12 or 13.8 volts DC though the AOR 7030+ prefers 15 volts for optimum performance, although it functions very well at 12 volts.

*Antenna Switches
Most receivers come equipped with the facility for 1 x 50 ohm input and 1 x 600 ohm input antenna with front-panel switching. I’d prefer to see at least 3 x 50 ohm inputs to allow ready access to a range of antennas. Strangely, the AOR7030+ doesn’t have an antenna switch so an external device is necessary.


Address :
59 Moat Lane
Town/City
Luton
County
Bedfordshire
Postcode
LU3 1UU  View Map
Contact Name
Paul Crankshaw
Email


URL
http://www.mwcircle.org/




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