[R-390] preselectors

[Bob Camp]

Hi

Sherwood Engineering has a pretty good page on comparing various radios 
http://www.sherweng.com/table.html . The amazing thing about the R-390 
is that it combines good sensitivity with good overload performance. It 
is not tops in either category. It's the combination of the two that 
makes the R-390 one heck of a radio.

	Take Care!

		Bob Camp
		KB8TQ



On Aug 20, 2004, at 9:58 PM, Bernie Nicholson wrote:

> The only case I could see for the use of a preselector with a 390A RX 
> is if you wanted to hear in duplex mode close to your transmit 
> frequency . Both Racal and Collins have produced boxes for this 
> purpose, I had a Pair of URC32 trancievers from one of our Oberon 
> class Submarines  that were fitted with Tracking Preselectors and I 
> was able to have Full Duplex QSO s with in the 80 meter band with with 
> 200Khz separation  and running 1Kw input .I have also seen similar 
> boxes for the 618T system to permit full duplex telephone calls on 747 
> aeroplanes ,I still own a Racal box called a preselector and 
> protection unit that I use in conjunction with my Ra17L ,it was 
> desighned so that you could opperate the reciever in a transmitter 
> hall and not burn out the rf coils when you tuned across the transmit 
> freq. and so you dont hear birdies associated with mixer overload This 
> box also has the facility to instataniously switch it out of circuit 
> so you can see what it is doing and I have never experienced a change 
> in signal to noise ratio and all these boxes do is Increase the 
> dynamic range of the system, further the dynamic range is increased 
> much more on the lower frequencies than the higher frequencies due to 
> the attainable Q of the tuned circuits dropping off as the frequency 
> goes up there are diminishing returns.But in a contest on 80 or 40 
> meters and someone running a kilowatt just down the road one can 
> opperate with impunity , or if you lived next door to a 50 Kw 
> broadcast station you would probablly gain from having one of these 
> boxes, the dynamic Range of the 390A is in the order of 80Db which is 
> pretty amazing for a general coverage reciever of this age. HOW GOOD 
> is it  well looking on the TENTEC site the published figures on the 
> Kenwood TF2000 is 69Db the FT1000Mp is 73Db and so on, so even after 
> all this time the 390A is still a FORCE to be reckoned with amongst 
> recievers, I hope I have explained the use of PRESELECTORS , regards 
> to all.
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