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Re: LF: Receivers

To: [email protected]
Subject: Re: LF: Receivers
From: Steve Dove <[email protected]>
Date: Tue, 13 Jul 2004 21:23:06 -0000
In-reply-to: <[email protected]>
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Sender: [email protected]
Hi Mike,

Icom R-75:

'Consumer Reports' and 'Which?' magazine four-star best buy.

As has been mentioned, the R-75 works very well out of the box at LF, and has become a fave amongst 'Lowfers' over here. I have a couple and they're mainstays for the 'Grabulators'.
Further to other remarks, under software control the AGC can be made 'Very
Fast', intended for use during scanning as a poor man's spectrum analyser. But
it is quite useful as an alternative to turning the AGC off and letting the receiver
clip/saturate on static crashes - 'Argo' seems to make nicer plots under 'Very
Fast'.
The receiver uses a single lowpass filter for 1.6MHz and below - no transition at
500kHz-ish. There is a fixed attenuator in this path of nominally 3dB, presumably
just to secure a sane source impedance for the filter. However, its removal
makes considerably more difference than that with highly reactive and hi-Z LF-ey
antennas - the input impedance of the first mixer is probably quite a bit higher
than 50R. No obvious nasty side-effects from the attenuator's removal and is so
considered a plus.
Inrad's 125Hz filter makes for a well worthwhile 'microscope'; for most
circumstances if the radio is in a house the TCXO is not worth it; the DSP option
is useless for LF; the noise blanker is amazing - allowing plots to be made under
lighting-dimmer noise if need be.

Kenwood TS-440:

Has a discrete front-end filter-set for 500kHz and below, with no fixed attenuator and is very sensitive even down to 100kHz. Optional filter (500Hz or 270Hz Kenwood, 400Hz or 250Hz Inrad) a must. Ho-hum noise blanker. Recommended - circuitry and performance almost identical to the highly-
regarded TS-850.


Kenwood TS-140:

A real surprise for an 'entry-level' radio. Very lively down to 200kHz, sensitivity dropping off towards 100kHz but still adequately sensitive at 136kHz - in fact this one here has been sitting collecting dust plotting DCF-39 for however long now.
Same front-end filter as 1.6MHz and below, but below 500kHz the fixed
attenuator is switched out - thank you Kenwood! There is tons of room to
kluge in a <500kHz filter in that position.

IC-781:

Very good at LF.  Just a bit too much radio for the job!


IC-751a:

Very sensitive at LF, but d r i f t s way too much for QRSS, and so can't be recommended except for a band-cruiser.
Hope this is helpful.

       Cheers,

               Steve





07/12/04 16:49:57, "Mike Dennison" <[email protected]> wrote:

I am compiling a list of receivers and transceivers suitable for 136kHz.




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