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LF: re Vaino's rx findings and my thoughts

To: "rsgb_lf_group" <[email protected]>
Subject: LF: re Vaino's rx findings and my thoughts
From: "Alan Melia" <[email protected]>
Date: Tue, 28 Sep 1999 21:55:13 +0100
Reply-to: [email protected]
Sender: <[email protected]>
Hi Vaino, I can confirm your findings on the AOR 7030+ . I have been using
one since March and I have found it just as good as you do. I also have a
HF150 and have tried a Palomar LF to 3.5MHz converter. To dispose of the
easy one first, the Palomar is not worth any consideration except possible
for BC listening, despite being used in front of a good HF transceiver with
300Hz CW filters.

The HF150 was much better than I would have expected. It is let down for
serious work by a poor shape factor on the SSB filter (it is not available
with a cw filter) Tuned to 138.05kHz the signal from DCF39 is not far
enought down the skirt (-60dB) and gives a trace on the waterfall display.
Its strong signal handling seems to be quite good ( I have a 1KW MF BC
station about 2 miles away and 500KW BBC World Service TX site about 10
miles away) It may be worth grafting a cw filter into it after the SSB
filter, and maybe cascading another SSB filter to improve the shape. If you
remove the battery carriers there is plenty of room for some daughter pcbs.

I bought the 7030+ as the first new bit if kit I've bought for about 12
years ( I am fairly stingy) impressed by the specification on strong signal
handling which I have suffered with the Kenwood R1000 , FRG7700/8800 and a
lot of the kit of that vintage. These are particularly useless as they put
in a 20dB attenuator below 2MHz! I must say in operation the 7030 lives up
to all its claims, and I think it holds the record as the only bit of kit
that has lasted 6 months in my shack without being 'modified' or 'improved'
(I don't count fitting the Collins 500Hz filter) The facility I like most is
the pass-band-tuning. I select LSB and put the 'carrier' on 138.10KHz (yes
it has got 10Hz resolution) and  I use the 2.4kHz filter to display band
activity on FFTDSP4. The pass-band tuning is stored as a function of the
MODE so I can pre-programme the 500Hz filter to interesting parts of the
band and drop it over a signal very quickly using the mode change button.
Thus on LSB mode (with the 500Hz filter selected) with a -200HZ offset I get
the QRS end of the band, on the CW position with about -1.3kHz offset I get
the centre of hand-keyed activity at 136.5, and the data mode can be tuned
to another area. Ok reading 1.5kHz tone CW is not optimum, but with a quick
button toggle I can tune the BFO to bring the tone down whilst not losing
the signal. This is maybe a bit fiddly when compared with transceive (I was
brought up on 'separates' when I got my ticket!) but it must be a listeners
dream (It certainly fulfills this listeners dreams) I haven't managed to
prise it off the aerial yet to do much in the way of measurements on it, and
my TF2002 sig gen has gone sick. I used a Farnell DSG1 synth audio gen and
an attenuator to try to measure the input terminal voltage of stations I am
seeing and copying on the waterfall. The problem with this is that it is not
intended for low level measurements and has a lot of signal leaking out on
the coax screen. The following tests were done at 73.00kHz.  The lowest
reliable signal I could apply was 0.1uV which gave 22dB S/N on FFTDSP (no
aerial noise of course) I estimate that I can copy cw at 20nV and probably
read QRS at 5nV. These may not be sensible levels....but it indicates why I
am hearing reasonable distances with a fairly useless antenna ( 16t loop
with Q of approx 15 !) This was using the internal preamp, and the dynamic
range is about 95dB at the frequency in this state. (It uses DDS generation
for the local oscillator to keep the reciprocal mixing noise down) Only
strong lightening crashes seem to reach this level on my aerial.  Stereo
audio output (from before the Vol control) with separate level and tone
controls (in software) allow you to feed the computer and audio processing,
or as I do run FFTDSP on one PC and Spectrogram on another. There is also a
20mV output at the IF (455kHz) available on the accessory socket. There is a
mod (official) to give an analogue S-meter output voltage (not linearised by
the processor as is the dispay bar graph)

On the hum problem there are separate RF and DC grounds. I have the dc
supply cable wound round an old TV line-output ferrite. It is possible that
grounding the negative side of this dc supply would help. I find it is
possible to couple in hum via the coax screen if you do not use an RF
ground. This is achieved by putting the ground terminal of the wire-aerial
input to a good RF ground. It make a lot of difference. Also make sure your
PC case is well grounded. I had one with a faulty 'earth' wire and could get
a tingle between the outers of the phono audio leads to the sound card and
the lead from the accessory plug of the radio.

All I can say is that if there are comedians trading in the earlier 7030 for
the 'plus' and there are good priced 2nd hand versions available, you will
have to pay a LOT more money to get a better receiver. The 'plus' only has
audio notch, more memories and a few other trimmings There is all the info
on the AOR web site to do the upgrade (a lot is software) which is well
within the capabilities of a confirmed 'Lowfer',and the basic performance is
just as good. I'm now looking for a narrower CW filter I can 'bodge'in as
there is a spare position (it will take 7 IF filters at 455kHz, it comes
with 5 fitted) I guess I might have to make this myself. I have played with
ceramic resonators but without success so far.
What more can I say ( Oh yes, its designed and manufactured in England not
Japan)  I'm hooked !!

I hope to be able to borrow a Lowe HF225 to compare soon (Watch this space)

I hope that lot is interesting and maybe useful. It is an expensive bit of
kit for 'just' a receiver, but I have not heard anyone else except Vaino
mention it in the LF context. His enthusiastic endorsement proded me to put
down my findings.

73 de Alan G3NYK
[email protected]

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