Re: SRF-M37V and SRF-M37W-Performance differences?


Michael Slattery
 

Hi Gary :)

Thank you for your kind thanks for my mod articles. I'm sorry that
some folk may have been misled into thinking the selectivity
enhancement would be much greater.

There was not that much effort expended in development. On obtaining
both the DT-210L and the DT-400W I was extremely disappointed by the
very poor selectivity. My gut reaction was that I had to do something
about it and whilst I was 'at it' I took a few photos reckoning that
it may be of use to someone somewhere!

I'm fully aware of the performance provided by the premium filters you
and others have been using for 9-kHz split DX chasing. I've used them
myself in my AOR AR7030 for many years but not yet in a ULR.

Some thoughts: I know you and Guy Atkins have spent quite some time
developing filter mods for various ULRs. I wonder whether it might be
worth investigating the Collins Low-Cost Series of mechanical filters
that have a superior passband ripple to ceramic filters possibly
enhancing the intelligibility of reception. Expensive, but when only
the best will do. Inrad have a 2kHz 8 pole variant:
<http://www.inrad.net/product.php?productid=19&cat=5&page=1>
or a 2.3kHz 10 pole variant:
http://www.inrad.net/product.php?productid=18&cat=5&page=1

In the DT-200VX and DT-400W, if space cannot be found for the filter
within the case maybe one of the AA cells could be disposed of to
create a space for the installation the filter. The remaining AA cell
bay could then be loaded with a 3.6V Lithium AA cell.

Thanks once again for your consideration.

73

--
Michael Slattery
Sheffield, UK

On Thu, 2 Apr 2009 23:24:13 EDT, you wrote:

Hi Michael,

Thank you for your work in developing the LTM450HT filter modifications for
the Sangean models, and for uploading the information to DXer.Ca.

Steve and I were working toward the specific goal of transforming the 450
kHz Sangean models into very effective 9-kHz split DX chasers for transoceanic
reception, such as we had successfully accomplished with the 455 kHz Eton
E100 model last summer. We knew before commencing the work that 450 kHz
"consumer-grade" filters are not comparable with the premium Murata CFJ455K5 filters
we used in the E100, but we wanted to try anything available, since a vastly
improved Slider loopstick had already been successfully transplanted into the
DT-200VX (as described in a DXer.Ca article), greatly boosting the model's
sensitivity.

Unfortunately, the project was probably doomed from the start, due to
unrealistic expectations. If you have ever used one of the premium 455 kHz Murata K
filters for transoceanic DXing, you will probably understand how quickly a
DXer can become spoiled with the phenomenal performance. Anyway, we never
meant to be dismissive of your LTM450HT modification for domestic DXing, and hope
you will understand that our 9 kHz-split DXing performance requirements are
far more demanding than those of the average DXer. We regret any impression
to the contrary.

73 and Best Wishes, Gary DeBock


In a message dated 4/2/2009 6:50:21 P.M. Pacific Daylight Time,
knallebo@... writes:




Whether the 450 kHz filter modification would be useless or not probably
depends on the type of DX you pursue.
Before carrying out a mod you have to determine what you expect.

As the author of the DT-210L & DT-400W filter mod articles, I find the
comment that the mod is 'not worth all the effort' frankly incredible!

The mods were not offered as a panacea for turning these radios into
9/10kHz-split DXers machines. That would be impossible with the type
of filters (6kHz @6dB BW) used. Rather, the articles were offered in
the spirit of improving the usability of these radios in the domestic
context. The give-away line in my article was 'the intrinsic quality
of the audio remains.' By implication therefore, the mod filter is not
especially selective merely an improvement on the original.

The moral of the story is to make sure any ULR you intend to mod for
9/10kHz-split DXing has a 455kHz IF system and the ability to tune in
at least 1kHz steps or better. 450kHz IF radios are a waste of time
since narrow filters with a good shape factor are simply unavailable.

Whilst agreeing fully with the remark by Steve about skirt selectivity
and filter size, I have to ask:

Was the LTM450HT filter used? Nothing else will bring much improvement
except for a LTM450IT or even narrower filter, if you could find one.
The 'T' suffix in the filter model number is important since these
have superior skirt selectivity over those without the 'T' suffix.

Living here in the UK I frequently wonder what North American DXers
mean by a 'high RF environment'mean by a 'high RF environment'<WBR>. Among
of one 150kW & two 400kW MF transmitters & less than 1 mile of two 1kW
MF transmitters.

The DT-210L & DT-400W filter mods have transformed the reception
capabilities of these radios close to these powerful signals. Before
the mod, five (9kHz) channels either side of the frequency of one of
these strong locals were rendered useless for weak signal reception by
the original filter. After the mod I am able to hear weak signals on
the immediately adjacent channels (±9kHz) with only a small level of
adjacent channel interference.

Perhaps your RF environment(Perhaps your RF environment(<WBR>s) are not r
that is the reason you are not reaping the reward from the mod?

--
Michael Slattery
Sheffield, UK

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