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


Gary DeBock
 

Hi Michael,
 
Thanks again for your filter modification work, and your kind comments.
 
Actually both Guy Atkins and Steve Ratzlaff are far more experienced in filter modification work than me, and I've simply managed to learn a few things by having the privilege of working with them. My own contribution to the ULR experimentation efforts here has been in loopstick improvements, in attempts to make these tiny radios as sensitive as possible. If you are a member of MWC, you may have seen a few of my fanatical loopstick articles that were published in Medium Wave News.
 
About a year ago, I learned the harsh lesson that sensitivity improvements alone were not going to make a major difference in chasing 9 kHz-split DX with Ultralight radios. A small radio needs both a major sensitivity boost and a major selectivity boost in combination, to make a radical improvement in overall performance.
 
By a tremendous stroke of luck, one of the primary filter experts in the USA (Guy Atkins) lived right in my small home town, here in Washington state. Our cooperation last summer (along with contributions by John Bryant) produced the first major breakthrough in ULR 9 kHz-split DXing performance, the fully modified Eton E100. Steve and I were attempting to create something similar with the DT-400W in the winter, but despite our unrealistic expectations, we ran up against the harsh reality that all the commercially available 450 kHz IF filters are mediocre for transoceanic DXing.
 
73 and Best Wishes,
 
Gary DeBock   
 
In a message dated 4/3/2009 7:45:52 P.M. Pacific Daylight Time, knallebo@... writes:

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@yahoo.co.uk 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'. 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(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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