Message-ID: <BA758C0BE28C4357BA0397250D08C4C0@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <F2308B40167B42B486EAD4657D9D78F6@AGB> <53E3983D.9050606@gmx.net> <D300C456F3F2421E913AD4C9D41EE57C@AGB> <776311A518F6F642962EC561A9184090D582E15B35@THSONEP02CMB01P.one-02-priv.grp> <FAA71B6A9A894028BC63ACFCCF4C4894@AGB> <776311A518F6F642962EC561A9184090D582E7469F@THSONEP02CMB01P.one-02-priv.grp>
In-Reply-To: <776311A518F6F642962EC561A9184090D582E7469F@THSONEP02CMB01P.one-02-priv.grp>
Date: Fri, 8 Aug 2014 14:41:11 +0100
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Subject: Re: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???
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Status: O

Ok Paul

The  Navy  has  extra  IF , the  slow  motion  tune  is  another  down 
conversion to , I think  50KHz  IF ?

I was  not  involved  with the  remote versions , but , yes  the boards are 
similar , the  ra1778  has a  memory  board  , which makes servicing a 
problem  , but  the  1.4 MHz   free  tune  bfo  is  a  little  under hand 
for  such a  price !  the ra6790 bfo is  locked in 10 Hz steps , main tune 
1 Hz , so its possible to tune  to  1 Hz , its reasonably  stable , or   can 
input  a  external  reference , I use  ma1723  exciter  for  mf .

Tnx-73 Graham

ps , there  is a working  Atalanta at  gb4fpr . I have the  Electra in the 
loft octal version hihi

--------------------------------------------------
From: "REEVES Paul" <Paul.Reeves@uk.thalesgroup.com>
Sent: Friday, August 08, 2014 12:47 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: RE: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???

> Hi Graham,
>
> I don't think the '117 had a beam deflection mixer either but I'm not 
> sure. I've got one in the garage awaiting (for several years now....) 
> renovation - will have to have a look. I didn't think the Navy version had 
> any significant differences apart from possible mods (a 7360 fits the bill 
> there) or external preselector for co-site tx operation but I think the 
> only one I have seen was at the museum at HMS Collingwood - and no 
> details, alas.
> All the rest of my Racal bits are 1772 and relatives, generally remote 
> control versions (6775? etc) - all work ok and show no signs of 
> deterioration (yet...). At least they provide spare boards for the 1772 if 
> needed!
>
> I have used the AFEDRI on 136 - worked quite well but was behind a 
> preselector adapted from a set of front-end coils for a Marconi 
> 'Atalanta'. Proper coils and capacitors -keeps all the rubbish out!
>
> 73s
>
> Paul     G8GJA
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org 
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Graham
> Sent: 08 August 2014 12:13
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: LF: Receivers for LF and MF 136 KHz @ 477KHz ???
>
> Hi   Paul,
>
> Yes , the  later version  , may be the  117  or the  fine  tune version 
> for
> the  Navy  used  the  7360 , probably  about  as  good  as  it  gets , I
> spent  some  time  on production  test  when the  ra1771/2  was first
> produced , that  was  long  ago  , I have a ra1778  and  ra6790gm , with 
> the
> lf  front  end ,  the start this  year , I sold all  the  ra17  set  up  ,
> ra17, pan adaptor , lf  adaptor [with rad-haz mixers] ssb adaptor , all of
> which , I had  not used  for  decades, all had failed  in one way or the
> other , working  or  not , seems  little  difference  in the  price , must
> of used   3  cubic yards of  cardboard packing ! the  sets  are  now  all
> round the  world .
>
> Noted on the  SDR , yes ,  I assume thats needed  due to  lack of  'bits' 
> ,
> there  was  an idea to  use  a  24 bit a/d  as  a  0>1 MHz sdr , aimed  at
> the   low  frequency  bands , but as yet  , waiting ..
>
> one of  the  £5 dongles would  work  as  pan adaptor  , showing  the  2/3
> MHz  IF out , only  problem, if the  ra17  has the  original  IF amp , 
> then
> the  LO carrier  also  shows  on the  trace , 100KHz  from the  tune point 
> ,
> I fitter the  modification , but the  rx-noise increased  , due to the
> second  valve  ,
>
>
> Q Have you  used  the  AFEDRIxx  on 136 . 477  ?
>
>
> 73-Graham
> G0NBD
>
>
>
> --------------------------------------------------
> From: "REEVES Paul" <Paul.Reeves@uk.thalesgroup.com>
> Sent: Friday, August 08, 2014 7:49 AM
> To: <rsgb_lf_group@blacksheep.org>
> Subject: RE: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???
>
>> Hi Graham,
>>
>> RA17 with beam deflection mixer? Surely not.......
>> I would certainly agree with you about the RA1772 (and extended family)
>> but I like using both - and a (fairly) complete set of RA17/MA79 plus
>> accessories really beats anything else in terms of looks! And it glows in
>> the dark too:)
>> I use an AFEDRIxx too. Works fine but really needs a preselector on HF
>> unless used as a panadaptor (behind an RA17 perhaps....), fortunately
>> Racal made nice preselector units too.
>>
>> 73s
>> Paul     G8GJA
>>
>> -----Original Message-----
>> From: owner-rsgb_lf_group@blacksheep.org
>> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Graham
>> Sent: 07 August 2014 21:36
>> To: rsgb_lf_group@blacksheep.org
>> Subject: Re: LF: Receivers for LF and MF 136 KHz @ 477KHz ???
>>
>> Yes Tobias,
>>
>> All  is not as it  seems , but as you say , adding  filtering , reduces
>> the
>> problems  , and  with  direct conversion  , the  noise  floor  is the
>> lowest possible , stability  is  at maximum , having only  1 oscillator ,
>> In
>> have  good  decode  results  on 477 using  the  £5 dongle  , behind  the
>> TX
>> atu and inv L ae
>>
>> For the  £150  sdr , the  description  lists  80 msps , which  , I assume
>> moves the  image  problems  out  side the  HF spectrum ? at  12 bits  ,
>> that
>> starts to  provide a  reasonable  , post processed  dynamic range ?
>>
>> 12- bit 80 MSPS A/D conversion
>>
>> I would  not  link the  barlow-wadley , too  closely  to  lack  dynamic
>> range , may  be a lack of  engineering  integrity , the  RA17  with
>> pentode
>> rf  stage  , then  later  cascode  , with  beam deflection  mixer , was
>> reasonable , though  there  was a  pre selector  for  use at  close 
>> tx/rx
>> sites ,  the  ra1771/1772  was  the  first  to  better the  ra17 , but
>> again
>> that also tends to  question the  models before ..   the  ra1772/1  is
>> fitted  with  rf-pre selector , for those 'unexpected' situations ,  the
>> ra6790gm , with  no  pre-amp  is the  closest  I have  seen  to  a 
>> bullet
>> proof  front  end , that  runs , where  the  ra1778 needs  the
>> pre-selector
>>
>> But in terms  of  noise  etc , one of these  'reasonable  sdr's'  may be
>> better .. I don't think I would  recommend any one  go  down the  racal
>> path  these  days !
>>
>> 73-G,
>>
>> --------------------------------------------------
>> From: "Tobias DG3LV" <DG3LV@gmx.net>
>> Sent: Thursday, August 07, 2014 4:16 PM
>> To: <rsgb_lf_group@blacksheep.org>
>> Subject: Re: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???
>>
>>> Hi Graham !
>>>
>>> This type of device has a dynamic range of 48dB at maximum (8 Bit), so
>>> they need help from a narrow-band frontend plus input-attenuators to
>>> reduce the load to the A/D-converter. The conversion speed is variable
>>> from 1 to 3 Megasamples/second, leading to a Nyqist-frequency of 0.5 to
>>> 1.5 MHz.
>>>
>>> This filter should have a deep attenuation above the Nyqist-frequency to
>>> avoid unwanted reception at harmonics/aliases of the sampling frequency
>>> (=
>>> "undersampling").
>>>
>>> The advertized usage of 100kHz to 30MHz (in direct-sampling method) is
>>> based on this normally unwanted harmonics/aliases, i.e. the receiver 
>>> uses
>>> a method that has become "famous" with the ancient "Barlow-Wadley"
>>> all-band receivers. (at least equivalent to). Their
>>> (large-signal-)problems of the past are reborn at the direct-sampling
>>> method of these DVB-T sticks. Without narrow-band selective frontends
>>> this
>>> is just a "proof of concept" and not a usable receiver.
>>>
>>> For the use at 136 kHz and 475 kHz a steep lowpass-filter (7 to 9 pole
>>> Tscheby with toroids) at (e.g.) 500kHz would be mandatory. An actual
>>> bandpass may not be necessary. Equipped with such filters the lack of
>>> resolution (8 Bit) will become more acceptable. Using a pre-amplifier
>>> without using filters will do no good.
>>>
>>> When home-brewed, such filters will not cost much, but it takes time,
>>> measurement-tools and effort to build and tune them.
>>>
>>> 73 de dg3lv Tobias
>>>
>>> Am 07.08.2014 14:13, schrieb Graham:
>>>> Receivers for LF and MF136 KHz@ 477 KHz
>>>>
>>>> A question,
>>>>
>>>> Startingat the£5dongleriggedfordirectsample , as
>>>> acheapeffectivestartingpoint
>>>>
>>>> A pre amp and  pre - selector [ band pass filter ] would  help  for
>>>> lf/mf
>>>>
>>>> Whatwouldbein a scaleofincreasingperformance[ notcost !]
>>>>
>>>> be seen asreasonable in terms ofconfigurationand hardware ?
>>>>
>>>> Any particular equipments  stand out   as  good cost/performance
>>>> choices ?
>>>>
>>>> Tnx
>>>>
>>>> Graham
>>>>
>>>> G0NBD
>>>>
>>>
>>
>>
>
>