From: REEVES Paul <Paul.Reeves@uk.thalesgroup.com>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Fri, 8 Aug 2014 12:47:34 +0100
Thread-Topic: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???
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Subject: RE: LF: Receivers for LF and MF    136 KHz  @ 477KHz   ???
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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
>>>
>>
>
>