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: [email protected]
[mailto:[email protected]] On Behalf Of Graham
Sent: 08 August 2014 12:13
To: [email protected]
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" <[email protected]>
Sent: Friday, August 08, 2014 7:49 AM
To: <[email protected]>
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: [email protected]
> [mailto:[email protected]] On Behalf Of Graham
> Sent: 07 August 2014 21:36
> To: [email protected]
> 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" <[email protected]>
> Sent: Thursday, August 07, 2014 4:16 PM
> To: <[email protected]>
> 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
>>>
>>
>
>
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