EMRFD Message Archive 314

Message Date From Subject
314 2007-01-07 17:15:57 James Duffey Use Preselector for Multiband DC Receiver
Brian - If you want to make a multiband DC receiver, I suggest that you
use a variable preselector. You should be able to get a 3:1 or more
tuning range. A dual gang broadcast band variable should work fine.
G3RJV has published such designs, but you can easily design your own. -
Duffey
--
James Duffey KK6MC/5
Cedar Crest NM 87008
DM65
315 2007-01-08 08:47:02 Kenneth Stringham Use Preselector for Multiband DC Receiver
Brian,

I recommend the preselector as well. You might
consider the Heathkit HW-7, 8. 9 methodology. It may
not be the best, but it works.

Ken

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319 2007-01-08 19:10:13 James Duffey Re: Use Preselector for Multiband DC Receiver
Yep, wanting it all in ham radio complicates matters greatly.

I had another thought. Many DDS VFOs have some sort of band switching
information available. You could use this to switch a bank of band pass
filters/preselecters without input from the operator. Or build your own
frequency detector switch from a PIC. Just an idea. - Duffey
--
James Duffey KK6MC/5
Cedar Crest NM 87008
DM65
321 2007-01-09 07:51:51 Brian George Re: Use Preselector for Multiband DC Receiver
James, That's a good idea as it's also fun using PICs! It would probably
have to be a separate frequency detector switch as the DDS module is
finished and there are no spare ports for additional features. I am
reluctant to delve into the software again as it took several weeks to
write, several more weeks to get it working properly and several more weeks
to work out why it works!!

I have done some more reading since the last e-mail and another thought
(which could work alongside your idea) would be to have good filtering
before the rf amp but only broadband matching between the rf amp and the
mixer. Apparently, this can be good practice in some cases, as an rf amp is
more prone to instability if it has a tuned input AND output stage.

If all else fails, I suppose it would feasible to have a bank of nine
low-pass filters, each with  BNC or SO239 sockets on the input and output,
and two coax fly-leads to select the band. Not very elegant but it would
avoid complex switching.

Thanks for your thoughts James - it's been very helpful. Will look out for
you on the bands and if you dig into the noise on 14 MHz and above, you
might hear my 20 watts trying to get through when conditions are
exceptional!

All the best,

Brian
G3ZOH

456 2007-02-11 12:37:33 Stewart Bryant Re: Use Preselector for Multiband DC Receiver
James Duffey wrote:

>Brian - If you want to make a multiband DC receiver, I suggest that you
>use a variable preselector. You should be able to get a 3:1 or more
>tuning range. A dual gang broadcast band variable should work fine.
>G3RJV has published such designs, but you can easily design your own. -
>Duffey
>--
>
>
>
Does anyone have a pointer to a suitable G3RJV design?

- Stewart G3YSX
463 2007-02-12 14:39:02 Nick Kennedy Re: Use Preselector for Multiband DC Receiver
I don't have a pointer to that one, but consider downloading the program SELECT_1.EXE from G4FGQ's site:
 
 
That's the late Reg Edwards.  His program designs the network for you.  It assumes an end-fed wire as an antenna and the wire's length and height are two of the parameters you input.
 
73,  Nick, WA5BDU

 
On 2/9/07, Stewart Bryant <stewart@g3ysx.org.uk> wrote:



James Duffey wrote:

>Brian - If you want to make a multiband DC receiver, I suggest that you
>use a variable preselector. You should be able to get a 3:1 or more
>tuning range. A dual gang broadcast band variable should work fine.
>G3RJV has published such designs, but you can easily design your own. -
>Duffey
>--
>
>
>
Does anyone have a pointer to a suitable G3RJV design?

- Stewart G3YSX


464 2007-02-12 16:57:46 jr_dakota Re: Use Preselector for Multiband DC Receiver
I don't have that one but here's one for a 1.8Mhz - 30Mhz preselector
used with a Mini R2

http://www.qsl.net/aa3sj/Pages/GCR2.html

JR

479 2007-02-15 07:35:44 patt896 Re: Use Preselector for Multiband DC Receiver - Another Preselector
Here is another similar design published in SPRAT by YU1LM:
A Tunable Bandpass Filter for All HF Bands (160m-10m)
http://www.qsl.net/yu1lm/homebrew.htm

Dick

480 2007-02-15 15:05:03 kd5nwa Re: Use Preselector for Multiband DC Receiver - Another Preselector
If you have trouble with QSL.com being to slow, I host a sub-domain
for him with decent speed at;

< http://yu1lm.qrpradio.com/homebrew.htm >


At 09:35 AM 2/15/2007, you wrote:
>Here is another similar design published in SPRAT by YU1LM:
>A Tunable Bandpass Filter for All HF Bands (160m-10m)
>http://www.qsl.net/yu1lm/homebrew.htm
>
>Dick
>
>
483 2007-02-16 15:58:11 jr_dakota Re: Use Preselector for Multiband DC Receiver - Another Preselector
Actually Dick, that was the one I was looking for and couldn't
remember where I saw it

BTW a kind gentleman gave YU1LM some room on a much faster server so
I'd recommend using this URL instead:
http://www.yu1lm.qrpradio.com/homebrew.htm

Excellent website, he's gotten more mileage out of CD40xx switches
than anyone I've seen. If a person wants to get into SDR on the cheap
and **not have to mess with SMT ICs** he has several designs with a
lot of bang for the buck and includes the PCB layouts .... I'm part
way through building the DR2-D versi