[minima] Re: A New Approach
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sat, 13 Dec 2014 10:29:41 -0500
On 12/13/2014 06:19 AM, Mvs Sarma wrote:
> Perhaps we need to change LO to lower side after some range. It would
> be tactfully be useful.
>
> in case we use DDS, perhaps the code needs to be little more intelligent.
DDS is more problematic as its has spurs of its own. Better if not
using 9850 as the newer parts
have fewer spurs at lower levels.
Allison
>
>
> On Sat, Dec 13, 2014 at 4:47 PM, Joe Rocci <joe@xxxxxxxxxx
> <mailto:joe@xxxxxxxxxx>> wrote:
>
> Allison,
>
> I'm still confused. Are you telling me that using a 9 mhz IF for
> 17m is inherently problematic, or are you telling me the way the
> LO was generated in that particular radio caused the problem?
>
>
>
>
> Sent from my tablet
>
>
>
> -------- Original message --------
> From allison <ajp166@xxxxxxxxxxx <mailto:ajp166@xxxxxxxxxxx>>
> Date: 12/12/2014 10:39 PM (GMT-05:00)
> To minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
> Subject [minima] Re: A New Approach
>
>
> On 12/12/2014 09:16 PM, Joe Rocci wrote:
>> Allison
>>
>> I can see where the required 27 mhz LO (high side injection)
>> would land right on the 27 mhz image frequency, but I don't
>> understand your math ( 22mhz _ 5mhz=27mhz range). Please explain.
>>
> VFO+ HFO to get LO injection +9mhz if. Look at the spur table
> for that its hideous.
>
> Low side or 9mhz +9mhz where the LO is (5+4mhz, or 14-5) is
> seriously bad.
>
> SI570 would be the way maybe but that was a tube/transistor hybrid
> where the
> VFO and HFO are solid state and everything else glows. There is
> something to
> be said for a pair of 6146s.
>
> It was a test of can I do this.
>
>
> Allison/KB1GMX
>
>
>>
>>
>> Sent from my tablet
>>
>>
>>
>> -------- Original message --------
>> From allison <ajp166@xxxxxxxxxxx> <mailto:ajp166@xxxxxxxxxxx>
>> Date: 12/12/2014 7:14 PM (GMT-05:00)
>> To minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
>> Subject [minima] Re: A New Approach
>>
>>
>> There was something I'd forgotten...
>>
>> For 17M radio an IF of 9MHz is extremely problematic. I know
>> this from adding 17M
>> to an old Tempo-one hybrid radio. I was able to but the LO had
>> to be above the output
>> ( 22mhz _ 5mhz=27mhz range). That and the Mixer (single ended
>> pentagrid tube) was
>> pure pain. I won but there is now one Tempo One with a balanced
>> mixer in the TX path
>> using sheet beam tube (6AR8) to do it. Its not obvious that a
>> 9mhz if would end up in
>> the 18mhz output but the mixer was important.
>>
>> I try to keep the IF non-harmonically related to the output and
>> far enough away to
>> avoid filtering issues.
>>
>>
>> Allison/Kb1GMX
>>
>>
>> On 12/10/2014 09:53 AM, Joe Rocci wrote:
>>> For the last several months, I've been quietly and slowly
>>> developing the components for a different approach to the
>>> Minima. I've written about some of the concepts here, but I
>>> never really laid out the whole thing. At the risk of creating a
>>> major fork in this group, I'm going to describe where I'm going.
>>> If there's serious interest, I'll put all this up on my own web
>>> site, along with a discussion forum for anyone who wants to
>>> follow along.
>>>
>>> Here are the key components:
>>> 1) A high-level front-end mixer based on my Quad FST3257 bus
>>> switch design. It accepts Si570 or Si5351 drive levels.
>>> 2) An IF at 9 mhz, but changeable according to the builder's
>>> tastes. I'm considering an optional dual xtal filter for SSB/CW,
>>> using bus switches for filter switching.
>>> 3) A totally different BiDi amp architecture. This one uses a
>>> single Hybrid Cascode amplifier with a complimentary NPN-PNP
>>> output stage. It easily develops 30 dB of gain, up to +10dbm of
>>> uncompressed output power, excellent input and output match, and
>>> about 3.5db noise figure according to LTSpice. It only draws
>>> about 18 ma. It has well over 70 db of voltage-controlled
>>> gain range that can be used for TX ALC as well as Rx AGC. This
>>> single amp is turned around from the Rx direction to the Tx
>>> direction with another FST3257 bus switch. It works very nicely.
>>> 4) A product detector made with another FST3257. It also accepts
>>> Si570/Si5351 drive levels.
>>> 5) Audio amplifier chain that is made with a single package of
>>> low-noise op-amps. This amplifier chain is used for Tx as well
>>> as Rx and is turned around with some left-over switches in the
>>> product-detector bus switch package.
>>> 6) Detectors for audio-derived Rx AGC and RF-derived Tx ALC.
>>> Both of these are optional.
>>> 7) Should be possible to use the Minima control system as a
>>> control foundation with relatively simple changes
>>>
>>> I've done some preliminary bench testing of the whole RX chain
>>> (minus input filters) and the 10db sensitivity is in the sub-1uv
>>> range. In Tx mode, it's putting out about 3-5 dbm. There are two
>>> easy to make binocular core transformers in the mixer (possibly
>>> one can be eliminated) and another in the product detector.
>>> Other than the FST3257 bus switches, everything else is done
>>> with a few 2N3904's & 2N3906's, a J310 and a pack of quad
>>> op-amps. Overall, I don't think the parts count is much/any
>>> higher than the Minima.
>>>
>>> This basic Xcvr sub-system can be finished off in several ways:
>>> 1) The input filters, which will be a separate board, can be
>>> individual switched bandpass filters (my preference) or a pair
>>> of low-pass filters as in the Minima. Based measurements I'm
>>> seeing, I'm pretty sure the LPF approach is workable with the
>>> 9mhz IF, although the IF can be built for other frequencies. In
>>> either case, I plan to use more FST3257 switches to select input
>>> filters.
>>> 2) AGC/ALC can be left out at the builder's desire.
>>>
>>> I'm calling this design the "BSS-1", standing for "Bus Switch
>>> Special". I started to draw the schematic in Eagle with the
>>> intention of making a PCB. Due to my own design tastes, I'm
>>> doing the first layout with SMD components. This generally
>>> results in smaller size and better performance.
>>>
>>> Although I fully intend to take this to fruition on my own, I
>>> sometimes get sidelined for long periods of time, so a group
>>> effort would keep things moving. If there's enough interest,
>>> I'll put up the forum I mentioned.
>>>
>>> Joe
>>> W3JDR
>>
>
>
>
> --
> Regards
> Sarma
>
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