[minima] Re: A New Approach
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Fri, 12 Dec 2014 22:39:35 -0500
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>
> Date: 12/12/2014 7:14 PM (GMT-05:00)
> To 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
>
Other related posts:
