[minima] Re: A New Approach
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sat, 13 Dec 2014 11:41:18 -0500
On 12/13/2014 06:17 AM, Joe Rocci 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?
>
>
More detail this time.
17M band is 18.068 to 18.168mhz.
If the IF is 9 mhz the second harmonic is 18, third is 27mhz and so on.
If the LO is below the IF then its 9mhz harmonics at 18 and 27mhz.
If the LO is above the IF at 27mhz, one of the if harmonics and add
54mhz in there as well.
Even if the LO moves up 100khz the result is other close in mix products
that
even with triple tuned filters are in the band or just outside.
If the LO is below the IF then its 9.1mhz harmonics at 18.2 and 27.3mhz.
If the LO is above the IF at 27.1mhz, one of the if harmonics and add
54.2mhz in there as well.
In those cases spurtune has a rather interesting results.
With Lo in the CB it just needs to be kept inside the box.
If you can keep them down to -50dbc its ok on transmit, still spur
terrible on receive.
Add to that a radio that generated LO using a VFO at 5 to 5.5mhz Plus a
HFO at 22mhz
to mix with that to get 27mhz just that alone needed extra treatment to
insure the LO was
clean (it was not). That was an additional complicating factor.
While I say I won and got it to what I'd call legal compliant I did
remove it after a while
as it was seriously being forced with traps and filters and didn't work
well. The primary
symptom was TX putting out power with zero drive that wasn't a
neutralization issue.
and a loud birdie at the second harmonic of the carrier osc crystal
(8.9985 or 9.0015).
It was a fun exercise in trying to suppress signals where shielding was
mostly
non existent.
For any minimal art radio on 9mhz IF don't do it. FYI: the Tentec
Eagle does 9mhz
(9.015 if actually) and does do 17M but there are funny noises(birdies)
when the
RX preamp is on. Its lots of balanced mixers and discrete per band
filters though.
IF the IF is moved to anything else the problem goes away if things are
reasonable.
At 8mhz the numbers are far cleaner and spurs much fewer. same for 10.
An IF of
20mhz required a trap to keep that under control.
This is why the manufacturers went with VHF if for the 160-6 radios with
continuous
tune receivers years ago. It was the "easy" solution more parts but easier.
A note and clearly not minima. Going to 45mhz IF, cheap monolithic
15khz wide
filters are common for that with SI570 at 45mhz and up works. Then down
convert
to any low HF IF for the gain and selectivity (9mhz filter and 36mhz LO
for example
and both being common). Problems are more circuits (simpler filters)
and FST
swtches do not work at LO of 45mhz and up, that would be best done with
common DBM. That would net a radio that does near DC to 30 plus 6M easily
and maybe 2M. Not advocating for that as it was presented as a strategy
for
those seriously looking to the next level. The Minima user interface still
works with that.
This is why I've made a lot of monoband radios. Its fairly straightforward
to build a high performing radio when hampered by fewer compromises.
Multi band is not much harder save for switching the filters if the number
of bands is limited. Then again purpose built radios are easier to
rationalize. Its the general use radio that gets complicated because,
"What needs to be there?" looms larger.
Allison/KB1GMX
>
>
> Sent from my tablet
>
>
>
> -------- Original message --------
> From allison <ajp166@xxxxxxxxxxx>
> Date: 12/12/2014 10:39 PM (GMT-05:00)
> To 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>
>> 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:
