Ka B/C overlap (Hughes) Thread

[Llew]

I suffer a lot from 'Sods' or indeed Murphys Law myself Llew ..
perhaps you should leave the Nags alone this week ..
;)

Too right mate. The problem is, we are hidebound by not having any info on the Hughes stuff at all. It's all guesswork, but we're struggling along nevertheless.

 

[Vipersan]

Hi Llew ..
Gone for a complete re-build using a Toko 27mhz tuned coil after having some success injecting the switch signal via the coil ..
Still a work in progress ..after removing all gremlins but one at the strart of the scan..
Not sure it'll ever be perfect as this gremlin appears to be a true harmonic somewhere around the 32nd ..
I'm going to try a different oscillator package as well ...this one has no control pin just gnd vcc and out..
but will run at 5v so am hoping to use the comparator generated switched 5v as vcc ..
I'll report back if there is any improvement ..
but in truth what we really need is a mini 27mhz bandpass filter ..
They do exist but can't find one off the shelf..
still a work in progress ..and this new build is on a second piece of verro ,,so still have the MK1 to go back to ..
The new build also has the comparator inputs to pins 2 and 3 reversed.
rgds
VS

http://217.34.103.131/pdfs/SXBP-27R5 .pdf

http://www.ebay.co.uk/itm/181176601...l?_from=R40&_sacat=0&_nkw=181176601343&_rdc=1

 

[Llew]

Always up for new ideas VS. Certainly looks an interesting variant

Can you post a schematic of this?

 

[Vipersan]

Always up for new ideas VS. Certainly looks an interesting variant

Can you post a schematic of this?

Certainly will when I have decided the best way to insert the Toko coil ..
The osc package hasn't arrived yet so not even sure if it will do the job..
The Toko coil is an off the shelf device ..
12 turns with an internal cap in parallel with that winding and 3 turns on the secondary ..untuned..
What I can tell you is that cap coupling the 12 turn winding to ground from the current sm osc package ..allows sufficient signal to pump into the secondary when simply inserted into the breakout line powering the rest of the pcb switch..
ie secondary 3 turn winding in series with the 13/18v supply to the pcb.
rgds
VS

 

[Vipersan]

Here is a scan taken at 9E eariler today ..with the bottom port of the Hughes blanked ...so the scan on the H cycle produces no output thus I can look for gremlins..
You can clearly see the nasty harmonic at the start of scan ...and an oddity which the 27mhz isn't responsible for at the top end of the V scan

I hope to elimate both ..but would be happy to simply reduce them.

rgds
VS

 

[Llew]

I'll give that idea a go, I've got a few Toko coils that could be modified I reckon. I do need a more satisfactory method of coupling the 27MHz to line, still have the gremlins appearing, mostly at the top end of the band.

 

[Llew]

Here is a scan taken at 9E eariler today ..with the bottom port of the Hughes blanked ...so the scan on the H cycle produces no output thus I can look for gremlins..
You can clearly see the nasty harmonic at the start of scan ...and an oddity which the 27mhz isn't responsible for at the top end of the V scan

I hope to elimate both ..but would be happy to simply reduce them.

rgds
VS

Do you get that top end glitch without the switch on?

 

[Vipersan]

Unfortunately yes ...but not seen it so far on the new build so may have eliminated that ..(MK1 in use when the scan was taken )
fingers crossed ..but then of course I've only tested the new switch in line with the comparator running and no 27 mhz osc integrated as yet..
I believe it is a glitch introduced by the Toko ..simply because of unsmoothed or badly decoupled circuitry ..
You'll notice a lot more ferrite beads in the new build.
rgds
VS

 

[Llew]

You could use a transistor to switch the oscillator on from the comparator, I haven't checked the max current the comparator will supply to switch on the oscillator (?)

 

[hvdh]

Have you considered a ready-made diplexer as I suggested a while ago?
This one (SEW 122 F) from Spaun looks intesting, because the crossover is around 200 MHz:
http://www.spaun.de/files/d50e1_de_SEW-122-F.pdf

More common ones with crossover around 900 MHz, from Spaun are the SEW 121 F or SEW 123 F.

 

[Vipersan]

You could use a transistor to switch the oscillator on from the comparator, I haven't checked the max current the comparator will supply to switch on the oscillator (?)

I may have to Llew ...but will try it supplying VCC direct first..
Lots to try ..but can't experiment till the new osc arrives..
The new osc device only draws 25ma ..so may be OK
rgds
VS

 

[Vipersan]

Have you considered a ready-made diplexer as I suggested a while ago?
This one (SEW 122 F) from Spaun looks intesting, because the crossover is around 200 MHz:
http://www.spaun.de/files/d50e1_de_SEW-122-F.pdf

More common ones with crossover around 900 MHz, from Spaun are the SEW 121 F or SEW 123 F.

I have considered a diplexer Hans ..but I'm trying to make the whole switch self contained with only in and out ...ie in line with no additional units..
I'm pretty darned close so far..
Llew's basically using the Diplex method already..but actually using a DC blocked splitter.
rgds
VS

 

[hvdh]

Just keep this option in mind then... reading these high isolation figures (40 dB ), I think the SEW 122 F has some good high- and lowpass filtering inside.

 

[Vipersan]

Just keep this option in mind then... reading these high isolation figures (40 dB ), I think the SEW 122 F has some good high- and lowpass filtering inside.

I certainly will Hans ..
I just wish I could get my hands on on the band pass filter I linked to earlier ..
Looks the business ..
http://217.34.103.131/pdfs/SXBP-27R5 .pdf
;)

 

[Llew]

I certainly will Hans ..
I just wish I could get my hands on on the band pass filter I linked to earlier ..
Looks the business ..
http://217.34.103.131/pdfs/SXBP-27R5 .pdf
;)

I can only find one supplier so far, here -

http://217.34.103.131/MCLStore/ModelPriceDisplay?
US supplier I think. Select country on the page for GBP price.
.

Quick Toko coil query VS. Is the secondary wound directly over the primary, or next to it (above or below) on the former?

 

[Vipersan]

Sorry Llew ..can't help with that as I haven't opened it up .
It is an off the shelf item and as such came pre wound.
These on ebay are the same I think ..
and a more accurate description of the ratio.
http://www.ebay.co.uk/itm/TOKO-MKXC...al_Components_Supplies_ET&hash=item27e72da815

actually 8 turns with 27pf cap ...and 2 turns ..
so my guestimate was in error..
How it's wound though ..no idea..
rgds
VS

 

[Llew]

OK, thanks for the link.

 

[Vipersan]

What do you think about this scan Llew ?
Same rules as last night ..
Blanked lower port to observe switching action and of course gremlins..
Scan at 9E ..
Using the original osc device (thought I'd try it in my new build)
Improvised new base for the osc so as to fit as a through hole component ..
pic to follow ..I'll upload it here ..
I suspect it radiates a good bit as I can detect the osc switching on and off with my scanner which is in the same room as the TBS card ...
But the IF cable must be acting as an aerial to some degree.
rgds
VS

 

[Llew]

That scan looks quite clean, although a few pimples seem to be observable on the carriers, which suggest there's some unwanted harmonics still getting through. Maybe not significant though.

I like your construction - those ferrites - you have two places where you've added them - I know the one that feeds the IF line, what's the other one going to/coming from?

 

[Vipersan]

I'll draw out the whole cct later today on paper and upload it ...
I ditched inline modulation of the signal to the IF in favour of cap coupling to both windings of the TOKO..
Also used some murata ferrite suppressors with centre pin cap coupled to ground as well as the inline ferrite beads..
I have plenty of both so can post you some to try if you need them.
Yes there are pimples on the line ...but rather pimples than BOILS..lol
;)