[minima] Re: Testing KISS Mixer - Some More Data
- From: "Steve VK2SJA" <vk2sja@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Mon, 4 Aug 2014 16:10:11 +1100
Hi Mark,
It will be great to be able to compare results!! Looking forward to it.
If Thomas is able to home-brew another one then we could have a three way
comparison.
I think I'm going to build a new mixer from scratch. Finding time between
now and this weekend is going to be tricky. Anyway, working on it as fast
as I can.
73, Steve.
> All
>
> Have been lurking and watching this one develop. Over the next few days
> I will blow the dust off my previous experiments with the KISS mixer,
> replicate this new schematic and report back. Steve - it will be
> interesting to compare results!
>
> Mark
> G0MGX
>
>
> On 03/08/2014 14:27, Ashhar Farhan wrote:
>> comrades,
>>
>> here is a circuit that's on my bench right now, it is a hotch potch of
>> several schemes that we have spoken about here.
>>
>> A: i am using the biasing scheme that is common to many vfos : let the
>> gate-source forward junction charge the gate capacitance to just about
>> conduction on the positive swing. this simplifies biasing even between
>> JFETs that are slightly mismatched.
>>
>> B. There's no center tap on the LO transformer. if you are using a
>> trifilar wound transformer, just lift the center tap off the ground
>> and let it float. Instead, we use a 10K linear pot (you could even use
>> a 100k preset if you have one) as a 'balance' control. it really
>> makes a difference.
>>
>> I have attached the circuit. The RF port is at the center tap of the
>> mixing tranformer (the one on the right), the IF is from the
>> secondary. This configuration is what we must use. The IF secondary
>> will probably fall below the needed inductance for lower RF
>> frequencies. but the RF at the center tap will go right down to
>> baseband.
>>
>> I don't have a spec an. so, probably steve will have to do the
>> measurements. The waveform was interesting. I got a 200 mV signal at
>> the RF port that was at twice the LO frequency (68 MHz). Steve, can
>> you open up the sweep to cover 0-80 MHz? You might notice it too. but
>> the 34 MHz LO appeared minimal. If the specan peeps could confirm the
>> performance, we could probably freeze this and start measuring the IMD
>> of this configuration and nail it.
>>
>> - f
>>
>>
>> On Sat, Aug 2, 2014 at 2:52 PM, Steve VK2SJA <vk2sja@xxxxxxxxxxx
>> <mailto:vk2sja@xxxxxxxxxxx>> wrote:
>>
>> Hi All,
>>
>> Latest batch test data.
>>
>> Mixer rebuilt with BNC connectors instead of audio RCA sockets
>> with RCA to
>> BNC adaptors. Result? Much improved consistency but still very
>> "touchy".
>> Sometimes I think that my BNC patch leads are no good (I didn't make
>> them). True lock-down may only come with hard soldering the
>> connections in
>> and out.
>>
>> With no analysis here are the tests.
>>
>> All tests with 20Mhz signal at -10dBm at mixer.
>> (AD8307 Power Meter now calibrated and within +/-1dBm agreement
>> with DSA-815)
>> LO signal provided by Si570.
>>
>> 500.jpg
>> Original Minima KISS Mixer.
>> 20Mhz -> RF IF -> SA
>> RX Mode.
>> LO can be varied by about 10dB.
>> Min LO seems co-incident with Max IF signal.
>> Screen shot taken after adjustment for Min LO.
>>
>> 501.jpg
>> Original Minima KISS Mixer.
>> 20Mhz -> IF RF -> SA
>> TX Mode.
>> Simply swap leads around.
>>
>> 502.jpg
>> Original Minima KISS Mixer.
>> 20Mhz -> RF IF -> SA
>> RX Mode.
>> Swap leads back again.
>> Re-adj. for Min LO which = Max IF.
>> Bias = 2.750v
>>
>> 503.jpg
>> Original Minima KISS Mixer.
>> 20Mhz -> IF RF -> SA
>> TX Mode.
>> Simply swap leads around again.
>>
>> 504.jpg
>> *Alternate Bias* KISS Mixer.
>> Used 220Kohm and 0.1uF to ground from centre tap of LO transformer.
>> J310 sources direct to ground.
>> 20Mhz -> RF IF -> SA
>> RX Mode.
>>
>> 505.jpg
>> *Alternate Bias* KISS Mixer.
>> Used 220Kohm and 0.1uF to ground from centre tap of LO transformer.
>> J310 sources direct to ground.
>> 20Mhz -> IF RF -> SA
>> TX Mode.
>>
>> 506.jpg
>> *Alternate Bias* KISS Mixer.
>> Used 220Kohm and 0.1uF to ground from centre tap of LO transformer.
>> J310 sources direct to ground.
>> Inserted 220ohm resistor between LO transformer and Gate of each
>> J310.
>> 20Mhz -> RF IF -> SA
>> RX Mode.
>>
>> 507.jpg
>> *Alternate Bias* KISS Mixer.
>> Used 220Kohm and 0.1uF to ground from centre tap of LO transformer.
>> J310 sources direct to ground.
>> Inserted 220ohm resistor between LO transformer and Gate of each
>> J310.
>> 20Mhz -> IF RF -> SA
>> TX Mode.
>>
>> 73, Steve
>>
>>
>>
>
>
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