.... which would... look something like the attached. Yellow is the current 30M LPF and purple is my new with one 38M trap.
M On 30/01/2014 17:39, Mark G0MGX wrote:
....or.... could we keep two traps at 20MHz and move the third up to 38MHz? or even add a fourth trap for the LO at 38MHz?Mark G0MGX On 30/01/2014 17:21, Mark G0MGX wrote:I just remade my 15M LPF and have a much flatter response and sharper roll off; I will try something similar with the 30M and see what the result is. We can rely on the traps to remove the 20MHz signal I would think.Mark On 30/01/2014 16:37, Ashhar Farhan wrote:Mark, the 18 mhz is, as i suspected, a problem. one possible resolution is to increase the 1st lpf to corner around 20 mhz. then, we can use a 20 mhz lpf upto 18 mhz and the second lpf from 21 mhz onwards. however, this problem is not very significant as the LPFs in the following stages may bury the 38 Mhz signal. There will, however, be a different nasty : the 38 mhz will intermodulate with the 18 mhz to create 20 mhz! you can see that blip in the 18 mhz scan.- fOn Thu, Jan 30, 2014 at 10:00 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:Here's a rather nasty looking sweep of the 30M LPF with everything in the box - not the same as when it was on the bench! I have some work to do! Mark On 30/01/2014 16:28, John Greusel wrote:The Softrocks use a SI570 divided by 4 and you can easily sniff our the LO with a portable radio. ------------------------------------------------------------------------ *From:* Mark G0MGX <mark.g0mgx@xxxxxxxxx> <mailto:mark.g0mgx@xxxxxxxxx> *To:* minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx> *Sent:* Thursday, January 30, 2014 10:17 AM *Subject:* [minima] Re: My Minima is Alive and well Here are some outputs as promised; it is definitely the 30MHz LPF in circuit above 15MHz, but I am surprised by the amplitude of the LO even when it is as high as 49MHz. I will check, check, check! Mark On 30/01/2014 16:05, Ashhar Farhan wrote:mark, note that the audio is 'hissier' than a usual transceiver, this is due to larger bandwidth. you could try a 0.1 across the two ends of the volume control to reduce the bandwidth. - farhan On Thu, Jan 30, 2014 at 5:44 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote: I'm very pleased with how it sounds; can't wait for the 1st QSO! I've just done some experiments this morning with a new design/replacement for the 15MHz LPF, which I can't get quite right as Farhan designed: http://g0mgx.blogspot.co.uk/2014/01/minima-remaking-15mhz-lpf.html I'll do the sweep requested later today as I move onto TX testing... Mark G0MGX On 30/01/2014 10:33, jerry@xxxxxxxxxxxxxxxx <mailto:jerry@xxxxxxxxxxxxxxxx> wrote: Good job Mark, the audio sounds great.I can't wait to finish mine. Jerry K5LRU -------- Original Message -------- Subject: [minima] Re: My Minima is Alive and well From: "Steve VK2SJA" <vk2sja@xxxxxxxxxxx <mailto:vk2sja@xxxxxxxxxxx>> Date: Thu, January 30, 2014 4:13 am To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx> Way to go Mark! I knew you'd finish before I even turned on the iron!! Good audio on the video. Thanks for posting. 73, Steve. Morning Team An update from me, RX demo video here: http://g0mgx.blogspot.co.uk/2014/01/my-minima-is-alive-and-well.html the RX sounds great! Mark G0MGX
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