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dirty multiband
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this is an idea, it might be illegal though, 1. remove the 7 MHz low pass filter from the PA, instead, put an 30 MHz LPF 2. add a toggle switch to bypass the band pass filter. make a band pass filter with a variable capacitor that tunes from 14 to 30 MHz. ? 3. Add two more switches to go up and down the bands on the raduino with the extra pins available.? At 14 Mhz, you ?will be radiating a fair amount of 28 MHz. Build your LPFs as you go along. Keep them on your antenna line.? - f |
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What's illegal is what you radiate which is not in specs. The FCC or ITU. or anyone else for that matter, doesn't care how you achieve that. Hi.
The real problem I see with this scheme is matching the IRF510 to all those bands with just a bunch of LPF's. This device is not the greatest choice above 40m. That along with various drain voltages may make a good match over the entire range a lot of work. It could be done if one is willing to accept lower power output on the upper bands...but WA2EBY did it. Why not? OTOH, he experimented long and hard for a proper layout for all those bands. This is probably a better scheme with a separate PA. john AD5YE |
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In fewer words, make the BPF tunable and kick the transmit LPF outside the box into the antenna line. Sounds legal enough to me, except some will undoubtedly get lazy and run without the correct LPF. ?Though I suppose they could do that on any multiband hack to the Bitx40. ?Would the tunable BPF work well enough without multiple tuned circuits? ? Given the sunspot cycle, maybe do this across 80/40/20? ?I'll probably just go for two plug-in filters. I haven't been very active. ?Built a few rigs over the years, ran some Arc5 WW2 surplus when I was in college in the early 70's. ?Have had one store-bought HF transceiver, the Swan 100MX is sitting on the desk in front of me. ?One of the few knobs is labeled "PRESELECTOR". ?The schematics show it placed exactly where the BPF is on the Bitx40, doing dual duty between the exciter and the PA, and between the antenna and the receiver. ?The schematic for this preselector, what with all the band switching they found necessary, looks quite busy. ?I count 90 R's and C's and L's and T's and D's and Q's. The Bitx40 is reminiscent of that 100MX, except the 100MX has a whole lot more parts in it. Jerry, KE7ER? |
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I think a dual Band 80 / 40 m would be quite easily achievable with the Raduino and a few switches or maybe a 20/15 version . More to think about . Thank you Ashhar for the idea . I have a BITX80v3 functioning and have a CW generator on it as well , so when I get the Raduino's and the other kit in the mail , I am going to see about building it into a"Twinbander " with SSB/CW capabilities ( BITX4080 ). I am liking these BITX40v3 boards .
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I've stripped the BPF off the board and building a 40/20 BPF. Then I'll build a 80/40 BPF. 73 Ken On Wed, Jan 25, 2017 at 10:04 PM, VE7BEE <obeebe@...> wrote: I think a dual Band 80 / 40 m would be quite easily achievable with the Raduino and a few switches or maybe a 20/15 version . More to think about . Thank you Ashhar for the idea . I have a BITX80v3 functioning and have a CW generator on it as well , so when I get the Raduino's and the other kit in the mail , I am going to see about building it into a"Twinbander " with SSB/CW capabilities ( BITX4080 ). I am liking these BITX40v3 boards . |
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For a dual bander, the band switching is easy.? mount three slide switches in a line:? one to flip the LPF, t he second to flip the BPF,? the third to toggle a logic level to the arduino. ?then tie all of them together to a small stick that you can pull and push to change the band. - f On Thu, Jan 26, 2017 at 8:37 AM, Ken <chase8043@...> wrote:
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I haven't worked on the LPF yet, but I have 40/20 BPF switched with relays. They are manually switched over for now. 73 Ken VA3ABN On Wed, Jan 25, 2017 at 10:20 PM, Ashhar Farhan <farhanbox@...> wrote:
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Two switches. Note that the junction of C6 and C7 is floating for DC. ?So one bandpass filter has a 10k resistor to gnd, and one has a 10k resistor to 5v. ?The main board has a third 10k resistor to one of the Raduino digital input pins. ?Could go into a Raduino ADC input and distinguish between as many bands as you want, each having a different dc voltage across two resistors between 5v and gnd. Of course, that's about the worst possible point to be injecting hash from the Raduino. ?Better take care with bypass caps and such. ?Might be better still to add an extra cap at the output LPF, and carry out this scheme over there. I assume we're talking DPDT switches, you want to switch both ends of each filter. ?They do make 3PDT slide switches, so another option would be to use the third pole over at the LPF for the logic level into the Raduino. Jerry, KE7ER On Wed, Jan 25, 2017 at 07:20 pm, Ashhar Farhan wrote: For a dual bander, the band switching is easy.? ? |
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Thoughts : on 40/80 BPF - 12 v relay triple pole . 40 M off ? - 80 M on . Relay adds extra capacitance in for 80 m across C2 / C4 / C6 about 600pf . I am not sure how much stray capacitance of the relay might contribute to the filter . mount the relay on a small perf board next to the BPF . Just an idea.?
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Buzz I had uploaded some BPF plots earlier this week and announced it. Look at Files > VA3ABN .> Bitx40V3 73 Ken On Wed, Jan 25, 2017 at 11:56 PM, VE7BEE <obeebe@...> wrote:
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Buzz(?) I haven't much chance to do any Bitx stuff. My employment ?is getting in the way of the hobby and I'm getting frustrated. ? hi hi I think the input and output impedance of the BPF must be changing when working with bands other than 40. I'm no expert and just learning filter design. My 20m BPF is not working very well and I think the impedance is causing the problem. This BPF is a triple tuned circuit and I have to read Wes' paper on this. I will let you know if I find anything. 73 Ken VA3ABN On Sat, Jan 28, 2017 at 11:00 PM, VE7BEE <obeebe@...> wrote: Ken , Got a look at the 80 M BPF , could use some improvement , but it will work with either 680 or 700 . 680pf ?appears to be slightly better . My plan for dual band is to switch in 600 pf across the 100 pf caps via relay unless I have a switch that will work . |