what buffer amp do i need to connect my sdr to my yaesu ft-707 to use it as a panadaptor,i am looking for a cct diagram so i can homebrew something,thanks.

I used a amplifier based on the PA0RDT "Mini-Whip" because of it's low input impedance and low noise floor.

You might be able to get away with just using the J-FET input stage and feeding the output to your SDR or, if that doesn't work, go with a plain jane PNP output transistor because you are not dealing with the wide range of signal strengths an antenna is exposed to.

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You could probably even get away with using a lower quality J-FET like the 2N3819 or MPF102 (or is it MPF101....been too long since I used one, I have oodles of 2N3819 so I use them for general purpose N-Channel J-FETs).

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I had a spare "PAR0DRT" "Mini-Whip" I prototyped for an oscilloscope low capacity wide bandwidth (to me 0 to 30MHz qualifies as wide bandwidth on my bench) scope probe. I built a compact version for the scope then reassembled the prototype as a general low input impedance buffer.

no schematic?

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There are at least dozens of variations shown on the web.

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This is one that works as promised....

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There is no way I can begin to explain intercept point without a lot of unsane math and graphics.

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The short answer, at some signal strength and amplifier fed two (or more) signals will start to mix with each other, IE intermod.

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A real world example. On the corner of Broadway and Main Street the 2M [140~160MHz] from a variety of sources will cause most amateur 2M transceivers front ends to 'collapse' and you'd hear the wildest mix of transmitters.

The only amateur transceiver I knew that began to withstand the intense RF at that location had "helical resonators" in the front end between the antenna port and RF stages.

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There are two types of intercept.

IP2

https://www.everythingrf.com/community/what-is-ip2

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IP3

https://www.everythingrf.com/community/what-is-ip3

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The PA0RDT, and other active antennas, can be modeled on a very short antenna coupled to a broadband RF amplifier.

The PA0RDT antenna works because the output transistor can withstand fairly high Ic, much more then most other affordable transistors.

There are other ways to get there but the PA0RDT is the simplest.

The FJET input device presents an extremely high input impedance with a very low gate capacitance.

MOSFETs have issues, many issues, that make them unsuitable for sane LF~HF active antenna designs.

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One of the nightmares of cellphone antenna systems is they have to deal with a lot of closely spaced RF signals with wildly varied signal strenghts.

If the cellphone companies had their way, there'd be no UHF TV, no 900MHz Part 15 license free devices, nothing but cellphones about 400MHz (and yea that'd wipe out the 70cm ham band and 400MHz business band).

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RF can get complicated really really fast.

It requires obscenely priced equipment to begin doing decent, repeatable, tests.

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We (local SW nuts) use a park that is located roughly equidistant between the 3 Lexington MW (AM BCB) transmitters.

590/630/1300 kHz.

By varying the length of the antenna element feeding the amp of the active antenna, one can achieve reasonably accurate IP comparisons for MW.

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Feel free to go to college, pick up and EE degree, become an amateur radio operator, be lucky enough to work in a 2way shop for a summer, then be taken under the wing of a retired Ph.D. who helped design some of the then state of the art RF systems.

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Like a point to point RF link at ~20 that required high gain, highly directional antennas, the system operated below the actual local RF noise floor.

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Another issue is a strong enough signal will cause any amplifier to go into gain compression. And that my friend is a story for another day. [though it is related to IP]

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The PA0RDT was the first practical, extremely short antenna, active antenna that actually worked. Of course there are a whole slew of "you gotta do this" to make it work right.

Simply put, you have to stop EMI, radio noise, from your home from reaching the antenna via the feedline [coax]. This is an extremely challenging theoretical exercise and will drive you crazy doing it in the real world.

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The site has an explanation of how these antennas work and what must be done to begin to achieve this.

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There probably need to be two new IO Groups, one for "Active antennas" [active E-Probe antennas] and EMI, what it is and mitigation.

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The last one is even more of a challenge then E-Probe antennas.

I've considered starting them but to do the job right would require about 10 times the time I can devote to it, and there is no point doing anything half assed.

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This is probably the best single resource into E-Probe Active Antennas. I suggest reading it and following all the links. Too many will return 'dead' but most will work.

The W0QE Active Monopole Preamplifier is one of the better designs out there.

And Chris Trask's designs are excellent but a challenge to find since his webpage went dark.

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In short, RF is a pain in the tush. If I had any sense I'd pick a different hobby. But then if I had any sense I'd be rich.?

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Re static electricity on an antenna....

Wind, simple dry wind can induce enough voltage on a ~100 foot, 30 foot off the ground, random wire antenna to light neon bulbs. And that's with insulated wire.

Rain, snow, sleet, freezing rain (dear God freezing rain on steroids!) and lowly flying insects can all induce, oh yea, almost forgot birds, can all induce static electrical charges on antennas.

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Helicopter blades can produce enough static when spinning to at least knock a man out cold.

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I installed a 10k bleeder resistor on my first 100 foot antenna that bled off most casual static.

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Now distant lightning, like distant 100 miles, could cause neon bulbs to explode, lightning at 30 miles would cause NE-1 (or was it NE-2 since I'm the only one who appears to have heard of NE-1) to explode like a blasting cap or shotgun.

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We video taped blasting caps going off in the air for a mine safety project. Very exciting project, very spooky project. We used Vietnam Conflict era "clackers" designed to set off claymore directional mines. There was something fun about pressing the lever on a clacker and having a blasting cap go off. We must has sat off about 200 for BATF and the US mine safety agency. The campus police closed off the largest parking lot on a Sunday afternoon and had men keeping lookyloos away.

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Now imagine that at 2:00AM on a school night. My parents weren't exactly upset, more concerned. The next afternoon Daddy installed ceramic based knife switches right out of a Frankenstein movie set, two switches, one to short the antenna to ground, the other to short the radio antenna to chassis.

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Yea my life has been a tad too interesting at times.

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[Were you ever silly enough to ride curled up in a heavy equipment tire down a 1000 foot slope of a hill 600 feet above local terrain? And end up in a river. Thought not. Now my parents were really upset over that one but I was 8 and my idiot cousins were 16 and thought it'd be a fun joke. It was actually quite fun. I'm told the tire bounced about 50 feet high before hitting the water. I had more trouble getting out of the tire before drowning in 20 feet of water then anything else. I was giggling as I swam ashore, my mother was sobbing, that was the moment I realized "Ought oh ... done messed up here.

My father made my cousins pull the tire from the river and cut it up with a oxy-acetylene torch."

THIS? seems to gone way off topic,all i wanted to know was how to homebrew a way too hookup my sdr to my? yaesu ft-707 as a panadaptor.

Use a PA0RDT Mini-whip as the buffer.

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do you mind explaining how to do that?.

Sigh

I have zero, no, as in "I don't know jack about the Yaesu FT-707.

You need to download a service manual and figure out

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Then you need to find the input to the final IF (if it is fixed frequency) and tie in with a 1k resistor and feed the output of that resistor to the input of the PA0RDT Mini-Whip.

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I mounted the PA0RDT mini-whip antenna inside the case of my R2000 and use a chassis mount female BNC connector to feed the RF from the PA0RDT mini-whip to my SDR. Note, the PA0RDT must be in a shielded container. I used an altoid tins box and the BNC connector holds the tin in place. I use the 1k resistor as the fed through to carry the 455kHz RF into the PA0RDT, I used a 3/8 in hole to pass the resistor and heat shrink tubing to protect the resistor from the sharp metal edges, a narrow width plastic straw would also work.

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I'm sorry I can't offer more detailed installation directions.?

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I can find the if of my 707 ok, S what your saying is to use the pa 0rdt antenna as the buffer/ interface between the rig and the sdr then?, cheers Paul m3vuv 73.

Yes

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707---->PA0RDT---->BNC---cable----->SDR

[No idea what RF connector your SDR uses, it could be BNC, SMA or God only knows what.

I used a BNC but you could use a "F"?

Does that make sense?

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Make that?

707 if ----1k resistor---PA0RDT---coaxial connector---> cable > SDR

IF = intermediate frequency

cheers+73 de m3-vuv

Please let us know if it works for you.

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