Forgive my ignorance... what's it do for you with this receiver? I looked up some data; it appears to be an LC filter with a movable inductor connected to a servo motor... so it improves signal rejection of anything outside a movable narrow-band pass filter? I'd have thought they had a solid-state equivalent that worked better by now.
Narrows the passband of the IF considerably. Allows you to pick CW signals out of all the muck. In the evenings on 40m there's a huge bunch of activity. Literally wherever you tune you can hear 3-4 CW signals at once because the default passband is 2.7KHz. This is a 500Hz filter so allows you to pick one signal out of that thus helping the grey matter handle it.
It's nothing fancy inside. Basically machine selected 455KHz high Q ceramic resonators and some capacitors. The main thing where the cost comes in is that the tolerance is tight as a duck's arse as there's about 5-6 resonators inside that all within 5-10Hz of each other or 0.002% on a batch of 6. Plus they have to be temperature stable over 0-40oC approx.
There are two equivalents here which unfortunately neither win for me. There's the opamps, where you can synthesize a pretty good bandpass filter easy enough. But this has two problems: poor noise figure (hissing like an angry python) and requires quite a few mA (think 30-50mA for enough to get the same skirt and noise figure). Then there's the DSP. The FT-450D had a DSP in it and it had variable bandwidth filter that could pick up anything. This was at the cost of a 1.1A standing current doing bugger all with the volume turned down and sounding like someone was farting in a trash can. Gah.
So mechanical filter: tight bandpass, good noise figure, zero current consumption, sounds good
Okay... so you get it close as you can with the radio, and this lets you crawl up & down inside its 2.7KHz passband to separate one carrier from another?
I had a AS Base-loaded multiband antenna that tuned that way back in the day... It was a PITA when it was cold or damp, but when it was warm & dry the thing was amazing.
I had one of them on my Land Rover with a Midland CB (and an illegal amp which gave you a zap if you touched any of the metal bits when TX ). I killed the antenna by forgetting to shove it down going into a car park ... CB was fun. Miss it terribly. Nothing here now. Not even truck drivers to wind up.
Yep, CB was great and there's literally 100's of CB sets for sale 2nd hand on Ebay and Shpock. Was yours AM or the legal FM but with a thumping great amp attached to push its TX power way above the stupid 4W limit imposed
LOL... I have a box of Cobra 29LTDs and Presidents around here somewhere I'm going to have to triage when it turns up... think there's probably some old TRS scanners and a marine XCVR in there too, IIRC.
Keeping it TEA...
Due to the "global swarming assache syndrome" that inevitably occurs whenever Resident Chump opens his lie-hole about anything, I decided to pull the trigger on that AliEx test cable order I was talking about earlier. I figured I can use them on any meter I have, whether I get the 3478A working right or not, and it was only $35.
https://www.aliexpress.com/item/50pcs-5color-Gold-Plated-Retractable-4mm-Stackable-Plug-Soldering-Type/1781741357.htmlhttps://www.aliexpress.com/item/TL320-12pcs-lot-R-B-1-0meter-High-Quality-13AWG-flexible-silicone-test-leads-4mm-straight/32681958679.htmlSo then, feeling clever, I decided to hop on over to Bang-me-good and get a couple meters of green silicone cable to go with those green cable ends... and it all turned to shi*.
I BARELY managed to get out of there for $83, and that included burning $10 worth of affiliate points.
Highlights include 2 kinds of shrouded 4mm jacks in case I decide to retrofit the 3478A:
https://www.banggood.com/Amass-4mm-24A-1000V-Banana-Plug-Connector-for-PCB-Board-p-1343899.htmlhttps://www.banggood.com/2Pcs-4mm-Nickel-Plated-Binding-Post-Banana-Jack-Socket-Plug-p-953213.htmlSome good old-fashioned 4mm solder & screw banana plugs in case I don't:
https://www.banggood.com/P3001-10Pcs-4mm-Multimeter-Test-Probes-Connector-Banana-Plug-Jack-p-1108651.htmlSome heat-shrink tubing kits that were just too cheap & convenient to pass up:
https://www.banggood.com/DANIU-Heat-Shrink-Shrinking-Tubing-Tube-Wire-Wrap-Cable-Sleeve-Kit-Set-p-1162246.htmlhttps://www.banggood.com/Soloop-328pcs-21-Polyolefin-Halogen-Free-Heat-Shrink-Tube-Sleeving-5-Color-8-Size-p-969574.htmliPX connectors just because:
https://www.banggood.com/10-PCS-U_FL-IPEX-IPX-Antenna-Mounting-Pedestal-Plate-SMT-Solder-Paster-20279-001E-01-p-1221544.htmlA couple BNC-4mm adapters because they were too cheap:
https://www.banggood.com/Hantek-HT311-BNC-to-4-mm-Adapter-for-Automotive-Diagnostic-Oscilloscope-Portable-Accessory-p-1334226.htmland some 2mm pitch leadscrew for a mod I wanna do on my 3D Printer:
https://www.banggood.com/8mm-300400500600mm-Lead-2mm-Stainless-Steel-Leadscrew-T8-Nut-For-CNC-3D-Printer-Reprap-p-1143904.htmlplus several handfuls of assorted XT60 connectors & boring RC odds/ends.
FM with a 50W Italian burner on it
Completely deregulated now. Surprised more people don’t use it. My 818 will receive it. Haven’t tried transmit.
Unlike the idiots here that use an illegal 200W crappy export radio to drive a barely less crappy amp to drive another semi crappy monster amp to go to shootouts to try and kill each other and their equipment. Apparently the RF hasn't sterilized them yet as they keep making more like them. I was like you, 50 burner in the car and a gain antenna at home. Radio was properly aligned and had a power mike attached. When people would tell me to turn off the amp, I would turn the mike down to zero.
Some years after I got out of Children's Band, the fellow I lived next door to got himself a rig and a linear (hacked 10m linears were everywhere at the time, even the corner store) ran some RG-59/U (too cheap to spring for RG-8, or too dumb to make his own cables) out to a car antenna vise-gripped to the wooden fence between our properties. Every freaking idiot word he ratchet-jawed until 2AM would come out over the stereo in the bedroom. First night my wife woke me up so I turned off the stereo and it seemed to go away. The next night, it started again, and kept cranking out even though the stereo was off and unplugged, and it made the touch-light in the corner go batshit crazy.
I knew then that it had to be literally feet away from our bedroom, so I went outside with a flashlight and there it was. I unclipped it, (thought about cutting the cable, but I knew the guy and had a beer with him every once in a while) unscrewed the cable and let it drop.
A few seconds later I hear "What the fuck?!?" and a minute or two of other choice expletives, then the screen door slam and him rustling around the grass. I walk around to the end of the fence and wait for him to come around, repeatedly smacking the Vise-grips and antenna mast against the palm of my hand.
When he does, he freezes, seeing me and his antenna. Before he can say a word, I shove them right in his face:
"Mike, you're my next door neighbor and I love ya, but I swear, you wake my wife at 2AM with this thing again and I'm gonna shove it up your ass. After I taser your rig to ashes."
"Buh...buh... buh...""You're making the lights in my bedroom flash like a discotheque, and it plays through my speakers even with the stereo unplugged. Get rid of that illegal amp & move the antenna some-fucking place besides right next to my bedroom." He just clutches his stuff to his chest and disappears around the fence without a word.
That was over a decade ago now... when I go back to San Antoine, I usually stop by with a 6-pack. We always laugh over it; it's like a ritual now or something.
mnem
Hey, at least now I'm not thinking about my dick in that hornet's nest...