Messages

106

The RF Workbench / Re: Loop Stick Ferrite Physical Connections

« on: May 08, 2019, 1752 UTC »

Thanks for the links, Josh.

I was familiar with the FSL from some reading while researching the RGP3 ferrite loopstick.  I opted to go with the RGP3 because it was less expensive and much more compact. 

I've decided to "splint" the the junction of the two bundles with small dowels or tongue depressors and be done with it.  After writing my post, I made the well-documented AM input jack modification to my pl880 (a five-wind loop is added to the end of the internal ferrite antenna and soldered to the unused sleeve connection of the jack, and the ground.) I added three winds to the end of the RGP3, and I tested with this "direct" connection. The mechanical intermittence was not noticeable as I steered the antenna.

I was blown away by the results. It was hotter with this connection than with proximity inductance. I took the opportunity to slide the coil along the ferrite and find the spot with maximum signal pickup, which probably unsurprisingly is about dead center.  I haven't had a chance to A/B yet, but it seems to pull in a better signal than the 36" cross-sized loop I made with the cardboard package bracing for a mirror my wife had purchased.  The tuning is extremely sharp and I may need to find an oversized knob or even spend on a vernier.

107

The RF Workbench / Loop Stick Ferrite Physical Connections

« on: May 07, 2019, 1935 UTC »

I'm building a ferrite loop stick comprised of two larger "rods" of 12 bundled rods, stacked end to end.  Each bundle of 12 is currently held tightly together with electrical tape on both ends.  I lined them up, then wrapped some more electrical tape over the joint.  There is the slightest of mechanical play between the bundles, but not within the bundles.

As I was checking the loop for proper inductance together with my air variable, I was also rotating the radio + ferrite assembly to test changes in signal.  I noticed some occasional wild oscillations of signal while handling the assembly, and I assume it is due to the imprecise and intermittent physical connections where the bundles meet in the middle, right where the coil currently sits. 

Any input on whether I should:

1) Move the loop to one end where it would then reside on a solid segment of ferrite ,
2) Put some Penetrox A between the bundles,
3) Figure a way to make that center joint mechanically stable.

Regarding these points:

1) I tested sliding the coil along the ferrite.  I don't know the EE theory here, but it seems the gain was highest with the coil in the middle, and I think I read that the inductance changes based on the position.
2) It seems intuitive to use a conductive paste between ferromagnetic materials, but I can't shake the feeling that's not how it works.
3) It will be tough, but not impossible, to get some stabilizing dowels inside the plastic cuff I am using.

108

Equipment / Re: Coaxial antenna connection question

« on: May 02, 2019, 1922 UTC »

You may want to use a transformer to connect the antenna to the coax.

^^Seconded!

I recently hooked an outdoor skywire to the center conductor of an old cable TV (rg59) run that makes ingress into my listening room to a female F-connector wall plate.  How lucky! 

That was a great first step. It brought in a huge signal, but also some huge noise.  It turns out the noise the shield is supposed to protect against still needs to go somewhere, and most likely it is directly (DC-) coupled to your receiver and your antenna.

I wound a 1:1 isolation transformer on a binocular ferrite core, and clipped the primary to the antenna/ground terminals on my receiver, and the secondary to the center conductor/shield of the cable. Now the coax shield cannot pass common-mode directly into the receiver.  It seems to have cut the noise down (but maybe it's just that psychological trick we use to make ourselves feel better.) However, that common mode still has a path to the antenna.

To defeat this, there is another refinement I intend to make:  another 1:1 isolation transformer for the antenna side with the antenna and an Earth ground (currently the wire just terminates to the center conductor of the cable and has no ground) working against center conductor and shield.  This leaves the coax "floating" so that common-mode cannot directly flow onto the antenna or into the receiver. 

A final refinement involves grounding the shield to its own Earth ground (NOT the antenna's Earth Ground!) to give the common mode current a sink.

I got these ideas from http://www.hifidelity.com/w3eee/ under "reducing noise."

My understanding is that this also provides some spark protection to one's receiver's frontend.

Amidon sells all the ferrite and wire you need to do this if you are interested, OP.

109

Equipment / Re: Advice on Tecsun vs Sony

« on: May 02, 2019, 1753 UTC »

Hello,

Though I don't have much to compare my (recently acquired) PL-880 against, the last month of operating it has exceeded my expectations and I consider it money well spent.  The FM is excellent, AM isn't so bad and now that I've built a milk crate tuned loop to supplement it is fantastic, and on shortwave it seems sensitive enough.  The autoscanning is handy, though I find it overlooks a bunch of stations and I've taken to spinning the dial.  People complain about the sync function:  I've never used sync before the PL-880, and while I've found it provides some bogus glitchy output on very unstable transmissions, it has made listening more comfortable for those signals with medium-strength and a bit of noise.  The SSB is easy to use as well. 

My other two radios prior to acquiring the PL-880 are a KX3 and GP-5 SSB.  Once I started into SWL in earnest, I found the GP-5 was easier to use but easily overloaded, whereas the KX3 allows for top-tier control (EQ, filtering, noise blanker and noise reduction) but isn't quite as ergonomic to carry around and stick to the end of a wire.  And it doesn't have FM, or built-in AM antenna, or any antenna for that matter.  Also, the speakers on both are not very good for enjoyable listening. 

I find the PL-880 fits a niche between them both, and am impressed with the fidelity from the speaker.

The major complaint I've seen from others and agree with is the exceedingly slow attack time on the AGC.  While it doesn't bother me so much on AM SW, listening to SSB chatter becomes a chore with the constant jackhammering at the beginning of sentences.

Since I've received the PL-880 I've found the magic of radio I've been missing since my 80's childhood, and have been staying up later than I should to DX AM and scan the SW bands.  I unreservedly recommend it.