{"id":33079,"date":"2018-07-05T07:00:23","date_gmt":"2018-07-05T11:00:23","guid":{"rendered":"https:\/\/swling.com\/blog\/?p=33079"},"modified":"2018-07-05T10:44:57","modified_gmt":"2018-07-05T14:44:57","slug":"guest-post-backpack-shack-3-0-part-3","status":"publish","type":"post","link":"https:\/\/swling.com\/blog\/2018\/07\/guest-post-backpack-shack-3-0-part-3\/","title":{"rendered":"Guest Post: Backpack Shack 3.0 \u2013 Part 3"},"content":{"rendered":"

Many thanks to\u00a0SWLing Post contributor,\u00a0TomL<\/a>, who shares the following guest post as a his Backpack Shack 3<\/a>\u00a0continues to evolve:<\/em><\/strong><\/p>\n

\n

Backpack Shack 3.0 \u2013 Part 3<\/h2>\n

by TomL<\/strong>
\n\"\"<\/a><\/p>\n

I have now gone overboard since I think bigger must be better. \u00a0The temptation was just too great and now there is an MFJ-1979 17-foot telescoping whip antenna in my car (with consequences).<\/p>\n

MFJ Angst<\/h2>\n

I have a love\/hate relationship with MFJ products because of what I think are useful ideas that are made somewhat poorly. \u00a0But I went ahead and bought the large whip since I figured they could not possibly screw up something so simple, right?<\/p>\n

Wrong. \u00a0As I excitedly tried to screw the supposed 3\/8\u201d-24 threaded end into the nice standard Firestik K-11 magnet mount, I realized I was turning and turning it but it was not going in!!! \u00a0I even had a small steel sliver of metal sticking into my flesh to prove I was not dreaming. The previous day, it had screwed in very tightly, but it did screw in. So, there I was after a long day of work, ready to listen to some SWL-Nirvana and I could not get the blasted antenna into the mount–? \u00a0That Firestik mount is a VERY standard 3\/8\u201d-24 female thread and the other third-party antenna shafts fit perfectly and easily EVERY time I use them. I hate $60 of poor workmanship and MFJ seems to be the poster child of overpromising and underdelivering.<\/p>\n

I was determined to make this work, by force if needed. \u00a0One of the Trucker antenna shafts by necessity had an extra coupling nut on it to allow the extra 18 inch shaft to connect, so I took it off there and tried to thread it onto the MFJ-1979. \u00a0It barely moved. Not to be thwarted, I dug out an adjustable wrench and 3\/8\u201d socket wrench with \u00bd\u201d socket and grunted and twisted and tightened until the coupling nut was threaded all the way \u201cup its shaft\u201d. \u00a0That is what I feel like telling MFJ! That coupling nut is never coming off and now that I truly have bought it and cannot return it, I might as well use it.<\/p>\n

\"\"<\/a><\/p>\n

The stainless steel telescoping rod is extremely thin and feels like it can bend and dent with any kind of mishandling. \u00a0So it resides collapsed in a 27 inch PVC pipe with plumbing pipe foam inside to baby it when it is not being used. It remains to be seen if I can remember to \u201cHandle With Care\u201d when extending\/collapsing it. \u00a0We\u2019ll see.<\/p>\n

Ready-to-go<\/h2>\n

OK, so using the 18 inch antenna shaft attached to the magnet mount, then the coupling nut on the MFJ antenna, I extended it to a total of about 13 feet. \u00a0With the DX Engineering Pre-amp turned on, and using the SDR Play RSP2<\/a>, I was getting many signals booming in. All the usual names we are familiar with \u2013 RMI, CRI, Turkey, Cuba, etc. \u00a0But also the noise level was very high. I know it is summer but I may have been overloading the Pre-amp a little bit. Here is an example, Radio Progresso from Cuba with some very nice acapella music but also a noisy background (plus, a noisy laptop computer pulse!):<\/p>\nhttps:\/\/archive.org\/download\/1806141258h11.54MHzSAMRFA4TibetanTinianIsAndKuwait\/180613%20-%200150h%20-%204.765%20MHz%2C%20SAM%20RProgresso%20Cuba.mp3<\/a><\/audio>\n

Click here to download MP3 audio.<\/a><\/p>\n

So I decided to come back in the morning before my workday started and see if the static crashes would have died down.<\/p>\n

Preamp Angst<\/h2>\n

The next morning I had everything hooked up again in the same spot at the Forest Preserve (located in a suburb of Northern Illinois). \u00a0I moved the Cross Country Preselector to be directly connected from the roof, then to the antenna switch on the \u201cBreadboard\u201d (see part 2<\/a>) to better prevent overloading. \u00a0I turned on the Verizon battery pack and nothing. No Pre-amp light. Switched it on, off, on, off \u2013 nothing. So, I thought I must have burnt it out the previous session?<\/p>\n

Later on, I found it was some sort of short in the switch and I will have to move the D-cell batteries to a backup battery pack. In the meantime, I had to do without the Pre-amp and was forced to extend the MFJ antenna all the way. \u00a0With the 18 inch extension attached to the magnet mount, that was a total of 18.5 feet from antenna tip to the top of my car roof.<\/p>\n

This was actually fortuitous since I was already concerned about overloading the Pre-amp or perhaps amplifying background noise. \u00a0This forced me to test it in a more \u201cbarefoot\u201d manner, hearing what it would natively hear without any Pre-amp. It was also lucky there was no wind to blow it over! \u00a0It seems that if one is in an RFI-quiet area with decent view of horizons, the 20+dB Pre-amp may not be needed, depending on frequency band involved.<\/p>\n

I have read that \u201cNorton\u201d style 10 dB Pre-amps and custom handmade transformer baluns are used by Dr. Dallas Lankford in his Low Noise Vertical antennas. \u00a0I don\u2019t want to get into winding baluns so I am using one Palomar Longwire Balun to simulate the \u201cmagnetic\u201d transfer. His design uses two, one 10:1 at the antenna and a 1:1 balun at the feedline into the house. \u00a0For more reading on LNV antennas, see these references:<\/p>\n