Friday, October 6, 2017

Experimental 2 meter / 70 cm dual-band high-gain flower pot antenna using RG6 coax


I decided to modify the original VK2ZOI Experimental
Dual Band Flower Pot Antenna to work with RG6 coaxial cable and utilize a ten-foot-long section of 1+1/4" PVC pipe that is found endemically here in the United States. This resulted in an antenna with SWR of about 1.0 on 146.52 MHz simplex, and 2.0 on 144 and 148 MHz.

Changes from Original Design

Compared with the original VK2ZOI Experimental Flower Pot:
  • Lengths of all segments were implemented as drawn in the VK2ZOI plan
  • "Double-shielded" RG6 that used both foil and light outer braid instead of RG58
  • Top coil: 4 tight turns of RG6. The total length of this cable segment was therefore changed to 630 mm.
  • Bottom coil: 4 loose turns of RG6.

The plans of mice and men...

My original plan involved using a bottom coil of 5 turns RG6. Using SELFRES3.EXE as the calculator, I back-calculated the self-resonant frequencies of the VK2ZOI coils: top coil from 125 through 150 MHz, and bottom coil of 135 MHz. I did not compensate for velocity factor differences and assumed solid-core RG6 has a similar velocity factor to that of solid-core RG58.

The parameters that I used for my RG6:
  • Coil width 5.6 mm
  • Conductor diameter 5 mm
  • Diameter of coil = 42 mm OD of PVC + 6 mm diameter of RG6 = 48 mm

# of Turns Solenoid length, mm Calculated resonant frequency, MHz
3 17 180
4 22 143
5 40 135
5 28 122

Play-by-play

With the five-turn bottom coil, the SWR measured 3 at 146 MHz and ~1.2 at 144 MHz. Trimming the top of the antenna resulted in a reduction of SWR at 144 MHz and 146 MHz to 2.5; further shortening then increased the SWR to about 3 at 146 MHz and was stopped.

Because of the seemingly sharp "knee"-like SWR increase at ~145 MHz, I hypothesized that my lower coil was imparting too much inductance with high Q as the bottom coil ended up being  a lot more tightly packed than I had expected. I therefore removed one turn from the bottom coil and my SWR dropped dramatically at 146 MHz to be nearly 1.0.

I used aluminum foil for coupling sleeve only on the bottom of the antenna at the time of testing.

Prelimiary result with only lower sleeve in place:
SWR 2 144 MHz, 1 @ 146 MHZ, 2 @ 148 MHz.
SWR ~ 1.5 throughout 70cm band.

Special thanks to Roger W7RC (espouses the benefits of RG6) and Bill KG7ULE for
practical advice via the 146.52 MHz Portland Graveyard Net.


Saturday, November 26, 2016

Wiskott-Aldrich Syndrome mnemonic

immunodeficiency, thrombocytopenia, eczema
 Wiskott is riding an ostrich.

The ostrich is sick because it has immunodeficiency; it has epistaxis due to thrombocytopenia and a lot of eczema eggs.

X-linked disorder that causes cytoskeleton rearrangement.

Wednesday, November 23, 2016

Cytochrome P450 Inducers & Inhibitors mnemonics

Moderately offensive mnemonics that induce CYP450:
Nevir drive your carb by Ma's pines,
through the barbwire fence, and
up the ramp
into St. John's woods.

De-phen-ding griseoly bear (on a cycle, "Phossy,") will mo'dafinetly attack your drunk ass.
  • Nevirapine
  • Carbamazepine
  • Barbiturates
  • Rifampin
  • St. John's wort
  • Phenytoin
  • Griseofulvin
  • Cyclophosphamide
  • Modafinil
  • Chronic alcoholism
Offensive mnemonic that off-puts, or inhibits, CYP450:
Ami and Quinn pro-teased Sonia'z azole with grapes and Clara's myce on the ciment floor.
  • Amiodarone
  • Fluoroquinolones
  • Protease inhibitors
  • Isoniazid
  • -azole antifungals
  • Grapefruit juice
  • Clarithromycin
  • Cimetidine

Tuesday, November 22, 2016

Neural crest cell / MEN2 mnemonic

Here's a word-picture to help remember the facts.
Two men "A" and "B" are wearing crowns (neural crests) and are both eating melon (melanocytes).

Man B is really tall and skinny (marfanoid) and has big orthodontics, and he chokes on the melon -- it's gone down his trachea! He freaks out! His lips and his eyelids are swollen!

Man "A," Larry, gives him a cricothyrotomy -- right in his larynx.

Now that it's 10AM, man B enters a muffin store in order to RETurn his melon. There are some seriously lumpy muffins inside...

Man "A" goes to the middle of the store. A swan in the middle of a simulated "sea" (C cells) wearing a royal crest is giving birth. The swan wields a para -- an M249 machine gun, and has HUGE thighs, 'cuz it has been using 'roids.

With the help of her dula, who is pounding on a tympani to help the swan count, she gives birth to a baby swan. Baby swan spirals around, covered in a membrane.

MEN2A/B is a gain of function mutation in the RET (tyrosine kinase) proto-oncogene found on chromosome 10. This affects cells derived from the neural crest. Both types are associated with pheochromocytoma and parathyroid hyperplasia (in type 2A) or Marfanoid habitus and mucosal neuromas (type 2B). These cells are derivatives of neural crest cells and are listed in order of appearance:
  • Melanocytes
  • Odontoblasts
  • Tracheal & laryngeal cartilage
  • Enterochromaffin cells
  • Parafollicular thyroid cells
  • Schwann cells
  • Adrenal medulla
  • Spiral membrane / tympanic surface


Monday, November 21, 2016

Benzodiazepine mnemonics

The Benzos have a contest crossing the Alps.

https://img0.etsystatic.com/053/0/8584318/il_340x270.718469136_liwi.jpg
TOM tries with an ox mid-day;
Team Lorax crosses the Alps in less than a day;
The heavy Latin girls, Flura and Chlora, take more than one dia.

Short-acting: triazolam, oxazepam, midazolam (t½ < 6 hrs.)
Intermediate: temazepam, lorazepam, alprazolam (t½ < 24 hrs.)
Long: flurazepam, chlordiazepoxide, diazepam. (t½ > 24 hrs.)

Thursday, November 3, 2016

HIV drug mnemonics

Sometimes all you need to do is recognize part of the word.

Nuclear reverse transcriptase inhibitors

NRTI and Aba did ten vudine (voodo) tricks.
  • Abacavir
  • Didanosine
  • Tenofovir
  • Zido-, Lami-, and Stavudine
  • Emtricitabine

Non-nuclear reverse transcriptase inhibitors

No, NRTI, Neva-raping Delaware's ef-favor!
  • Nevi-rapine
  • Delavirdine
  • Efavirenz

Fusion inhibitors

Mars virus docs, 120, enfer (enter) virus 41.
  • Maraviroc - blocks GP120 and inhibits "docking" or attachment to surface receptors
  • Enfuvirtide - blocks GP41 and inhibits "entry" or viral penetration into the cell

Others

Protease inhibitors all end in -navir ("Never tease a pro-tease.")

Integrase inhibitors all have -tegr- integrated into their names.

Monday, October 3, 2016

Microbiology: mnemonics, Baitisj-style

This post is primarily for medical students.

My brain doesn't work well with normal mnemonics, so I have to create sentences that use multiple letters from the organisms.

Aerobic bacteria:
Mona's heart and lungs need air.
  • Pseudomonas
  • Nocardia (cardia = heart)
  • Mycobacterium (infest the lungs), good enough for me
Anaerobes:
Ana's mice fuse bacteria and robes together in her closet.
  • Actinomyces
  • Fusobacterium
  • Bacteroides
  • Clostridium
Obligate intracellular:
Outside, it was rilly cold and chlammy, so I went inside because I needed to ATPee with my rilly chlammy cox.
(needs host ATP)
  • Rickettsia
  • Chlamydia
  • Coxiella
Facultative intracellular:
I listened in as the facultative French Legion pestered my nice salmon brood.
  • Listeria
  • Francisella
  • Legionella
  • Yersinia pestis
  • Neisseria
  • Salmonella
  • Brucella
 Catalase-positive:
Because she was Aspergers at heart, Mona Ecolied (coiled) her candid list around her serrated cattle-staff instead of her helical book-holder.
  • Aspergillus
  • Nocardia
  • Pseudomonas
  • E. coli
  • Candida
  • Listeria
  • Serratia
  • Burkholder
  • Helicobacter pylori
Urease-positive: (this is the only acronym that works for me.)
Struvite stones? PEe CHUKSS!
  • Staph. epidermidis
  • Proteus
  • Cryptococcus
  • H pilori
  • Ureaplasma
  • Klebsiella
  • Staph. saphrophyticus

Encapsulated bacteria:
Jesus (GBS)! Mona klubbed HIs nice, pnew-ly-colied salmon capsule.
  • Group B Strep
  • Pseudomonas
  • Klebsiella
  • Haemophilus influenzae (type B)
  • Neisseria meningitidis
  • Strep. pneumoniae
  • E. coli
  • Salmonella