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Topics - Lamewolf

1
Antennas / Off Center Fed Dipole
July 03, 2020, 09:39:56 pm
Been away for a while and just got back on tonight, so I thought I would share the antenna I have been experimenting with that seems to work gangbusters and most places without a tuner.  Its an off center fed dipole that covers 80, 40, 20, 17, 12, 10, and 6 meters.  The initial resonance is set to 3.450 mhz (yes, below the band edge) to get the bands 40 and up at resonance.  But to move 80 meter resonance up the band without changing the other bands you put a capacitance between the balun and the long leg of the antenna.  I operate around 3.825 mhz and two 180pf 5KV caps in series gives me around 95pf @ 10KV and gets my swr on 3.825 a 1.2:1 for no tuner operation.  2:1 swr points on 80 meters starts at 3.745 mhz and extends to the top of the band where its only 1.8:1.  Below 3.745 I do use a manual tuner if I'm using the amp, but if I'm running barefoot, the tuner in my Icom 7300 matches it just fine.  40 and 20 meters needs no tuner at all, but 17 meters is a little above 2:1 - around 2.3:1, so I use a tuner there too. 12 meters needs no tuner at all, and 10 is usable from 29.0 to 28.680 without a tuner, and six meters is a bot above 2:1 but again, the tuner in the 7300 takes care of that no problem.  On WSPR mode running only 3 watts, I'm being heard all over the US and Europe with it.  The balun is a hybrid balun  that contains a 4:1 Ruthroff voltage balun to convert the antennas feedpoint impedance of around 200 ohms to 50 ohms, then it has a 1:1 Guanella current balun between the 4:1 and the coax to block common mode currents from the outside of the coax shield.  Hope some of you decide to try it, its been a real success here and fun to build !
2
Antennas / End fed half wave for 60 meters
May 27, 2017, 08:58:47 am
Been experimenting again with end fed half waves and methods of matching them.  Build a broadband matching transformer to use with my EFHW 60 meter antenna and its working great !  Its flat on 60 meters and close enough (2.5:1) to use with my built in ATU in my FT-450AT on 30 meters and 15 meters.  Thought I would share a diagram on the transformer.
3
Just thought I would share a couple of diagrams with the group on my modified off center fed dipole that is working great so far.  The modification is the addition of a 120pf 5KV capacitor to move the 80 meter resonance more toward the center of the band without effecting the upper bands.  The cap also has a 1 megohm 5 watt carbon resistor across it to protect it from static damage.  The diagrams also have swr readings for my particular antenna - ENJOY !
4
Antennas / Interesting mod for off center fed dipole
December 01, 2016, 08:19:28 am
My homebrew off center fed dipole has always needed a tuner on 80 meters, but I discovered that by adding a 80pf to 130pf high voltage capacitor between the balun and the longer wire it lowers the swr and moves the lower swr up the band somewhat.  My best swr on 80 was 2.4:1 at 3.5 MHz and quickly rose as I tuned up the band.  I operate around 3.810 to 3.830 where the swr was around 3:1.  I found a 120pf 5KV disc cap in my junkbox and decided to try it and it moved the useable swr up to 3.850 and dropped it to 1.5:1 with a <2:1 swr from 3.750 to around 3.950.  The value of the cap determines the resonant point, so by varying the value, you can move the resonant point around within the band.  Also, put a 1 megohm 3 watt non inductive resistor across the cap to protect it from static charges.  Anyway, I can now operate 80 meters on some of my favorite frequencies without a tuner.
5
Antennas / A different take on the off center fed
September 29, 2016, 10:06:12 am
Wondering if anyone here has ever used one of these ?
If so, let us know how it worked out and how well the match was.

http://www.g7fek.co.uk/software/G7FEK%20antenna.pdf



Rick - KC8AON
6
Antennas / Microlight 40M OCF portable antenna
September 16, 2016, 10:57:12 am
Going to go ahead and build my microlight off center fed dipole to use with my Icom 703 and its built in ATU.  The balun will be a 3 core design using three FT50-43 cores.  Two of them will be wound as a 2 core guanella current balun and the third will form a 1:1 choke and all be mounted on a fiberglass board for the center insulator and then seal with liquid tape, and use some very flexible #20 rubber insulated wire a friend gave me for the antenna sections.  It will be fed through 33' of RG316 coax that I ordered and terminated into a BNC connector.  Using the BNC so it can also be used with a couple of small QRP homebrew tuners that I use with my Yaesu FT-817.  The balun will probably handle around 20 watts at most but that's ok as the 703 is a 10 watt rig and the 817 is a 5 watt rig.  But I know the ATU in the 703 will handle it just fine on all bands 10 thru 40 if it does need an ATU.  I will initially make the antenn for 10 thru 40 meters but may also make up a set of extender wires to make it work also on 60 & 80 meters when needed.  The antenna will be supported for portable use by my 31' Jackite telescopic pole as an inverted V.  Should prove out to work quite well even at 10 watts !
7
Antennas / Tactical All Band End Fed HF Antenna
September 08, 2016, 10:58:04 am
http://vk6ysf.com/hf_tactical_%20antenna.htm

Anyone tried or experimented with the type of antenna above ?  Thinking of trying to build one just for kicks.
8
Subject says it all, so lets hear from everyone - what HF portable antenna do you use with a good description.
9
Antennas / KC8AON's Tips for End Fed Wire Antennas
April 14, 2016, 10:16:58 am

1. If your tuner has enough range to match it on all the bands you want to operate without using a balun or unun, then don't use a balun or unun as this only adds losses to the system.
2. If you have the room, use a half wave end fed wire for the band of interest.  This can be matched with an easy to build LC network and is less dependant on a ground system or radials and is very efficient.
3. Be careful when near the end of any end fed wire as certain frequency/length  combinations can produce high voltages which could cause a shock, arching, and or fire. Always use insulated wire and insulate the ends of the wires with electrical tape if they are low enough for humans or animals to come in contact with it.
4. If you are using a quarter wave or end fed random wire, also use at least one quarter wave length counterpoise wire from best performance. Run this wire 180 degrees from the main wire.
5. The best place for the tuner when feeding an end fed wire is at the feed point of the wire, this helps eliminate  feed line losses due to a high swr on the feed line.
6. If a manufacturer is selling an all band end fed antenna that "must use a tuner for all band coverage", one needs to understand and expect that the antenna will work but will have losses and will not be a top performer.
10
Check it out: http://www.spiderbeam.us/product_info.php?info=p252_Aerial-51 Model 404-UL.html  About 14 ounces including 40' of feedline and handles 200 watts !
11
Antennas / Off Center Fed Dipoles with hybrid balun
March 08, 2016, 07:53:23 am
Just built a new off center fed dipole for 6 thru 80 meter operation.  Nothing special about the antenna since its the standard 45' - 90' split to cover 80, 40, 20, 17, 12, 10 and 6 meters, but since they are notorious for common mode current on 80 meters, I decided to do a hybrid balun on this one to tame the CMC (common mode current).  The balun is a 4:1 Ruthroff voltage balun wound on an FT240-61 core with 12 bifilar windings, and that is connected to the feed line through a 1:1 choke that is wound with 18 turns of Teflon insulated coax similar to RG174 coax rated at 100 watts on an FT140-43 core which equates out to about 6000 ohms of choking impedance to keep RF off the coax shield.  But cores are mounted in the same box to which the antenna is connected to by stainless steel eyebolts.  The 1:1 choke will limit me to 100 watts but I never run more than that anyway, but with the choke in place I should get radiation form the antenna only and not the feed line which also results in more accurate swr readings.  Will hoist it up sometime this weekend to give it a try and will post results here.
12
Antennas / 60 meter end fed half wave and an update
January 19, 2016, 07:22:42 am
Gang,



Recently I put up a sloper for 160 meters and have found out that 160 is just too noisy at my location and I'm not using it much at all.  So when time allows, I will be shortening the wire to somewhere around 88 feet which is a half wave on 60 meters and will be feeding it with a little homebrew Lmatch circuit.  Got the Lmatch built last night and put it on the analyzer and I can get a good match with anything from 1000 ohms to 5000 ohms just by adjusting the variable capacitor.  So once I get the wire the right length, I will put the matching unit in place and fine tune it for 60 meters.  The low end and feed point will be about 7' above ground with the high end around 65 to 70 feet.  60 meters seems to work well for regional comms, and this way I won't have to worry about fiddling around with a tuner like I do when I use my off center fed dipole there and being a half wave it will be less dependent on a ground or counterpoise but the ground side will be connected to my ground system for safety.  So has anyone else used an EFHW on 60 meters ?

UPDATE:

The 60 meter end fed half wave (88' of wire) is a success.  Dropped the high end of the 160 meter antenna down yesterday and shortened it to 88' and pulled it back up, then installed the Lmatch at the feed point.  Before I mounted the Lmatch, I put a 4400 ohm carbon resistor across the terminals and adjusted the variable cap to get a 1:1 swr, then once mounted and the wire was connected, I checked it with the analyzer and it had only risen to a 1.2:1 swr on all 5 channels.  The 1.2:1 stayed the same both with and without the ground wire connected indicating that the wire length is resonant, but I did leave the ground wire connected because the Lmatch also has a 100mH choke between the antenna terminal and ground to help bleed off any static charges to ground.  Eventually though, the Lmatch will be replaced by an impedance transformer similar to the ones used in the Par EndFedz antennas, but mine is being wound on an FT240-61 core.  The transformer should allow operation on 60 meters and hopefully be close enough to also use on its second harmonic on 30 meters, but we'll see.  I actually have the transformer built, just still got some tweaking on it to get it right.  But so far I'm having trouble getting a good match with it and may just leave the Lmatch in place since I am able to work anyone I can hear on it.  Even worked Ocala Florida from my home in Southern Ohio on it with great signal reports !



KC8AON
13
I've built a few interfaces for digital comms in the past but they have all been for computers with a serial port.  My new Dell laptop has no serial port and I wanted to simplify connections to just one cable from the laptop to the interface and one cable from the interface to the radio.  Since I usually only run qrp power levels, i didn't worry about using isolation tranformers in my design and have even built interfaces in the past without them and have never had any problems.  Audio is coupled through capacitors though so I guess it is somewhat isolated that way.  I looked at various vox circuits on the web and built a few of them to key the ptt with but just couldn't seem to get them to work.  The core of the interface is a very cheap USB soundcard for audio connections and a 2 transistor vox circuit to key the PTT line.  One transistor a 2N3904 acts as an amplifier to drive another 2N3904 a a switch to activated the PTT line.  In various circuits I found on the web, they all used either 1uF or 2.2uF coupling capacitors in the circuit but I could not get the circuits to work even after checking and double checking everything to find it all done right.  After a lot of head scratching, troubleshooting, and study, I decided to design my own circuit.  With other designs, the best I could do with the PTT was to make it chatter in and out of transmit and I found that it was the low value caps being used, so I included 10uF caps in place of the lower values and only have 2 transistors where a lot of them had 3.  With the new circuit, it keys the rig very quickly and returns a split second later after transmission to receive as it should with on air reports of clean sounding audio.  The USB soundcard is mounted inside the enclosure with the vox circuit and the USB port protrudes through a hole in the back of the enclosure for connection of a USB extension cable.  Also on the back is a 5 pin DIN plug for connections of cables made up for various radios, so to change rigs only requires changing cables.  So far I have a cable that will fit my Icom 703, 706Mk2, and my 718, one for my little Yaesu FT-817, and one for my old Yaesu FT-840.  So far I have tested the interface for short periods up to 100 watts without any problems but the circuit also has .01uF bypass caps on all output connects to bleed RF off of it which seems to work well.  Included is a schematic of the circuit in case someone would want to duplicate it.  The 5 volt DC power connection, ground, audio in and out to the soundcard are made by opening the case of the soundcard and soldering small wires direct to their proper place.  The soundcard is then closed back up and mounted using double sided tape to the enclosure.

UPDATE:  Been notified I omitted R1, 2 & 3 values !  R1 & R3 are 4.7K ohm and R2 is 100K ohm - sorry !
14
Technical Corner / 60 meter tech talk roundtable
February 13, 2015, 02:07:29 pm
Just wondering how many folks here have 60 meter capability ?  If so, would any of you be interested in a 60 meter tech talk roundtable - discussing anything technical such as kit building, modifications, antennas etc etc ?  Lets see how many would be interested and possibly set it up.
15
Antennas / 80 thru 6 meter Off Center Fed Dipole
January 28, 2015, 01:10:29 pm
OK, I built my own 4:1 Guanella current balun using two FT240-61 cores and #14 solid copper insulated wire, got the wires attached - 44' and  89' with some extra folded back on the ends for fine tuning, and getting good results so far on the air.  The swr on 80 meters is only down to 2.3:1 at 3.5 MHz, but I will be tweaking the feed point position to tray and get that lower.  On the other bands, 40, 20, 17, 12, and 10 meters its 2:1 or less except for the upper end of 10 where it steadily climbs upwards to about 3:1 which is normal.  Anyway, been working some DX with it on 40 meters and having a lot of fun experimenting with it.
16
Antennas / Radio Shack
December 09, 2014, 03:26:51 pm
Went to Radio Shack last night to see if they had any RG8X (Mini 8) coax, the guy takes me over and grabs a box with RG6, 75 ohm TV coax and heads for the cash register.  I tell him thats not what I want, I asked for RG8X and that is RG6.  Then he says the only other coax we have is PL259 coax.  I tell him that a PL259 is a connector for coax not the coax itself.  He tells me, "I know what I'm talking about, trust me its a type of coax".  So I say show it to me.  He goes to the other side of the room and picks up a box of RG58 coax and says, "this is PL259 coax cable".  So I pointed out on the box that it is RG58 coax with PL259 connectors on it, and he says "Oh, ok - I thought the PL259 was the number of the cable".  Anyway, they didn't have any RG8X coax at, but could order it in 100' boxes.  Before I left I asked them if it was true they were changing the name from Radio Shack to The Phone Booth ?  The guy says, "I don't know, maybe they are".  He didn't get it and didn't have a clue I was joking !



Thought you guys might get a chuckle out of this !
17
Guess my original post "Vertical Half Rombic" wasn't interesting enough.

Anyone here ever experimented with a Vertical Half Rombic antenna ?  Its basically and end fed antenna that is fed with a 9:1 unun on one end and has a 450 ohm non inductive resistor termination on the other end and can cover 160 thru 10 meters without a tuner and is configured like an inverted V.  Getting the materials together to build one, once I get it together and tested will post the results here.

This antenna requires no tuner for all band operation and can be setup quick in the field.  Needs only one support too - very easy to setup.

Here's a link to a pdf with info I am using to build mine: http://www.korpi.biz/hr.pdf
18
Net Activity / 60 Meters ?
October 29, 2013, 08:39:08 am
Anyone here doing anything n 60 meters ?  Not much activity there when I listen, thought it might be a good place to congregate in the evenings for a preppers round table.  What say ye ?

Lets all make it a habit to try and check channel 3 (5.357 MHz) around 7pm eastern time each evening for prepper activity !
19
I had an enclosure that is the same physical size of my Yaesu FT-817, so I figured it would be nice to have a matching manpack portable tuner to go with the 817.  So I dug around in my junkbox and came up with all the parts to build this little Tmatch tuner that has a socket on the front panel to attach a whip antenna.  So far it will tune a 6' telescopic whip on 10 thru 40 meters and with the addition of a base loading coil it will also tune the whip on 60 & 80 meters.  The tuner will also tune coax fed antennas, endfed wires, and with the addition of a small outboard 4:1 balun, it will also tune antennas fed with balanced feedline.  I have had it on the air from my house on my 40 meter extended double zepp and the tuner matches it 10 thru 80 meters, and yesterday I had it out in the back yard on the 6' whip and worked Italy on 17 meters with it and I'm in Ohio !  Only got a 3x9 signal report, but the operator in Italy did hear me ! :)