Stay at Home Series: The MFJ-17754 40/20 Trapped Dipole (
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- Опубліковано 29 лип 2024
- We review the MFJ-17754 40/20m trapped dipole wire antenna and do the first part of the tuning, that of the 20m band. Another video will cover the 40 meter band. The antenna as sold is deliberately too long, so you will definitely have to tune it before use.
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The connectors to hold the "extra" wire length using screws and clamps is very innovative. I have the 80/40 version in my attic. I tuned it using the MFJ-269 Analyzer. I just tuned the bands like the manual says, shorted the wire without cutting it (folding it back and screwing down the clamps), and Bob's Your Uncle. It will vary depending on the context it's installed so adding the wire length IS good customer service. 73
Thanks Dave. You do such a thorough job.
Great Job explaining the antenna. I had the 40/80 version and it was far off too. I really thought I was doing something wrong cutting off so much. Had it been in the instructions I would not have felt bad doing it and I thought I was just tuning it and not messing it up in the long run.
Good evening Dave. Stay healthy!
What great views of the San Juan's from the sleeping Indian to Mt. Sneffels! Well done.
Thank You.
Great video Dave.......before my divorce and having to sell the QTH this was my goto 80/40 dipole antenna and it worked great at about 35' in the air.... Lot'sa 40 meter FT8 dx late at night. 73/k6sdw
Great show. Good lighting and sound. Lots of good infromation . From Bill KD9HWH.
Dave, your videos are an incredible resource. I am a new HAM (VE3EJN). Your reference station videos are such a great addition to the community. I am learning so much. 73.
Thanks Dave,
Curt WA2JSG NJ
You have about 70 feet there. I am new on HF and made my own 49:1 and put up about 66 feet of wire, (started about 70 feet and trimmed it down) and got 40M, 20M, 15M, 10M Better than 1.5:1! MY first antenna! I can tune in 80 with my MFJ 949E! They should be able to do better than they did!
Hi Dave- I just purchase this antenna for my attic and found that I have to fold it back about 2 feet on each side for the 20-meter tuning. I hate having the three strands of wasted wire going to the metal bracket. I would like to physically cut the wire down to make this antenna look like it did out of the box only at the correct length for 20-meters. Do you know how much wire I could cut off each end and if it is safe to do this?
If you live on a ranch and have plenty of room then what about a end fed mile long long-wire antenna driven via a 16:1 UNUN which connects to your transceiver.
Can you say if this antenna could be used effectively as an inverted V?
I got my 40/20 up today using a 15ft NVIS mast and ran the wires out at 68 degrees, adding 19ft of anchor cord to make an Inverted V. Initial resonant points at SWR 1:1 were at 5.8, 12.4 and 35.4 MHZ at the end of a 50ft length of RG8x with a MFJ-915 Line Isolators up at the dipole T. My yard isn’t too big so I flipped a rock in the central Rock Harden, and hammered a 2ft 1" galvanized pip down with a 1-1/4" pipe above ground to mount my fiberglass mast over. I hammered the 1"-to-1.25" junction below grade, in a small pot, so I can unscrew the pipe and just put the rock back on top when not in use. I’ll just put it up for Winlink NVIS 40m as needed. Stay tuned for my own tuning experience - I appreciate this video giving me a head start!
OK! I shortened my 20m wire by 36" each side and my SWR from 14.0-14.35MHz ran from 1.7 to 1.3, I lengthened it out 4" and now 14.0-14.35 SWR is 1.3 to 1.7. So maybe just pulling the Inverted V legs out or loosening them will give me a few tenths of an SWR +/-. But a sweep showed my low band SWR low climbed fro 5.8 to 11.2 MHz! I'm not sure how to deal with that ... add wire to the 40m end? Hmmm... I have a few feet I could trim from the 20m end to graft on. Any thoughts?
Dave, thanks for your channel.
Question about these narrow bandwidth wire antennas...I know that for short mobile verticals, they sometimes add short radials as a capacitance hat on the end/tip. Could a similar device be used to increase the usable bandwidth of a wire antenna?
The inductors and "capacitors" in shortened antennas actually increase Q and narrow the bandwidth. However, you can use such things to shorten an antenna if you don't have enough space. You can tune it to the part of the band you use most.
Howdy Dave,
I guess you're not allowed to toot your own horn until all of the job is complete... haha!
As part of the reference station, are you planning on including a remote tuner at the antenna? Always nice to make the transmitter happy with a perfect 1:1 match.
73 - John - N7GHZ
How many decimal places are needed in formulas that are rough approximations in the first place? Thanks for showing the process in enough detail that it is useful. Good job Dave.
2 to 3 significant digits is good for most circuit design except for frequency- determining elements.
Very painful when you cannot find your horn Peace and Happiness to you
Hi Dave
How long was the coax used when taking your measurements?
What type of coax was it?
Another great video, I have enjoyed tbem very much.
100' of RG-213
@@davecasler Thanks
are those traps? they look like loading coils to me. Are they one and the same?
These could be good for a Parks on the Air folks.
Very interesting info Dave. I wonder what the readings would be if the antenna were brought to a height of 33 feet ? Did anyone ever tell you that you have the patience of Job ? Oh, you wife did ? LOL
Hi, height above ground effect?
Some, yes.
Will it tune on 15?
No.
Instead of cutting can't you just fold the ends of the antenna to tune it shorter?
I didn't cut. I just wrapped the excess back on the antenna.
I often wonder what MFJ would be like if the CEO actually gave a hoot about quality.
20 meters was easy but 40, has issues. The height above ground and having it as a V makes it tolerable. If I pull it taunt or raise up to 40 foot high, the 40 meter goes over 3.0 SWR. (20 meters stays 1.5 SWR) Bill n3lhq
You can adjust the ends for 40. It won't cover the entire band, so you'll have to choose where you tune it. I tuned mine for the 40 meter phone band.
This website may help you all with these types of antennas.
www.amateurradio.bz/40_80_meter_antenna.html
Probably made it too long in order for you to buy an antenna analyzer.
It sounds as though you should have removed 31" PER SIDE.
It does.
I have to say…… This is one of the most difficult antennas I ever dealt with…… Two days and I can only bring in the 20M portion…… I might as well have built it from scratch….. Couldn’t even get 40M in with my tuner……. A little more information would have been nice MFJ…… Maybe label the coils what band they’re for?…. Or tell you you have to shorten the wires….. For what little performance this antenna offers it’s not worth the effort……. Highly NOT recommend……