Feedback Loops

    One of the Local QRPers came around the bend and made his way up the hill.  This one was in a lot better shape that the last time we had seen him, presumably because he had taken out a membership in the local gym.  There was a lot less puffing and a lot less sweat when he made it to the verandah and sat down.

     "Well", he said, "I've been thinking."  This was cause for immediate interest because when a QRPer starts thinking, often the unexpected arises.  "The solar cycle is stuck.  The flux is 68, and has been for a long time.  It won't be rising in the foreseeable future.  Sunspot Louie hasn't seen a thing in almost two months.  The Palos Verdes Sundancers have given up!"  We rather doubted this pessimistic prognostication was correct, but we nodded for him to continue.  "You know, I've been using my trapped triband beam for a long time," he began, "and I am going to replace it with a monobander.  I found a 4-element beam on the swap shop.  The fellow wanted a lot for it, but it only had been in the air for 2 years.  So I drove over to his QTH and snapped it up this morning before anyone else had a chance.  It's all ready to go on my tower next weekend.  I already have my tribander for sale.  Some sucker will buy it!"

     We were about to ask for more details, but before we could he continued as soon as he'd caught a breath.  "I was reading the Internet, and digging through some old magazines, and I saw my trapped beam only has 5 dB gain on 20 metres, and this monobander has 8.2 dB.  That's a heck of a lot of difference!  Over 3 dB.  That would make my signal jump out in the pileups, and it makes sense to be king of 20.  I bet I'll get a dozen new ones over the winter with it.  Who cares about 15 and 10?  They are never open anymore!  I even asked Red Eyed Louie when he'd heard any DX on 28 MHz, and he says he can't remember."

     We thought about this for a bit, for this was not the first time DXers have discussed antennas and gain.  "Seems like a lot of difference", we said slowly, "3 dB is hard to get.  Are you sure you are not comparing dBi and dBd?"  The QRPer looked at us with a glare and snapped, "What's the difference?  dBs are dBs.  The fellow told me it was a killer beam.  Why wouldn't a 4 element monobander on a 26 foot boom have 8.2 dB gain?"

    We tried logic.  "All dBs are not equal.  dBb is the gain referenced to a dipole and dBi is the gain referenced to an isotropic radiator.  There is a difference of about 2.14.  You can bet the monobander specs are expressed in dBi and your tribander is dBd.  If you correct the monobander to use the same units, then the gain is 6.1.  So you really are just getting about 1 dB.  That's only a 6th of an S-unit.  You'll never notice the difference.  Your tribander might have traps, but it has 7 elements on a 24 foot boom.  No doubt 4 of them are active on 20, and the only difference is about 1 dBb of trap loss."

     The QRPer was looking confused, and then said with a defiant look, "Stop taking away gain from my new antenna before I even get it up!  It has to be better than that.  The fellow who sold it to me said he got DX with the first call every time.  He said to ignore gain figures and all those comparison charts.  He says the real proof is with the on-air performance.  Says you know you are going to bust the pileup as soon as you hear it.  Why would he say that if it wasn't true?"  He pointed his finger at us to emphasize the point. "And I think he's on the DXCC Honor Roll, too!" 

     We looked at the QRPer for a moment, and decided not to tell him there is no Santa.  "Well, if he told you it is a one-call antenna, then probably you made a good move.  He wouldn't tell you that if it wasn't so.  When you get it in the air, let us know how it works.  Make sure you have it ready for the fall so you can get the fellows on Midway the first day.  Just be a Believer and it will bring you more DX than you ever got with your old antenna!  Just with one call, too.  You will think the Great Days of DXing have returned!"

     He smiled broadly and walked down the hill, satisfied that he had a solid edge over all of the locals.  An hour or two later one of the older and more crafty QRPers came by.  "I sold my 20 metre beam today.  Got a good price for it too.  The guy who bought it thought I worked Honor Roll with it.  Most of my DXCC credits came on 15 and 10 with my vertical during the last two cycle peaks.  I think I have 201 on 20.  Now I can order the kit for that 4-square I've wanted for 80 so I can add to my DXCC Challenge totals.  I think I have 20 worked dry.  I saw a cheap tribander listed on the swap shop this afternoon.  That will work just as well, and give me 15 and 10 as a bonus for when the sunspots return.  I phoned the fellow, and he said he'd have it down by the weekend."  He looked at us smugly, expecting a reply.

     We simply nodded and looked out over the bay.  Sometimes it is best to say nothing.  Especially when the flux is stuck and circular deals are being made to ensure one's perch on the DXCC is maintained.  More properly put, if it isn't broke, let them fix it anyhow!  We recalled the advice of the Old Timer who told us years ago that it is best not to disturb a balanced feedback loop.  DX IS!

This story is in the public domain and may be reproduced in any format. - VE1DX

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Last updated 15 December 2020