[NLRS] 70-cm Antenna Dilemma - Part II

[Dr.Gerald N. Johnson]

---- Original Message -----
From: Carl Estey [mailto:cestey at mn.rr.com]
Sent: 6/7/2006 9:44:42 PM
To: NLRS at mailman.qth.net
Subject: [NLRS] 70-cm Antenna Dilemma - Part II

> 
> 
> Many thanks to everyone who responded.  Here is the collective knowledge I
> gained from all of the responses and some answers to your comments.
> 
> The consensus is that that the unknown antenna is a KLM 440-16X.  That is
> correct - and I confirmed this from a 1995 AES catalog.  I do have a KLM
> 440-16X.  The specifications shown are:
> Bandwidth - 420-450 Mhz
> Gain - 14.0 dBd
> F/B - Greater than 20 dB
> Balun - Coax "N" 4:1 2kW
> Beam - E = 28 deg; H = 32 deg.
> Boom Length - 10 ft 3 in

A workable antenna providing all the aluminum to aluminum connections in the feed section actually make contact. The gain probably isn't quite as high as claimed. Expect more like 11 or 12 dBd at CSVHF. Which is a good place to test old and new antennas. Look at the driven element connections. Every one of them depends on squeezing plastic to put pressure on the connection. In time the plastic (the DEFINITION of "plastic") relaxes and kills the pressure. And I've had problems with the solder where the feed wire joins the balun.
> 
> The 19th edition of the ARRL Antenna Book does have a large amount of info
> on various K1FO antennas however the 70-cm version is only 22 elements - and
> what I have is 25.  I still need data on the 25-element version.

One or the other of CCI or Directive systems sells 22 and the other sells 25 elements. And some articles in QST or some antenna handbooks show a wide variety of K1FO. Either 22 or 25 works well (though I prefer the M2 feed system for wet and icy conditions) and there isn't a big difference between them. Remember for an optimum yagi (which K1FO's are) it takes doubling the boom length to make a 3 dB change in antenna gain. So the difference between 22 and 25 elements is small, probably under 1/3 dB.
> 
> There was a suggestion that I try a MFJ antenna analyzer to check the balun.
> That would be great but I don't have one.  I do have a MFJ that covers 160 -
> 144 Mhz but doesn't make it to 432.  Anyone have anything I can borrow?
> 
> There was a suggestion that the connector in the radio might have a bad
> solder joint.  I would guess that to be unlikely since the radio is a Yaesu
> FT-897 and the same connector is used for 2-meters and 70-cm and 2-meters
> works well.  
> 
> Someone else asked if I am sure the is ok?  The problem is exhibited on both
> TX and RX.  The initial test was between Vince, K0VZJ and my station in
> Bloomington with results at noise level to a maximum of 4 S-units.  The
> second test was with Matt, KA0PQW tonight and the same results - noise level
> to S-2.  Also, I noticed that the solid state amplifier SWR warning light
> came on.  So the problem is mutual to TX and RX.
> 
> There were some other good questions asked - and here are my replies:
> Was it the same feedline ?  No - I had the problem with a 66' run of new
> LMR-400.  Then I tried a 48' run of Andrews 7/8" heliax.
> 
> Same jumpers in the shack ?  No.  A new LMR-400 ultra 15' jumper from the
> heliax to the radio.  Same results with a 15' jumper directly to the antenna
> at 8' above ground.
> 
> Same radio or transverter ?  No.  I did try my Microwave Modules 432-28
> transverter and had the same results with Vince, K0VZJ.
> 
> Same preamp ?  No external preamp.
> 
> How good are you measurements (i.e., 20 dB above the noise) ?  Probably not
> good at all as they are based on the Yaesu FT-897 S-Meter and my assumption
> that a S-unit equals about 6-dB.
> 
> How do you KNOW that you're down 40 to 50 dB ?  Who/what says ?  Like I
> said, somewhat guessing.
> 
> The K1FO antenna has not made it up the tower yet and the tests were solely
> in the backyard from a 8' mast with a 15' LMR-400 jumper to the FT-897.  The
> odd thing is that no amount of tuning the T-match got the SWR as shown on
> the internal FT-897 meter to get to 1:1.  The best I got was at 430 Mhz.
> 
> Where/how did you measure the SWR ?  AT the antenna(s), or at the end of the
> feed line in the shack ?  Like I said, the measurements were with the
> radio's internal meter.  I do have a Bird 43 and slugs for 440 Mhz so I will
> check it out.
> 
> Thanks to everyone who responded.  It has given me some things to think
> about.
> 
> 73
> Carl Estey WA0CQG
> wa0cqg at arrl.net
> (952) 250-3110 (Cellphone)
> 
> 

73, Jerry, K0CQ