Topband: Somebody mentioned Quads

[donovanf at starpower.net]

Hi Herb, 

Dielectric loading causes insulated wire to have a lower velocity factor than bare wire. 
The velocity factor of your particular wire can be determined experimentally. 

This is exactly the same as the dielectric loading that occurs when ice covers 
our quads and Yagis (I sure you're forgotten about that in the Virgin Islands!) . 
Ice increases the VSWR and in extreme cases reverses the directivity of a Yagi. 
This is exactly the same as what you're experiencing with insulated wire. 

All of the loops (reflectors, driven elements, directors) in your quad are now resonant 
at a significantly lower frequency than intended. As far as I know, the only was to 
solve your problem is to shorten all of the wires or replace them with bare wires. 

73 
Frank 
W3LPL 

----- Original Message -----

From: "Herb Schoenbohm" <herbs at vitelcom.net> 
To: "topband" <topband at contesting.com> 
Sent: Friday, July 26, 2013 10:33:06 PM 
Subject: Topband: Somebody mentioned Quads 

I need your help on this: Recently my top mast snapped with the passage 
of Hurricane Chantal. Amazing the fiberglass three element Tri-band 
Cubex Quad survived with the spreaders bent like noodle soup into the 
tower guy wires. I took the quad down and decided to restring it since 
the #14 bare stranded did not look that good. I replaced all the quad 
loop wires with exactly the same measurement but used #14 solid 
insulated wire. Everything remained the same but now the quad has the 
lowest VSWR at the lower band edge and no longer covers 14 or 21 
entirely without a 3:1 VSWR. Ten meters however works fine with a broad 
dip at 28.3 which is the same as before. I have made four unanswered 
calls to Cubex's voice mail with no reply. This brings up my question 
could the velocity factor of bare stranded #14 copper to insulated #14 
solid have that much impact on the driven element is frequency and 
bandwidth. I can probably restring the quad driven element on the tower 
on each band....or....should I simply feed it with a gamma match on each 
band. My plan this weekend is to take the MFJ 259B up the tower and 
measure what is there on each band. 

I bought a Cubex Quad so the entire bands could be covered without the 
VSWR default on by Alpha kicking in. On the antenna I use a 3/4 wave 
RG-11 matching transformer. I had the also a 3/4 wave RG-11 matching 
piece on 15 but when i went to sa direct 52 ohm coax feed I can operate 
on CW . However the VSWR shoots up to 2:1 above 21.100. I can not 
shorten the 15 meter section anymore with out the whole thing looking 
like a Hex beam. This brings up the question: Can I put in a series 
capacity (I could start with a variable) small door knob to shorten the 
self resonant frequency of the loop. I have never seen this done before 
but if I cancel out the residual inductance and have the impedance near 
to 50 ohms plus or minus i could reduce the VSWR at least? 

I know I should have done all this on the ground before raising the 
monster quad....but I thought if I kept all the measurements the same 
the antenna would perform the same. Thus your help and suggestions are 
needed. 

Thanks, 


Herb Schoenbohm, KV4FZ 

P.S. To get this back on Top Band subject....with the quad I lost nearly 
25 per cent of the top loading my A4S provided before on 160 meters. 
Something to consider when deciding what to buy.... as my only top 
loading now is the quad's 18 foot boom. I still have a 30 foot stinger 
on the top but even connecting the quads feed lines with a ground strap 
to the boom did not amount to being worth the effort. My tuning box at 
the base of the cage feed just does a bit more adjustment for a slightly 
less efficient 160 meter vertical. 
_________________ 
Topband Reflector