> I did some antenna range tests with my MonstIR, varying the driven element
> length while leaving the director and reflector fixed.
> You can improve the SWR bandwidth doing this, but the gain and
> F/B drop off as you get away from the optimum frequency
> to which the parasitic elements are tuned. You really need to
> tune all 3 elements as is done in the MonstIR.
> Rick N6RK
### I was under the assumption, reading the F-12 specs... that when the DE
was tuned for 7070............ the yagi was good for 7000-7280 khz . It
appears that the swr rises slowly on the high side of resonance.
## Now it seems that the 2:1 swr may well be 280 khz.... but the F/B and
possibly the gain is not any where near 280 khz. If I recall.... most
3 -el yagi's when tweaked correctly, don't even have the freq for max
gain coinciding with the freq for best F/B
## 300 khz wide on 40m... is like 600 khz wide on 20m....... and this
340N uses 85% of full size els... ranging from aprx 52' dir.... to the
59' ref. That's a tall order. Plan B might be to include relay
box's and coils at both the REF and the DIR..... and allow for 2-8 x
segments on each parasitic ele. I was trying to avoid that scenario..
like the plague. Looks like I will have to go that route, in order to
get half decent fb/gain across the band.
## I also have the F-12 40m relay box... which consists of 2 x 12 ga
thnn coils... and a dpst deltrol relay [ identical to a P+B 12 vdc relay]
The contacts of the relay have gone int.. brand new, out of the box ! I
applied.. "cool amp" which is silver plating paste to the contacts.. and
presto.. back to zero ohms again. I have used that stuff on buss bars,
contactor's and all sorts of stuff. Then a tiny bit of... "conducto
lube" was also applied . It's just grnd up silver powder.. in grease.....
made for sliding contacts. I also replaced the 12 ga thnn coils with
8 ga polyimide magnet wire, etc. The real fix is to use vac relays.. and
be done with it.
### I can easily get at the DE... plus the tower that's being installed this
spring is a HDX-689... so the 40m boom will only be 25' above grnd.. with
tower nested. The boom, when tilted.. will allow the dir/ref to touch my
roof... for access.
### I have a few of these motor driven caps.... and will be using an
identical cap on my old EF-180B f-12 80m rotary dipole. I'm not
happy with my F-12 3 x relay/6x coil / 8 x segment switch box. It
needs 8 x coils and 4 x relays to do the job right [ 16 x segments]
If spst vac relays are used.... 8 x relay's required. I came to the
conclusion that one motor driven cap makes more sense, that 8 x coils and 8
x vac relays !
### the project started with the 80m F-12 dipole... and since the motor
driven cap was to be used... I thought, why not use the other cap on the
340N DE ! Now it appears that I'm in a 40m dilemma.... and that
I'll have to add coils and relays to the dir /ref..... and a motor driven
cap to the DE. I need to be able to cover the entire band. The motor
cap is 9 lbs. Adding one to a DE is no big deal.... but I'm not abt to add
caps to the dir/ref.. due to weight constraints.
## I don't have the room for a monstIR 40m yagi. My buddy had one up
135'.... which promptly destroyed his new OR-2800 rotor in one week flat.
## I was going to try and keep the 40m yagi .. "simple"..... but I see
there is no free lunch... so this will be yet another gong show.
Later............. Jim VE7RF
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