no c general tunna

[K5IIA]

got my link coupled tunner, ahla k1jj style, put inline temp today.... yesterday i had got the feedline put together.

so far have it taped on 80m and 40m. working great.  it is feeding an 80m dipole for the moment untill i put the 160m dipole up.

working great.

hope i did the pictures right.

[KE5YTV]

Looking good Brandon. 


Mike

[K1JJ]

Beautiful job, Brandon!

That coil link looks quite strapping and well mounted.

Now you need to add a turns counter for the vac variable to keep from counting revolutions...

I would also mount a set of standoffs for the feedline coming in. Otherwise the wires are floating around and will eventually short out on hot parts, etc.

Ummm... the front of the vac cap shaft assy is hot. (The whole cap floats for RF) You really should have some kind of insulation between the alum and the wood. Wood gets damp in humidity and might start a fire with big RF from your 813 rig, esp if high impedance matching. You want an insulated shaft there, of course, or you fingers will get burned with RF when the rig is keyed. The input cap is OK as-is and is not hot on its rotor.

How long did it take you to dial in and find the proper taps for 1:1 swr for both 75 and 40M using the MFJ-259?  Your picture shows the 75M taps? Looks like you have them balanced - tapped in the same amount on each side - good.

[WA1GFZ]

Nice job!

[K5IIA]

yea i ment to put something under it and got caught up in the moment and forgot.

it took about an hour i guess. what threw me off i started the cap at max capacitance and that was way off. i backed it fully out and the tap points started jumping out everywhere. i played with it for a while just to find the broader deeper dips hahaah if that is the way to put it.

yea so far things to do its..

isolate the vac cap
make some kinda of an isolated shaft extension
find a turns counter
and add a padder to the input cap for 80m

and i gues put some pexiglass or something around it to stop lizards and stuff from crawling on my air cap and moving its setting. its in the shed if i didnt mention that hahahah

but yea man k5uj donated the inductor and i love it. i also had a bigger vac cap donated from n4csv but decided to swap it for this capand use it for my other project.

[w3jn]

Another satisfied K1JJ tuna customer!

[WQ9E]

Nice looking construction!

If you don't find one in your junk box, Max Gain systems has some nice turns counters:  http://www.mgs4u.com/RF-Microwave/turns-counting-dials.htm 

A lot of my projects have one or more RF parts I got from Allen at Max Gain.

[K5IIA]

Another satisfied K1JJ tuna customer!

Yes i am!!! He had great tech support also. I must also say the price for the information and helpfull hents was well within my budget!!!

I am very greatfull for all the help i received on this project.

Now to the hard part. finishing it. for me that is the hardest part to keep working on something and add the finishing touches once i haved it clip leaded enough together to work hahahaah

Thanks for the info on the turns counter i am going to try to hold off and maybe pick one up at a fest a little cheaper. Right now its not to bad 80m is one turn from min cap and 40 is 10 turns hahahahhaha

there is supposed to be a wright up in electric radio for dec on replacing rf theromocouples with a cheaper cirucit. i am not sure if it is out yet but i need to get a copy and subscibe i guess i will call them today. i plan to put some form of a current meter on each leg of the output to make sure its balanced and add something neat to look at. cant have to many meat tors.

[K1JJ]

Brandon,

Yep, many of us have trouble putting the final touches on projects. It almost like we have it finished in our minds - next!

You will probably pay close to flea mkt prices for quality turns counters from Allen at MaxGain. He has great prices there. They are in big demand and anything under $40 for the METAL type is good. Stay away from those plastic black ones. I've used them for years and one by one the plastic counter gears get trashed. At this point I've replaced all but one with metal counters.

Speaking of hot tips, here a suggestion I gave Brandon that I haven't seen posted here before. It's about the value of striving to make all our antennas for a particular band as close to 50 ohms j0 on our favorite operating freq.   For 75M, Brandon plans on this openwire fed 2 half-waves in phase PLUS a pair of phased dipoles switchable east/west.

My suggestion:
"The striving for 1:1 swr is not really to reduce transmit power loss so much, but rather to give you a normalized 50 ohms, no reactance, antenna system. This way in the future you can tune up the rig into any antenna or 50 ohm dummyload and be able to switch to it without retuning. This is important for fast TX A/B comparison antenna tests later. You also want the RX to be matched when you compare S-meter readings, etc.    Ie,  For your favorite freq, try to get all the associated antennas for that band as close to 50 ohms as possible.   For the coax antennas, you may need to add or subtract some feedline until the end of that coax reads close to 50 ohms j0 on the MFJ.    The actual swr is always the same down the line as the input to the antenna at the feedpoint - but the impedance will vary down the coax if NOT matched 1:1 at the antenna. At 1:1, a coax matched antenna will always read 50 ohms j0 no matter how long the coax is - a mismatched coax impedance reading will vary.   Get it?"

In my own shack, I normalized the input to my four 75M antennas to about 50 ohm J0 on 3850. I can get on 3850 (compromise freq) and see no need to retune the rig as I go through the various antennas on transmit. Also, the receiver s-meter readings are more accurate between ants for tests when matched the same.


T

[KD6VXI]

" Also, the receiver s-meter readings are more accurate between ants for tests when matched the same."


Tom,

Wouldn't the RXer also develop more voltage across the input (better SN ratio among other things) when matched to it's input impedance?

Or is this just another way of saying what you where?

--Shane
KD6VXI

[w3jn]

The guess meter is normalized for a 50 ohm generator (ie antenna) impedance, generally.  In modern rigs the lowpass or bandpass filters are also normalized to 50+j0 - anything much beyond that the filters' responses become unpredictable.

[WA1GFZ]

Just put a 6dB pad between the RX and tuner to normalize the RX to 50 ohms.

[K5IIA]

works great on 20m also

[ke7trp]

I have played around matching receivers and the seem never work best at 50 ohms.  Some are decent there and some are not. Depends on the model. The R390 does not. The Sp600 Does not.   The Icom does.  Any of the hallicraftes rigs are exepecting 600 or 300.  Does it matter?  Most of the time no.  Some rigs have an ant tune knob and you can mimick this in a small box if you are out for the perfect recieve.  I use a little ham fest $5 MFJ mobile tuner.

KW matchboxes have the option to use the RX contacts for the reciever. These can jump the tuner.  The test is simple. Tune for TX, Find a stable signal and retune to see if you get a big gain in RX performance. On some of my recievers you will get a very large increase in signal NOT going through the tuner.

This is why I want to make a receiver buss in the shack with lines for each reciever along with a muting buss.  This way if I key any rig up, They all mute and they are all on and isolated all the time.  I can then pick and choose which reciever to use and match them independantly.

The tuner looks great.  Good find on that coil form!

C

[K1JJ]

Hi Clark,

Interesting that some RX's work better at other than 50 ohms.  I guess the idea is to keep all the antennas at about the same impedance for convenience - to be able to switch them around and compare apples to apples. Using a tuner to interface and optimize the group of antennas of the same impedance to the RX  gives the same result too.

From what I understand, a mismatch will not change the S/N since noise gets attenuated just as much as the desired signals. This assumes the attenuation is not so bad that it puts the signals below the RX noise floor. An extreme example would be using a 75M coax-fed dipole on 160M - deaf.

When working on 6M, I was told that the feedline can generate thermal noise and degrade the S/N. This is when a preamp is needed at the antenna feedpoint itself.

All said, I enjoy my antennas to be roughly the same impedance as I move around a particular band. They sometimes do not track each other due to sharper-tuned Yagis vs: dipoles, etc, but close enuff on my favorite freqs to be usable for A/B measurements.

T

[WA1GFZ]

You only need the pad if you want to use the RX the preset the tuner. most receivers are not 50 ohms and it does not matter if the noise figure is low enough.