857d is battery power but not really ‘floating’ as the USB ground is connected to a macbook (mac charging). As I see it the “rf ground” (or outer part of the coax) is not linked to the USB ground of course.
So, as I have no rf ground at the moment from the TX connector of the 857d to the antenna (coax → 3to1switch → coax → tuner → long coax → UNUN → wire antenna) is one ‘sort of floating’ part???
The analyser is connected to one of the 3to1switch ports. the ground of all coax around the switch is connected so I think we can say is part of antenna setup above for all measurements.
OK, I think I can see what you have there.
I would use the RigExpert just to get an idea of the settings of the MFJ ATU on the bands you wish to use, and then use those settings as an initial guide before “fine tuning” the “live” set-up.
Some form of counterpoise i.e. a length of wire hanging out of the window perhaps and connected to the RF Earth of the ATU would probably improve thing quite considerably.This counterpoise will become part of your aerial.
Well I think it is likely a matter of the different errors in the directional coupler in the rig and the coupler or bridge in the analyser. No two SWR meters are going to agree for anything other than 1.0:1.
The end fed arrangement you are using is notorious for having rf crawling all over the place at the tx end hence all bets are off when it comes to comparing measurements. An earth or counterpoise and a 1:1 current balun on the tuner input might bring the readings much closer.
The counterpoise can be a metre of wire, a tapped coil and a metre of wire. Adjust the taps on the coil for max received noise then switch in the ATU.
I have used a MFJ analyser to check quite a few antennas and I think that it is not as accurate as you might hope from the resolution of the readings or even from it’s spec. If the battery voltage sags a little the readings change which is a concern and when the volts are too low the frequency display becomes unstable.
Also it is affected by rf coming down the antenna from FM and TV tx’s, etc. These signals look like reflected power.
Nevertheless it mostly gives a good general idea about the antenna impedance at different frequencies but I would not use it to tune an antenna tuner nor to make accurate impedance measurements. A small resistive bridge would be better for adjusting an ATU.
I would be wary of many of the cheap wide range analysers on the market. Just ask who wrote their spec. A test engineer or a salesman? What does a professional instrument cost?
I use a separate SWR meter - one that I have some idea of it’s accuracy - for determining SWR or if tuning an ATU I often use the SWR meter in the rig.
The reason for using the inbuilt SWR indicator is not that they are exceptionally accurate - they aren’t - but it’s the reflected power indication that the rig uses to protect the rig by backing off the output. It works into the ALC ccrt usually. So even if the match is perfect if the inbuilt unit says it is not then that is what the rig believes.
If the tuner can give the inbuilt indicator what it thinks is a low VSWR then the rig will be happy.
The inbuilt ATU does not see the FM and TV signals due to the LP filters in the rig.
So by all means use the analyser when testing but use the inbuilt SWR meter (and an earth or counterpoise) for adjusting the ATU.
I just realised that the latest issue of QST; March 2015, has an article about an endfed dipole hanging off a fibreglass pole sticking out of a window a few floors up… ! Seems to describe your situation, hi!
Have you any way of accessing this issue of QST? If not, email me off the reflector, QRZ.COM is OK
just realise that I probably checked a different thing. I have to search for it again and come back. Thanks again!!
(sidenote though, I dont have a ‘balcony’, especially a balcony based on the US sizes )
EDIT: after all you said Mar 2015!! I was definitely wrong
Connect the counterpoise or earth to the metal case of the ATU - ie what the screen of the coax connects to.
A separate heavy earth wire from the ATU earth terminal to the rig earth terminal might help a little.
An alternative to the counterpoise is to connect 1 to 2 metres of wire on the coax side of the balun at the antenna. That is feed the antenna a little bit in from the end. It makes a significant reduction in current on the cox outer.
From your photo, posted previously, and the description of your current set up, I’d say it was very possible!
I operated from a small bedsit, without a balcony, for a couple of years without problem. I restricted myself to 40-10 metres but that was easily achieved with pole (about 3 metres) stuck out the window and dangling a half wave piece of wire. End feeding is simple and extremely effective.
Those that insist on centre feeding dipoles are missing a trick!
With a 10m pole you’ve already got enough length for an end fed dipole on 20-10 (and beyond).
Center load it with some inductance and it will easily accommodate 30m. Dangle a few more metres off the end and 40m is a piece of cake.
Get rid of all that coax.
My own setup here is a random length end feed.
The feeder is 1 metre long. That’s long enough to get from my rig to the window where the wire enters.
It may not be the best antenna in the world, but it certainly works it
There’s loads of info on EF dipoles on the web, probably the best place to start is here or here.
I bet I have misunderstood the differences or types of end fed dipoles.
I do get the off centre ones (two parts, one longer that the other, asymmetric but somehow reasemples a two-pole thing) but in terms of “end fed” configurations, I only had in mind things like http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf (this is what I have at the moment, design wise) and other end fed antenas that dont have ‘two legs’ (dipoles), please excuse my rather unporfecional use of words
I have followed the thread.
I am aware of your circumstances.
I have a spare Steppir vertical/horizontal antenna - it covers 40-30-20-17-15-12-10-6M. It becomes resonant within seconds of changing bands/frequency. It is the MkII. I have kept it as back up but never needed it so… I currently use a MkIII - email me if you want more info. We are only about 60 miles apart.
Good luck in any event.
For the next couple of months (until I move home) its a no no probably! (plus, “As with all ¼ wave verticals, ultimate performance depends a good radial system” from the site, no real room for good radials!)
Four is not necessary, you can get by with as few as one radial for an elevated quarter wave, and in fact if you run it indoors from just outside the window you can shorten it and tune it to the operating frequency by inserting the appropriate tuned circuit or loading coil. I remember a Radcom “Technical Topics” item about an elevated quarter wave vertical with a single radial bent back under the vertical to make a narrow inverted “T” shape which was reported to work well.
Hello Brian, must go as ‘Wolf Hall’ is on shortly so brief reply.
The SDA 100 tunes the element to within 2kc of the frequency.
The earlier Mk11 is less precise. The bands 40-6M the same though.
So four radials cut for quarter wave 40-20-12-6 works- 100% - I know I have done it!
You do not need 1)atu 2)coils/traps etc. which is why the SteppIR beams/verticals sell!
You cannot apply such thoughts to a vertical when the element is at resonance - tech topics etc.