BIG BANDSWITCH

[flintstone mop]

Hello All
Hopefully a good day to rest.
I thought I had arrived and made a nice tuner for my top loaded vert. on 160M with elevated radials and shift it to 40M.
Picture this:
            Cushcraft MA160M top loaded 27foot vert,
             Tuner box at base.
             Motorized  vac variable in series with transmission line. Cap can be switched out for 160M, switched in for 40M
             Motorized inductor connected ACROSS feed to base of VERT and GROUND
               
Used this successfully on a Unihat vertical that was not top loaded. It worked 160M-40M.
I noticed after some QSO's with some DX that the amp kept shutting down.
Ended play time and noticed with steady carrier that SWR was sky high. Yet when checked with MFJ analyzer everything is perfect. FLAT and no reactance.
I go out to tuner box and the poor motorized coil is black and major arcing had been taking place.
I REinstalled my 3/8 inch tubing coil and everything is solid again,,,,,,,,,,,BUT now I cannot remote tune, coz the coil is no longer remote.

I would love to pick some brains to get or design a HEAVY DUTY "bandswitch" that can be stepped or switched to change taps on this big daddy coil. It must be extreme high voltage that killed the poor motorized coil.


The coil ACROSS the base of the vert and ground creates a type of transformer and better matching. It has worked in past creations.
TNX
FRED

[W3SLK]

Phred, my RCA SBA-1K amp uses "channel" that can be automatically switched to. for tuning one band to the next. It switches in the coil and the proper amount of C when it was originally tuned. I don't recall the circuit details to well but it involves using precision pots for both tuning and switching. If I can I'll try to isolate the diagram on the schematic and post it here. That would work for you. You could set up the same type of system and tune for optimum output/SWR and then switch to it as needed.

[Detroit47]

Fred

How about multiple vacuum relays? It may be a little expensive but it would be bullet proof.

John N8QPC

[flintstone mop]

OK that's a good one!!! I do not think vac relays are that high.
I only need about four taps. One to make 160M happy and a few more for various parts of the 40M band.
thanks
Good idea

Im backing away from my last comment. Not cheap,,,,,surplu$$$$$ sales is well over $100 and Fair Radio about the same. Think I have one laying around from another project.


Fred

[Detroit47]

Fred

I have used these latley not bad  for $ 60.00 with shipping. Rf parts has a 12 volt coil for $ 100.00 http://cgi.ebay.com/New-Gigavac-G18-SPDT-Vacuum-Relay-26-VDC-HV-Switch-/390264096377?pt=LH_DefaultDomain_0&hash=item5add8d8679
http://www.rfparts.com/relay_vacuum.html
I've used some of the Russian stuff it was OK but watch the shipping charges.

John N8QPC

[K1JJ]

Fred,

Over the years I've bought a ton of parts from Bond, Allen Bond. (Max-Gain Systems)

He usually has loads of vacuum relays at great prices. Check him out and see what's there.



http://www.mgs4u.com/mgslink.htm

T

[K5UJ]

You want to switch 3 or 4 taps on a coil remotely right?  I'm not real clear on the circuit i.e. what you are trying to do but I think you are trying to put a single lead on one of 4 taps and you want to switch between them.  i.e. a single pole four throw switch.  I think I have that much right. 

The thing you need is called a RF contactor.  It is essentially a high voltage high current relay built for RF.  They are found in AM hot tower ATUs (Antenna Tuning Units--broadcast speak for a matching network at the base of a hot tower).  They are built to be motorized and are usually employed with directional phased tower systems for when the pattern has to change quickly at dawn and dusk. 

If you google RF Contactor you'll get some information about them  Cardwell and Kintronic make them.

Now, here's the problem--they cost way more than you probably want to spend.  So, you have to come up with an acceptable ham radio alternative. 

If I were you, I'd keep a lookout for some kind of big ceramic rotary switch.  You need to find something like a Radio Switch, single throw 4 or more poles.   You find your tap points on the coil and solder copper straps to them and come away to the switch.  You need a ceramic shaft decoupler for the switch.  If it has more than the needed number of poles, remove them so you have four that are spaced apart.  Also remove the index so the shaft throw rotates freely.  Mount the switch and solder the coil tap strips to the poles.  You need to get a slow electric motor that can rotate the shaft under power.  you energize the motor and the shaft rotates through the taps while you are looking at the feedline in the shack with a swr analyzer.  When the vswr drops you have the right tap.  stop the switch and adjust the variable cap.  put it all in a wx proof box.  if you have a big enough switch like a Radio switch with silver plated contacts (you can find them at hamfests) spaced half an inch you should be okay up to many KV.   

Rob

[flintstone mop]

Thanks for the very good tips guys. I have to re-think what I'm doing here, in the name of experimentation. I guess I would like to A-B the vertical on 160 compared to a dipole. The original intent. The elevated radials are the main attraction.
It was accidental with the vac variable in the tuner that the vert was happy on 40M with no reactances.
After the RF fire on the poor var inductor, I'm a little hestitant to spend more money on the vac relays. It's like "I'm almost there to experiment with 160M and 40M with elevated radials"........just need to spend another $200.
I think the XYL going out on a 10 degree morning at 6AM might be cheaper. "honey move the big clamp to the green mark on that big round copper thing out there,,,wear some boots,,, looks like it snowed again.

Fred

[Ed/KB1HYS]

Two of those straight handled battery powered screwdrivers would work FB as motors, low volt DC devices good torque, low speed and reversible. Small size, too.

[flintstone mop]

NOPE!!
We were there for just 2 mos.

Fred