Posts Tagged ‘MFJ 1788’

Part 4 Lets look at some condo antennas

At our old condo the loop loops like a covered piece of furniture.
Good afternoon everyone, it's time to have a look at getting on the air from a condo. I have been living in a condo for about 6 years now and really have only had one antenna BUT I have tried some that really did not work at all and some that did a so so job. Operating from a condo does have it's challenges:
- most likely you are in a highly populated area with other large condo's around you.
- very small foot print for an antenna.
- In some cases the condo unit is small which limits your space for the ham radio "stuff".

Well now that I have you listing your radio on QRZ.COM for sale lets look at some of the advantages of being in a condo.
- In most cases you are high up as for me in one condo I was 60 feet up and in this one I am 160 feet up.
- Your balcony as most are made of metal make a good ground plane for some antennas.
- Your ham skills are challenged with regards to antennas, power output and mode of operation.
OK the last two points above I was really stretching for some positives but for sure height is in most cases a major advantage.

In this post lets look at some antennas that may work from a balcony. The antenna I use as you may already know if you are a regular reader of my blog is the MFJ 1788 mag loop. Now I have had many comments as well as emails saying that the mag loop is pricey. It's very true it is and most mag loops are not cheap as I also have the Chameleaon CHA P loop 2.0 mag loop for portable op's which also is a pricey antenna. I did save my pennies and spent some coin on the MFJ 1788 and not to turn this post into a review of MFJ but quality is not noted on the Eham review site with regards to most MFJ products. I did have a small issue with my loop but I repaired it and since that time (6 years ago) the loop has given me no issues at all. In no way am I saying that the mag loops are the only way to go.
A very unique looking antenna that is great for balcony operation is the Isotron antennas  these antennas get a very decent review on Eham and I know of a ham who uses one and has had great success with it. These antennas are small, no ground plain needed and they can be purchased as mono band or multi band. Also they really don't look like an antenna. With antenna when you want to use it you put it out and when done take it in. In the present condo I am in this is how I use my MFJ loop it's only out when I am using it.
The loop at our new location 
Another antenna worth mentioning is the new Elecraft AX1 for 20/17/15m and rumors are they may be extending the band coverage soon.  It comes with a 13 foot radial wire and has a max output of 30 watts.
Depending on the size of your balcony a wire antenna dipole antenna can be used. When we were looking at condos some balcony's were huge and could support a homemade wire dipole antenna. Two antennas I have tried that did not seem to work for me is a mono whip antenna mounted vertically  with pre-cut radials...did not work at all. I also could not get the MFJ 1788 to work horizontally at my new place I had to mount it vertically. I also tried mono whip antennas in a dipole configuration and it did work but way to large for the balcony.
In my next post I am going to talk about what modes of operation I found to work best for me and how it opened a new door for me in ham radio...........oh and by the way from my condo setup as I was writing this post I was able to make contact with IK4UPB on 20m.

Striving for a better bandwidth

Original shape of coupling loop 
My last couple of posts have been dealing with extending the bandwidth of my MFJ 1788 loop antenna. With the loop the lower the SWR the more bandwidth I  have before I have to retune the loop. Up to this point I have tried moving the antenna ALL over my balcony and the best SWR at that point was at best 1.6 with the loop in the horizontal position. I then gave the loop a go in the vertical position something I had never done before. I was surprised that the loop had a better SWR, I was able to get it down to 1.4 SWR. One last suggestion given to me was to adjust the internal 10 gauge coupling loop. Today I took the section of the cover off that exposed this coupling loop and moulded the loop from it's "0" shape to more like an egg shape. with doing this I was able to lower the SWR do 1.2 to 1.3 depending on the band I was on.
New and improved shape

The MFJ loop finally has a decent SWR match!!

Homemade vertical mounting....."thing"
After doing some "playing" with the location of my 1788 mag loop on the balcony and getting really nowhere with lowering the SWR. The lowest I could get it was 1.6:1. I decided to go vertical with the loop to see what happened. Now those of you that have the MFJ 1788 loop know there is a bracket that comes with the loop for just this purpose. Well when I moved I know I put this bracket somewhere safe...........and it's still there as I can't remember where this "safe" place is!  I did try putting the loop vertical bout a month ago but at the time I was tired from all the fiddling around on the balcony and my vertical attempt was very hap-hazard. That approach did not seem to work for me either and I just left it at that. As time passed I decided to take a more serous approach at mounting the loop in a vertical position. I went to the hardware store and picked up some metal conduit and the finished product was a decent looking mount that allowed the loop to be vertical.  In a vertical position I knew the antenna would be directional but if the SWR was lower that was just fine with me. Low and behold on a certain place on the balcony the SWR is 1.4:1 which I am pleased with.The loop is still mounted inside a tripod on the balcony and you can see some holes in the tubing. When the new loop vertical bracket is placed inside the tripod tubing I slide a pin through. This stops the loop from spinning if a wind comes up. The next step will be to put some watts into it and see what
happens! It just really gets me how time just flies and all the non ham things pop up which make me very happy that in just over a  year I will be retired. I will have as much time as I need to get things done (not just ham things) I can't see myself getting board......well that is the plan anyway. Now I did mention in my last post about an update on the Sun SDRpro 2 rig that is going to have to wait for about 1 more week.

In The Loop! – First Impressions of the MFJ-1788

Was feeling pretty chuffed after repairing the MFJ-1788 'Super Loop' and couldn't wait to try it out! So for a couple of evenings of experimenting I put the loop in the garden on a 5ft pole held up by a heavy drive-on stand with 20m (65ft) of RG58 running into the shack.

Temporary test setup
I chose the easy option of using FT8 to do some testing, selecting the 30m FT8 frequency initially. I tuned the loop and was met with a cacophony of signals, far louder than my usual OCFD would receive. Working with around 30 Watts had a few contacts in a brief 30 minute session, including a nice one in Greece with SV1IW.

PSKReporter showing where I was spotted
What was striking was the lack of noise and just how tight the tuning was, indeed I had to tweak the tuning a couple of times during tests, a slight adjustment either way and the signals just disappeared. I checked out 40m and 20m as well with similar good results.

I had a few more sessions and a few days later I tried it out to receive the Shortwave Radiogram broadcast from Bulgaria on 9400kHz, this time as it was a broadcast band had to use my ear to do the tuning, adjusting till I heard a rise in 'noise' and signal.
I have now got the loop up on a rotator and mounted slightly higher up with a shorter length of RG213 (not on the video) it is still quite low and unfortunately is slightly shielded to the south by the neighbours metal roofed building,

I am very happy with the loop. Transmission wise it unsurprisingly doesn't seem a huge improvement over the OCFD on its resonant bands, it scores over the OCFD is on its 'non-resonant' bands such as 30m and 17m. But the massive improvement is in receiving, signals are stronger and noise is much lower, picking up some more distance signals even given the poor conditions.
The antenna cannot be said to be a pretty thing to have in the garden! The tuning is very particular, in the video I show the 'auto tuning' isn't ideal. It requires the radio to be putting out a signal into a mismatched load for what could be nearly a minute. Not good for the radio and is a source of QRM during this time, the usual technique of tuning slightly off a QSO frequency is more problematic due to the sharpness of the resonance. You can still tune off frequency and then tweak with the slow tune buttons to bring it in. I've noticed that on some of the higher bands it occasionally doesn't auto-tune because the 'dip' seems very short/sharp and the controller doesn't react in time and overshoots especially using low power settings.

I also have had issues trying to operate the radio remotely, I have tuned it up on an FT8 frequency in the morning and then later in the day logged in to try to make a few QSOs during a coffee-break to see the loop has drifted out of resonance. This can only be down to the loop getting warm in the summer sun.

I am still evaluating the antenna but am looking at making a better controller, over on where this blog is syndicated, I have had a number of kind comments including one from Elwood Downey, WB0OEW who pointed me to his published design of a controller, using a similar method to what I was toying with. Thanks Elwood.

73 for now, more updates soon.

The antenna farm

In The Loop! – Repairing a MFJ-1788

Over the last few years I've seen various musings about magnetic loop antennas and their supposed efficiency and performance. I had even toyed with the idea of building one considering the eye-watering prices commercial ones are sold for! Sadly that idea had been added to the big pile of 'to-do' projects.

Earlier this year I spotted a posting on social media by a member of my club who had brought a MFJ-1788 second hand who was having issues with it not working. I had offered some advice on its repair and glibly offered to take it off his hands should he want to dispose of it. A few months later I got a message asking if I was still interested? I certainly was at the price he wanted.

I collect it at the club meeting a fortnight ago still with a 5ft pole still attached as a bonus! Thankfully it fitted in the car (just).

Loop as purchased, with pvc tape covering loop

Control Box

I downloaded the manual and schematic from the MFJ website and I saw there were conspicuous warnings about using an 'isolated' power supply both in the manual and on the back of the controller, with ominous warnings of damage if you didn't. Most shack supplies have the negative/black pin connected to the chassis/ground.

The controller had come to me supplied with a standard fused lead, you know the ones that come to connect your ATU/SWR meter lamp to the shack supply? Mmmm.. my spider sense was tingling!

I pulled out a small double-insulated 12V plug-in supply from my collection (you can spot them as they often have a plastic earth pin) and with nothing else connected powered up the controller. The meter lamp came on and some of the LEDS briefly flickered and heard a few clicks from the internal buzzer then nothing. Pressing buttons did nothing and then I caught the unmistakable scent of burning electronics!

Opening the box up on the bench quickly spotted the source, the regular had well and truly smoked, but since nothing had been connected the short must have been in the controller itself (and it was not the dodgy wires that look like they had been victims to a wayward soldering iron)

Inspecting the rest of the board it was clear that it had been repaired (badly) once before, the two main transistors/FETs (Q1/Q5) used to control the motor clearly showed signs of being replaced (misaligned and with tell-tale scorching from an hot air gun)

a SMD diode had been swapped and one of the 'fine tune' switches had been replaced, its removal had obviously been problematic taking with it some of the through hole copper and adjacent tracks which had been lifted/damaged.


Before opening up the box I had expected to see 'through hole' components and DIL logic ICs not for it to be all surface mounted. Undaunted I went through the parts list and decided to get replacements for all the semiconductor parts not knowing at this stage what I would have to replace. Getting two of each device in some cases five or ten of each due to minimum order quantity, the staggering cost was £8 ($11) including postage!

While waiting for the parts to arrive I decided to check out the actual antenna head. I removed the plastic covering and attempted to extract it from the pole..

First issue I had was the mounting. One bolt had seized, the nut inserts are held in quite soft aluminium so not surprisingly the insert came out out the mounting when trying to remove it. Using grips to hold the insert the bolt still refused to turn and in the end it sheared off with very little force! Obviously quality fittings these! 

The variable capacitor was suffering a common problem due to poor quality control, the fins had gone out of alignment. Each fin is a separate assembly held on a shaft with a nut to compress them together. It is a simple fix, just realigned and tightened the bolt. The limit switches and motor connection were okay (another common problem) Applying a voltage to the coax connector the motor turned fine, reversing the voltage reversed the direction of turn, the vanes going fully in and fully out before the limit switches activated.

The components arrived prompty and so I got the hot air gun out and set about repairing the board.

I started off replacing the regulator (and the damaged power track) and Q1/Q5 and we had the flickering of life. Pressing the AUTO TUNE button the LED lit and there was 9V across the antenna connector, pressing the other AUTO TUNE button had -9V across. This is why you need an isolated power supply since it reverses the voltage to control direction. The radio doesn't see any of this voltage due to the bias-t arrangement. However if the supply shared the shack ground you would short out the supply, but the current would go via all those delicate electronics! Which is what I think had happened.

It soon became clear that most devices had suffered damage and so I ended up replacing the regulator 78L12, Q1 (SN7002 FET), Q2 (MMBT3906), Q5 (MMBT3906) all the logic ICs CMOS 4001, 4011 and 4066 and the LM324 Quad op-amp chip. I also gave the board a good clean since was covered in grime and flux residue.

Once I was happy the controller was reassembled and connected to my FT-857D on minimum power and the loop antenna propped up against the side of the shack. Success! I was able to successful tune it as per the instructions on 40m and 10m, the two extremes of operation and could here the telltale rise in receive noise as it became resonant.

I have yet to put the loop up in situ for a proper evaluation but have refurbished an old TV rotator to mount it on. I have fitted some nice new quality bolts. The black insulating tape round the loop has been removed, preferring the silver look myself.

Waiting to be put on the pole

Shiny once again

Assuming it does performs and will find out this weekend, I have paid a total of £65 ($90) (£50 for the initial purchase the rest for replacement parts) which is an absolute bargain as to buy new it is expensive.. very expensive!

One of the main supplier in the UK, have it on sale for £699 ($940) but this includes their engineers inspecting and rebuilding each one before shipping! (Can only be due to poor build quality control and warranty claims) the RRP seems to be around £570 ($770)

It does amaze me how much this units costs new. While the loop construction is generally good, the mounting fittings appear to be poor and the issues with the capacitor and quality control are widely reported.

The components in the controller are not expensive, the switches, meter, box are the usual MFJ fare and the design is quite old (the PCB has copyright 1998 on the silk screen) the auto-tune process requires the radio to be putting RF into a mismatched load for up to a minute and even with low power and SWR protection this isn't good for the radio PA.

Perhaps most surprising is given the risk of damage due to incorrect use is why firstly the loop isn't supplied with a power supply anyway as they only cost a pittance and secondary why their isn't any protection built in? I intend fitting a simple 100mA fuse to offer some protection should a problem occurs.  

If the loop performs it may be another project to build a better controller, there are a few designs out there on the internet using Arduino and DDS devices to create auto-tuners. Has that pile of potential projects just grows taller?

73 for now.. and promise to post a bit more regularly 

Spring tuneup on the MFJ 1788 Loop antenna

Oliver was going to watch over the operation
Each year around this time I bring the MFJ 1788 Mag loop in to take the covers off and have a look around to see how it has faired over the past year. This antenna has been great for me with my very restricted condo situation. I have been able to get all around the world on CW with most of the time 5 watts QRP. I am about 60 feet in the air, it's on the balcony and we do have other condo's all around us but having said that I have been very pleased with the performance of the loop. At first tuning the
Cleaned covers

loop took some time but now I really have the hang of things and am able to tune it in no time. Most of the time the SWR is flat or very close to flat on all bands it's designed for. Now as for band width on 15m it's very nice but as you move closer to 40m it gets very narrow but it is what it is. When reading the reviews of this antenna on Eham many have mentioned how the antenna when new from MFJ had an issue or two. My antenna also out of the box had an issue with the tuning box with a switch that had to be replaced. I purchased the antenna through DX engineering and they were very fast to have MFJ send me a replacement switch.
Now back to my yearly maintenance, the antenna is covered with a patio table cover to help it look like balcony furniture and funny thing is it does not affect the SWR at all so the cover is kept on all the time. This year I picked up a new cover as the old one was 4 years old no longer water proof and showing it's age. I removed the plastic covers  and cleaned the inside out which were really not all that dirty. I found as I do each year some loose nuts and bolts that require
Keep track of parts 
snugging up but this year I noticed one of the nut/bolt combination seemed to have some burning on it. This was one of two nut/ bolts that help secure the loop to the tuning cap. All other nut/bolt combinations were fine it was just this one that I ended up replacing with close substitution from my nut/bolt collection.  I have posted a picture of the nut/bolt that was removed, any suggestions as to what may had happened? The nut/bolt was not at all loose and it was only this nut/bolt that had an issue. One other thing I like to do is run the tuning cap full turn in both directions looking for smooth operation, spacing moving fins against the stationary fins and the function of the micro switches that stop the tuning cap at the end of each end.  Overall the antenna was in great shape and just to make sure once it was all back together and covered with new cover I tuned it through each band to make double sure all was well.
New cover and ready to go
Nut/bolt that was replaced
New nut/bolt installed

Checking fin alignment 

FT8 from zero to fifteen seconds

A FT8 contact
Well I took the FT 8 plunge this weekend, I have read many blog and twitter posts about it and it's such a cool digi mode! After watching some YouTube videos  I downloaded WSJT-X 1.8.0 bata software. The only changes I made was I  went into the General tab and set up some custom "behavior" settings:
1. Double-click on call sets Tx enabled.
2. Disable Tx after sending 73
 All the Radio settings were passed from the older release to the beta release. I found as others have posted that the FT 8 section of the band is very busy for a brand new mode it sure has caught on very fast. Watching the YouTube videos was a big help as this is a very fast mode compared to other digi modes. In the past with JT8 and JT65 I was able to get some blog writing done when operating BUT this new mode you have to pay attention. If you are searching and pouncing the software is very automatic when you make contact with a station as it moves through the contact process on it's own. I have up to this point only made State side contacts but having said that with the solar conditions that's great for my QRP.

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