Friday 24 April 2020



Having spent some time putting together a 6M SlimJim, I decided to use the antenna analyser that I'd borrowed from my friend G0FRL to have a look at other antennas around the house.

Why?? Well after the simple Slim Jim made a fool of me, I wondered just how resonant all the Manufacturer's antennas that I'd paid good money for were. Surely, these giants of technology and knowledge would be pumping out antennas that were showing all signs of being resonant. And surely the antennas which came with radios should be spot on? 

Anyway, I got into the idea of testing them but without any idea of what the results would really mean. So let's get started - the analyser is an MFJ-259B which means that it's the older model without the UHF coverage. Despite its age, it still feels rugged and reliable. The rotaries work perfectly with almost no spiking.

The first test was to see if there's a difference between a FAKE Diamond SRH805S Stubby. Visually, it's easy to spot the fake! But how much difference is there in reality? I use these stubbies on my Yaesu and Kenwood handies with an OpenSpot2 and a DVAP Dongle. No need for a large rubber duck around the house and garden!

Result? Not a great deal. They both show high impedance and the fake shows a 30% higher SWR than the real one. In real life, they both do what I want them to.

I then wondered what the FT3 and D74 rubber ducks would be like.

As you can see, there's not much in them - the impedance is good on both, but the FT3 duck has a fractionally better SWR. Nevertheless I would have hoped for better SWR from both OEM antennas. With just 5W you don't want to be losing much to reflection.

Many people dump the supplied rubber duck and opt for an independent such as the COMET SMA3, so let's look at one of those....

Hmmm, not too good eh?? Probably better sticking with the OEM.

So what about a cheapo Baofeng rubber duck? Surely that's gonna be totally rubbish - The whole radio cost less than the Comet SMA3!

Oh! That's not as bad as I thought! Impedance is a little low, but the SWR is much better the the Comet.

The vast majority of people buy a UNIDEN UBC125XLT to monitor the AirBand and you'd expect the supplied antenna to be perfectly tuned to that band. Well let's have a look. I'll tune in to Manchester Airport's Tower frequency...

Rather disappointingly, the impedance of this rubber duck was very high at the EGCC frequency and if it was capable of transmitting, there would be an SWR of 2:1.  I did a bit of a sweep with the analyser and it found the best match at 160MHz - not much use. Yes, yes, I know it's not critical for RX, but if you're going to manufacture an antenna that will be tuned to the AirBand 90% of the time, might as well make it resonant there, no?

I wonder how my Discone would fair?? I'll test it on the AirBand frequency and then at 2M (you can transmit on this particular discone).

WOW!!! Very respectable! And how many snooty people mock discones??? So how does this compare with my Diamond S300?

SWR flat as a witches tit. Nice job Diamond! Impedance oddly inflated, but the antenna works superbly.

The last VHF antenna to be tested was the YHA63 which comes with the Yaesu FT-818ND. I tested it on 2M and 6M. I wasn't expecting much - and I wasn't disappointed...

Very high impedance in both configurations and pretty poor SWR to boot. No doubt fine at 1 or 2 Watts but I wouldn't want to have a lengthy 5W QSO with those figures. 


Now for some HF readings. The ribbon cable Slim Jim that I just built for 6M works fine, but how does it do on other bands I wonder? Let's see if any are workable....

Well that's not too bad considering the simple light weight design. One could easily work all these bands with a tuner. How about my 66ft EFHW?

Pretty good! In fact, this antenna is pretty good on all bands (again, considering its super simple design). 

SO THERE YOU HAVE IT! No doubt useless, but it kept me out of trouble for a couple of hours, LOL. If no one else did, I found it quite interesting to see how far away from resonance some antennas appear to be despite being designed for a specific band.

I'm sure there's one hell of a lot more to this dark art and it's all a waste of time without considering many other factors, but it got me used to working with an analyser - something I've never done before.

I guess I'll have to give Bob his MFJ-239 back and buy my own. In fact, while I'm on the subject, I noticed that Bob had fitted 10 Zinc batteries inside the machine and so I replaced them with high quality Alkalines as a thank you for the loan.

Zinc batteries scare the bejabers out of me - especially when fitted inside something that only sees occasional use. They often develop a leak and end up destroying the battery case!

As you can see above, one of the batteries 
has become discoloured.

Notes about Zinc vs Alkaline
1. A zinc battery uses an acidic electrolyte while an alkaline battery uses a basic electrolyte
2. Alkaline batteries have much higher capacities compared to zinc batteries
3. The can is the anode of the zinc battery while alkaline batteries uses a zinc powder within the can
4. Alkaline batteries have a much longer shelf life compared to zinc batteries
5. Zinc batteries are prone to leaks while alkaline batteries are not
Thanks for looking.

73, M7MCQ.


PE4BAS, Bas said...

Very nice review/experiment with the MFJ259B Tom. I got one myself and use it a lot. It is not as fancy as other analyzers but simple and good. I don't use batteries in it as they are empty within a few minutes, I always use a 12V supply or a 12V external battery. 73, Bas

MadDogMcQ said...

Thanks for visiting Bas. Always appreciated. I am attracted to the simplicity of the 259B but I also like the idea of something more modern. Can't make my mind up. And then there's the fact that you don't really use them much (relatively speaking).

73, Tom. M7MCQ.