The Wellbrook ALA1530LNP Loop vs. The MFJ-1886 Loop

The hands down winner – the Wellbrook ALA1530LNP

I mentioned that I was very pleased with the MFJ-1886 loop – mainly because I was able to get an open box item at HRO Oakland, and none of it had been used. It was going to be a store display model, but they never went ahead and put it up. The store had several other loops on display – but they were all transmit loops.

Anyway, I had a chat with Andy Ikin at Wellbrook, and told him what I was going to do and it just turns out he did a technical evaluation of the MFJ-1886. Here is what he found:

Mechanically the antenna is very sturdy. Performance wise, it is disappointing when one compares to the established ALA1530. The MW gain is low i.e. 10-15dB below the ALA1530. Overall the HF gain is approx. 5dB lower. The MW IOP2 is approx. +50dBm and IOP3 is +28dBm

The poor IOP2 is mainly due to the absence of a balanced input transformer. The amplifier uses 2 x MIMICs in a pseudo balanced configuration i.e. it uses the output transformer to achieve a balanced input. Hence, by using  50 Ohm input z MIMICs in anti-phase gives an input z of approx. 200 Ohms.

The measured Input z over most of the design bandwidth is quite high at approx. 144 Ohms. Also the input has a 290 Ohm resistor to ground on each Amp. input. Hence, the input z is a combination of the 200 Ohm MIMICs loaded with two 290 Ohm resistors. The amp.  is only matched to the loop in the mid HF band. Normally a 500kHz to 30MHz wideband loop would have a nominal input z of approx. 15 Ohms. Therefore, there is a considerable loop/amp. mis-match at MF plus input attenuation in this frequency range.

Considering that MIMIC amps afford a high noise figure at MF plus an increase in NF due to the low z  loop shunting the amp. I would expect overall NF between 15 to 20dB . This is not going to bode well for NDB listerning.

The Amp. gain at 1MHz is 9dB increasing to a max. of 18dB at 10MHz. I have added 1dB to take into consideration 50 to 144 Ohm mismatch.

The low MW gain appears to compensate for the poor IMD performance.

On the air I haven’t been able to get past the fact that when I phase the Wellbrook ALA1530LNP against the MFJ-1886 that there is no contest. The MFJ loop seems to have half the output that the Wellbrook does, so after two days of testing, I’ve decided that the MFJ is what I said it is – an entry level loop that is well made and I would further that by saying its fine for general purpose HF SWL, but its NOT a great loop for 160M. You do get what you pay for – that’s for sure, and MFJ has a great “low cost option”. The problem is – on 160M, that’s not a great deal after all – the extra couple hundred dollars is much better invested in the Wellbrook Loop.

So – one way or another, I hope to have two Wellbrook loops phased and powered by the NCC-2.

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